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January 22

Readers Anxious to Hear Bush's Space Plans

We received many thoughtful e-mails about our commentary, The Reasonable Cost of Putting Humans on the Moon and Mars. Most readers were in favor, generally speaking, of eventually putting humans on Mars. But not everyone thinks now is the time. Some figure it should never happen. Others have lingering concerns, like

Tony: I don't favor the current initiative if (1) it is a smokescreen for military development of the Moon and (2) it detracts from spending for space-borne and very large telescopes.

Roger: When President Kennedy announced our first initiative to land a man on the Moon it had a profound effect on students and spurred many to enter these kinds of college programs, and that led to many of the fantastic technological advancements that have been made. Over the past few decades, however, fewer and fewer students are enrolling in those programs. A push to head back to the Moon could be just the boost that is needed to get America back on a technological path, enhancing our ability to compete in our increasingly technological world.

David (in the UK): Many countries can help in this project, like Britain, Russia, China, Europe and Japan. To any Americans: don't let President Bush keep this to just America. Allow other countries to join in and help. Be not only proud of what America can do together, be proud of what the world can do together.

Keith: Does anyone seriously think that we will encounter fewer challenges setting up a Moon base and going to Mars than we have encountered with ISS? The problems will certainly be more complex and costly by orders of magnitude.

Jack: We should continue to focus on sending robotic rovers -- not humans -- into space. It is certainly much cheaper and, as we're witnessing with the current robot Spirit, can still perform most of the scientific study of the planet that humans could do. I too would love to see a permanent base on both the Moon and Mars but now is not the time. There are still too many problems on earth that need to be addressed (poverty, various cancers, terrorism, etc.). The increase in funding that NASA would need could be much better spent here on Earth.

John: We need to embrace challenge and risks -- these, as well as the NASA reorg you referred to, will likely be the greatest psychological challenges. However, lucid and efficient leadership will fix much of it.

Dan: Consider the two states that will benefit the most, Florida, and Texas, also matter most to this President. His brother is governor of Florida, where according to The New York Times, 14,000 people are employed in space industries. Texas is the President's home state, so no surprises here either. You can't complain about politics as usual here, but sometimes you have to ask.

[RRB: Florida is home to Cape Canaveral, from where the shuttle and other rockets launch. Texas boasts the Johnson Space Center, in Houston, which controls all manned space flights.]

James: It is important that people understand, factually, exactly how much this is going to cost and that is very, very reasonable with respect to how much money the United States has.

Mark: I have been a fan of space travel and exploration for as long as I can remember. I am in favor of man reaching out to learn more. However, I often find myself at a loss of words when friends ask why human should be in space at all. Why should we spend the billions of dollars that we do when that money could be better spent here on Earth? How would you reply?

RRB: Questions like this probably make political life harder than most of us imagine. Here's what you might say:

Billions of other federal dollars (and a lot of state and local funds) are spent to support all manner of non-critical endeavors (beyond food, shelter and clothing), often with long-term benefits that cannot be easily measured and sometimes cannot be imagined.

Public television and radio along with other arts programs are good examples. Theaters and stadiums are often constructed with city and state money. On a more important but level, but still not crucial to human survival, education is a huge spending priority at all levels of government. Nobody in their right mind would argue. Spending on education might not be as critical as spending on disease eradication or feeding the hungry, but if you don't do the former you'll never make a dent in the latter.

Point being that humans are societal animals, and we depend on a lot more than the basics to give us rich lives.

Space exploration is somewhere south of education and north of football stadiums on my priority list. Its benefits are evident. A good space program inspires students to study the sciences. Some will pursue careers in the space program, others might shift gears and become medical researchers. Perhaps one will discover a cure for cancer. Meanwhile, medical spinoffs of the space program (not to mention general technology, like digital cameras) are numerous. As my commentary pointed out, MRI and CAT scans are a direct result. And here's a story about emerging technologies that could save lives.

Dec. 16

Preserving Our Solar System
(Or Where have all the Selenologists Gone?)

Readers filled the Mailbag with comments and suggestions about yesterday's story on the Xerox-like generic use of solar system to describe other star-and-planet combinations. Astronomers are not in agreement over the usage. Neither, it's clear, are SPACE.com readers. A mere handful of the comments:

Sean Williams: As a professional science fiction writer [Sean's web site], I've been using "solar system" for years. Perhaps this is one of those times when the genre is one step ahead of the field.

Jerry: In the annals of science fiction, you will find an overwhelming agreement. The "Solar System" is where we live. "Star Systems" are places we visit.

Thomas: Your article about naming solar systems reminds me of the old days when geologists studying the Moon were called selenologists. Then those studying Mars had to come up with a name, and so on. It was quickly realized that the whole thing was getting out of hand and the terms "planetary geologist" and "planetary scientist" were coined, even though "geo" refers to Earth (at least in some purists' minds). However, a term such as "extrasolar planetary system" doesn't exactly roll off the tongue. Purists may just have to learn to roll with it.

Ray: How about stellar system instead? Then ours is both a stellar system generally and a solar system locally.

Denver: Perhaps a whole new word for stellar sphere of gravitational dominance is needed -- a parallel to "galaxy" with no inherent English meaning. "Astropety" seems like a good start.

Barry: I think as we find planets around other stars we should name those systems after the star they orbit (Vega System). To do otherwise smacks of prejudice reminiscent of the Earth as the center of the Universe.

Jeff: I think one of the most telling things about conventional use of the term "solar system" is the fact that astronomers tend to talk about "our solar system" rather than "the solar system". This suggests strongly that most astronomers assume that the phrase "solar system" is a generic description, not a proper name. In contrast, astronomers don't say "our Jupiter", nor even "a Saturn". Those are clearly proper names, which either don't require articles, such as "the" or "a", at all, or which are incorporated with definite articles in the context of phrases such as "the planet Jupiter" or "the planet Saturn". Probably the "exception that proves the rule" is "the Moon" vs. "moon", because the word "moon" can be used either way. Typically, if one uses a definite article such as "the" on the word "moon", and particularly if the "M" in "moon" is capitalized, everyone understands that you are talking about Earth's moon. On the other hand, if an indefinite article is used together with all lower case letters, as in "a new moon of Jupiter was discovered last week", we all understand that the term "moon" is being used in its generic sense, talking about any natural satellite circling a planetary body.

Dec. 10

More Reasons to Return to the Moon

The recent article 10 Reasons to Put Humans Back on the Moon generated a few other reasons to go back, from invigorating enrollment in college science courses to using the Moon as a platform for destroying or diverting asteroids that might one day be found heading toward Earth. Here are a couple of other good ideas readers sent in:

Dave: One is for the purpose of giving aspiring minds something to aspire to. I cannot imagine how many careers have been affected by the original 'moonshots.' Space exploration is one of those enticing and tantalizing prospects that sparks the imagination, even for those of us who are not 'rocket scientists.'

Robert: The study of life origins may be connected to the molecular make-up of comets. Since we already have plans to chase down and analyze comets, wouldn't it be nice if we studied the water at the lunar caps instead of looking at it just for our own exploitations? It is, after all, arguably the residue of comet collisions.

December 3

What Would Happen Upon Entering a Black Hole?

Kaizad writes: My friend is curious to know what happens when you enter a black hole.

RRB: Tell your friend to take up skydiving, rattlesnake training or some other comparatively safe activity. Anyone would be torn to bits or vaporized long before getting inside a black hole's sphere of inescapable influence.

Stuff near a black hole is accelerated to a significant fraction of light-speed and superheated to a gaseous, plasma state.

Suppose technology overcame that problem. Fine. Once inside, you'd be "infinitely stretched in one direction and infinitely squeezed in two other directions," as one theorist describes it. "That is sometimes called 'spaghettification.'"

Truth is, nobody knows for sure what's going on inside the "event horizon" of a black hole, a sphere inside which nothing can be seen because even light can't escape. There might be a theoretical loophole for survival, however. More on that here.

A Question of Time and Light-Years

Our recent story about a Eta Carinae, a star on the verge of exploding, prompted several readers to wonder if the event already occurred and we just don't know it, given the fact that the object is about 7,500 light-years away.

Jay writes: Unless my admittedly limited scientific knowledge has failed me, couldn't Eta Car have exploded in a life-ending supernova 7,499 years ago, and Earth would be none the wiser right now? Should we be staring at the sky in rapt anticipation? Or is there some way of determining if the star is intact right now?

RRB: Knowledge has not failed you. We see the star as it existed 7,500 years ago. It took that long for its light to traverse the space between us. In fact everything we see occurred in the past. Even our Sun is about 8 light-minutes away, so when we bask in its glow we're feeling radiation that left the solar surface 8 minutes prior.

Eta Carinae could indeed be quite different now -- in an Eta Carinae time frame -- from what we know of it in our present time. And, since we don't know how to do anything faster than light speed, we'll just have to wait to (possibly) learn more.

November 28

Why Doesn't the Milky Way's Black Hole Suck Everything In?

Our recent story about the Milky Way's central black hole, now said to be heftier than once thought and rotating at a quick clip, generated quite a few e-mails. One question stood out, because it pops up frequently:

Mike writes: A black hole is said to suck everything around it into it. If so, why is it not sucking stars and other space elements into it?

RRB: Black holes don't really "suck" everything into themselves. The misimpression is the fault of scientists and we journalists, who are always looking for interesting words to simply describe complex phenomena in space.

A black hole's gravity works just like any object's gravity. It is a function of mass and distance.

The best way to grasp the similarity: If the Sun suddenly became a black hole and retained its exact mass, it would exert the same gravitational pull on the Earth. The only difference we'd notice would be the alarming lack of light. (That presumes, of course, that some magical transformation had taken place -- the Sun in reality won't become a black hole, because it is not massive enough. Only very massive stars, which live short and violent lives, can collapse into black holes. The Sun, instead, will swell into a red giant and, likely, vaporize Earth.)

So a supermassive black hole, like the one at the center of our galaxy, exerts its gravity like some hypothetical supermassive star. The effect on nearby gas is to accelerate it to near light-speed and swallow it. The effect on Earth is very little; gravity decreases with distance but never goes away.

Supermassive black holes contain far less than 1 percent of the mass of their host galaxies, astronomers have learned. So yes, they are behemoths, and they do anchor many galaxies and provide a central axis for galactic spin, but they co-exist nicely with their hosts.

November 18

Is Space Station at Risk from Leonids?

Terry writes: I am curious about the reasons behind the lack of concern over the inhabitants of the International Space Station. Given the speed of the impacts and the varying sizes of particles, why arent our satellites, space crews etc. in danger?

RRB: Spacecraft are put at some increased risk during a meteor shower. Satellites, for example, can be shorted out by an impact [Learn how]. The Hubble Space Telescope, in space for more than a decade, has endured numerous hits. It is pitted from end to end, and even got a big hole torn through its high-gain antenna. But it has survived.

NASA made a fair amount of fuss prior to the 1999 Leonids, and nothing happened. They made another fuss prior to the 2001 shower, and again there were no reports of serious damage. This year's Leonids are not offering up many more particles, if any, than other annual showers, so the risk is not greatly enhanced and NASA hasn't made any fuss.

In any event, the space station is well-protected against anything up to about an inch in diameter. Leonid meteoroids are rarely larger than a pea.

November 6

Which is Farther, Voyager or Pioneer?

Our story Nov. 5 about the Voyager 1 spacecraft reaching the "termination shock" near the edge of the solar system prompted a few readers to question whether it is really farther away than any manmade object.

Lochan writes: I thought Pioneer 10 and 11 would have reached the termination shock earlier. Weren't those two probes launched before the Voyager series?

RRB: No and yes. Pioneer 10 launched on March 2, 1972 and was for years farther from Earth than any manmade object. Voyager 1 left the planet on Sept. 5, 1977, ultimately going in the opposite direction as Pioneer (Voyager 1 is heading north, above the plane in which the planets orbit).

On Feb. 17, 1998, Voyager 1 inched out Pioneer 10 for the distance lead and has held it ever since.

Pioneer 10's radioisotope power source has decayed. It made what scientist presume to be its last contact with Earth on Jan. 23 of this year. As a NASA press release put it, "Pioneer 10 will continue to coast silently as a ghost ship through deep space into interstellar space, heading generally for the red star Aldebaran, which forms the eye of Taurus (The Bull)." Pioneer 11 is not as far and has not been heard from since 1995.

November 5

Questions about the Recent Wild Solar Activity

Readers had many questions about the recent, historical round of 10 solar flares in two weeks and their associated space storms (called coronal mass ejections, or CMEs) that hit Earth. I got behind with the Mailbag because the flares just would not stop -- blame it on the Sun! -- but here, finally, are some answers (recent additions at the top):

Kurtis writes: Is there a possibility that since humans have really only existed for .01% of our Sun's total lifetime, that the Sun is in the process of returning to its norm, and everything we have seen so far in the history of our star has been atypical and the recent activity is just the Sun resuming its normal pattern?

RRB: Hmm. I might buy some of that. You're right that scientists don't know enough about the Sun to predict all the nuances of its cycles and extremes.

We have good records of solar activity for just four centuries (starting with Galileo's observations of sunspots -- see below) and scant written records going back a few more centuries. Tree rings and ice core samples give strong clues about what the Sun was doing hundreds and even many thousands of years ago. But we don't know much about what it really used to do. The Sun is about 4.6 billion years old.

However, studies of other stars like our Sun -- younger and older -- provide indirect evidence for the Sun's past and likely future, so scientists are not totally, ahem, in the dark.

Now, all that said, a study earlier this year suggested -- this is not proven -- suggested that solar activity has been increasing for the past century, perhaps longer. Keep in mind, though, this old weather forecaster's axiom: A single bad storm, or even several in a row, does not signal a shift in long-term climate patterns.

Lynn writes: The way the Sun has been acting is kind of scary. Just what the heck is going on for so many out-of-season eruptions? Are the scientist beginning to wonder if something big is headed our way ... something never before seen from our Sun?

RRB: The series of powerful flares is indeed unusual. But there is no cause for serious concern beyond the effects possible from the individual storms (to satellites, communication and power grids). Humans on the ground are not in danger.

Like any star, the Sun is volatile. Imagine a campfire: It might burn calmly for a long stretch and then suddenly whip into a temporary frenzy. You might be surprised, but you'd think of it as relatively normal. That said, solar physicists will no doubt look into this amazing series of storms in hopes of learning more about what's behind them. The Sun remains largely mysterious.

By "out-of-season," you mean that the 11-year solar cycle peaked about two or three years ago and activity is generally in decline. That's true. Interestingly, though, historical data show that more major flares occur at this stage of the cycle than during the period of maximum solar activity. Just one more mystery.

Earnie writes: How fast does the Sun rotate on its axis? Is it likely that the current sunspots will still be active on the next rotation or next several rotations of the Sun? How long do sunspots last on average?

RRB: The Sun spins once on its axis every 25 days at its equator. It takes about 35 days for the ball of gas to rotate near its poles. Sunspots sometimes form and fizzle in a matter of days. Other times they last weeks.

Any of the three large sunspots seen over the past two weeks could rotate back into view in about two weeks.

Here's a cool fact: Galileo Galilei, back in 1612, discovered the Sun's rotation by noting the movement of sunspots. When he died in 1642, he was blind. Some accounts blame his blindness on an infection, but most experts agree looking at the Sun had something to do with it. Never look at the Sun! But here's a neat and safe way to see sunspots. Also, check out Galileo's sunspot drawings.

Ann writes: Any chance these solar flares can interrupt airline travel or flight capabilities?

RRB: That possibility exists. The flare on Tuesday, Oct. 4 disrupted radio communications -- causing a total blackout at some wavelengths -- and increased radiation at high latitudes, such as the polar routes taken in trans-Atlantic flights. Last week, communications with pilots were disrupted. And some airlines rerouted planes for more southerly passages, based on a first-ever alert issued by the FAA.

There is little agreement on whether a typical passenger is at any great risk, however. NOAA estimates an airline passenger can experience as much radiation as 10 chest X-rays during a geomagnetic storm. This figure is debated. Experts do agree that anyone on a high-altitude jet, or an astronaut in space, is exposed to more radiation than someone on the ground. More here.

Laura writes: With all the recent activity the Sun has been sending our direction what could we expect if our protective geomagnetic field begins to weaken, or worse, what if our magnetic poles were to reverse as they have done many times in the past history of the Earth?

RRB: The magnetic field can get temporarily tired, one expert told me, so that back-to-back storms -- separated by hours -- might be more effective in penetrating Earth's natural defenses. This situation was set up last week, but we survived. Storms separated by days are not thought to gain any easier entry, however, at least not according to present knowledge. I'm not aware of any studies suggesting short-term solar activity can have anything to do with reversing Earth's magnetic field.

Jason writes: Is the space station shielded heavily enough for such activity from the Sun. That kind of exposure of radiation for such a long time cannot be good for anyone.

RRB: You're right that extra doses of radiation pose health risks. NASA monitors what astronauts are exposed to and limits their time in space. During intense storms, the residents of the International Space Station retreat to the Russian Zvezda service module -- the most protective. They did so several times last week. More about what the crew did last week is here. And here is a story about the radiation risk in general. Also, here's some interesting news about the radiation risk at Mars.

George writes: Is the Sun possibly preparing to enter the red giant phase of life? Are these flares a sign of the end for us?

RRB: No. The Sun is middle-aged at 4.6 billion years. It won't start swelling into its red giant phase for a few billion years. When that happens, anyone remaining on Earth will indeed be in trouble.

Mike writes: What is the likelihood of the CME affecting the asteroid belt? Does the CME have enough force to alter any of the asteroids?

RRB: I'm not aware of any studies done to quantify this. The orbits of asteroids are altered by sunlight. It's called the Yarkovsky effect and, over time, a rock's orbit and rotation change ever-so-slightly due to the constant radiation pressure. A flare would presumably add to that effect, but it's such a minor thing in the grand scheme that it would not have any near-term consequences, like redirecting a space rock immediately to Earth.

Scientists have pondered using the Yarkovsky effect to deflect an asteroid, if one were ever determined to be on a collision course decades or centuries down the road. Simply paint it white, perhaps, and let the Sun gently nudge it off course over the years.

Declan writes: Last week there was an article about an unexplained shadow (or storm), below and to the right of Jupiters Great Spot. Then this week, another highly unusual (nay unique) event takes place with the appearance of two huge sunspots and associated storms, in a period when the Sun is supposed to be winding down to minimum activity. Has anybody investigated the possibility that the two events may be in some way connected?

RRB: The spot on Jupiter was probably a locally generated atmospheric phenomenon, according to astronomers who regularly watch the gas giant planet. There's no reason I know of to think such spots -- similar ones have been seen before -- would have anything directly to do with increased solar activity, though solar energy in general certainly affects Jupiter. In this case, the Jovian spot came and went before the Sun got active, however.

October 24

What is that Jovian Spot?

The mailbag is stuffed with letters about the recent story on Jupiter's strange spot. Thanks for all the spirited questions and comments! But before you write, let me tell you what the spot is not: It is not thought to have anything to do with the Galileo probe that recently crashed into Jupiter. It's not related to the monoliths of science fiction.

It is probably an atmospheric disturbance, though a comet or asteroid impact can't be ruled out. Some seasoned observers do not think the spot is all that unusual. The latest version of our story was posted at 9:40 a.m. ET on Friday and is here.

October 20

What Makes Stars Shine?

Anthony writes: Why do the stars shine at night?

RRB: Each star makes its own heat and light, through thermonuclear fusion, just as the Sun does. In the process, the nuclei of atoms are forced together in the Sun's core, under intense pressure and temperatures that can reach 28 million degrees Fahrenheit (16 million degrees Kelvin).

Not all thermonuclear fusion is the same, though. In the Sun and other stars of similar mass and age, it involves mostly hydrogen and helium. But slightly more massive stars can rely on mostly nitrogen and oxygen. [Learn More]

All other stars are much farther away than the Sun, so we don't see them during the day because the Sun outshines them.

At night, with no sunlight to interfere, the other stars become visible.

Some stars are visible because they're fairly close, within a few light-years. Others are hundreds of light-years away but are more massive and brighter than our Sun, allowing us to see them across such tremendous distances. Only a few thousand stars are visible to the naked eye from Earth, but there are many more out there -- probably 200 billion to 400 billion just in our Milky Way Galaxy.

Interestingly, during the day you can see some stars, with a telescope, if you know where to look. And sometimes the brighter planets (which don't make their own light but shine by reflected sunlight) are visible during the day. This past summer, for example, Mars was easy to find near dawn and was visible to the naked eye well after sunrise -- as long as one didn't lose track of it! [The 10 Brightest Stars]

Jim writes: What is a jet contrail?

RRB: I assume you're referring to our recent story about a mysterious "fireball" over Wales, said by scientists to possibly be a contrail. The word is short for "condensation trail," and one forms when water in the atmosphere condenses as ice around exhaust particles. Engine exhaust produces only a small portion of the water that goes into persistent contrails, according to the U.S. Air Force. [Learn More]

Significant contrails tend to form at high-altitude where the air is cool and only when it is also moist. Dry regions like the Southwest tend to see fewer of them.

Contrails are more than just temporary marks in the sky. A recent study showed that space shuttle exhaust could be carried high into the atmosphere, where it drifted over the North Pole and created a special type of cloud visible only at night. For a neat picture of a shuttle contrail, see today's Image of the Day.

Another study after the Sept. 11, 2001 terrorist attacks, when no commercial jets were in U.S. skies, found contrails effect temperature. The temperature range at the surface was more than one degree Celsius (about 1.8 degrees Fahrenheit) larger when the manmade sky markings were absent.

Finally, contrails can hint at weather to come. Depending on the temperature and the amount of moisture in the air at a jet's altitude, contrails can either evaporate quickly or persist and grow. Lack of contrails indicates dry air and possibility of continued fair weather. Contrails that linger for hours and spread across the sky suggest moist air that might precede a storm.

October 15

Readers Doubt Explanation of Mystery Photo

Many readers wrote about our story on a mysterious photo of an apparent fireball in the sky over Wales. The picture was first said to be of a meteor; later, researchers concluded it showed the contrail of the Concorde.

But no one can fully explain the explosive appearance. The best guess by scientists: sunlight reflecting off exhaust particles. Some readers aren't buying that explanation. Below are a just a few of the comments we received. Unfortunately, the questions inherently posed remain unanswered.

Meanwhile, a lengthy account of the event, by Marco Langbroek of the Dutch Meteor Society, is available in the archives of CCNet, an electronic newsletter that carried much of the discussion about the picture.

Dan: I'm sorry, but if that's a picture of the Concorde, it didn't survive. This story has gone from the sublime to the ridiculous. Next they'll be claiming it's a weather balloon....or maybe Venus....or swamp gas; yeah, that's the ticket!

Peter: I know the Concord is fast, but at the apparent altitude (it's not visible in either photo) the apparent speed of an aircraft would be quite different from the apparent speed of a meteor. That one datum would support or refute the possibility of the phenomena being caused by a high-flying aircraft contrail or "false Sun."

Jonathan (not the photographer) writes: The so called scientists that are trying to fool everyone that this is a Concorde contrail, well, are they having a laugh?!? It is clearly not from the Concorde, as it is nowhere in sight, plus the contrail is at a too steep an angle to be from the Concorde. If the Concorde is producing a contrail at this angle then it is clearly in trouble again.

Mark: It is indeed a contrail. The "fiery" head is visible only after sunset when the upper portion of the contrail is in darkness and the lower portion (which is farther west) is still lit by the Sun. A person seeing a video would not mistake this for any sort of fireball. The still photo gives the illusion that it is in rapid motion -- which it was not.

William: A meteor is any object that comes into contact with the Earth's atmosphere. It can be of any material--manmade or natural. The object is a meteor fireball. However, whether its origins are natural or manmade cannot be determined.

James: A jet contrail is water vapor. These photos show a smoke trail. I have spent over 16 years in Marine Corps Aviation and this never occurs when dumping fuel (not unless you want to blow the plane up). Planes do dump fuel, but the fuel dump is designed to prevent an ignition. Jets that dump fuel for propulsion, like an afterburner, you would see the plane in front of the fireball and the fireball is a thin, bright, streak.

October 13

Lessons from an Eclipse

James writes: I need your help. I am a middle school science teacher. I usually teach life sciences, including anatomy and genetics. This year for some reason my students have an increased interest in astronomy. They want to get together for the upcoming lunar eclipse. Since I am a novice astronomy buff, I need info on how to present this evening to them.

RRB: Whether you are a teacher or parent, the total lunar eclipse of Nov. 8 can serve as a great launch pad for teaching some simple things about how the solar system works.

Start by explaining the basics. A lunar eclipse is just Earth's shadow falling on the Moon, and one can occur only during a full Moon. Why? Because that's when the Sun, Earth and Moon are lined up. Show them the graphic on this page.

So why isn't there an eclipse at every full Moon? Because the Moon's plane of orbit around the Earth is a bit tilted compared to Earth's path around the Sun. I think of it as an imaginary dinner plate (the Moon's orbital plane) that sits both above and below the kitchen table (Earth's orbital plane). Sometimes the Moon is above or below the shadow that Earth casts into space.

You might also discuss the phases of the Moon, so your students will know where it goes when it's not full and obvious in the night sky. And don't miss the chance to explain how the Moon was probably made. The leading theory is that it formed when a Mars-sized object slammed into Earth -- that'll get their attention!

Arm your students with some specific information about the eclipse, such as when it occurs and that they need a clear view of the horizon. Then on the evening of the event, tell them to ponder all these things as they watch the Moon be "eaten," which is how many ancient cultures (who didn't know anything about orbital mechanics) viewed lunar eclipses. Perhaps give them a printable map of the Moon so they can identify a few major features -- visible with the naked eye -- while they watch the eclipse unfold.

All this might seem to have little to do with life science. But here's your tie-in: Most scientists figure the Moon served a crucial role in the initial habitability of Earth and the evolution of life here.

Lucky for you, an eclipse requires no special equipment. Just tell the kids to dress warm and bring their eyes and imaginations.

September 30

Space Mailbag: Visible Planets - 6 or 7?

More than 200 people wrote our Night Sky columnist Joe Rao about his recent column, Sky Surprise: Seeking the Sixth Visible Planet. Most focused on one point. Joe wrote that most astronomy texts list five planets that are visible to the unaided eye, but that the true answer to this trivia question, when posed as such, is that there are six, with Uranus being right at the threshold of naked-eye visibility.

Here's a typical note Joe received:

Charles writes: I think that seven planets are visible without a telescope, since the Earth is a planet and it certainly isn't invisible.

Joe Rao responds: Writing Night Sky for SPACE.com these past 19 months is sometimes like playing a game. The game is this:  I do my best to treat a subject accurately and concisely and the readers do their best to catch me out in errors.  The readers often score points, though rarely disastrous ones, and I make the necessary corrections in public. I've received scores of e-mails just like the one above, in essence saying: "You said the number of visible planets is six . . . I count seven!" I could change the text, and I really came very close to doing so. However, I think, we will leave well enough alone, and keep Uranus as the sixth visible planet.  Technically, all of you who have written in are indeed correct. You can certainly "see the Earth," but for simplicity, I think we'll confine our viewpoint here to the "moving stars" that old-time skywatchers named for ancient deities.

September 23

Listen to a Black Hole

After reading our story, Black Hole Strikes Deepest Musical Note Ever Heard, several readers were curious whether they could actually hear the sounds of a black hole. That is sort of possible.

Edward Morgan of MIT took X-ray data from a black hole named GRS 1915+105 and translated it into audio signals. The audio files are posted on this NASA site.

What a Scream

Other reader queries about the Black Hole story above led to a follow-up article, Sounds in Space: Silencing Misconceptions. In it, a reference to screaming in space was worded differently than what was in several readers' memories.

C. G. (Jere) Justus writes: The original quote (from the "Aliens" movie) is, "In space, no one can hear you scream." There's a subtle difference between that and your version, "In space, you can't hear yourself scream."

Your hypothetical astronaut COULD hear herself shout, because of conduction of sound through her body from her vocal apparatus to her eardrums. However, an equally "brave and clever astronaut" nearby could NOT hear her shout (whether or not he had "safely removed" his own helmet).

In science fiction stories, there have been scenes where two astronauts converse without radios by touching their helmets together. In such a case, sound is transmitted through the air inside their helmets and the solid material from which their helmets are constructed. Of course, as soon as the helmets lose contact with each other, sound transmission would cease. I don't know if any real astronauts have ever tried this experiment.

Bruce writes: I loved the movie "Alien," but never liked the misconception that they presented. Let's look at the three ways to scream in space.

One, you are in a ship, or station, where there is atmosphere. Sound carries just fine, the scream would be heard by yourself, and anyone close enough. Two, you are out on an EVA, you have a helmet on; you scream, you can hear it just fine.

Three, you are in vacuum, without a helmet, and assuming that you scream before eight seconds or so, you expel the air in your lungs and scream. Bone conduction would allow you to hear your scream. If you were lucky enough to be entering a pressurizing airlock, you would live to tell the tale.

September 22

Planets in Strange Star System?

Jim writes: Given the discovery of a brown dwarf pair around the star Epsilon Indi at 1500 AU, could it still be possible for planets to orbit the primary star in stable orbits?

RRB: I'm not a theoretician, but there's nothing inherent in a triple star system like Epsilon Indi to prevent planets from orbiting the main star. But an expert in planetary orbits would have to run some serious numbers to firmly answer your question.

Any mass around a star, be it a large planet or a pair of orbiting brown dwarf stars, prevents other objects from existing in stable orbits in certain locations.

Astronomers expect that future space-based observatories will begin to find planets similar in size to Earth around other stars. Such worlds, if they exist, are simply too small to be found with present methods.

September 19

What Existed Before the Universe?

JP writes: The article about how the universe may be formed by a black hole [Sept. 17] does not explain at all how the universe came to be. For the theory to be true you assume that matter already existed. I have not heard of one evolutionary theory that can explain the existence of everything realistically. If there is one please tell me.

RRB: There isn't. No one knows what existed before the universe as we know it, or what form things might have been in. Since we can't see into or beyond the Big Bang (regardless of how that event played out) it's something that may never be learned.

This, of course, makes for an area of study ripe with interesting theories. Some cosmologists think the universe is cyclical, and that the Big Bang was not so much a starting point as a restarting point. Other theorists suggest the Big Bang involved a collision of two universe-like membranes. Other variations have our universe as just one of many.

In all these scenarios, though, nobody can say where the stuff of the present universe came from.

September 16

Good Luck Finding the Star with Your Name on It

We got a number of e-mails about Monday's article, Name a Star? The Truth about Buying Your Place in Heaven. Among a range of comments were these:

Steve writes: Are stars assigned names by these companies duplicated? I wonder if the same company "registers" a name to the same star, or if different companies use the same star. Even if I knew I was getting a novelty item, I still would like to know that there aren't 100 others out there looking at the same star they "named."

RRB: I mentioned in the article that another company could certainly apply someone else's name to "your" star. In fact, you could start a company and do the same!

Most of the companies say they do not give multiple names to a given star. Interestingly, though, there are only about 6,000 stars visible from Earth with the unaided eye, and most of those are very difficult to find for the average observer. So if a given company has named more than 6,000 stars, then they're applying names to stars that only experienced backyard astronomers could ever find, as our next reader notes.

Jim writes: When people "buy a star" they think they're getting a Sirius or a Deneb or one of the Pleiades. What they're actually getting is a 24th magnitude fly speck in Hercules' armpit that would take a clear night on Mt. Palomar to find.

Nick writes: What might have been worth mentioning is that occasionally there are equally novel 'immortalizing' gifts to give somebody that are more genuine. A few years ago I entered my name, along with those of several of my family members, into a database on NASA's Web site. According to them, the names were etched onto a sliver of silicon and would be attached to the Stardust probe. Also according to them, when the sample container returns, it would be on display at the Smithsonian along with a searchable copy of that database. We'll see. I didn't find an 800 number or a customer service email address, so I'm skeptical. ;)

RRB: I think NASA will make good on their promise, if they can get the return module to successfully parachute into the Utah desert in 2006. By the way, there are more than a million names etched onto two silicon chips aboard Stardust, including about 58,200 names that are also inscribed on the Vietnam Veterans Memorial in Washington, D.C.

September 12

Are We All Sitting Ducks?

Readers often have thoughts and concerns about asteroids, including the known history of them hitting Earth, and their presumed potential to do so again. This letter came in response our Sept. 9 story about an unnecessary asteroid scare generated in the media:

K.B. writes: Someday we will find out about an asteroid that will hit the Earth. Hopefully not in our lifetimes, but it will happen someday. Shouldn't we have something planned to do about such a worldwide, possible human species-ending catastrophe?

RRB: Asteroid experts generally agree with you that this needs to be looked into, and that eventually Earth will be slapped with another large asteroid impact.

And there are meetings nowadays about how to divert or destroy a space rock, along with limited funding into research that will help answer the question. One study suggests simply painting the thing and letting sunlight send it off course. Another report has looked at how a space-based missile defense system might do the job.

But, as you note, not much has been done. Astronomers have found it challenging just to get funding for asteroid search programs.

One important thing to keep in mind is that if a big one is headed our way, most experts agree there will almost surely be years to ponder it. Technology can advance in a hurry when needed!

Clovis writes: I was wondering if you were in a deep valley on Mars wouldn't the air be more dense than on the surface? And if you could find a cave at the bottom wouldn't it be a good place to look for life?

RRB: Yes to both questions. Hellas Basin on Mars is about 4.4 miles (7 kilometers) deep. Pictures of it are blurry just because there is so much more air in the basin than above other parts of Mars. You can see the basin in recent Hubble Space Telescope pictures. Here's more about the idea of caves harboring life, and some have suggested humans could use Martian caves as initial habitats.

September 9

Many readers responded favorably to our recent commentary NASA Has a Vision, It's Our Nation That Needs Glasses. Among those who disagreed, some felt the opinion piece missed the mark about what needs to be done with NASA and the space program. Others didn't have their facts straight. Read the comments >>>

Connie writes: I really enjoyed Ed Grafton's photo of Mars. I wish I could do something like that. Thank him for bringing the planet a little bit closer to home, along with the humbling realization that something much bigger than ourselves exists out there.

RRB: We'll pass your thanks along to Ed.

September 2

A Hole in this Story

Several readers wrote to contest my claim regarding how much dirt is in a hole in the ground measuring 1 foot by 2 feet by 3 feet. (If you haven't read this Mystery Monday article about black holes, do so now before ruining what's become a double punch line.) I said that unlike black holes, which are stuffed with matter, a hole in the ground has nothing in it.

George writes: If this hole is in my backyard, it actually does have something in it, namely 6 cubic feet of air.

RRB: Yes, you're right. I should have been more precise. And as another readers suggested, their might even be some dirt in there -- in the form of wafting dust.

Aug. 29

Mars Mania swept the planet this week, carrying with it a lot of e-mail into the Space Mailbag. Here are some that several readers asked:

Why is Mars red?

RRB: Mars is covered in iron oxide -- what we call rust. It gives the planet its color. But even though we call it the red planet, Mars isn't truly red. Up close, in images from the surface and in new pictures taken with the Hubble Space Telescope, Mars looks more orange than red.

Or, maybe rusty would be the best way to describe it. Our Night Sky columnist Joe Rao describes it as the color of a desert under a glaring Sun, which is just what Mars is.

Can I still see Mars?

RRB: Yes! It remains very bright and large through early September and is a fine skywatching target into October. [Details]

Why has it been 60,000 years since the last close encounter, but it will take only 284 years until the next?

RRB: The unusually close approaches tend to bunch up in time partly for two reasons. The non-circular orbits of Earth and Mars actually rotate through space, and things are aligned favorably right now. And I mean right now in the sense of a centuries-long time frame.

Also, the shape of Mars' orbit, which is out-of-round by about 9 percent, is undergoing change. The red planet is getting closer to the Sun on what is called perihelion, its annual nearest-to-the Sun position. And it's drifting farther from the Sun on its yearly aphelion, the counterpart to perihelion.

This would tend to make the potential proximity to Earth shrink, since a close approach like the one this year occurs when Mars is at perihelion at almost the same time that it comes to opposition (when it is exactly opposite the Sun in our sky). Things are set up for really close approaches to be more common, and more extreme, during the present millennium. The situation has been heating up: An abundance of them have occurred over the past 5,000 years. The mechanics of it all just happened to really come together during your lifetime!

For a fuller explanation, read about the science of the orbits, and also see the Top 10 closest approaches since 3000 BC.

Could Mars and Earth Eventually Collide?

Michael writes: I read the Mars article [debunking rumors that Mars and Earth would collide this year]. You go on to say that in [284] years Mars will be closer. So in the future, like 100,000 years, could the two planets eventually collide, or wind up like Neptune, and Pluto with the interchanging orbital patterns?

RRB: Definitely not in the next 100,000 years. And there is no research I know of suggesting that the orbits of Mars and Earth will ever interact. If anyone finds otherwise with some respectable new computer model, it would be big news and you'd read about it on SPACE.com!

Back when the solar system was young, though, it was more crowded and collisions were more frequent. In fact, most experts believe our Moon was created when a Mars-sized planet crashed into the newborn Earth, more than 4 billion years ago.

Aug. 28

Some interesting Mars musings:

Entertaining Mars

Geoff writes: I wanted to say I really enjoyed your SPACE.com article about Mars' appearances in various entertainment media [By Tariq Malik, 8/24/03].

I just had to add one more musical appearance, a fairly significant one: Jeff Wayne's "War of the Worlds," a rock opera retelling of the original H.G. Wells story (as opposed to a modernized adaptation of the story, as the George Pal film was). It had some pretty heavy hitters involved, such as Richard Burton as the narrator, and vocalists like Phil Lynott of "Thin Lizzy" and Justin Hayward of "The Moody Blues."

Tariq Malik replies: Thanks for the reminder, Geoff. We can't believe we forgot Wayne's original 1976 cast recording depicting Wells' classic. In fact, one SPACE.com managing editor of indeterminate age fondly remembers listening to Hayward crooning "Now you're not here!" from Forever Autumn, as well as David Essex singing about founding a brave new world with "a handful of men." It was a hit during an era of operatic rock, as Meatloaf's 1977 Bat out of Hell proved.

Jeff Wayne's War of the Worlds also inspired a video game of the same name, developed for PC and console machines in the late 1990s.

On a more visual note, Gerry from the San Diego of the Mars Society offers this resource for more Mars movie mayhem.

Mars in the Classroom: Marconi and Tesla

Janet Brand, a teacher at Wellington High School in Wellington, OH, writes: I am enjoying your web site on Mars and plan to use it this first week of school to seize the opportunity to teach my Earth Science students about Mars. I have to tell you, however, that Marconi did not invent the wireless, Tesla did. [Mars: The Solved and Unsolved Mysteries, 08/25/03]

The accolades that Marconi got for the invention were later reneged and Tesla was given credit for the invention. Tesla was also the first to listen to space noise although Marconi may have claimed he listened to Mars.

I am fond of Tesla because we owe him so much and he has been grossly overlooked by history. Luckily for us, PBS produced a wonderful biography of Tesla.

RRB: Thanks for setting me straight, Janet. The PBS site has more about the Marconi vs. Tesla issue. I hope your students read the Space Mailbag, too, and learn the value of writing to the media when you see something amiss!

Mars Musings

Eric writes: You wrote that the atmospheric of Mars is only 1% of Earth's [Mars Dust Hints at Water, 08/21/03]. You made me go to the calculator to translate that into laymen's terms.

Assuming sea level pressure is 1000 millibars, then 1% or 10 millibars translates into a pressure altitude of over 80,000 feet. Suddenly, it means something. Mars isn't anything like our own environment. Am I going to have to go back to the texts to figure out the boiling point of water at that altitude? Anyway, I just reminding you that a layman can't imagine what 1% of something really is, be we can all relate to how cold and thin the air is at 39,000 feet and how much thinner and inhospitable it would be at 80,000 feet.

Cathy writes: The fact that Mars has polar icecaps [See New Hubble Photos] speaks volumes. Maybe there were dinosaurs there prior to the icecaps and dust storms.

RRB: Perhaps something like that! But most scientists suspect Mars never had much more than microbial life, at best. If science and mission spending progress well, we might find out in the next 20 years or so, maybe sooner.

Coming to the Mailbag by Noon ET Friday: Readers' questions about Mars

August 21: Mars Mania

The close approach of Mars Aug. 27 is keeping the Space Mailbag stuffed. Sorry if I haven't responded personally! The most common questions: When, where and how can I see Mars? The answers: Almost anytime, anywhere, and it's really easy. Details below. Plus: How to borrow a really big telescope.

Blame it on Mars

This week's inaugural Mystery Monday feature, Mars Will Not Kill You, generated quite a bit of e-mail. The story debunked some rumors about how the red planet's close approach would supposedly cause ill effects on Earth.

Some folks said thanks for doing the dirty work of supporting real science. Others said I'm full of, well, we'll leave those in the bag. This one was just plain fun to read:

Randy Wilkinson writes: I enjoyed your article in SPACE.com detailing worries people had about the proximity of Mars. Lately due to a number of anomalous occurrences (funky things that appear to be out of the ordinary) at home and at work I, in jest, have taken to blaming the close proximity of Mars for these happenings.

Thinking back to 1971 though, (last close proximity of Mars) I remember that one as a pretty strange year too. Maybe there is something to the planets effecting our lives. ;-)

RRB: This story is not over, so don't miss next week's Mystery Monday. You'll find it on our home page on Aug. 25.

Lochan writes: Isn't Venus more Earth like in dimension, mass, atmosphere (and smog!!) than Mars? [Refers to our Aug. 19 story, Earth vs. Mars.]

RRB: In many respects, Venus is more like Earth than is Mars. Earth and Venus have almost identical diameters. But Venus is a hothouse, almost surely inhospitable at the searing surface. Humans could not get there alive. Some scientists speculate there may be zones of hospitality high in the Venusian clouds, where microbes might live, but that remains unproved.

Mars is just half the diameter of Earth, but it is more hospitable. It would be no picnic, but humans could survive there with technology that's pretty much developed now. And microbes could easily survive on Mars, most scientists say, if there is liquid water. That's one of the biggest ifs in science these days. And just because something could survive doesn't mean it ever existed in the first place.

One day in the distant future, even Pluto might be more livable -- a veritable oasis -- than Venus is today.

Aug. 19

Want to See Mars? No Telescope? Borrow a Big One!

Steve Barker writes: Where is the best place to view [Mars] if you are not fortunate enough to own a telescope?

RRB: You can see Mars with your naked eye from anywhere [Viewer's Guide]. But as I suspect you've figured out, it's just a bright point of light. So if you don't have a telescope, borrow one -- but borrow a really good one!

The way to do that is to contact a local astronomy club or planetarium and find out who is having skywatching events and when. These "star parties" occur all around the country, and more of them are planned for August than normal.

Backyard astronomy enthusiasts are known for their gracious propensity to let you look through their big 'scopes. After all, what good's an "oooh" without an echoing "aaah."

The Planetary Society has a big list of events geared around the Aug. 27 close approach of Mars.

You can also search the web for your home town and "astronomy club," then e-mail or call the organization for information. Some universities have large telescopes, too, and they open them to the public now and then. You should be able to find out about your local university by scouring its web site for an astronomy department.

Powered Down! Due to the power outage in New York, incoming Mailbag items sent Thursday evening, Aug. 14 though early Saturday morning, Aug. 16, likely did not arrive. We regret the inconvenience.

Correction: Orion (Not) Visible Above NY

Once our e-mail began working again after power returned to New York, we received several letters pointing out our mistake regarding the visibility of Orion over the city along with more faint stars than normal [Blackout Closes NASA Center, Reveals More Stars above New York, 03/08/15]. Yes, there were more stars visible, but those of Orion, of course, since it is a winter constellation. We regret the error and thank the many readers who wrote to inform us, including those whose e-mails never arrived due to the blackout. The story has been fixed.

Aug. 15

Mars: The Talk of the Planet

Mars has become the talk of the planet. This planet, I mean. Articles about the historical close approach Aug. 27 are popping up in major newspapers and on radio and television (and it's been on the Internet since Nov. 8, 2002.)

And so the Space Mailbag is getting a lot of questions from around the world about the event. We will feature some of the most interesting (and troubling) of these as part of an important story Monday, Aug. 18 (see the SPACE.com Home Page then). Meanwhile ...

Benny B writes: Im from Belgium and I want to know if I can see Mars from here.

RRB: Sure you can! This is a worldwide event. You'd have to be from Mars or live in a cave -- quite literally and constantly -- to miss this celestial extravaganza.

Mars is bright right now and will stay so for weeks. Any night, any morning, now or at the moment Mars will be closer than ever in human history (Aug. 27), or right on through September. Details here.

Remember, though, that Mars will never be more than a point of light to the naked earthbound eye.

Bill Adams: When Mars makes its closest approach to Earth later this month, will any other planets still be closer to Earth at that time (i.e. Venus or Mercury)?

RRB: No. Mars will be less than 34.65 million miles (55.76 million kilometers) away, as we've reported. I checked out the others using Starry Night software: Venus will be 160 million miles (258 million kilometers) from Earth. Mercury will be 66 million miles distant (106 million kilometers).

Venus, for the record, is the only night-sky object besides the Moon that can outdo the brilliance Mars will attain this month. But neither Venus nor Mercury are visible now because they're in almost the exact same line of sight as the Sun and so are overpowered in our daytime sky. And as you know, Bill, Saturn (which is visible in the morning sky right now, to the east) is much farther away than Mars.

For fun, you might want to check out our list of the 10 Brightest Stars.

And, below: Mars as Big as the Moon?

The following humorous e-mail came in response to our Science Tuesday article about a new classification system for objects in the outer solar system, which currently go by crazy names like TNO, Plutino and cubewano.

Andy writes: In regards to naming those trans-Neptunian objects [TNOs]: Why not designate them as pnp or pno with an ecliptic or non-ecliptic designation. Pnp would be for 'plus nine planet' if equal to or exceeding Pluto's mass, pno would be for a less massive 'plus nine object'.

Something newly found might be a pnpne (a pinpine?) if it were larger than Pluto and not in the ecliptic plane, or a pnoe (a dyslexic pony?) if smaller than Pluto and in the plane. Maybe this is bs, but whatever the nomenclature settles at, it should be easily deciphered. And there should be agreement among astronomers regardless of the naming system.

With [my] stupid system you'd get:
a) pnpe (pin pea?) for plus nine planet in the ecliptic
b) pnpne (pin pine?) for plus nine planet not in the plane
c) pnoe (pony) for plus nine object in the plane
d) pnone (pin one) for plu nine object not in the plane

Maybe the last two could be called ponies and wild ponies .... pnies are smaller than horses and a wild one would be expected to bolt its pasture. Pins for the first two seems all right because regardless of size these trans-Neptune objects are difficult to find .... like needles in a haystack.

Aug. 13

Leave Hollywood Out of NASA

Readers by and large responded positively to our recent commentary "Call Hollywood! NASA Needs a Makeover", but a few SPACE.com readers felt NASA and its astronauts' deeds stand on their own two feet without having to resort to the antics of mere entertainers. Read the Comments >>>

Aug. 12

When, Where and How Should I Watch Mars?

Several readers have inquired about how best to view Mars now or on Aug. 27, when the red planet will be closer than ever in human history.

Tiffany writes: I do not own a telescope, but do have a pair of binoculars. If I go outside tomorrow night will I be able to see any sign of it? ... On the 27th: Where is the best place to view it? I am in a very industrial area and wanted to know if I should go somewhere that is less populated.

RRB: The great thing about this celestial event is you don't need any special equipment, nor any special location, to partake. Anyone, regardless of how bright or populated their viewing conditions, can find Mars. And you can do it tonight. In fact you should. Don't wait until Aug. 27, but instead check Mars out now and watch it grow slightly brighter over the next two weeks.

Go out after 10 p.m. and look low on the southeast horizon. You can't miss Mars -- it will be the brightest object in the night sky other than the Moon. (Mars and the Moon are together this week.) You can see Mars through the night (it will rise high and move into the southern sky). By dawn, Mars is in the southwest. You can even see it after the Sun comes up if you don't lose track of it while day breaks. [Mars Watch: Maps and more]

Use your binoculars (or a small telescope) to try and resolve Mars as a disk, rather than a point of light. Don't expect to be blown away, but it's worth trying. Now if you're hoping to see surface features on Mars, you'll need a pretty expensive telescope, probably more than $300 and at least 4-inches in diameter. But don't make a quick decision and invest in junk that won't do this or any task well. Do some research first; you can start with our Telescope Buying Guide and our Ten Steps to Rewarding Stargazing.

How Big Will Mars Appear?

Betty writes: I was e-mailed an article that says on Aug. 27 Mars will appear to be the size of the Moon from the Earth. Is that true?

RRB: No. Not even close. To the naked eye, Mars will just look like a very bright star. It's not even quite as bright as Venus (which is often called the Evening Star; but Venus isn't in the our night sky right now). The significance of this close approach is that Mars will be closer than at any time in nearly 60,000 years.

It's like a pole vaulter setting a new world record that's just a fraction of an inch higher than the previous. You can't really see the difference from the stands, but you understand the historical significance and, if you like pole vaulting, would not want to miss the event.

Viewer's with large backyard telescopes are understandably excited, as the proximity of Mars means better viewing of surface features. [Related story on what to look for]