Venus, Mars and Saturn light the cold, frosty evenings of winter as the New Year opens up, but 2006 will be hardly a week old when Venus plunges rapidly down into the sunset.  Mars, meanwhile, fades into the distance. 

As warmer weather approaches, Saturn takes over to dominate the milder evening skies of late winter and early spring, only to be replaced in turn by Jupiter later in the spring and summer.  Meanwhile, speedy Mercury will pass in front of the Sun in early November, then joins Mars and Jupiter to form a tight triangle in the dawn skies of early December. 

Sound like a busy year for planet watching? Let's take a look at the visibility of each of these worlds during 2006.

MERCURY: Mercury usually appears as a bright "star" with a yellowish or ochre hue. At its best evening apparitions, it can be found almost directly above where the Sun has set, being visible for up to 90 minutes after sundown.  As viewed from the Northern Hemisphere, such an opportunity will come between Feb. 10 to March 3.  It will also be positioned to the north of a razor-thin crescent Moon on the evening of February 28.

During its best morning apparitions, you'll find it positioned almost directly above where the Sun will rise up to 90 minutes prior to sunup. Such an occasion will come between Nov. 18 to Dec. 9 and it will appear to ride well to the north a slender sliver of a crescent Moon on the morning of November 19. On Nov. 8, a transit of Mercury will take place, with the planet appearing in silhouette as a tiny black dot on the Sun's disk. This event will be visible from the Americas, the Pacific Ocean, Australia, New Zealand and eastern Asia.

VENUS: Always appears brilliant, and shines with a steady, silvery light. It starts 2006 very low in the west-southwestern evening sky at dusk for the first several days of January.  It then passes roughly between the Sun and the Earth (inferior conjunction) on Jan. 13 and makes its transition into the morning sky. 

You'll find it during the final week of January, low in the east-southeast sky at the first light of dawn and it will continue to be a prominent morning object right on through the end of August.  It will then be hidden again by the bright solar glare almost through the balance of the year.  Passing through superior conjunction on Oct. 27, it will then return to the evening sky, though not likely readily visible for most until the waning days of December.  During late January and through much of February, it will resemble a beautiful crescent in steadily held binoculars and telescopes. 

Venus will reach its greatest brilliancy in the morning sky on Feb. 17.  Venus will appear to pass very close to Saturn on the morning of Aug. 27; the planets will appear low to the eastern horizon and separated by only about a half-degree (the apparent width of the Moon).

MARS: Shines like a star with a yellowish-orange hue.  This will evolve into an "off year" for Mars, although it will be just coming off a splendid opposition during mid-autumn of 2005.  It will appear brightest in 2006 on New Year's Day, still glowing brilliantly at magnitude -0.6 in the constellation of Aries and outshining all the stars in the sky with the exception of Sirius and Canopus.  It will then be 72 million miles from Earth, but it will also be receding from us each night thereafter and hence will be getting progressively fainter.

By March 1, it will appear more than 3½ times dimmer and by May 9 it will have fallen into the ranks of a second magnitude object.  Mars will pass just over one-half degree from Saturn in the evening sky of June 17.  A month later, it is all but gone from view, becoming too deeply immersed in the solar glare to be seen.  It will be in conjunction with the Sun on Oct. 23, becoming a morning object. Not until about the middle of December will it emerge from the bright morning twilight. 

JUPITER: will appear as a brilliant "star" with a silver-white luster in the constellation of Libra, the Scales. It will be primarily a late-night/early morning object from January through April. 

By May and June it will be visible most of the night and will continue to be a convenient evening object through the end of October.  It is at opposition to the Sun on May 4.  It will disappear into the Sun's glow in early November and will again become visible in the morning sky during early December.

SATURN: Usually shines like a yellowish-white "star" of moderate brightness. It will be primarily a late-night/early morning object through much of January.  By late January into February it will be visible most of the night and will continue to be a convenient evening object through the middle of July.  It is at opposition to the Sun on Jan. 27 and will also have two close encounters with other naked-eye planets in 2006. 

It will pass just over one-half degree from a much-dimmer Mars on the evening of June 17 and will lie a similar distance from the much-more dazzling Venus on the morning of Aug. 27. Saturn is located within the relatively dim stars of Cancer, the Crab.  On February 2 and again on June 5, Saturn will be situated just below the beautiful cluster of stars popularly known as the "Beehive."  The famous ring system is visible in telescopes magnifying over 30-power.

From mid-March until the beginning of May, the rings will be tilted at a 20º angle toward Earth. You should take full advantage of this circumstance, because, we won't see the rings tipped 20º or more to our line of sight again until the year 2014!

URANUS: can be spied with the unaided eye under a clear, dark sky.  However, it is more easily seen in binoculars.  At magnitude +5.7, it is located in Aquarius and is at opposition to the Sun on Sept. 5.

NEPTUNE: is an 8th magnitude object visible in binoculars and in 2006 resides in Capricornus, the Sea Goat.  It arrives at opposition on August 11.

PLUTO: the smallest and most distant planet is, at magnitude 14 (about 900 times fainter than the faintest star visible to the unaided eye), the most difficult to observe.  You'll need a very dark sky, at least an 8-inch telescope and a finder chart to locate it.  In the constellation of Serpens, the Serpent, it's at opposition on June 16.

The Highlight of 2006: A Planet Trio

Jupiter, Mercury and Mars will engage in a most intriguing pre-Christmas gathering, very low in the east-southeast sky during the second week of December. The best time to look will be around 6:30 a.m. local time.  Unfortunately, the low altitude, plus this gathering's proximity to the Sun likely will render Mars invisible (or nearly so) to the unaided eye.  Binoculars are strongly recommended.  In contrast, Mercury and Jupiter should be more readily visible to the eye with only slight difficulty, as they will shine much brighter than Mars.

The trio will be most compact-fitting within just a 1-degree circle-on Dec. 10.  On this morning, the three planets will resemble a compact arrowhead pointing west, with Mars at the arrowhead.

There will also be separate conjunctions between Mercury and Mars (Dec. 9), Mercury and Jupiter (Dec. 10) and Mars and Jupiter (Dec. 11).  Also, for binocular viewers on the morning of Dec. 10, Mercury will appear to lie very close below and to the right of the second magnitude star Graffias in Scorpius, the Scorpion.


Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.

DEFINITIONS

1 AU, or astronomical unit, is the distance from the Sun to Earth, or about 93 million miles.

Magnitude is the standard by which astronomers measure the apparent brightness of objects that appear in the sky. The lower the number, the brighter the object. The brightest stars in the sky are categorized as zero or first magnitude. Negative magnitudes are reserved for the most brilliant objects: the brightest star is Sirius (-1.4); the full Moon is -12.7; the Sun is -26.7. The faintest stars visible under dark skies are around +6.

Degrees measure apparent sizes of objects or distances in the sky, as seen from our vantage point. The Moon is one-half degree in width. The width of your fist held at arm's length is about 10 degrees. The distance from the horizon to the overhead point (called the zenith) is equal to 90 degrees.

Declination is the angular distance measured in degrees, of a celestial body north or south of the celestial equator. If, for an example, a certain star is said to have a declination of +20 degrees, it is located 20 degrees north of the celestial equator. Declination is to a celestial globe as latitude is to a terrestrial globe.

Arc seconds are sometimes used to define the measurement of a sky object's angular diameter. One degree is equal to 60 arc minutes. One arc minute is equal to 60 arc seconds. The Moon appears (on average), one half-degree across, or 30 arc minutes, or 1800 arc seconds. If the disk of Mars is 20 arc seconds across, we can also say that it is 1/90 the apparent width of the Moon (since 1800 divided by 20 equals 90).