Now is a great time to use Venus, which is unmistakably bright in the Western sky at sundown, to identify a pair of stars: Polllux and Castor. The three objects are nearly in a line Friday night, June 11 (shown here). On subsequent nights, the stars will move lower and away from Venus. On June 14, a thin crescent moon will hang just below Venus.
Credit: SPACE.com/Starry Night Software
Venus appears so dazzling that it's now capturing the gaze of countless millions soon after sunset, and this week for those situated north of the equator it will appear to stand higher in the western twilight sky than at any other time this year.
Weather permitting, this brilliant lantern-like planet will shine more than 25 degrees high at sunset and still about 15 degrees above the horizon as the last bit of twilight glow fades. For comparison, your fist held at arm's length covers roughly 10 degrees of the night sky.
It's All Downhill from Here
What is unusual is that while Venus is now at the pinnacle of its evening visibility, its greatest elongation (angular separation) from the sun is still more than two months away, in late August.
The reason for this paradox can be traced to the difference in declination between Venus and the sun Declination is a coordinate on the celestial sphere, and is analogous to latitude on the Earth's surface. The declination of an object is how many degrees it is north or south of the celestial equator.
Right now, Venus and the sun are positioned about 23 degrees to the north of the celestial equator, which is about as far to the north as either object can appear. But in the coming days and weeks, Venus will appear to slide rapidly toward the south, causing it to appear to steadily lose altitude in the sunset sky.
When it reaches its greatest elongation from the sun on Aug. 20 it will be nearly 20 degrees south of it in declination. So it will be noticeably lower in the sky at sunset, as well as appearing to set more toward the south of due west.
And since both the sun and Venus will continue to head south through the balance of summer and on into the fall, Venus will become increasingly more difficult to see.
By October, it rapidly sinks out of sight; from mid-northern latitudes we'll have to struggle to catch it very low in the west-southwest soon after sunset during the opening days of the month. Venus will become hopelessly lost in the glare of the sun shortly thereafter, as it falls past it ? inferior conjunction ? on Oct. 29.
But at least for now, evening viewers are seeing Venus at its very best for 2010.
Some striking conjunctions
Skywatchers using their unaided eyes and binoculars will see some dramatic Venus conjunctions (when the planet appears near another object) during the next couple of weeks.
In the dusk of Friday evening, June 11 for instance, Venus strikes an interesting pose with the "twin" stars, Pollux and Castor in the constellation Gemini, forming a nearly straight and horizontal line in the sky.
But that's not all. A lovely crescent moon, just 2 1/2 days past new phase, comes onto the western stage on June 14. [Stunning full moon photo.]
While they won't appear exceptionally close, Venus and that slender sliver of the moon will still make for a pleasing tableau in that Monday evening's west-northwest sky, Venus appearing to ride well above and slightly to the right of the moon.
Then Venus continues on a beeline toward the Beehive star cluster (M44) in faint Cancer, the Crab, arriving there during the evenings of June 19 and 20.
Wait until about an hour after sunset and use binoculars or a wide-field telescope to detect the cluster as a faint sprinkling of stars just to the lower left of Venus.
On June 18 Venus will be just 1/2 a degree northeast of 5th magnitude star Eta Cancri. It will be at the northwest edge of the Beehive the next evening, and at the northeast edge of the cluster the night after that.
Normally, the Beehive is visible to the naked eye as a hazy spot of light, but right around these nights the close proximity of Venus will likely overwhelm any chance of spotting the cluster without optical aid.
You should be able to detect the small, dazzling, yellow-white gibbous phase of Venus in your telescope if the atmosphere is calm and you observe as early in twilight as possible, before Venus has sunk too near the horizon.
And on June 23 Venus will stand about midway between the stars Pollux and Regulus.
Venus at midnight?
Not a few astronomy texts and stargazing guides will tell you not to bother looking for Venus at midnight, since it always sets within a few hours of sundown and is usually long gone from the sky by the middle of the night.
However, this week, since we are getting near to the time of the summer solstice, the sun appears to be setting practically as late as it can set. In addition, most parts of the United States and Canada are now on daylight saving time.
As a consequence, even though it's setting only about 2 1/2 hours after sunset, Venus is setting rather late for most places: generally within several minutes of 11 p.m. local daylight time. However, if you live near the western boundary of your local time zone or at a latitude north of 45 degrees, Venus will be setting close to, or even after the stroke of midnight.
From Indianapolis, Indiana, for instance, Venus will set at 11:47 p.m. EDT. From Winnipeg, Manitoba, Venus will set at 12:09 a.m. CDT.
And for Houghton, Mich., Venus doesn't set until 12:22 a.m. EDT, while those who live in Edmonton, Alberta can enjoy their view of Venus until well past 12 midnight ? 12:33 a.m. MDT to be exact!
- Gallery Venus Seen From Around the World
- Photos Venus Crosses the Sun, Part 2
- Telescopes for Beginners
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.