When the sun goes down tonight, step outside and look south. Beaming through the twilight is one of the prettiest things you'll ever see - a tight three-way conjunction of Venus, Jupiter and the crescent Moon. The event is visible from all parts of the world, even from light-polluted cities.
People in New York and Hong Kong will see it just as clearly as astronomers watching from remote mountaintops. Only cloudy weather or a midnight sun (sorry Antarctica!) can spoil the show.
The great conjunction offers something extra to Europeans. For more than an hour on Monday evening, the crescent Moon will actually eclipse Venus. Astronomers call such an event a "lunar occultation." Venus emerging from the dark edge of the Moon is a remarkably beautiful sight. Sky watchers across Europe will be able to see this happen:
For Europeans
If you have been watching the western sky after sunset the last few evenings you cannot fail to have noticed two bright lights drawing closer together. Venus and Jupiter have been playing out the most spectacular sky show of the year and on Monday, December 1st they will be closest together, just two degrees apart. What marks Monday as extra special though is that Venus will be occulted by the Moon. The planet disappears in daylight for people in western Europe and reappears in a darker sky in th eearly evening.
For Eastern Europeans, this eye-catching sight will be visible in complete darkness.
The disappearance can be observed in steadily held binoculars or a telescope but great care should be taken lest you accidently sweep up the Sun when scanning the sky. The reappearance will be fascinating to watch as Venus will burst back into view from behind the Moon's limb.
Such favorable circumstances are quite rare for any given location. For
example, the last time London was treated to such a favorably placed Venus
occultation was back on Oct. 7, 1961.
And after 2008, there will not be another similarly favorable Venus
occultation for the United Kingdom until Jan. 10, 2032.
Conjunctions
A conjunction of the two brightest planets won't happen again until March, 2012. During this particular Venus and Jupiter conjunction, these two brilliant worlds appear 2 degrees apart. That's about the width of your finger at an arm length away.
It's possible - but extremely rare - to see two planets appear to merge into a single point of light. The last time two planets met up at the same spot on the sky's dome was in the year 1818, when Venus passed in front of Jupiter. Tonight and tomorrow night, look for Venus, Jupiter, and the crescent moon in the west after sunset.
Conjunctions of two planets are fairly common. The planets often meet and appear close together in the sky. But an occultation - or covering over - of one planet by another is very rare. Two planets won't meet again in the sky for another 247 years - or until Venus occults Jupiter in the year 2065.
The Planets
Venus has adorned the southwestern twilight sky since late August. No other
star or planet can come close to matching Venus in brilliance. During World
War II, aircraft spotters sometimes mistook Venus for an enemy airplane.
There were even cases in which Venus drew antiaircraft fire.
This winter, Venus is the unrivaled evening star that will soar from
excellent to magnificent prominence in the southwest at nightfall. The
interval by which it follows the Sun will increase from nearly three hours
on Dec. 1 to almost four hours by Jan. 1.
It's probably the first "star" you'll see coming out after sunset. In fact,
if the air is very clear and the sky a good, deep blue, try looking for
Venus shortly before sunset.
Jupiter starts December just above Venus and is moving in the opposite
direction, dropping progressively lower each evening. By month's end Jupiter
meets up with another planet - Mercury - but by then Jupiter is also
descending deep into the glow of sunset. In January, Jupiter will be too
close to the Sun to see; it's in conjunction with the Sun on Jan. 24.
Also on Monday evening, you may be able to see the full globe of the moon,
its darkened portion glowing with a bluish-gray hue interposed between the
sunlit crescent and not much darker sky. This phenomenon is sometimes called
"the old moon in the young moon's arms." Leonardo da Vinci (1452-1519) was
the first to recognize it as what we now call "earthshine."
As seen from the moon, the Earth would loom in the sky some 3.7 times larger
than the moon does for us.
In addition, the land masses, the oceans and clouds make the Earth a far
better reflector of sunlight as compared to the moon. In fact, the Earth's
reflectivity varies as clouds, which appear far more brilliant than the land
and seas, cover greater or lesser parts of the visible hemisphere. The
result is that the Earth shines between 45 and 100 times more brightly than
the moon.
Keep in mind that this head-turning display of three celestial objects
crowded together is merely an illusion of perspective: the moon will be
only about 251, 400 miles from Earth, while Venus is nearly 371 times farther
away, at 93.2 million miles. Meanwhile, Jupiter is almost 2, 150 times
farther away than our natural satellite at 540.3 million miles.
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