Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2002 December 4 
Posted on 12/03/2002 11:14:19 PM PST by petuniasevan
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2002 December 4
Explanation: Gliding toward today's total eclipse of the Sun, the crescent Moon has been rising early, just before dawn. And as a prelude to its close solar alignment, the Moon also completed a lovely celestial triangle, closing with bright planets Mars and Venus on the morning of December 1. While the total solar eclipse can only be seen from a narrow corridor, skygazers around the globe could appreciate this lunar-planetary conjunction. This view is from near Nashville Tennessee, USA, and finds brilliant Venus at the lowest corner of the triangle with a much fainter Mars immediately to the right of the Moon. The Moon's crescent is overexposed, but details of the lunar night side are revealed by earthshine. Above and to the right of the trio is Spica, brightest star in the constellation Virgo.
Speaking of Jupiter, our closest encounter this orbit will be at the end of January. Jupiter will be 4.33 A.U. distant, shine at -2.6 magnitude, and will have an angular size of 46". On the other hand, at the end of August it will be on the other side of the Sun (appearing to be very near the Sun) at 6.38 A.U. and very hard to pick out of the glare though still at -1.7 magnitude and 31" angular size.
Note that Jupiter's "year" is about 12 Earth years.
Earth's orbital motion is responsible for most of the change in distance to Jupiter.
Why is the the object with the bigger angular size (Jupiter) not as bright as the object with a smaller angular size (Mars) at close Earth encounter? Answer: Both are reflecting sunlight, but Jupiter is over 3 times as far from the Sun as is Mars. Thus it doesn't get as much light to reflect. So although Jupiter is twice as reflective as Mars, it only gets a tenth the sunlight Mars gets. So even though Jupiter appears bigger in angular size, it still doesn't QUITE shine as bright as Mars at its best does.
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