Hey! What are those bright stars in the west right after sunset?

Monday, August 29th, 2005 at 04:25 PM by Dave

(Click on image for full-size version.) The September 1 Conjunction of Venus and Jupiter as visible from Saint Cloud, MN at 8:30 pm CDT.

You’re right, they are stars…but only if you happened to be an ancient Greek. The ancient Greeks called all bright points of light in the night sky "stars." However, the two bright stars you see in the west are what the ancient Greeks refered to as "asteres planetai" (loosely translated, "wandering stars"). These "asteres planetai" were set apart from the majority of stars which don’t move in relation to one another. These "asteres planetai" are what we call in modern English "planets." We now know that planets are large bodies that revolve around the Sun. Enough of the history lesson.

The brighter of the two planets visible in the western sky is Venus. Venus is found between the Earth and the Sun. Jupiter, on the other hand, is found beyond the Earth’s orbit. By having Jupiter on the other side of the Sun and Venus between the Earth and Sun, they appear to be close to each other. In reality they are very far apart.

(Click on image for full-size version.) The “Triple Conjunction” of Venus, Jupiter, and the Crescent Moon as visible from Saint Cloud, MN on Sept. 6 at 8:15 pm CDT. The images in this post were generated using Starry Night Pro 5.0 by Imaginova.

On September 1-2 they will be the closest together in the sky. This is called a conjunction. This situation for these two planets will not occur again until February 2008. The distance between these two bodies at this date will be 1 degree of arc or the apparent thickness of a person’s pinky finger at arm’s length. Remember that this is the apparent distance between them from our point of view, not the actual distance.

What may be even more beautiful will occur on evening of September 6 when a slender crescent moon will appear with these two separating planets to form a “triple conjunction”. When this happens it will form a compact triangle (as shown).

Enjoy the night sky!

Posted in Astronomy News, Outreach

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