Star Cluster to Pose With Venus in Night Sky

A brilliant star cluster will make an appearance with Venus this week, making it a rewarding celestial target for skywatchers equipped with small telescopes.

This coming Friday, May 21, Venus will pass just north of the beautiful star cluster Messier 35. The two will fit comfortably in the low power eyepiece of most telescopes, weather permitting.

The open star cluster will appear below Venus on Friday evening in the constellation Gemini. It is one of the largest and brightest star clusters in the sky. This sky map shows how to spot Venus and the star cluster.

Messier 35 is about 3,000 light-years away from Earth, about as far as the farthest stars we can see with our naked eye. This star cluster is almost exactly opposite the center of the Milky Way Galaxy in our sky.

Venus is gradually getting nearer to the Earth. This week it will be 1.3 astronomical units distant, an astronomical unit being the average distance between the Earth and the sun.

In a telescope, it looks like a tiny gibbous moon. By Aug. 20, it will be at its greatest elongation from the sun, 0.7 astronomical units away, and look like a quarter moon.

From there it quickly moves between the Earth and the sun, passing just below the sun on Oct. 29, only 0.3 astronomical units away, and moving into the morning sky. Even more startling is its change in size, from 12 arcseconds in diameter this week to a full arcminute on Oct. 29, five times larger in diameter.

The next time Venus passes between us and the sun will be on June 5, 2012, when it will actually pass directly in front of the sun, in what is called a transit of Venus.

It last did that in 2004, and won't do it again until 2117, so this will be the last chance to see a transit of Venus in your lifetime.

What does "Messier 35" signify? It is the 35th object in a catalog prepared by French astronomer Charles Messier in the 18th century. Messier (1730?1817) was primarily interested in comets, and began to keep track of objects in the sky which could be confused with comets in the telescopes of the day. These objects constitute what we call today "deep sky objects": astronomical objects mostly located beyond the stars we see every night in the sky.

Nowadays the objects which Messier catalogued are favorite targets for most amateur astronomers with telescopes.

Observing all of these 110 objects is a useful project for beginning astronomers, since they include the brightest and best objects in the night sky. Make a start on your "Messier list" tonight as Venus guides you to Messier 35.

• Gallery — Venus Crosses the Sun, Part 2
• Images — Messier Objects in the Sky
• More Night Sky Features from Starry Night Education

This article was provided to SPACE.com by Starry Night Education, the leader in space science curriculum solutions.