10 May 2006

Jupiter and the Full Moon

As Summer approaches, there are three major planets visible in the night sky. Saturn continues to glow high in the western sky after sunset near the twin stars of Gemini. Mars is lower in the west, a slowly fading red "star" visible after sunset. But the new giant of the evening sky is Jupiter which is just arriving in the east after sunset and will remain a blazing bright object in the sky for the Summer.

This month Jupiter is visible in the south-east sky. It is at "opposition" which means that the Sun, Earth and Jupiter are all in a straight line in early May. For that reason Jupiter rises at sunset, reaches its highest point in the sky at midnight, and sets at sunrise. Additionally it is closest to the earth and is therefore brightest and looks the largest when viewed through a telescope.

The full Moon passes very close to Jupiter on the nights of May 11 and May 12. Given Jupiter's intense brightness, it will still be very distinct next to the full Moon. You can notice on these nights that stars near the Moon will nearly fade from view but the brightness of Jupiter is so strong that it remains easy to spot. The one star that will remain somewhat visible is Spica, the brightest star in the constellation Virgo. On the diagram you can see that the Moon will be very near Spica on the evening of May 10.

If you have a small telescope or binoculars it's worth viewing Jupiter because you can see the four largest moons of Jupiter near the planet. Through 7x or 10x binoculars they will be small points of light in a straight line near Jupiter. Through a telescope they are quite distinct and line up beautifully. These four moons are known as the Galilean moons because they were first observed and documented by Galileo.