Western Slope Skies - 5/23/14

May 23, 2014

Mercury in Evening Twilight

Have you ever seen the planet Mercury? When conditions are near optimal, Mercury is easy to see. However, optimal conditions are rare, and many casual observers search for Mercury without success. This is because of the planet’s proximity to the sun.  The safe time to view Mercury is after sunset or before sunrise, depending upon the Mercury's orbit.

Mercury is the closest planet to our Sun, taking just 88 days to complete an orbit and is best seen when it is close to its greatest elongation. This means that its distance from the Sun from Earth’s perspective from the Sun is greatest. This perspective view is called “angular separation”!

Our solar system’s innermost planet will be well positioned to view in the evening sky for the next several days, reaching its peak separation from the Sun on May 24th.  Find a place that has a fairly flat north- northwestern horizon.  Mercury will become fairly easy to find about 35 minutes after sunset and remain visible for about 50 to 80 minutes before it sets in the north-northwest.     

The Greeks gave Mercury two names: Apollo, for when it appeared as a morning star, and Hermes, when it came as an evening star. In Roman mythology Mercury is the god of commerce, travel and thievery, the Roman counterpart of the Greek god Hermes, the messenger of the Gods. The planet probably received this name because it moves so quickly across the sky.

Because of Mercury's small size and nearness to the sun, the planet is often hard to see from the Earth without a telescope or binoculars. When viewed through a telescope, Mercury can be seen going through changes in shape and size. These apparent changes are called phases and resemble those of the moon. They result from different parts of Mercury's sunlit side being visible from the Earth at different times.

Should you use a telescope or binoculars to view the planet, always use extreme caution when observing objects close to the sun.