The waxing gibbous moon glides close to the the star Spica this evening, on May 21, and pairs up with the planet Saturn tomorrow, on May 22. The moon will pass relatively close to Spica and Saturn for the next several days, as the moon moves in its endless orbit around Earth.
Of course, in reality, the moon’s nearness to Spica aor Saturn tonight is just a line-of-sight illusion. The moon never gets close to Spica in a true sense because the moon orbits Earth at only about one light-second away – while Spica is 260 light-years away. Saturn, though much closer than Spica, is still a very distant 74 light-minutes away from Earth right now.
Saturn has been fairly close to Spica throughout 2013 so far, and it will stay in the vicinity of Spica for the most of 2013. While the moon stays in any one constellation of the Zodiac for two or three days, Saturn stays in the same zodiacal constellation for up to two or three years. You can distinguish the star Spica from the planet Saturn by color. Spica radiates blue-white while Saturn appears golden. You may need binoculars to see their colors in the moonlit glare tonight or for the next several nights, but you’ll clearly see the contrast after the moon moves on.
Spica is the 15th or 16th brightest star in the sky (it’s neck-and-neck with the star Antares, in terms of brightness). Spica is a close double star, and both stars in the Spica system are much hotter and brighter than our sun. In fact, there is some evidence that there are as many as three more smaller, fainter stars in the Spica system.
A tip for finding planets in our night sky. Each month, the moon pairs up for a day or two with other bright stars such as Regulus in the constellation Leo, Antares in the constellation Scorpius and Aldebaran in the constellation Taurus. These stars are located on or near the ecliptic – or path of the sun, moon and planets – in our sky.
On the other hand, you’ll never hear of the moon or Saturn near Polaris the North Star. If someone tells you they saw the moon or Saturn near Polaris, you’ll know that can’t be so. The moon and the planets have a set path in the sky, approximately the same path as that followed by the sun each day. That path is the ecliptic. Meanwhile, Polaris is far to the north on the sky’s dome, in a part of the sky the moon and planets never visit. So that’s your tip for finding planets: always look for planets along the same path across our sky followed by the sun and moon.
Bottom line: Tonight – May 21, 2013 – look for the bright waxing gibbous moon to appear near the star Spica in our sky.