Tonight – April 30, 2018 – the almost-full waning gibbous moon is sweeping in front of the constellation Libra, where, it so happens, the dazzling planet Jupiter also resides. Seek for Spica, the brightest star in the constellation Virgo, above the moon and Jupiter. In a little over a week, Jupiter will be its May 9 opposition, so it’s shining at nearly its brightest and best for this year.
How many of you have birthdays between October 31 and November 23? We ask because the sun shines in front of Libra at that time of year. This year, in 2018, the sun enters the constellation Libra on October 31 at 7 UTC and leaves Libra on November 23 at 12 UTC. Of course, this constellation is lost in the sun’s glare at that time of year, so you won’t be able to see Libra then. The month of April is always a much better time of year for viewing Libra than in October and November.
Because the bright moon is now passing in front of Libra, the drenching moonlight will make it difficult to see the starlit figurine of the Scales right now. But the moon will drop out of the evening sky in a week or so, and then Libra’s faint stars will come into better view, assuming you’re away from city lights.
City or country – moon or no moon – Jupiter will be easily visible. Jupiter is the fourth-brightest celestial body to light up the heavens, after the sun, moon and Venus. Venus is out at evening dusk and nightfall, but sets in the western sky at early evening. Jupiter, near its May 9 opposition, will be a very prominent sight in the eastern sky after sundown for the coming month, and it’ll remain prominent through May and into June.
In other words, we’re now nearing the best time of year to see Jupiter. It’s now rising in the east when Venus is setting in the west. Jupiter stays in any constellation of the zodiac for roughly a year, and 2018 presents your opportunity to use Jupiter to learn the constellation Libra.
Jupiter is fairly close to Libra’s two brightest stars, Zubenelgenubi and Zubeneschamali, on the great dome of sky. Use Jupiter to more easily find these two modestly bright stars when the moon moves out of the evening sky in another few days.
You can’t miss Jupiter, but these Libra stars – without Jupiter – are a bit harder to locate. The chart below shows you one way to find them:
Bottom line: On April 30, 2018, let the moon guide you to Jupiter, and then let Jupiter escort you to Zubenelgenubi and Zubeneschamali, the constellation Libra’s two brightest stars, after the moon drops out of the evening sky in May.