A Meeting between Venus and Jupiter. Photo courtesy ESO/Y. Beletsky.
One of the more interesting astronomical sights is when two celestial bodies appear to visit each other in the night sky. Sometimes called conjunctions or appulses, the events often include some combination of planets, the moon, or the sun.
Over the weekend, on April 3 and 4, Mercury and Venus appear in a close pairing as they pass just three degrees apart. (Extend your arm with your index and middle finger pointing at the sky, the distance across spans about three degrees.)
Venus is a cinch to spot. Look west after sunset and the first point of light that appears near the horizon is Venus. It is shining brightly at magnitude -3.9. Mercury is three degrees to Venus’s right and a bit lower. (For observers in the Southern Hemisphere, the orientation between the planets will be slightly different, with Mercury appearing almost directly below Venus.) Mercury will be shining at magnitude -0.5, which, while bright for Mercury, is still only about five percent as bright as Venus. Don’t worry if your weekend is clouded out, the planets will keep close quarters for a week following this pairing.
Formally, a conjunction is when two objects get within five degrees of each other and share the same celestial longitude. Venus and Mercury will be close enough this weekend but will never quite share the same longitude; therefore this pairing is technically called a quasi-conjunction.
Another unique astronomical event occurs this weekend, but it’s one that you can’t observe. On April 3 at approximately 5:30 p.m. PDT, the Earth will be exactly 1 Astronomical Unit (AU, or 93 million miles) away from the sun. This is the average distance of Earth’s orbit around the sun. About half the time Earth is a bit closer to the sun (as it was on April 2) and half the time it is a bit farther than 1 AU (as it will be on April 4).
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Whitt loves clean, clear, and dark skies. Kelly
studied English and Astronomy at the University of Wisconsin-Madison and
worked for Astronomy magazine. She is currently the Feature Writer for
Astronomy and Space at Suite101.com. You can follow her on Twitter