A reminder to keep an eye out for halos around the moon and sun. We’re outside more often during the warmer months with more opportunities to notice things in the sky. Yesterday I caught the bottom edge of a colorful solar halo while making that first buzz with the lawnmower through a jungle of dandelions. Halos are created when light is bent or refracted by billions of microscopic, pencil-shaped ice crystals in cirrostratus clouds. Most have a radius of 22 degrees, making them 44 degrees or “four fists” in diameter. If you see thin, wispy clouds that stretch like a veil across the sky, halos may be in the offing.
Being outside in warmer weather also makes it easy to follow Venus’ quickening exit from the evening sky. Remember when it set at midnight? No more. 45 minutes after sunset tonight, the shining planet will be only 15 degrees high (a fist and a half held at arm’s length) in the northwest. A week from now that shrinks to 10 degrees and by late May, it’ll be lost in twilight’s glow.
Venus is rapidly closing in on Earth, growing larger all the time. You should now be able to see the planet as a tiny crescent moon in 10 power binoculars. Make sure to focus sharply and observe in early twilight, when the planet’s glare is reduced. Venus undergoes phases just like the moon.
When it’s on the opposite side of the sun from Earth, it looks “full”, but as the planet catches up with ours, Venus’ phase shrinks to half and finally a crescent before gliding between the Earth and sun. If you observe Venus regularly through the end of the month, you’ll see the crescent enlarge and grow thinner as the distance between the two planets shrinks.
After crossing the solar disk on June 5 during a rare transit, Venus will swing west of the sun and pop out days later in the morning sky at dawn. It will still be a crescent, but because it will then be on the other side of the sun as seen from Earth, the “left” or side of the planet will be illuminated as a thin crescent. The flip-flopping crescents are fun to see in binoculars and telescope; there’s no better demonstration of how Venus keeps on truckin’ along its orbit. As for the June 5 transit, I’ll have more on how to view it soon. It will be the last time in our lives we’ll be able to see one.