Astro Bob: Is spring a mirage? Mercury returns at dusk
Weird things happen to the sunrise sun, plus we revisit the dawn planets and meet our first evening planet in a long while.
Spring is something of a mirage here in northern Minnesota. Every time the snow melts back a bit, a new storm refreshes it. The other day, 5 inches fell, followed by a chill wind and nighttime temperatures in the teens.
Only the rising chorus of fox sparrows, juncos and robins reminds us that despite the appearance of winter, spring is underway. I don't mind, really. We live in a world of fuzzy borders. It keeps things interesting.
While we're on the topic, there was a classic inferior mirage at sunup Tuesday morning over Lake Superior. As the sun rose, a second sun shone below it on the water. Such a bizarre sight! The cause is the same as the more familiar water-puddle-in-the-road mirage. We know that's not water on the hot road ahead, so what are we seeing? Turns out it's the sky.
The heated surface warms the air directly above it. Light from the sky streams down to the heated air layer, which acts like a lens and bends the light back up and into our eyes. Instead of road, we see skylight. For all the world it looks just like water.
As the sun rose, its light spread across the water and rocky shoreline, getting the day off to a golden start. Later, I checked on the progress of the two large sunspot groups that recently rotated into view. Region 2994 is still ripe for flares, fanning hopes for possible aurora sightings later this week or next. Timing would be ideal as the moon is now departing the evening sky.
My real reason for getting up early this morning revolved around the planets. Like you I was eager to see all four — Jupiter, Venus, Mars and Saturn — lined up in a row across the southeastern sky about an hour before sunrise. And while I saw them all, it wasn't easy without careful observation. Later, as the sky grew brighter, binoculars were a big help in pulling out fainter Mars and Saturn.
Venus is bright and the perfect place to begin. To its right are Mars and Saturn. Jupiter shines below and left, buried more deeply in the twilight glow. Binoculars magnifying 10x or more and braced against a car top or fence will easily show the gas giant as a disk. To see Saturn's lovely rings clearly, you'll need a small telescope that magnifies at least 30 times.
I saved the best for last. We finally get an evening planet! Mercury returns at dusk low in the northwestern sky starting this week (April 19) and continuing through the first week of May. This will be its best evening appearance of the year for northern hemisphere skywatchers and our first chance in several months to see a planet at dusk instead of dawn.
Mercury climbs higher and becomes better placed for viewing later in April. I'll have more information for you next week about its upcoming conjunction with the Seven Sisters Cluster. See you soon!
"Astro" Bob King is a freelance writer for the Duluth News Tribune.