Astro Bob: Is spring a mirage? Mercury returns at dusk

Sunrise mirage — It may look like a giant balloon or atomic bomb blast, but of course it's the sun, captured rising over Lake Superior on April 19. The bright "second sun" at the horizon is a mirage similar to the "water puddle" mirage you've seen on hot roads in summer. Warmer air near the surface — or in this case warmer water — bends the light of the sun near the lake's surface upward to create a second partial image below the real sun.

By Bob King

April 19, 2022 05:29 PM

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.

Inferior-mirage-Wiki-Ludovica-Lorenzelli-DensityDesign-Research-Lab-crop.jpg — In an inferior mirage, warm air at ground or water level (with colder air above) causes some of the light rays leaving a distant object to be bent down and then back up to our eyes, creating the illusion of a second image below it.

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.

Sunspots April 19 — The two big sunspot groups, Region 2993 (top) and 2994, are joined by a brand-new, unnumbered spot just rotating into view April 19. Sunspots near the edge of the sun appear squished or foreshortened because the sun is shaped like a sphere. We view them off to the side and around the sun's curvature. It takes about 14 days for the sun's rotation to ferry a sunspot across the solar disk. The three biggest spots in this photo are several times larger than the Earth.

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.

Quad planets — Although this map is set for April 21, all four planets will be in about their same positions through Saturday morning, April 23. Jupiter's visibility and brightness will greatly improve in the next two weeks as it climbs away from the sun. Compare this map to the photo below.

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.

Four planets — It's difficult to photograph the four planets because they're only visible from my latitude in a bright sky for now. I took this photo of the quartet over Lake Superior in Duluth, Minn., on April 19 at 5:30 a.m. It accurately captures their naked-eye appearance.

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.

Mercury finder late April 2022.jpg — This week, Mercury starts out low and bright (magnitude -0.9), but gradually moves farther from the sun and higher up in the northwestern sky in the coming weeks. Over the next few nights, look for it low in the west-northwest sky starting 45 minutes after sundown. It will be the only bright star in the area. Bring binoculars to assist.

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: 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.