Your late April evening lineup
We have a nearly straight diagonal line of celestial bodies this week in the early evening, low western sky. You don’t need binoculars or telescopes to see them, just your God-given eyes. From the lower left to upper right, you’ll see a parade led by the bright star grand marshal, Sirius, followed by the red giant star Betelgeuse, and then the super-bright planet Venus with another bright star, Capella, bringing up the rear.
Sirius is the brightest nighttime star seen throughout the year in Marshall. In late April Sirius shines away in the low southwestern sky close to the horizon. Look for it as early as you can because it sinks below the horizon less than two-and-a-half hours after sunset. Sirius is the brightest star we see at night mainly because it’s so close to the Earth, about eight-and-a-half light-years away. With one light-year equaling almost 6 trillion miles that would put Sirius at nearly 50 trillion miles away, which believe it or not, makes it a close-by star! For extra credit take a look at Sirius with binoculars or a small telescope. You’ll love what you see! Sirius will take on the appearance of a kaleidoscope, randomly flashing a wide variety of multiple colors. That’s not the true nature of Sirius, but rather the optical effects of the thicker layer of Earth’s atmosphere near the horizon. Sirius’s light has to negotiate through a lot of air. Turbulence or wind shear in the atmosphere makes all stars twinkle. In the much thicker atmospheric shell near the horizon there’s so much turbulence that it bends the light from Sirius by varying amounts causing Sirius to put on quite a show!
Next in the parade is Betelgeuse, the next brightest star you see to the upper right of Sirius. Betelgeuse is the second brightest star in the famous constellation Orion the hunter that’s already partially below the horizon. Even to the naked eye you can easily see it has an orange-red hue. Betelgeuse is categorized as a super red giant star, and at times swells out to a billion miles in diameter. Our own sun isn’t even a million miles in width. Betelgeuse has been in the news lately because it appeared to be dimming in brightness earlier this year but is starting to brighten up again. That could be a sign that Betelgeuse will soon explode as supergiant stars do. Don’t wait up for it though! Soon in astronomical terms can mean up to a million years in the future. Betelgeuse is more than 500 light-years away, so when it does explode it won’t damage our home planet.
The next bright “star” to the upper right of Betelgeuse in the western sky is the planet Venus. It’s very bright, mainly because of its highly reflective and thick cloud cover that completely engulfs this Earth-sized world. The clouds bounce a lot of second-hand sunlight our way. Venus is also about as bright as it can be because right now, it’s nearly as close as it ever gets to Earth, only 42 million miles away. Through a telescope or binoculars Venus resembles a crescent moon. The planets Venus and Mercury go through the same phase cycle as the Earth’s moon, in a much longer duration, because their orbits around the sun lie within the Earth’s orbit.
Capella, the caboose star in the celestial parade, shines away a little to the upper right of Venus. It’s 42 light-years away, and the brightest star in the strange constellation Auriga the Charioteer. Forget about Auriga resembling a chariot driver. The constellation looks more like a lopsided pentagon with Capella at one of the corners. Capella is known as the “she-goat” star. That’s because that’s where a mama goat is clinging to the shoulders of the chariot driver. Go figure! Astronomically Capella is not just one giant star but two giants and two smaller stars, all revolving around each other every hundred days or so. It’s believed the two giant stars may be separated by only 62,000 miles!
If you happened to check out this parade on Sunday night, 4/26, the new crescent moon will be joining the lineup. It will be perched just to the left of Venus and should be quite a sight. As a big bonus, if skies are really, really clear, you’ll be able to see a beautiful phenomenon called earthshine. Not only can you see the bright sunlit crescent slice of the moon’s disk, but you can also see the rest of the moon bathed in a pale gray light. That light is second-hand sunlight bouncing off the Earth’s reflective atmosphere and onto to the moon.
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is also the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and at adventurepublications.net.