Constellations reflect the seasons. Groups visible in winter evening sky like Orion and Gemini are called winter constellations. Virgo and Leo define the spring sky while Sagittarius and the Summer Triangle highlight summer nights. In mid-April I wouldn’t normally draw your attention to a winter constellation but Auriga the charioteer — a winter star pattern if there ever was — stands handsomely in the western sky this time of year. Venus also shines nearby to assist us in finding it. I couldn’t resist.
Although the 5-sided figure represents an ancient Greek character holding the reins of a chariot, the chariot itself is missing. Reflecting the sometimes ad hoc nature of constellation creation, three stars near his shoulder represent the goat Amaltheia, who suckled the infant Zeus, and her two kids. The trio is nicknamed “the Kids” and forms a sort of mini-constellation within Auriga called an asterism.
Auriga’s pentagonal outline always reminds me of a child’s drawing of a house with its cute peaked roof and a yellow sun shining off to one side. This house of stars has several “windows” each decorated with a showy star cluster, the celestial equivalent of a potted flower. From left to right they are M37, M36 and M38. Sharp-eyed observers can see all three with the naked eye from rural skies, but the rest of us will be delighted to see them with ease in binoculars.
Each looks like a small fuzzy spot of blended light from hundreds of individual stars. A small telescope will resolve all three into neat heaps of twinkling suns. A star cluster begin life as a massive cloud of dust and gas which collapses under its own gravity to congeal into stars. Capella is chariot dude’s brightest star, the sixth brightest in the sky and located 43 light years from Earth.
Sometimes Capella is called the “Goat Star” because in a separate myth Auriga is depicted as a goatherd. Powerful telescopes reveal that the star is actually double, composed of two closely orbiting suns just 60 million miles (96.6 million km) apart, equal to just two-thirds the distance between the Earth and sun.
The brighter, named Capella Aa, is yellow giant star 93 times brighter than the sun and 27 times as large. Capella Ab is also a yellow giant but a little smaller and fainter.
A reader wrote me a few days ago describing a bright, shimmering object in the northwestern sky that puzzled her. It moved during the night and then reappeared the next night. After she related details of the time and direction I knew it could only be Capella. Bright stars, when they’re low in the sky and their light passes through the bottom of the atmosphere, often twinkle like crazy. Thousands of individual air cells, each with a slightly different temperature and density, cross the line of sight between you and the star, bending its light this way and that, making it appear to “dance”. Like Sirius, Capella is a notorious “twinkler”.
The next time it’s clear, and you’re outside admiring Venus in the western sky, raise your gaze a little and enter the house of Auriga. All are welcome there.
*** SPECIAL EVENT: Stuck at home because of COVID-19? You can still enjoy the sky! Join me for the Night Sky Explorer — Launch into Skywatching on Zoom and on Facebook Live brought to you by Voyageurs National Park. I’ll teach basic skywatching techniques, discuss upcoming sights in the night sky and answer your questions during three live, online sessions. The first takes place on Tuesday, April 21 from 4-4:30 p.m. See you then!