Ready For Summer Skies? Say Farewell To Winter First

Many of winter’s constellations line up at eye level across the west and north in late twilight this week and next. Catch them before they’re gone! Created with Stellarium

The grass mocks me. A couple weeks ago, it was brown. Now it’s suddenly green, overgrown. The thought of mowing more than an acre every week with a self-propelled lawnmower weighs on my mind. Spring’s moving fast, and summer will soon be here. And yet.

And yet at dusk, we can look west and still see the twinkling remains of the winter sky. There they are, all arrayed at eye level: Canis Minor the Lesser Dog with its alpha star, Procyon; Gemini the Twins and the level-to-the-horizon luminaries Pollux and Castor; Perseus the Hero hunkered down low in the northwestern sky; Auriga the chariot driver with big, bright Capella twinkling in the deepening blue; and the W of Cassiopeia finally a W instead of an M or zigzag.

Find a spot that’s offers a wide open view from west to north sometime in the next week and get a look at these winter’s celebrities before the curtain falls. Except for Cassiopeia, which is circumpolar from mid-northern latitudes, all the others are gradually drifting westward, dropping lower each night until they transition from the evening into the morning sky.

View of Earth’s orbit seen from above the northern hemisphere. As our planet moves to the left or counterclockwise around the Sun, the background constellations appear to drift to the right or westward. This causes constellations and planets in the western sky to gradually drop lower every night, while those in the east rise higher. Credit: Bob King

Stars and planets alike drift to the west over the weeks and months as a result of Earth’s annual motion around the sun. When passing a car on a freeway, you first see it ahead of you then watch it recede behind you as you pass. As the Earth revolves around the sun, we see a constellation or planet “up ahead” or in the morning sky, then pass it, when the star group appears highest in the evening sky, and finally watch it recede out the “back window” into the western sky.

Because the freeway Earth travels is basically circular, the whole cycle repeats every year. Constellations that appear high up at nightfall in spring are called spring constellations, those in winter, winter constellations and so on for each season. As you’ve probably guessed by now, this blog is just another way for me to avoid gassing up the mower. Hmmm … what else might I write about?