As summer's end approaches, constellations trade places
It is still officially summer for three more weeks, but summer is doomed. The Labor Day weekend signals the end.
Astronomically, summer is defined as lasting until the fall equinox, when the sun crosses the equator heading south for the year. That will happen at 5:51 a.m. on Sept. 23. But even now, the shift from summer to fall is apparent in the evening stars.
For instance, look straight overhead at nightfall and you can spot bright Vega, the Summer Star. It is one of the brightest stars in any season. For a few minutes around 8:35, Vega will be so close to the zenith that you can imagine it would fall on you if it became detached from the sky.
All spring and summer Vega has been climbing up to this position. The beginning of September marks the start of Vega's long, slow descent in the west for the fall and early winter.
Whenever Vega is highest overhead, the teapot-star pattern of the constellation Sagittarius is also at its highest, balancing much lower due south. The teapot appears about the size of your fist held at arm's length. Its triangular spout is on the right, and it tilts as if to pour, as shown here. It also has been climbing at dusk all summer, and starts its decline about Sept. 1.
To the right of the teapot, in the southwest, Jupiter is already well down on the way to its seasonal exit. Look for twinkly-orange Antares below Jupiter by about three finger-widths at arm's length.
Turn further right and look northwest. There is the Big Dipper, with its bowl to the lower right and its bent handle to the upper left. The Big Dipper dominated the high sky of spring and summer evenings; now it is on the way down to its November and December lows.
Look equally high in the northeast to spot the flattened W of the constellation Cassiopeia. The righthand side of the W (the brighter side) is tilted up. Cassiopeia is a landmark of fall and winter, and it is opposite the Big Dipper. The two revolve around the north celestial pole, trading places with the cycles of the year. They pass each other on about Sept. 1, with the Dipper descending to become lower at nightfall and Cassiopeia becoming the higher constellation.
Another shift occurs due west for bright Arcturus, the Spring Star. Look due east equally high for the Great Square of Pegasus, the signature star pattern of fall. (It's a bit bigger than your fist at arm's length, and balances on one corner.) Every Sept. 1, Arcturus and the Great Square shine at the same height above opposite horizons at dusk.
But the balance tips; Arcturus begins sinking, and the Great Square becomes ascendant.
These natural cycles, visible to anyone who looks up and pays attention. were probably more familiar to your great-grandparents than you, as our lifestyles are increasingly indoors.
But you do not have to go along with this trend. Learn, and pay attention. It really matters whether that bird on the fence is a blue jay or a bluebird, and your life will be richer for knowing the difference and why it matters. Among the stars and planets, new discoveries are announced almost daily, but they only take on meaning if you can tell Jupiter from Arcturus over your own backyard.
It is only through this kind of personal connection, I believe, that people begin to take in the grand perspectives that science has revealed the last few centuries - our place on a small planet in an immense universe, our place in a rich, evolving biosphere that took several billion years to develop to this point - and why we should shed old myths and superstitions that have proven false in favor of bigger truths.
After all, that is how these truths were worked out, bit by little bit, by people noticing things in the natural world, wondering about them, and paying close attention.
Alan M. MacRobert is a senior editor of Sky & Telescope magazine (SkyandTelescope.com). His Star Watch column appears on the first Saturday of every month.
