With summer’s luminaries dropping from view, a new season opens up in the evening sky. Pegasus slides into view in the east shortly after night falls, marked by the Great Square. The constellations that form the “celestial sea” — Capricornus, Aquarius, Pisces, and others with a watery theme — flow across the south during the night. The Milky Way arches high overhead during the evening, putting on a grand display from sites with dark skies.
This Week's Stargazing Tips
September 16: Mars and Antares
The planet Mars is in the southwest as night falls, shining like a bright orange star. Not far to its left, look for equally bright Antares, a star that shines with the same orange color.
September 17: John Goodricke
A star with a demonic reputation climbs the northeastern sky this evening. Algol represents the head of Medusa, a monster that’s part of the constellation Perseus. The star fades and brightens, which may have helped inspire its reputation.
September 18: Moon and Companions
The Moon has a couple of bright companions before dawn tomorrow. The brilliant planet Jupiter stands to the lower left of the Moon, with the fainter star Procyon a little farther to the Moon’s right or upper right.
September 19: Moon and Jupiter
The planet Jupiter shines like a brilliant star to the upper left of the Moon early tomorrow. Binoculars reveal its four largest moons. One of them is covered with giant volcanoes while another may have an ocean of liquid water beneath its icy crust.
September 20: Moon and Regulus
Regulus, the brightest star of Leo, the lion, stands close to the left of the crescent Moon at dawn tomorrow. Regulus consists of at least four stars, although only one of them is bright enough to see with the eye alone.
September 21: Autumnal Equinox
Autumn arrives tomorrow at the autumnal equinox, the day on which the Sun crosses the equator heading south. Over the next three months the Sun will move even farther south, bringing shorter, cooler days to the northern hemisphere.
September 22: Autumnal Equinox
Under the astronomical calendar, today is the autumnal equinox. The Sun crosses the equator from north to south, marking the start of autumn in the northern hemisphere and spring in the southern hemisphere.
Check last week's tips if you missed a day.