September 18, 2026
First-Quarter Moon
The Moon is at first quarter today. Sunlight illuminates exactly one-half of the lunar hemisphere that faces Earth. The sunlit portion of the Moon will increase until the Moon is full on September 25 — the Harvest Moon.
September 19, 2026
Circumpolar Stars
The Big Dipper is low in the northwest at nightfall, and in the northeast at first light tomorrow. W-shaped Cassiopeia is just the opposite — in the northeast at nightfall, and the northwest at dawn.
September 20, 2026
Errai
Polaris stands almost due north, so all the other stars in the northern hemisphere appear to wheel around it as Earth turns on its axis. But Polaris will slide away from that spot. About 1,200 years from now, it will be replaced by Errai, in Cepheus the king.
September 21, 2026
Fall Equinox
Day and night will be just about equal the next few days for the entire world. That’s because fall arrives in the northern hemisphere tomorrow. It’s the September equinox, which is the moment the Sun crosses the equator from north to south.
September 22, 2026
Mirach
The binary system known as Mirach forms the second-brightest star in the constellation Andromeda, which is in the east and northeast as night falls. The system’s main star, Mirach, is almost 100 times wider than the Sun and almost 2,000 times brighter.
September 23, 2026
Neptune at Opposition
Neptune was discovered 180 years ago today. And the planet is at its best this week. It’s in view all night and it shines at its brightest. But you need a telescope to see it. At nightfall it’s to the upper right of much brighter Saturn, which is low in the east.
September 24, 2026
Autumn Star
The best sign in the night sky that fall has arrived is the appearance of the “autumn star.” It’s the only bright star that puts in its best showing during the nights of autumn: Fomalhaut, the leading light of Piscis Austrinus, the southern fish.
September 25, 2026
Neptune Opposition II
Neptune is closest to Earth for the entire year. The planet shines at its brightest. You need help to see it, but its location is easy to spot. At dusk, it’s between the Harvest Moon and the planet Saturn, which looks like a bright star to the lower left of the Moon.
September 26, 2026
Harvest Moon
The Moon is full today. But it’s not just any old full Moon. It’s the best-known of them all: the Harvest Moon. Tonight, the planet Saturn is quite close below the Moon at nightfall, and stays close throughout the night. It looks like a bright star.
September 27, 2026
Moon and Saturn
Saturn stands to the right of the bright gibbous Moon in early evening. The solar system’s second-largest planet looks like a bright star. It will stay close to the Moon all night.
September 28, 2026
Winter Preview
You can get a preview of the evening skies of winter in the hours before sunrise. Highlights include the constellations Orion and Gemini, along with Sirius, the brightest star in the night sky. All of them are high up at first light.
September 29, 2026
Kaus Australis
The stars of Sagittarius form the outline of a teapot. But in Greek mythology, the constellation represented a centaur — half-man, half-horse — holding a bow and arrow. Its brightest star, Kaus Australis, is at the lower right corner of the teapot.
September 30, 2026
Saturn at Opposition
Saturn puts in its best appearance of the year over the next few nights. On Sunday, it will line up opposite the Sun. It’s closest to Earth then, so it shines brightest and it’s in view all night. It looks like a bright golden star, low in the east at nightfall.