Sagittarius

Where the galaxy's center hides

Sagittarius, the Archer, is a zodiac constellation in the southern part of the summer sky. Its fame comes from what lies behind it: the center of the Milky Way, our home galaxy, is in this direction, about 26,000 light-years away.

We cannot see the center itself, because thick clouds of dust block its light. What we do see is a crowded band of stars, glowing gas and dark lanes. Few parts of the sky hold so many targets in such a small space.

The Sun passes through Sagittarius each year from about mid-December to mid-January, so the constellation is hidden in daylight during northern winter.

Because the galaxy's bright core lies here, Sagittarius is also the favorite region for Milky Way photographs. A camera on a tripod with a 20 to 30 second exposure picks up colors and dark lanes that the eye cannot see.

How to find it

In July and August, look south about an hour or two after dark. From 40°N, Sagittarius stays low, with its bottom stars only about 10 to 15 degrees above the horizon, roughly a fist and a half at arm's length.

First find Antares, the bright reddish star in Scorpius, which is easy to spot low in the south. Move left (east) about two fists and you reach eight stars shaped like a teapot, with a lid on top, a handle on the left and a spout on the right.

Another route starts at the Summer Triangle. Follow the Milky Way down from Altair and Aquila toward the horizon; where the band becomes thickest and brightest, the Teapot sits right beneath it.

The main stars and their names

Most of the star names here come from Arabic and describe parts of the archer's bow. Kaus Australis (Epsilon Sagittarii), the brightest at magnitude 1.85, means roughly 'southern part of the bow'. It marks the bottom right of the Teapot, about 143 light-years away.

Nunki (Sigma Sagittarii), magnitude about 2.1, sits on the handle; its name comes from an old Babylonian word. Kaus Media and Kaus Borealis, the 'middle' and 'northern' parts of the bow, form the left side of the spout and the lid's top.

A curiosity: the stars labeled Alpha and Beta are faint and lie far south, near the horizon for northern observers. The Greek letters were not given strictly by brightness here.

Deep-sky objects for binoculars and small telescopes

The Lagoon Nebula (M8) is a cloud of glowing gas where new stars are forming, about 4,000 light-years away. In binoculars it looks like a soft gray patch with a small star cluster inside, just above the spout.

A little higher lies the Trifid Nebula (M20), split by dark dust lanes, though a small telescope helps to see them. Further up, the Omega Nebula (M17) looks like a bright streak with a hook, sometimes called the Swan.

Near the lid, M22 is one of the brightest globular clusters in the sky, a ball of hundreds of thousands of old stars. Between these, the Small Sagittarius Star Cloud (M24) is a window through the dust into a dense field of distant stars. Open clusters M23 and M25 are nearby too.

Mythology

The archer figure is very old. Babylonian astronomers showed the god Pabilsag here as an archer with wings and two heads, more than 3,000 years ago.

The Greeks drew a centaur, half human and half horse, aiming an arrow toward Antares, the heart of the Scorpion. Some writers linked him to Crotus, a satyr who invented archery, rather than to the wise centaur Chiron, who is usually placed in Centaurus.

In Turkish the constellation is called Yay, and many other cultures saw different shapes in the same region, often focused on the dark lanes of the Milky Way rather than the stars.

Practical observing tips

Choose a site with an open southern horizon, free of trees and city glow. A moonless night between late June and early September is ideal, and the hours around 10 to 11 p.m. put the Teapot at its highest.

Let your eyes adapt for 20 to 30 minutes and use only a dim red light. Then sweep slowly upward from the spout with binoculars. Dark lanes, star clouds and fuzzy patches will appear one after another.

Observers further south, for example around 35°N or below, see Sagittarius higher and clearer. If you travel south in summer, it is worth taking binoculars.

A planisphere or a free planetarium app helps you check where the Teapot will be before you go out. Planets such as Jupiter or Saturn sometimes pass through Sagittarius, because it lies on the ecliptic; a very bright 'extra' star in the Teapot is usually one of them.