Riding low in the summer sky is the constellation Sagittarius, looking like a teapot and containing some of the finest deep sky objects.
Credit: Starry Night® Software
One of the greatest pleasures on a warm summer evening is to sit outside and enjoy the riches of our Milky Way galaxy, with one such treasure ? a cosmic teapot ? making a terrific target for skywatchers this week.
To spot this humble teapot in the sky, the key is the constellation Sagittarius, the archer centaur. Eight of the brightest stars in Sagittarius form an asterism called "the teapot," which appears low on the southern horizon.
(This graphic shows how to spot the teapot asterism in the summer sky.)
An asterism is an obvious grouping of stars, too big to be a star cluster and too small to be a constellation. The most famous asterism is the Big Dipper, known as "the Plough" in Britain, the seven brightest stars of the constellation Ursa Major.
The Sagittarius teapot has its handle on the left, its spout on the right, and its lid on top. The rich star clouds and nebulae of the inner Milky Way rise from its spout like clouds of steam.
Seeing our Milky Way
Most people in our modern world have never seen the Milky Way because of the light pollution which pervades our urban skies.
In his book "NightWatch," author Terence Dickinson tells the story of how many people in Los Angeles flooded emergency phone lines after a late-night earthquake knocked out the power to report a strange silver cloud in the sky: Our Milky Way galaxy.
So, the first requirement for seeing the Milky Way is a really dark sky, which you will only find far from major cities. If you're in the northern part of North America, it will help to have a clear southern horizon, as the center of our galaxy is deep in southern skies.
Although the teapot's "steam" can be appreciated with the naked eye, it is at its best when viewed through a small binocular, say 7x50 or 10x50.
How to see the cosmic teapot
Start with the spout of the teapot and sweep slowly upwards. Even in less than perfect skies, you will see large clouds of distant stars.
First you encounter two of the brightest emission nebulas in the sky: the Lagoon Nebula (Messier 8) and the Trifid Nebula (Messier 20). Both of these are active star-forming regions like the Orion Nebula.
The Trifid Nebula (one "f") is named for its three-part appearance, not for the Triffid (two "f"s) aliens in Jun Wyndham's book "Day of the Triffids."
Further north you will encounter two more emission nebulas, the Omega or Swan Nebula (Messier 17), and the Eagle Nebula (Messier 16), site of the famous Hubble image of the "pillars of creation." Between the Omega and Trifid Nebulae lies one of the most intriguing objects in the sky.
Charles Messier, noted 18th and 19th century French astronomer, catalogued this as an open star cluster, Messier 24, but he was mistaken. Its true identify has only recently been discovered. It is not a cluster of stars at all, but instead is a window through the intervening clouds of dust in the Sagittarius Arm which lets us catch a glimpse of the inner Norma Arm of the milky way, 15,000 light years away from us.
Returning closer to the teapot, some of the most brilliant star clusters in the sky can be found.
The Sagittarius Cluster (Messier 22), just above the lid of the teapot, is the third brightest globular cluster in the sky, brighter than the more famous Hercules Cluster. To the right of the teapot's spout, across the border in Scorpius, lie two of the richest open clusters: the Butterfly (Messier 6) and Ptolemy's Clusters.
When we look into Sagittarius, we look towards the core of the milky way galaxy. The center of our galaxy is marked in the chart, but you won't see anything there, either with naked eye or binoculars. That's because of the clouds of dust and gas in the Sagittarius Arm which block our view of the core, 27 thousand light years away. Only through X-ray and radio astronomy is it possible to study the innermost regions of our galaxy.
- Gallery Amazing Milky Way Photos
- Beginner Astrophotographer Telescopes
- More Night Sky Features from Starry Night Education