That’s Sagittarius in the southwest sky

  • Fri Sep 7th, 2012 9:07am
  • Life

By Mike Lynch

About 9 p.m. this week, when enough evening twilight has been chased away, look in the low south-southwest sky. Without too much trouble you’ll see a teapot hanging diagonally by its handle.

A distinct triangle of three bright stars make up the spout on the lower right side and a trapezoid of four stars on the upper left make up the handle. In between and above the handle and the pot is a single star that marks the top of the teapot.

This celestial teapot is formally known as Sagittarius the Archer. The uppermost right star in the handle is called Nunki, pronounced Nun-Key. It’s a star 225 light-years away or a little more than 1,300 trillion miles away. If you were to put it side by side with our sun it would be more than 3,000 times brighter.

According to Greek and Roman lore the constellation Sagittarius is supposed to outline a half-man/half-horse flinging an arrow to the west. With a little imagination you can almost see that. The spout stars outline the bow with the tip of the arrow at the tip of the spout.

The four stars of the handle would be the cocked elbow of the shooter. The top of the teapot would be his head. Seeing Sagittarius as a teapot is so much easier. The teapot nickname is relatively new to stargazing, evolving in the past 65 years or so.

If you’re lucky enough to stargaze at Sagittarius in the dark skies of the outer suburbs or the countryside, you’ll easily see a band of light arching overhead, stretching all the way from roughly the northern horizon to the southern horizon. This is the famous Milky Way Band, the thickest part of our home galaxy.

The Milky Way band runs right into Sagittarius. The center of our Milky Way Galaxy is right in the direction of the little teapot.

That part of the Milky Way band around Sagittarius is fairly bright. Even with a small telescope or a pair of binoculars you’ll find many, many star clusters and nebulae. Some of the better ones include the Eagle Nebula (M16), the Swan Nebula (M17) and the Trifid Nebula (M20).

The M numbers are Messier catalog numbers. The Messier catalog is made up of the brighter clusters, nebula, and galaxies. A great website to find these in the night sky is stellarium.com.

Above the spout of the teapot is what almost looks like a puff of steam. That puff is astronomically known as M8 or the Lagoon Nebula, a bright emission nebula, one of the larger and brighter star factories we can see. This is a huge cloud of hydrogen that is the raw material to mass manufacture stars. The Lagoon is more than 5,000 light-years away and roughly 100 light-years in diameter.

Stars form when denser pockets of hydrogen gas within the cloud gravitationally collapse, causing the temperatures in the core of these condensed balls to rise into the millions of degrees. When these high temperatures are reached, the extremely complicated process of nuclear fusion begins, and the ball of gas lights up into a star.

Even with a small telescope you can see many new young single stars and clusters of stars. These new young stars are very hot and are huge producers of ultraviolet radiation. All this energy atomically energizes the surrounding hydrogen gas and causes it to glow like a fluorescent light.

Mike Lynch is an astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and is author of the book, “Washington Starwatch,” available at bookstores. Check his website, www.lynchandthestars.com.

The Everett Astronomical Society: www.everettastro.org/.