Astro Bob: Spot of tea, anyone?
Iced or hot, enjoy a sip while we get acquainted with Sagittarius, home of the heavenly teapot.
I like the rich taste of coffee, but mostly I'm a tea drinker. It's simple to make, packs a modest caffeine punch and tastes and smells good. Who doesn't like cradling a hot cup of anything in their hands?
Sagittarius makes me think of tea. The constellation's brightest stars outline a simple kettle, just like the one in the "I'm a Little Teapot" song with its handle and spout. By late July, the Teapot is slowly moving toward center stage in the southern sky.
How high it is depends on your latitude. From the southern states it bubbles up above the treetops in the southeastern sky as soon as it gets dark. But if you live in the north it never climbs higher than the bottom quarter of the sky, so you'll need an open view in that direction to see more than just the lid and spout.
Recently, I spotted the whole pot from a nearby field around 10:30 p.m. local time in late twilight. During the third week of July, it's highest in the sky around local midnight. By the end of the month, it reaches that point almost an hour earlier.
The Teapot is only part of the larger constellation Sagittarius the Archer, who gambols directly behind Scorpius the Scorpion as they both slide westward across the summer sky. Years ago I was surprised to find out that the familiar Teapot is actually the archer's bow fitted with an arrow aimed squarely at Scorpius. The rest of the figure outlines a centaur, a mythological creature with the head, arms and torso of a man and the body and legs of a horse.
Sagittarius originated in ancient Sumeria where he was known as PA.BIL.SAG, a god of war and hunting depicted as a centaur with wings. The Greeks adopted the figure — without the wings — and passed it along to us as Sagittarius. The name derives from sagitta, the Latin word for arrow.
The Teapot reference came much later. I can't find a mention of it my early 20th century astronomy guides, but it's been in use since at least the late 1930s. Since that time observers have expanded on the idea. Above and left of the kettle you'll now find the "Spoon," while below the figure a lemon wedge awaits squeezing. My favorite tea metaphor is the billowing Milky Way which issues from the spout like a cloud of steam.
Along the eastern (left) side of the constellation, the "lid star" paired with the handle form yet another asterism, the Milk Dipper. This "little dipper" of the southern sky also subs as a utensil for adding milk to your tea, popular with British drinkers. Unlike the Teapot, Milk Dipper has been in use since at least the 19th century and refers to a ladle for "dipping" into the Milky Way.
The Teapot spans a fist and a half across or about 15°. It's home to one of the brightest, densest regions of the Milky Way, making it an absolute joy to explore in binoculars or a telescope.
Fittingly, when we look in the direction of the constellation we're also facing the center of the Milky Way galaxy and the supermassive black hole throbbing in its core. Located 26,000 light-years away and hidden by clouds of stardust from supernova explosions, picture it in your mind's eye a short distance above and to the right of the spout. Restive and ravenous, the 4-million-solar-mass beast awaits its next meal.
While Sagittarius A* remains beyond our ken, we can revel in the bounty of star clusters and nebulae that light up these star clouds. All the objects I've labeled in the photo are visible in binoculars and small telescopes from moderately dark to dark skies on nights when the moon's phase is less than half.
M8 is the brightest nebula of the summer season and as easy to spot in binoculars as winter's Orion Nebula. The sparkly open cluster M25 will also surely catch your eye. The M stands for Messier as in Charles Messier, who compiled a catalog of the brightest clusters, nebulae and galaxies in the late 18th century.
With the waning moon now rising after midnight, we've got more than two weeks of dark skies ahead to sip in the wonders of the Sagittarius Milky Way. So what'll it be — black, green, white, oolong, puer or herbal? Black with a gram of sugar for me.