THE SOUTHWORTH PLANETARIUM
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Altitude: 10 feet below sea level
Founded January 1970
Julian Date: 2459282.18
2020-2021: XCIX
"Why don't stop playing because we grow old. We grow old because we stop playing." -George Bernard Shaw
THE DAILY ASTRONOMER
Thursday, March 11, 2021
Exploratorium XXX: Whirlpools and Wild Ducks
Today, inspired by the unseasonably warm weather, we embark in the exploratorium to two different celestial locales: one is a wild star cluster and the other is one whirlpool of a spiral galaxy.
First for the flock of ducks!*
The "Wild Duck Cluster" Located in the constellation Scutum the Shield,
this cluster was so named as it resembles a flock of wild ducks in flight. These "ducks" are merely some of brightest stars within one of our region's richest and most compact galactic star cluster. Image by Rawastodata
The galaxy teems with galactic star clusters: clusters of relatively young stars gravitationally bound within the galactic arms. These clusters, such as the Pleiades and Hyades, contain a few hundred members spread out over an area spanning less than 100 light years. The Wild Duck Cluster is much richer, with an estimated stellar population of nearly 3000 stars! It is so bright, in fact, that this cluster is just under naked eye visibility despite being more than 6,000 light years away! In comparison, the Pleiades and the Hyades star clusters are 440 light years 153 light years away, respectively.
Though it isn't visible to the unaided eye, one can find the Wild Duck Cluster with binoculars. Your binoculars are likely more powerful than the telescope that 17th century German astronomer Gottfried Kirch (1639-1710) used when he discovered this cluster in 1681. In 1764, French astronomer Charles Messier included it in his catalog with the designation M11, meaning 11th entry.
Finding the "Wild Duck." The Wild Duck Cluster (M11) is technically within
Scutum the Shield, but can be found just south of Aquila the Eagle, the Summer Triangle's southern constellation. Image by washedoutastronomy.com
If one is out in the early morning scanning the skies just south of the Summer Triangle, be sure to observe the region about eight degrees south of Altair, the brightest star within Aquila the Eagle, There, lurking within the inky black of deep space, is a beautiful little flock of wild ducks.
Thirty seven million light years from Earth one finds the beguilingly beautiful Whirlpool Galaxy. Here one can behold a nearly perfect example of a pure spiral galaxy, in which spiral arms curl away from a spherical center so as to lend the entire structure both a vertical and horizontal symmetry. Astronomers believe that the galaxy's current symmetry is a result of its interaction with it companion galaxy, NGC 5195. Were one to observe our own beloved Milky Way from a distance, one would note that the center is barred, not spherical.) Though it contains more than 100 billion stars, the Whirlpool Galaxy is only about 45,000 light years in diameter, less than half the estimated size of the Milky Way. This size is derived directly from the galaxy's angular dimensions and distance, recently measured at 23 million light years.
The Whirlpool Galaxy, or M51, is a beautiful spiral galaxy about 23 million light years from our solar system. We observe the Whirlpool and its companion NGC5195, a smaller galaxy that will soon become incorporated into M51. (Image: National Optical Astronomy Observatory)
When Charles Messier first observed this galaxy in 1773, he discerned very few features and actually described it as a faint nebula devoid of stars. However, in 1845, astronomer Lord Rosse (1800-1867) discerned its spiral structure. It was the first instance in which such spirals were observed in nebula. However, these nebulae were still then believed to have been intergalactic objects. Only in the early twentieth century did Edwin Hubble establish that many of the objects once perceived to have been inside the Milky Way were actually far outside of it.
We now know that the Universe harbors an abundance of galaxies, the population of which might even exceed the number of stars within our own Milky Way. While we cannot see our home galaxy from an external viewpoint, we can observe other galaxies and from observations of their structures infer the design of the Milky Way. The Whirlpool provides us with a very nice, though not precisely accurate, reflection of our own island Universe.
*Collective nouns are the most beautiful things the English language has ever produced apart from the phrase "Heat Index Warning." Not only are they specific to animals, peoples and things, they often change depending on what the animals or people are doing. When ducks are in flight, they travel in a "flock," but when they are on the ground, they are said to be moving in a "brace," or a "badling." A gathering of ducks on water is said to be in a "team," a "raft" or a "paddling." Makes one wonder what one could call a collection of pointless footnotes.
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