The Sea Goat

Last night the cats fought over who would sleep under the blankets against human warmth and in the sheepskin-lined cat bed. It was a frantic feline version of musical chairs, and when the music stopped, it was every cat for him-or-herself.

This was my first clue that the first nip of autumn was in the air and that flannel sheet season was nigh. My second clue was the “prime time” prominence of fall constellation Capricornus the Sea Goat, which can be seen approaching the meridian from the east about an hour after sunset, when the sky’s just gotten good and dark. It will soon dislodge Sagittarius the Archer— just leaving the meridian, heading west— from its summertime domination of our view to the south.

Capricornus (kapp-rih-KORN-uss) is one of the twelve constellations of the zodiac. This band of constellations is significant because it straddles the ecliptic, the imaginary line that represents the path the Sun appears to take across the sky, as seen from Earth. Because the Earth, Moon, and planets all lie in roughly the same plane as they orbit the Sun, we see the Moon and the planets stick close to the ecliptic as they cross our sky.

You might say the ecliptic represents the plane of our platter-shaped solar system. But I like to think of it, and the zodiacal constellations that encompass it, as the celestial parade route upon which I’m sure to see a procession of planets float by.

Case in point: there are currently two planets passing through Capricornus, Jupiter and Neptune. Jupiter is easily seen with the naked eye; it’s the blazing “star” in the southeastern sky and the first luminary that pops out at you after sunset. Right now you can use Jupiter to help pinpoint the location of Capricornus, should you be unfamiliar with its star pattern.

Viewing Neptune (not a naked-eye object) requires a star map or software application that shows current planet positions, and large binoculars or a telescope.

Star map created with Your Sky

About an hour after your local sunset time, locate bright Jupiter. Using the map above and the relative position shown for Jupiter, trace out in the sky the star pattern shown. This is the asterism (recognizable star pattern) known as the Bandanna, and it contains the brightest stars in Capricornus.

Capricornus in Johannes Hevelius's 1690 star atlas
Courtesy of Linda Hall Library of Science, Engineering and Technology

Trust me, you’re far more likely to learn to recognize a stellar bandanna than a sea goat. I like Mesopotamian and Greek mythology— and tales of animal metamorphosis— as much as the next person. But honestly, what sort of perverse storyteller would find it necessary to graft a fish’s tail onto the head and body of a goat? It's so grotesque as to defy understanding, so perhaps we should just wave the white bandanna of surrender.

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Here in the valley of the Rio Grande, the first nip of autumn means sweet relief from stifling summer heat along with the sweet smell of roasting New Mexican chiles. It also means I’ll be harvesting one of my favorite deep-sky objects from the telescopic depths of Capricornus. More on that later. Right now, I’ve got to air out my cozy flannel sheets and clean my high-power eyepiece.

Sweet.

Astronomy Essential: The four gas giant planets don’t have solid surfaces.

It’s hard to comprehend that no interplanetary traveler of the future will ever step out onto the surface of Jupiter or Saturn— even with the right protective space suit. Those gas giants are, as the name suggests, composed of gasses: primarily the elements hydrogen, helium, methane, ammonia, and oxygen.

On the two gas giants farthest from the Sun, Uranus and Neptune, the normally gaseous elements are believed to take liquid or semi-solid form. Gas-infused slush and frigid “seas” of liquid hydrogen, helium, methane, and ammonia make these two ports of call no less inhospitable than their vaporous neighbors.

Cassie's Cluster

Note: There will be no September 17 post so that I may prepare for the STAR-HOPPERS weekend workshop in astronomy for grandparents & grandkids. Enjoy the September 10 post or browse my older posts. I'll be back with a new post on September 24.

Messier 52 in the constellation Cassiopeia the Queen is one of my favorite open clusters. I like its rich star field and its somewhat fan-shaped appearance. I also consider it a big plus that it’s easy to find.

An open cluster is a loose collection of stars that formed around the same time in the same nebula (cloud of gas and dust). You might think of an open cluster as a sort of family group.

Messier 52, or M52 as it is commonly known, is one of the 110 celestial objects in the catalog of famed 18th century French astronomer and comet-hunter Charles Messier (pronounced MESS ee yay). This catalog is used extensively by amateur astronomers as an observing list, since it contains some of the “best and brightest” deep-sky objects in the night sky. Messier discovered M52 in 1774, while “chasing” a nearby comet.

M52 is easy to find because you can use the distinctive Lazy W asterism (star pattern) of Cassiopeia to locate it. Grab your binoculars, and let’s take a look at Cassie’s cluster.

1) About an hour after your local sunset time, face north. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your left shoulder to the west, and you’ll be facing approximately north.

Looking north to Cassiopeia's Lazy W
Star maps created with Your Sky

2) Look for a W-shaped group of stars east of the meridian. This is the central asterism of Cassiopeia, the Lazy W. Cassiopeia is a circumpolar constellation, one that circles the North Celestial Pole, the imaginary fixed point in the sky directly above the North Pole. Luckily for us, there is a star extremely close to that point in the sky, which serves as a navigational marker. This is Polaris, the North Star.

Cassiopeia and the other circumpolar constellations appear to make a complete counterclockwise circuit around the North Star, over the course of one day. But they’re not really spinning around the North Star. This apparent motion, or the way they appear to move in our sky, is caused by the rotation of the Earth, as it spins on its axis like a top, 24/7.






3) From Shedar (SHEDD-er), the lower right star of the W, draw an imaginary line through Caph (KAFF), the upper right star of the W. Then extend that line the same distance again past Caph, plus a skosh. Train your binoculars on that spot, and you should see a fuzzy patch. With a small telescope, you’ll be able to resolve the stars in the cluster, that is, they’ll separate into distinct points of light.

M52 lies around 5,000 light years from Earth. One light year is the distance light travels in one Earth year, nearly six trillion miles. The cluster is estimated to contain 200 members.

The open cluster M52
Credit: AURA/NOAO/NSF

Two hundred family members in one place at the same time makes for quite a reunion. Pass the potato salad, please.







Astronomy Essential: The universe began with the Big Bang.

The Big Bang is a widely accepted scientific theory of the origin of the universe. It postulates that about 13.7 billion years ago, the visible universe was extremely dense and extremely small— about the size of a dime. This singularity suddenly expanded to create the large-scale universe, which continues to expand today.

Many astronomers accept that a Big Bang event is the best current explanation for some key observable features of the universe, such as: its continuing expansion from a smaller, denser state; the microwave radiation “glow” that is present throughout the universe; a consistent abundance of simple elements such as hydrogen and helium throughout the universe, even in the oldest objects; and a limit on the age of stars in the cosmos.

Horse Trade

In addition to the center of the galaxy, the spout of the Teapot asterism in the constellation of Sagittarius the Archer points to a whimsical naked-eye object in the Summer Milky Way. This object requires a dark sky to see it, but it’s worth a trip away from city lights.

The object is actually a two-fer, two objects in one economical package. Both are dark nebulas, and they lie across the “star river” of the Milky Way from the Teapot, in neighboring Ophiuchus the Snake Handler.

Dark nebulas (NEBB-yoo-luhs) were once thought to be empty areas in the sky where no stars existed. Now we know they are areas of thick dust— dust so dense it obscures the light of the stars behind it. Dark nebulas are sometimes named for the objects they resemble. It is human nature, after all, to attribute patterns or meaning to random visual events, for example, seeing animals or faces in clouds. This practice even has a name: pareidolia (pronounced pear-eye-DOH-lee-uh).

The first of our two objects is a dark nebula called the Pipe Nebula. You can see from the image below that it looks like the stem and bowl of a smoker’s pipe. This will be the easier of the two shapes to pick out.

For our second object, the Pipe becomes the hindquarters of a horse, and his front half extends away from the Milky Way, as shown in the next image. This is commonly known as the Prancing Horse Nebula.

You should be able to make out the equine's torso and head, as well as his raised front leg.

Here in the American Southwest, this object is more commonly known as the Burro Nebula, or simply the Burro. Burro is derived from the Spanish word for donkey and usually refers to the undomesticated version of that animal. There’s a wild burro population of about 3,800 in the American West. These animals are the descendants of those first introduced into the desert Southwest by the Spanish in the 1500s.

The Burro, with lowered head and upraised leg on the right, hindquarters on the left.

The glowing star cloud above him makes it look as though he is carrying a pack.
© T. Credner & S. Kohle, AlltheSky.com

You can have your prancing horse. I’ll stick with my burro. He eats a lot less.

Astronomy Essential: The Earth’s magnetic field protects us from the solar wind.

The Earth is a magnetic object, that is, it acts like a magnet, because it has an iron core. As with any magnet, the Earth generates a magnetic field that surrounds it. This magnetic field is called the magnetosphere.

The magnetosphere deflects the solar wind generated by the Sun. The solar wind is a stream of charged particles traveling at over one million miles per hour. Without the magnetosphere to protect it, Earth’s atmosphere would be vaporized by the solar wind.