Features

River of Dreams
Catron County author Uncle River's alternate universes

Building Multiculturalism
Casa de la Cultura President Mar’a Eugenia Trillo

Another Side of the Story
Remembering a slain family, 50 years after the In Cold Blood murders

Hiking How-To
Here's how Jerry packs and prepares for Apacheria outings

Rabbit Moon
What did the ancient Mimbres people see in the moon?

Fellow Travelers
November brings flocks of migrating Sandhill Cranes to New Mexico

Underground Silver City
2009 Writing Contest Winner

Columns and Departments
Editor's Note
Letters
Desert Diary

Tumbleweeds:
Lincoln: Self-Made President
Apache Homeland Cafe's Last Chance?
The Robots are Coming
La Esperanca Vineyard & Winery
Tumbleweeds Top 10

Business Exposure
The Starry Dome
Ramblin' Outdoors
40 Days & 40 Nights
The To-Do List
Guides to Go
Henry Lightcap's Journal
Borderlines
Continental Divide

Special Section
Arts Exposure

Arts News
Gallery Guide

Body, Mind & Spirit
Deaf Community
Qi Gong

Red or Green
Dining Guide
Table Talk

HOME
About the cover

  D e s e r t   E x p o s u r e   November 2009


banner

Constellation of the Month: Grus, the Crane

When can a fish give birth to a bird? When they are constellations in the sky, and astronomers create new constellations out of old ones. Our constellation of the month, Grus, the Crane, was originally part of last month's constellation, Piscis Austrinus, the Southern Fish. In 1595 and 1596, Dutch navigator Pieter Dirkszoon Keyser and Dutch explorer Frederick de Houtman made a series of observations of the stars of the southern sky. These were in unknown territory for the European astronomers of the time.

Star map Grus

Click the image to enlarge

 

The constellation of Grus, the Crane, sits right below the constellation it was carved out of — Piscis Austrinus, the Southern Fish. This constellation is populated by galaxies, most of them rather faint. This chart depicts the sky at 7 p.m. around the middle of the month.

The separate observations of these two Dutchmen were combined by Dutch astronomer Petrus Plancius to create 12 new constellations, including Grus. Plancius chose the crane because that bird was considered by many to symbolize watchfulness. His new constellations made their debut in late 1597, or early 1598, on a 14-inch celestial globe Plancius prepared in collaboration with Amsterdam cartographer Jodocus Hondius the Elder. Grus first appeared in a sky atlas when Uranometria was published in 1603 by Johann Bayer.

In terms of size, Grus is the 45th largest constellation (out of 88). Not being particularly large and not being in the Milky Way, Grus has few objects of interest. Its brightest star is Al Nair, Arabic for "the bright one," a contraction of a longer name that means "the bright one in the fish's tail." This is a rather hot, blue star about 101 light-years away. It is a spectral class B subgiant that spins on its axis once in just under a day.

The deep-sky residents of Grus consist solely of galaxies. One of the brightest in this constellation is NGC 7418, a face-on spiral galaxy, somewhat like our own Milky Way. It is quite bright for a galaxy, shining at magnitude 11.4, and very large (2 minutes-of-arc by 1.8 minutes-of-arc).

Galaxies are among the many nebulae discovered since the invention of the telescope. In the 17th century, astronomers simply cataloged all the fuzzy glowing patches in the sky as nebulae. Galaxies like NGC 7418 were listed as "spiral nebulae." Astronomers would speculate on what these nebulae were. Wherever possible, astronomers would gather them together into groups that had common characteristics. The spiral nebulae were an obvious group that could be studied to learn more about the universe.

All of these spiral galaxies were relatively small. By the 1910s, astronomers were arguing amongst themselves whether these spiral nebulae were small clouds scattered throughout our Milky Way galaxy or were actually huge objects very far away. The debate culminated on April 26, 1920, at the Smithsonian Museum of Natural History's Baird Auditorium. There, two well-respected astronomers presented technical papers addressing "The Scale of the Universe."

Harlow Shapley argued that the Milky Way was the only galaxy and all the visible nebulae are a part of it. If the Andromeda Nebula (galaxy) were external to the Milky Way, Shapley said it would be 8 million light years away, a distance that astronomers of the day could not believe. In addition, astronomer Adriaan van Maanen claimed he had observed the Pinwheel Galaxy (M101) rotating. If this were actually an external galaxy, Shapley argued, it would have to be spinning faster than the speed of light, which was impossible. Shapley also pointed to "novae" that had been observed in Andromeda that outshone the center of nebulae. According to Shapley, these novae would have to be impossibly bright if they were in an external galaxy.

Heber Curtis argued that the spiral nebulae were actually far outside the Milky Way, making them very large "Island Universes." He showed that the Andromeda nebula had more novae than all the rest of the Milky Way. If it were indeed part of the Milky Way, why did it have so many more novae than anywhere else in our galaxy? Curtis also compared the dark lanes in Andromeda to those in our own Milky Way.

Curtis was persuasive and eventually astronomers came to believe that the spiral nebulae were spiral galaxies, as we now understand them to be. The novae in Andromeda turned out to be supernovae, which far outshine normal novae and can easily become as bright as the host galaxy. Van Maanen's report of seeing the rotation of the Pinwheel Galaxy turned out to be false; it is impossible to see the rotation of the Pinwheel Galaxy in even a century, let alone a few years. Neither side had all the correct facts, but this event has come to be known as "The Great Debate" or the "Shapley-Curtis Debate," even though it was not a debate in the traditional sense.

In this instant, science changed its mind and a new truth was found that better fit the observations that had been made for many years. It expanded our knowledge of the universe by expanding the size of the universe to encompass billions of galaxies spread throughout a 156 billion light-year-wide (and expanding) universe.



The Planets for November 2009

The last planet left in the evening sky is Jupiter, moving slowly eastward in Capricornus. Jupiter is about halfway up in the southern sky as it gets dark and sets around 11:15 p.m. The King of the Gods shines at magnitude -2.4 and is 39.4 seconds-of-arc across.

Watch the Skies
(all times MST)

 

Nov. 1, 2 a.m.: Standard Time resumes

Nov. 2, 12:14 p.m.: Full Moon

Nov. 11, 8:56 a.m.: Last Quarter Moon

Nov. 16, 12:14 p.m.: New Moon

Nov. 17, 9 a.m.: Leonid Meteor Shower peaks

Nov. 24, 2:39 p.m.: First Quarter Moon

At mid-month Mars' disc is 8.8 seconds-of-arc across. It continues to grow as we approach opposition at the end of January. Rising around 10:30 p.m., the Red Planet starts the month in Cancer, and slips into Leo just as the month ends. Mars shines with a reddish light at magnitude +0.2.

Saturn is moving slowly eastward in western Virgo. The yellowish planet is magnitude +1.0 at mid-month. Saturn's rings are tipped down 3.8 degrees with the northern face showing, its disc 16.5 seconds-of-arc across. Saturn rises around 2:30 a.m.

Venus and Mercury are too close to the Sun to be visible, with Venus in the bright morning twilight and Mercury in the bright evening twilight as the month ends.

November is the month of the famous Leonids meteor shower, which every 33 years produces a brilliant display. This year the peak is at New Moon, so there will be no interference from the Moon. The best time to look is on the morning of Nov. 17. The meteors will appear to radiate from the constellation Leo. So dress warmly and find a comfy chair to sit and watch the sky for these meteors, and "keep watching the sky"!



An amateur astronomer for more than 35 years, Bert Stevens
is co-director of Desert Moon Observatory in Las Cruces.



 



Return to Top of Page