December 28, 2021: The Great Andromeda Galaxy is nearly overhead at the end of the evening twilight.
by Jeffrey L. Hunt
Chicago, Illinois: Sunrise, 7:18 a.m. CST; Sunset, 4:27 p.m. CST. Check local sources for sunrise and sunset times for your location.
As early winter sets in at the mid-northern latitudes and the evening planets dance in the southwest after sunset, look for the Andromeda Galaxy.
This amalgamation of stars is the closest galaxy system to our Milky Way.
To locate it step outside at the end of evening twilight. That’s about 100 minutes after sunset. The galaxy is overhead; that is, straight up.
Use a binocular, because the galaxy will spill out of a telescope’s eyepiece. A binocular can capture nearly the entire feature.
Cataloged as the 31st entry in the 18th Century comet hunter’s list of fuzzy objects that were not to be confused with comets, Messier 31 (M31 on the chart) was subject of intense interest about a century ago. Was it a spiral cloud within our Milky Way or another bundle of stars, a galaxy – a stellar island in the universe?
By the early 20th Century, nearly 15,000 cloudy, nebulous objects were cataloged. Some of them turned out to be star clusters and gas clouds.
In 1917, astronomer Harlow Shapley published a map showing the sun’s location compared to the center of the galaxy by mapping globular star clusters. He was able to determine their distances and sizes.
Globulars are special because their chemistry is different from the stars in the plane of the galaxy, that make the familiar constellations, and they revolve around the galactic center outside the galactic plane.
During the second decade of the last century, Edwin Hubble found stars that varied in brightness. About a decade earlier, Henrietta Levitt, an astronomer at the Harvard College Observatory, found a relationship between the frequency a star changes brightness and the star’s intrinsic brightness.
By comparing the apparent brightness of a star with its true brightness, the distance of the star is measured. Today, this is a fundamental measurement for finding distances to nearby galaxies.
Hubble’s first estimation was that M31 was about 1 million light years away, far outside the boundaries of our galaxy – an island of stars in the universe.
With spaceborne telescopes, Andromeda is studied in many “colors,” some wavelengths of “light” that are invisible to the human eye and mostly filtered by Earth’s atmosphere. The other wavelengths indicate the temperatures of the objects studied, from cool gas clouds to intensely hot exploding stars. In space, the blurring effects of the air are removed to get complete views of the nearest star system.
To find the galaxy, set outside and look high in the south. Locate the Great Square of Pegasus. The box is fairly large. The four stars on the corners are about the same brightness as those in the Big Dipper.
The constellation Andromeda begins at Alpheratz. Star hop from Alpheratz to Delta Andromedae (δ And on the chart). Both fit snugly into the same binocular field. Then jump to Mirach. This star is distinctly reddish in a binocular, but it does not fit into the same field as Delta. Then turn toward Mu Andromedae (μ And). The galaxy easily fits into the same field of view as this star. It looks fuzzy. Depending on the outdoor lighting in your area, you’ll see a larger extent of the galaxy with fewer outdoor lights.
For those who live in more rural areas, the galaxy is easily visible without optical assistance, likely the farthest thing visible without the help of a telescope or binocular.
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