The Sky This Week, 2013 October 22 - 29
Messier 31, the Great Andromeda Galaxy
Imaged at Fishers Island, NY, 2013 July 31
The Moon wanes in the morning sky this week, wending her way through the bright stars of the Great Winter Circle before ending the week among the rising stars of spring. Last Quarter occurs on the 26th at 7:40 pm Eastern Daylight Time. Luna may be found near bright Jupiter before dawn on the mornings of the 25th and 26th. On the morning of the 29th look for the Moon at the south apex of an attractive triangle with the bright star Regulus and the red planet Mars.
As the Moon edges toward the morning sky we can take advantage of the crisp autumn evenings to explore some of the sights of the season’s "deep sky". Gone are the hazes and humidity of summer. Gone as well are the mosquitoes, which tend to ruin many an observing session in the warmer months. The stars of late summer seem to linger in the west, and the three bright stars of the Summer Triangle, Vega, Deneb, and Altair still dominate the high western sky at the end of evening twilight. From dark locations you can still enjoy a leisurely binocular tour of some of the Milky Way’s best star clouds with their embedded star clusters and gaseous nebulae.
By 10:00 pm another geometric figure approaches the meridian. Made up primarily of second-magnitude stars, the so-called "Great Square" of Pegasus is nonetheless quite prominent, mostly due to the paucity of other bright stars in the area. As we look out in the direction of Pegasus we’re looking out of the plane of the Milky Way toward the vast reaches of intergalactic space. The dominant type of deep-sky objects that we see in this area is thus the faint light smudges of far-flung galaxies. Large amateur telescopes can track down hundreds of these within the bounds of the square, but there is one that’s located in this general area that you can see with no optical aid at all. Start your search at the upper left corner of the square at its brightest star, Alpharatz. You should notice a "chain" of stars leading off toward the east. Find the second (and brightest) star in the chain, a golden-hued star called Mirach. Now "hop" up past two faint stars to where you’ll see what appears to be a detached piece of the Milky Way. That smudge of light is the combined light of some 400 billion stars that make up the Great Andromeda Galaxy, Messier 31. At a distance of some 2.5 million light years this is the most distant object you can see with the naked eye. Binoculars will begin to show its lenticular shape, and if the sky is very dark you may notice two smaller satellite galaxies, M32 and NGC 205. As you increase the aperture of the instruments that you train on M31 its structure becomes more evident, but it will stubbornly refuse to resolve into stars. Instead it shows light of a most exquisite character, likened by the 17th Century telescope pioneer Simon Marius as "the light of a candle showing through horn". My favorite feature is the almost star-like nucleus which we now know harbors a massive black hole with a mass of millions of sun-like stars.
Returning to the humble neighborhood of our little solar system we can now enjoy the bright glow of Venus in the southwestern sky during evening twilight and the first hour of dark-sky time. Although she is bright enough to cast shadows in dark locations, this particular apparition won’t allow her to climb high enough in the northern sky to observe this phenomenon. However, you can watch her as she progresses through the last of the summer constellations, drifting eastward toward the "teapot" asterism of Sagittarius.
Jupiter now rises at around 11:00 pm, accompanied by the bright stars of the winter constellations. Early morning skywatchers can follow his progress as he follows Orion into the crisp night air. Thanks to the later shift from Daylight back to Standard Time, which will occur on November 3rd, we can also see him at his best in the pre-dawn hours at around the time many of us wake up for work or school. I have been getting some wonderful views of Old Jove, setting my telescope up before retiring and enjoying my first cup of morning coffee at the eyepiece. As an added bonus, we’ll have the Moon to look at as well this week.
I had my first good look at Mars earlier this week as the red planet has finally cleared the roofline of my house before the onset of bright morning twilight. His disc is still quite tiny in the eyepiece, but a number of features are prominent. Most obvious is the planet’s white north polar ice cap, which should stand out prominently in virtually any telescope’s view. Fortunately, the planet’s disc is beginning to grow as Earth begins to close the distance gap. By the time of Mars’ opposition next spring it will be nearly four times bigger than it is now.