Galaxies
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The Andromeda Galaxy – M31
Our nearest neighbor galaxy at a distance of approximately 2.5 million light years. It is the most distant object visible to the naked eye under moderately dark skies.
In this image we can see the main galaxy flanked by two of its satellites. Above the plane of the galaxy appearing to be a ‘fuzzy snowball’ close to the left side is M 32 and below in the direction of the right corner, is M 110. These dwarf elliptical galaxies are just two of the satellite galaxies belonging to the Andromeda system.
For most of the history of astronomy, galaxies were lumped in with all the rest of the nebulae seen in the sky. In the classic sense, a nebula was defined to be any object that one could not resolve in to a pinpoint of light like a star or a disc like a planet. Basically anything that was a fuzzy, hazy patch was called a nebula.
Although the Andromeda nebula was observed to possess specific characteristics like a spiral structure, little else was thought to differentiate it from nebulae in general. It was further believed that our Milky Way was the only galaxy and that these objects were a part of our galactic system.
In 1864, William Huggins, used spectrographic analysis to study objects in the sky. By spreading out visible light across its spectrum (like with a prism), Huggins was able to see that these spiral nebulae had spectra that more closely resembled stars than the emission line spectra of gaseous nebulae known to be in our galaxy. How could this be?
While some scientists accepted that there were extra-galactic nebulae, their true nature remained a mystery until Edwin Hubble made his ground-breaking discovery regarding the Andromeda Nebula in the mid-1920’s. Building on the insight of Henrietta Leavitt who, in 1912, determined that certain kinds of variable stars, the Cepheid variables, could be used as guides to estimate distances in space, Hubble set to work making observations at Mount Wilson.
Within the Andromeda Nebula, Hubble found 12 Cepheid variables and by observing how bright they became and how long it took them to complete a brightness cycle, he began to make calculations to estimate the distance to this extra-galactic nebula. When he completed his observations and began to crunch the numbers he came up with a distance estimate of 900,000 light years. At the time, the generally accepted size of the Milky Way was thought to be about 100,000 light years. So this finding meant the nebula was very far away.
Hubble then turned his attention to other extra-galactic nebulae and found Cepheid variables within them as well. He also began to note that there were other stars called novas that would flare up rapidly. And he found a type of star cluster called a globular cluster.
With his distance estimates and observations of objects in these extra-galactic nebulae, Edwin Hubble helped prove that these nebulae were, in fact, separate galaxies some like our own. He proposed what became known as “The Island Universe” theory.
Through the work of Edwin Hubble, we gained a sense of scale within the universe and we began to explore the idea of universal expansion.
There is so much more to learn. I marvel at the fact that Hubble’s work happened not even 100 years ago!
For this image, I used an SBIG ST-8XE CCD camera at prime focus, unguided on my Takahashi FC-76 refractor at f/5.9. Total number of frames by color: L35/R30/G30/B30 with 60 second sub-exposures. Color frames were binned 2×2. Data sets captured with Maxim DL Processed with Maxim DL and Photoshop CS4.
Imaged September 19th & 20th 2009 at the Okie-Tex star party – Kenton, OK
