Abstract
We now discuss objects that every amateur astronomer has usually seen at least a handful of—galaxies.
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Notes
- 1.
The Milky Way Galaxy is often referred to as the “Galaxy,” with a capital letter; any other galaxy is simply a “galaxy.”
- 2.
Although a few stars may, after an immense amount of time, break free of a galaxy’s grip and become intergalactic wanderers.
- 3.
Or, at times, a rugby ball.
- 4.
See Chap. 2 for a description of HII regions.
- 5.
Recent research has shown that the Large Magellanic Cloud, often classified as irregular, is in fact a spiral galaxy, even though it bears little resemblance to the classic spiral shape.
- 6.
We will discuss this addition to Hubble’s classification shortly.
- 7.
This process is believed to occur when galaxies collide and meld into one another, forming a new, entirely different galaxy with a new morphology, possibly a giant elliptical.
- 8.
There are other classification schemes; the Yerkes (or Morgan) scheme that uses stellar spectra to determine the classification, along with the classifications for active galaxies.
- 9.
Sagittarius A* is now believed to be made of two components—SgrA East and SgrA West. The former is a supernova remnant, and the latter is an ultra-compact, non-thermal source, i.e., a black hole.
- 10.
Recent analysis suggests that the density around the center of the Milky Way is about a million times greater than any known star cluster. It is probably made up of living stars, dead stars, gas and dust, and of course a black hole.
- 11.
To get a sense of scale, consider that the Mercury is 46 million km from the Sun at perihelion.
- 12.
Of course, I don’t really have to mention that if you have a medium-to-large-aperture telescope, then the number of galaxies visible to you is vast, and the detail you will be able to see will astound you!
- 13.
Be aware, however, that with small apertures, knowing the inclination won’t really matter much, the galaxy will still look like a dim, diffuse blob.
- 14.
The Local Group is a cluster of several galaxies, including the Milky Way. It consists of M31, M33, M110 and M32, the Large and Small Magellanic Clouds and about 25 other dwarf galaxies, including Leo I and II, And I and II, the Draco, Carina, Sextans and Phoenix dwarfs.
- 15.
Cepheid variables are used as “standard candles,” for measuring distances to other extra-galactic objects, and where discussed in Chap. 10.
- 16.
The galaxy M83 lies at the same distance and has reportedly been seen with the naked eye.
- 17.
Additional members of the Local Group are being found at regular intervals. These are small and indistinct, thus their difficulty in being observed!
- 18.
# Indicates number of galaxies in cluster/group as seen through a telescope.
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Inglis, M. (2015). Galaxies. In: Astrophysics Is Easy!. The Patrick Moore Practical Astronomy Series. Springer, Cham. https://doi.org/10.1007/978-3-319-11644-0_14
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