Galaxies are huge groups of hundreds or thousands of millions of stars, all gravitationally interacting, and orbiting around a common center.
Galaxies contain:
classes of galaxies are:
spirals (Sa, Sb, Sc),
barred spirals (SBa, SBb, SBc),
elliptical (E0 to E7),
SO (intermediate between S and E)
irregular.
We belong to a spiral galaxy (a Sb) containing obscuring dust and interstellar gas, with many young blue stars in the spiral arms, and old red stars in the core.
instead Ellipticals have little interstellar material, and few young stars. Tend to have sizes of tens of thousands of light years. Their distances are measured by various methods, including Cepheid variable stars. These stars change in brightness in such a way that it is possible to calculate the distance, and hence of the galaxy that contains them. At the core
apparently all contain a huge black hole.
Galaxies contain:
- stars planets star clusters
- atomic hydrogen
- molecular hydrogen complex molecules composed of hydrogen, nitrogen, carbon and silicon and other elements
- cosmic rays.
classes of galaxies are:
spirals (Sa, Sb, Sc),
barred spirals (SBa, SBb, SBc),
elliptical (E0 to E7),
SO (intermediate between S and E)
irregular.
We belong to a spiral galaxy (a Sb) containing obscuring dust and interstellar gas, with many young blue stars in the spiral arms, and old red stars in the core.
instead Ellipticals have little interstellar material, and few young stars. Tend to have sizes of tens of thousands of light years. Their distances are measured by various methods, including Cepheid variable stars. These stars change in brightness in such a way that it is possible to calculate the distance, and hence of the galaxy that contains them. At the core
apparently all contain a huge black hole.
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