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10. Stars and galaxies
| 10.10 |
What are galaxies?
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| Galaxies are collections of stars, planets, gas, dust, nebulae, etc that form "islands" in the general emptiness of space. Powerful telescopes have now detected over 1 billion galaxies measuring from 1,000 light years to 10 million light years across. Most galaxies are found in groups; very few are found on their own. | ||
| For example, our own galaxy (The Milky Way) is a surrounded by at least eight galaxies within a 500,000 light year radius. The word galaxy comes from the Greek work gala, meaning milk. | ||
| Only one star- our own Sun- is near enough to the Earth to be seen, even by the most powerful optical telescopes, as more than a point of light. Some nearby stars can be crudely resolved using the special technique of speckle interferometry, a process whereby large numbers of images can be combined to form one. Current estimates suggest that there at least 100 billion stars in our galaxy. | ||
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