Monday, August 6, 2018

Open questions about center of the universe, Outer space, closest galaxy, Andromeda



Is Earth at the center of the universe?


The Greek philosopher Aristotle proposed that the heavens were composed of 55 concentric, crystalline spheres to which the celestial objects were attached and which rotated at different velocities, with the Earth at the center. People believed this for almost 2000 years, until Polish astronomer Nicolai Copernicus proposed that the Sun, not Earth, was the center of the solar system. His model, called a heliocentric system, said that Earth is just another planet (the third outward from
the Sun), and the Moon is in orbit around Earth, not the Sun. While this might be true of our solar system, astronomers cannot see the whole universe through their telescopes, so no one knows where the true “center” of it lies.



What is outer space?



 

Outer space, sometimes simply called “space,” are the areas between Earth and the Moon, between the planets of the solar system, and between the stars. Space is not completely empty. It does not contain any air, but it does contain a few specks of dust and atoms of gases.
 



Which galaxy is closest to ours?
 

The nearest big spiral galaxy to our galaxy, the Milky Way, is the Andromeda galaxy. Appearing as a smudge of light in the constellation Andromeda, this galaxy is about twice as big as the Milky Way. It is about 2.3 million light years away from us, although its vast size and luminosity make it visible to the naked eye. In fact, it is the most distant object that can been seen from Earth without a telescope.




Why is the Andromeda galaxy so special?


Andromeda has a bright disk that scientists believe spans as much as 260,000 light years—almost twice the size of the bright disk seen in photographs. The outer disk emits nearly 10 percent of the galaxy’s total light and may be made up of stars stripped from smaller galaxies that strayed too close. 

In 2007, a team of astronomers announced the discovery of low-metallic, red giant stars up to some 500,000 light years from Andromeda’s core. This discovery suggests that the galaxy is much larger than scientists originally thought, and that Andromeda’s glowing halo may actually overlap with that
of the Milky Way.

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