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Our Vast Universe

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Astronomy seeks to answer intriguing questions about the universe and celestial objects. Both children and adults ponder "How was the universe created?" and "How far away are the stars?"

In the beginning, the universe was very small, very dense, and extremely hot. Temperatures were too high for any elements to exist. Eventually, as the temperature fell, it became cool enough for atoms to form. The first element to form was hydrogen, the simplest element of all. Later came the formation of the first galaxies, and then the first stars.

Skygazing:

For more information on our Universe read Skygazing: Astronomy through the seasons, NRC's weekly articles.

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In 1916, using mathematical models, Albert Einstein predicted that the universe was expanding, although he had a hard time believing it. Later, observations by Vesta Slipher and Edwin Hubble confirmed that this was true.

This observation led to the notion that the universe had, at one time, been concentrated in one place then began to expand about 12 to15 billion years ago. This event is now referred to as the "Big Bang". The expansion of the universe is still going on today -- we can observe distant galaxies moving farther away from us, carried by the expanding universe.

How far away are celestial objects from Earth?

When looking at Space using the naked eye, binoculars, or a telescope, we are observing the past because it takes so long for light from a distant celestial object to travel to us even at a speed of 299 792 km/sec. Earth's Moon is some 400 000 kilometers away, and it takes less than two seconds for the Moon's reflected light to reach the Earth. The light from the Sun takes about 8 1/3 minutes to travel to Earth, while the light from the next closest star takes 4 1/3 years to reach our planet. Light from the nearest galaxy takes 150 000 years.


Origins of Stars and Galaxies
Astronomers believe that most stars are born inside cold, dark molecular dust and gas clouds. Such clouds are found inside galaxies, systems of immense size containing literally billions of stars. And there are billions of galaxies in the universe!

Astronomers are puzzled by many observations about galaxies. How were individual galaxies created from the material that emerged from the Big Bang? Why aren't they uniformly spread across the sky? Do galaxies look the same today as when they formed billions of years ago? Why do we see only about 10% of the matter that observations tell us must be present in galaxies?

Black Holes
When they run out of fuel, the most massive stars die and are believed to leave behind black holes. They are extremely dense, massive objects whose intense gravity prevents any material, or even light, from escaping. These black holes may be the precursors of much more massive ones found in the centre of galaxies. The first evidence of smaller black holes was found in our Milky Way and the nearby Magellanic Clouds by Canadian astronomers. They were studying stars that give off copious amounts of X-ray radiation.

Supermassive black holes are found in many galaxy centres and contain from a few million to several billion times the mass of our Sun. In 1987, a Canadian astronomer discovered evidence of a massive black hole in the centre of the Andromeda galaxy. Astronomers remain fascinated by the very existence of black holes, which can help to explain so many of the unusual phenomena in the Universe. But if they are truly 'black' in the sense that no light escapes from them, how do astronomers detect their existence at all? They use instruments called spectrographs to study the motions of material that is sped up as the Black Hole draws it in.