Ever looked up at the night sky and wondered: What is up there?
Like your ancestors before you, you would be mistaken if you thought that it's just the Earth down here and the stars up there. Instead, the night sky encompasses everything that is, or ever was, in the Universe. You see, the really wacky thing about looking up at the sky is that you are looking not just into the depths of space, but also the depths of time.
Let me explain. Light travels at about 300,000 kilometers per second (186,000 miles per second) -- that's pretty fast. In our day-to-day lives, this doesn't pose a problem; the light entering my eyes from the display in the coffee shop window takes an almost immeasurably small period of time to get to me. To all intents and purposes, I see the display as it is right now.
However, the distances in space are so vast that it takes more time for light to reach us.
We see the Moon as it was 1.3 seconds ago; the sun as it was 8.3 minutes ago; the nearest star 4.2 years ago; the most distant galaxy as it was about 13.3 billion years ago. The most distant object you can see with your naked eye is the Andromeda Galaxy and even that is about 2.3 million light-years away which means you see it as it was 2.3 million years ago. Just by looking up, you can see back in time. Crazy.
So all those tiny points of light represent different points of time in the history of the Universe and that's how astronomers can build a picture of how the Universe has evolved. But the tiny points of light you see aren't all just stars, certainly the vast majority is, but turn a telescope to the sky and you will find an entire cosmic zoo of objects just waiting to be explored.
Starting closer to home, our local star, the sun, is about 150 million kilometers (93 million miles) away and it's the energy generated in its core from the fusion of hydrogen into helium that makes life on Earth possible.
Moving away from the Sun are four tiny rocky planets, Mercury, Venus, Earth and Mars. Interestingly Mercury isn't the hottest planet even thought it's closest to the sun; it's Venus that has the highest temperatures and the reason is simple. Due to its dense atmosphere, heat that reaches Venus from the sun can't escape into space. Surface temperatures can reach around 500 degrees Celsius -- hot enough to melt lead!
Moving on through the asteroid belt we enter the realms of the gas giant planets: Jupiter, Saturn, Uranus and Neptune, all of which dwarf the Earth. Jupiter itself, the largest of the planets could consume about 1300 Earths and still have a little room for dessert! For the main part, that's it for the solar system -- including a whole host of satellites orbiting the main planets and countless minor planets (including Pluto) and comets.
The nearest star to our own is Proxima Centuari and it lays just over 4 light-years away. Depending on the method of transport, if we were to use today's technique of gravitational slingshots around other planets, the quickest transit time would be 19,000 years!
If we continued on through the stars, we would be able to see newly-formed clusters of stars and ghostly glowing clouds of gas and dust where stars are either forming or have recently died.
Eventually though, after many millions of years, we would pop out of our own and start a very long haul through the vast empty space between galaxies. Looking back at the Milky Way we would see something that resembled a big spiral of glittering stars.
Read more at Discovery News
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