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Asked by Mason The Amazing :) to Andrew, Hina, Ian, Kathryn, Leah-Nani, Xu on 14 Jun 2018.
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Kathryn Burrows answered on 14 Jun 2018:
Light in free space travels at roughly 300 000 km/s, this is very fast! But it is not instantaneous. Here on Earth where distances are short we do not notice it so much but in Space distances are huge! The sun for example is 150 000 000 km away from the Earth. speed = distance/time, so travel time is distance traveled / speed. If you work it out this means that light from the sun takes about 500 seconds to reach us, which is about 8 minutes. The sun could explode or turn off and nobody on Earth would know for 8 minutes! In this way when we look at the sun we are looking back in time, we are looking at what the sun was doing 8 minutes ago. Now think about how much farther the distant galaxies are from us, when we look at the stars we are looking not at light emitted/radiated/shone now but light sent out thousands or millions of years ago.
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Leah-Nani Alconcel answered on 15 Jun 2018:
By the time the light from distant galaxies reaches us at Earth, it has been traveling for millions (or even billions) of years. So when we see them through our telescopes, we’re seeing them as they were millions or billions of years ago.
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Andrew Margetts-Kelly answered on 20 Jun 2018:
By the time the light from those galaxies gets to us a lot of time has passed. So we are looking at that galaxy as it was a long time in the past. If it blew up today, we wouldn’t see it blow up for millions of years; so effectively we are looking at the past.
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Even when you look at the sun you are looking into the past, you are see the sun as it was 8 minutes ago.
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Interesting if some light shines on earth and goes off into space, then just happens to get bent round a large star or black hole and comes straight back at us, we can see the earth as it was in the past.
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