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distance from the sun - trees and sun in march

Winter aphelion – astronomical distances and Earth’s orbit

No wonder it is so cold in the southern parts of Australia at the moment! We have just moved into the aphelion, or that moment when the Earth is at the longest distance away from the sun. As of July 7 at 2:46 am, we will be at the furtherest point away from the sun.

At a mere 152.1 million kilometres, it seems understandable that we are a bit chilly at this time of year. The elliptical orbit of the sun brings the Earth another 5 million kilometres closer at the periphelion. The periphelion happens just after the December solstice, which is probably why summers are so much warmer in the southern hemisphere, but does not explain the more brutal winters in the northern hemisphere over that December – February period.

How do they measure such large distances?

It seems to be such an astronomical number, that 152.1 million kilometres, and a friend at work and I started to discuss how on earth can they even MEASURE that kind of distance. It turns out that some very bright sparks back in 1961 worked out that if they sent radio waves out to space, they could measure the time it took for them them to get back to earth, and given that they knew the speed of sound, they could calculate the distance.

How long does it take for the sun’s light to get here anyway?

When I read that the sun was 152.1 (million) km away, at this Saturday’s aphelion, I couldn’t get my head around the idea that we sit in the winter sun and (try) to soak it up, on a lovely sunshiney day. We did a calculation. The speed of light is 300 million metres per second. Can you believe that? Zip! Therefore, the time that it takes for light to get from the sun to the earth is 8 minutes and 20 seconds. Not really that long, considering the distance.

Beautiful winter sun

What a beautiful star it is. How much do I love sitting in the winter sun and soaking it up.

It really is mind boggling though, and I definitely feel the difference of those 5 million kilometres between December and June.

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