The Half-Astrophysicist Blog

Happy Perihelion Day!

Today was passed perihelion, the point at which Earth is closest to the Sun in its orbit. Earth passed this point at about 5UT (midnight EST so for some in the continental U.S. we technically passed aphelion on January 1st local time). Earth’s orbit around the Sun is not a perfect circle so we end up a little bit closer to the Sun (147.5 million kilometers away) in January than we do in July (152.6 million kilometers away).  Of course you all know that the seasons are caused by the fact that the Earth is tilted about 23.5 degrees so the northern hemisphere gets more direct sunlight and longer days in June and July and less direct sunlight and short days in December and January.

Now a lot of people find this hard to believe, but you can prove it to yourself. I went out today and took a picture of the Sun around noon. My original intention was to go out in July and take another picture when the Sun is at aphelion (its farthest distance) in early July and then compare the two pictures and see if I could tell a difference. But like a kid on Christmas, I had a hard time waiting and realized that I took a lot of pics of the Sun on June 5th, 2012 during the transit of Venus! June 5th is about a month before aphelion, but I started wondering if I could tell the difference with the pics I took that day. I had to dig them out and find out!

The picture on the left is the one taken last June as you can tell by that fact that, well, Venus is hanging out there. The picture on the right was taken a little after noon local time today (and you can even check today’s spacewether.com site to verify the position of the sunspots).

Sun-ComparisonAnd I think you can tell the Sun appears ever so slightly larger today than it did back in June (and I don’t think I have the pics perfectly aligned…I think the one from today is a pixel or two too low so the difference might be slightly understated).

I took this pics using my trusty Canon Digital Rebel Xti and the Canon EF 70-300mm zoom lens at 300mm of course. I used a Rainbow Symphony solar filter that cost $10 and fits the lens right out of the box. So I guess what I am saying here is, you don’t need a lot of fancy equipment to do this so I encourage you to go out and try it for yourself!

Now I still plan on going out on July 5th of this year (or the closest clear day I can) and get the aphelion pic. If I can get it even a month before aphelion, getting it right on the day should make it even a better comparison (and I will try to learn to align the pics better by then too!)

January 2, 2013 - Posted by | Astrophotography | , ,

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