Happy aphelion!

Bad Astronomy
The entire universe in blog form
July 5 2012 10:59 AM

Happy aphelion!

Today - July 5, 2012 - at about 04:00 UTC (a few hours ago as I write this) the Earth reached aphelion, the point in its elliptical orbit when it's farthest from the Sun.

According to the US Naval Observatory, we were 1.016675058 Astronomical Units from the Sun at that time. An AU is the average distance from the Earth to the Sun, and is defined as 149,597,870.7 kilometers (92,955,807.2 miles).

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Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

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That means that at aphelion the center of the Earth was 152,092,424 km (94,505,851 miles) from the center of the Sun.

Over the next six months we'll slowly approach the Sun again until we reach perihelion - the closest point in the Earth's orbit to the Sun - on January 2, 2013, at about 05:00 UTC.

When we're farther from the Sun it appears a little bit smaller in the sky, but you'd never notice. For one thing, staring at the Sun is a bad idea! For another, the change is so slow day by day that it's impossible to notice anyway. For a third thing, the total change over the course of six months isn't very big either. Astronomer (and friend of the blog) Anthony Ayiomamitis took two pictures that show this:


These are from aphelion and perihelion in 2005, but the scale is always about the same every year. As you can see, the change in the Sun's size isn't terribly big.

So even though you may not notice it, it's still neat to think that after the past 183 days or so we've been steadily moving farther from the Sun, and now we're on our way back in. And even neater... the Earth has done this over four and half billion times before. So it has some experience here.



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