Aphelion – July 4th July 3, 2009
Posted by baldricman in astronomy.Tags: aphelion, apsis, earth, july 4th, orbit, perihelion, sun
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Tomorrow, July 4th, the Earth will be at it’s furthest point from the Sun, in it’s eliptical orbit. This is known as “Aphelion” (with the closest point known as the Perihelion).
Orbits of the Inner Planets
The effect? Well, contrary to what you may think, this does not really effect our seasons in any meaningfull way. The seasons are, of course, created by the tilt of the Earth on it’s axis, in relation to the Sun. However, the Sun will appear slightly smaller in the sky, by roughly 3% (No, you won’t notice that)
This happens once a year, at more or less the same time, and the following table gives the date and time (GMT) of each aphelion. (Table from wikipedia page here)
| Year | Perihelion | Aphelion | ||
|---|---|---|---|---|
| Date | Hour | Date | Hour | |
| 2007 | January 3 | 2000 | July 7 | 0000 |
| 2008 | January 3 | 0000 | July 4 | 0800 |
| 2009 | January 4 | 1500 | July 4 | 0200 |
| 2010 | January 3 | 0000 | July 6 | 1100 |
| 2011 | January 3 | 1900 | July 4 | 1500 |
| 2012 | January 5 | 0000 | July 5 | 0300 |
| 2013 | January 2 | 0500 | July 5 | 1500 |
| 2014 | January 4 | 1200 | July 4 | 0000 |
| 2015 | January 4 | 0700 | July 6 | 1900 |
| 2016 | January 2 | 2300 | July 4 | 1600 |
| 2017 | January 4 | 1400 | July 3 | 2000 |
| 2018 | January 3 | 0600 | July 6 | 1700 |
| 2019 | January 3 | 0500 | July 4 | 2200 |
| 2020 | January 5 | 0800 | July 4 | 1200 |
You can see a good representation of the difference in the apparent size of the Sun, in the form of a composite image (from 2 photos, one at Aphelion, one at Perihelion), on the NASA site over here.
Interesting stuff!
Funnily enough I always thought the aphelion happened during December, which is why Northern Hemisphere winters seem colder than the Southern. But I guess that reasoning quickly falls apart. E.g. why are Southern Hemisphere summers generally hotter than Northern Hemisphere summers. So, in short: thanks for enlightening me!
Hey Carel, thanks for commenting. As far as I understand, our seasons aren’t affected by apheliona and perihelion, at least not noticeable…. but I actually can’t think of why southern hemisphere summers would be warmer, as you say. Perhaps the lower land mass in the the south? (I know the oceans are important in this regard, but don’t know exactly *how*…)