By: Geoff Gaherty
Published: 01/02/2013 08:12 AM EST on SPACE.com
If the sun looks a little larger than usual today, you're not seeing things. Today (Jan. 2) marks the time when the Earth is at perihelion, the point in its orbit at which it is closest to the sun.
During perihelion, the Earth is exactly 91,402,560 miles (147,098,161 kilometers) from the sun.In actuality, you most likely can't see any difference between the apparent size of the sun today and its appearance at aphelion (when the Earth will be farthest from the star).The difference is only 3.4 percent, too small to be detected with the naked eye.
On average, the Earth is about 93 million miles (150 million km) from the sun. It will be farthest from the sun on July 5, when the Earth reaches aphelion, a point 94,508,960 miles (152,097,427 km) from the sun. The closest and farthest differences from the sun are very similar because the Earth’s orbit is very close to being circular. In fact, as planetary orbits go, ours is close to perfect.
Only Venus and Neptune have more circular orbits than the Earth. On the other hand, if you look at the diagram of the orbits of the four inner planets accompanying this story, you may easily see that Mercury and Mars have orbits which are seriously eccentric.
Astronomers use the term "eccentric" in its original mathematical sense, meaning "away from the center." A perfect circle has an eccentricity of 0. A straight line would have an eccentricity of 1. Everything else in between is an oval of some kind.
Here's a look at the innermost planets of the solar system in order of increasing eccentricity:
Looking at the diagram, the orbits of Earth and Venus look almost perfectly circular, while that of Mars is slightly closer to the sun towards the bottom. Mercury's orbit is very much closer to the sun on the right. If you look closely, there is a little tick mark on the orbits to indicate where perihelion lies. Don't confuse this mark with the little wedges which denote the orbital nodes, the points where the orbits cross the plane of the ecliptic. The Earth appears right next to the tick mark on its orbit marking perihelion in the image.
So what is the difference for the inhabitants of Earth when our planet is at perihelion instead of aphelion? The Earth is slightly warmer than it would be otherwise, about 4 degrees Fahrenheit (2.3 degrees Celsius). [Earth Quiz: How Well Do You Know Our Planet?]
This perihelion effect is very minor compared to the effects of the tilt of our planet's axis. During December in the Northern Hemisphere, the North Pole is tilted away from the sun so that we receive less sunlight every day.
At the same time, the South Pole is tilted towards the sun, so the Southern Hemisphere receives more sun and experiences summer. In June, the situation is reversed and we have summer in the northern hemisphere and winter in the southern hemisphere.
The only effect of perihelion is that the winters in the Northern Hemisphere are very slightly milder than the winters in the southern hemisphere at the equivalent latitudes. Not as many people live as close to the South Pole as do close to the North Pole, so humanity isn't affected much.
So enjoy that "big" January sun, and look forward to the longer days to come as Earth moves around its orbit to the point where we really receive more sun and spring arrives.
This article was provided to SPACE.com by Starry Night Education, the leader in space science curriculum solutions. Follow Starry Night on Twitter @StarryNightEdu.
Copyright 2013 SPACE.com, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
Our 2024 Coverage Needs You
It's Another Trump-Biden Showdown — And We Need Your Help
The Future Of Democracy Is At Stake
Our 2024 Coverage Needs You
Your Loyalty Means The World To Us
As Americans head to the polls in 2024, the very future of our country is at stake. At HuffPost, we believe that a free press is critical to creating well-informed voters. That's why our journalism is free for everyone, even though other newsrooms retreat behind expensive paywalls.
Our journalists will continue to cover the twists and turns during this historic presidential election. With your help, we'll bring you hard-hitting investigations, well-researched analysis and timely takes you can't find elsewhere. Reporting in this current political climate is a responsibility we do not take lightly, and we thank you for your support.
Contribute as little as $2 to keep our news free for all.
Can't afford to donate? Support HuffPost by creating a free account and log in while you read.
The 2024 election is heating up, and women's rights, health care, voting rights, and the very future of democracy are all at stake. Donald Trump will face Joe Biden in the most consequential vote of our time. And HuffPost will be there, covering every twist and turn. America's future hangs in the balance. Would you consider contributing to support our journalism and keep it free for all during this critical season?
HuffPost believes news should be accessible to everyone, regardless of their ability to pay for it. We rely on readers like you to help fund our work. Any contribution you can make — even as little as $2 — goes directly toward supporting the impactful journalism that we will continue to produce this year. Thank you for being part of our story.
Can't afford to donate? Support HuffPost by creating a free account and log in while you read.
It's official: Donald Trump will face Joe Biden this fall in the presidential election. As we face the most consequential presidential election of our time, HuffPost is committed to bringing you up-to-date, accurate news about the 2024 race. While other outlets have retreated behind paywalls, you can trust our news will stay free.
But we can't do it without your help. Reader funding is one of the key ways we support our newsroom. Would you consider making a donation to help fund our news during this critical time? Your contributions are vital to supporting a free press.
Contribute as little as $2 to keep our journalism free and accessible to all.
Can't afford to donate? Support HuffPost by creating a free account and log in while you read.
As Americans head to the polls in 2024, the very future of our country is at stake. At HuffPost, we believe that a free press is critical to creating well-informed voters. That's why our journalism is free for everyone, even though other newsrooms retreat behind expensive paywalls.
Our journalists will continue to cover the twists and turns during this historic presidential election. With your help, we'll bring you hard-hitting investigations, well-researched analysis and timely takes you can't find elsewhere. Reporting in this current political climate is a responsibility we do not take lightly, and we thank you for your support.
Contribute as little as $2 to keep our news free for all.
Can't afford to donate? Support HuffPost by creating a free account and log in while you read.
Dear HuffPost Reader
Thank you for your past contribution to HuffPost. We are sincerely grateful for readers like you who help us ensure that we can keep our journalism free for everyone.
The stakes are high this year, and our 2024 coverage could use continued support. Would you consider becoming a regular HuffPost contributor?
Dear HuffPost Reader
Thank you for your past contribution to HuffPost. We are sincerely grateful for readers like you who help us ensure that we can keep our journalism free for everyone.
The stakes are high this year, and our 2024 coverage could use continued support. If circumstances have changed since you last contributed, we hope you'll consider contributing to HuffPost once more.
Support HuffPostAlready contributed? Log in to hide these messages.