Moon makes year's closest pass to Earth in full phase
“Supermoon” officially arrived about 7 a.m. Sunday morning, with the moon making its closest swing by Earth this year. About a half hour later, the moon reached full status, making it appear 12 percent larger and 30 percent brighter than a regular full moon.
Don't worry if you missed it. The effect should linger for a few nights, meaning Monday and even Tuesday should give a good sense of this year's supermoon.
The show is the product of a cosmic quirk. Because planets and moons orbit in ellipses, not circles, there are times when they are closer to what they're orbiting and times when they're farther away. For moons, the point when they're closest to their planet is called perigee; the point farthest away is called apogee.
For Earth and the moon, perigee and apogee happen once each month, because the moon orbits the Earth once every 27 days. But because of small inconsistencies in the orbits, the moon's closest approach and its farthest distance are always slightly different.
The moon hit its monthly perigee Sunday morning, but what makes it worthy of the name “supermoon” is that it was the closest perigee of 2013. Moreover, because it coincided almost perfectly with a full moon, the effect was enhanced.
The moon's farthest apogee this year has already happened and is set to repeat itself next year during the Jan. 15, 2014, full moon. To see the visual difference in size between a perigee and apogee moon, click here.
But what makes the moon so special? If everything in the solar system orbits in an ellipsis, shouldn't we have a “supersun,” too.
In fact, we do. Since we orbit the sun once a year, supersuns only happen once a year. Our closest swing to the sun, called perihelion, also already happened this year, and will happen again on Jan. 4, 2014. (An “un-supersun,” when the sun seems smallest at aphelion, is just around the corner: July 5.) But will there be this much buzz next January with sungazers filling Twitter with pictures of a gigantic sun? Don't count on it.
The reason? the sun is obviously much farther away from Earth than is the moon, so the effect is not so noticeable. For Earth, the distance between aphelion and perihelion is about 3 million miles. But even at perihelion, the Earth is still 91 million miles from the sun.
In addition, Earth's orbit around the sun is more nearly circular than is the moon's orbit around us, with only Venus and Neptune having more circular orbits than Earth. Mercury has the most eccentric orbit – ranging from a perihelion of 29 million miles to an aphelion of 43 million miles – meaning it has a truly dramatic supersun (if you can stand the 800 degree Fahrenheit temperatures on the sun-side surface).
By contrast, the moon's orbit around Earth is the most elliptical orbit of any major moon in the solar system. Combine that with the fact that the moon is comparatively close to Earth, so it looks large in our skies, and supermoon earns its name.
Show commenting policy
TribLive commenting policy
You are solely responsible for your comments and by using TribLive.com you agree to our Terms of Service.
We moderate comments. Our goal is to provide substantive commentary for a general readership. By screening submissions, we provide a space where readers can share intelligent and informed commentary that enhances the quality of our news and information.
While most comments will be posted if they are on-topic and not abusive, moderating decisions are subjective. We will make them as carefully and consistently as we can. Because of the volume of reader comments, we cannot review individual moderation decisions with readers.
We value thoughtful comments representing a range of views that make their point quickly and politely. We make an effort to protect discussions from repeated comments either by the same reader or different readers.
We follow the same standards for taste as the daily newspaper. A few things we won't tolerate: personal attacks, obscenity, vulgarity, profanity (including expletives and letters followed by dashes), commercial promotion, impersonations, incoherence, proselytizing and SHOUTING. Don't include URLs to Web sites.
We do not edit comments. They are either approved or deleted. We reserve the right to edit a comment that is quoted or excerpted in an article. In this case, we may fix spelling and punctuation.
We welcome strong opinions and criticism of our work, but we don't want comments to become bogged down with discussions of our policies and we will moderate accordingly.
We appreciate it when readers and people quoted in articles or blog posts point out errors of fact or emphasis and will investigate all assertions. But these suggestions should be sent via e-mail. To avoid distracting other readers, we won't publish comments that suggest a correction. Instead, corrections will be made in a blog post or in an article.
- Fetal parts in Planned Parenthood lab shown in 4th video
- Feds eye use of federal dollars for ads for for-profit colleges
- Ex-Cincy cop pleads not guilty, posts bond
- Blankenship’s attorneys want mine blast evidence out of trial
- Minn. man accused of slaying protected Zimbabwean lion says he thought the trip was legal
- Feds accuse Philadelphia congressman Fattah of corruption
- Hope dims for Fla. teens lost at sea
- New TSA administrator vows training to address security gaps
- McClatchy: Emails on Clinton’s private server contain Benghazi information
- Minn. dentist laying low in slaying of lion
- Christian college in Illinois to stop providing health care over Obamacare