Chris McKitterick (mckitterick) wrote,
Chris McKitterick

Astro-Image of the Day: Moon at its biggest & brightest on Friday.

You might have noticed that the Moon seemed especially bright last night. Sure, the snow on the ground had something to do with that, reflecting moonlight all over the place, but there's more to the story. It really was brighter, and will be even more so tonight and over the next few days.

Some full Moons look larger than others. Why is this? Sure, sometimes it's the illusion caused by the Moon rising over buildings or other objects we recognize, and our brains go, "Whoah, it's huger than that whole farm!" But the Moon actually does increase in apparent size throughout the month. Here's a comparison of the full Moon at its smallest and at its largest:

Click the image to see the story.

The reason this happens is that the Moon's orbit is not a perfect circle; far from it, it's a lopsided ellipse with the near edge about 30,000 miles closer to us than the far edge. Here's an image that illustrates this:

Click the image to see the story.

When the Moon is full, it's at its brightest. When it's nearest us (at perigee), it's at its largest. Because brightness is based on the amount of surface area that's lit, well, you'll get your brightest Moon when it's both full and at its closest approach to the Earth. It's not always at full when at perigee, because orbital mechanics move apogee and perigee all over the place. So on Friday, December 12, when the Moon is both full and at perigee, it'll be 14% larger and 30% brighter than this year's previous full Moons.

So get yourself outside over the next few days to see the biggest, brightest Moon you'll see for at least a year!

Tags: astronomy

  • Post a new comment


    default userpic

    Your reply will be screened

    Your IP address will be recorded 

    When you submit the form an invisible reCAPTCHA check will be performed.
    You must follow the Privacy Policy and Google Terms of use.