Published:
Dec 22, 2004

# Christmas Moon

The smallest full moon of 2004 will brighten the nights around Christmas.

Rudolph coughed and sneezed.
Ahh-choo! His nose was really red.
The doctor nodded ruefully.
"He has to stay in bed."

a bad one, plain to see.
He wasn't going anywhere
with Santa Christmas Eve.

Rooftops dark and tricky.
(Hey ... where'd the chimney go?)
That's what Santa has to deal with
absent Rudolph's rosy glow.

But Santa is a cheery soul
and a smart one, too.
He quickly had a bright idea:
"I know what to do!"

Using special Santa-magic,
he conjured up a moon,
a full one, round and shiny.

Who needs Rudolph? That old prune!

So... to those of you who don't believe
in Santa, here's the proof:
Look out the window Christmas Eve
at the moonlight on your roof.

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December 22, 2004: No Rudolph? No problem. This year there's going to be a full moon to light up the nights around Christmas.

It's a special full moon, too: the smallest of 2004. Soaring high in the sky, it might remind you of a shiny white Christmas ball for your tree. Don't bother reaching for it... it's 406,700 km away!

Technically speaking, the moon isn't 100% full until Dec. 26th. But that's perfect timing for Christmas carolers and Santa. The practically-full moon on Dec. 24th and 25th rises early, lighting up streets and rooftops as soon as the sun goes down.

What makes this full moon small? Answer: The moon's lopsided orbit.

Although astronomers often say the moon "circles" the Earth, it doesn't, not exactly. The moon's orbit is really an ellipse. One side of the ellipse is 356,400 km from Earth; this is called perigee. The other side of the ellipse is 406,700 km from Earth; this is called apogee. Apogee is about 50,000 km farther from Earth than perigee.

Right: The apparent size of the moon at perigee (top) and apogee (bottom).

When the moon is full and near apogee, we get an extra-small full moon. Such is the case this Christmas.

Even the smallest full moons are very bright. They outshine Sirius, the brightest star in the sky, by twenty-five thousand times. They cast shadows, and provide enough light to read by. Finding chimneys? It's easy!

If you get binoculars or a telescope for Christmas, take a look at the moon. It's absolutely beautiful--a world so close to Earth that you can see its craters and mountains and "seas" in exquisite detail. The moon is deserted now, but in the years ahead, according to the new Vision for Space Exploration, people will be walking around up there.

Enjoy the moonlight and Merry Christmas, from Science@NASA.