Tag: phase

NASA Goddard rocks the Moon

By Phil Plait | March 2, 2012 7:00 am

Wanna know what the Moon will look like at any time this year? And I mean what it really looks like, shadows and all?

Then go to the NASA Goddard Science Visualization Studio, where they have an amazing applet that shows you the Moon’s appearance on an hourly basis for the entire year!

Most times, websites showing you the phase of the Moon do it in big time chunks, like once per day or even per week, or they have a low-res image of the Moon with the dark part blacked out. But this one from NASA lets you enter the date and hour, for very high time resolution photo-realistic pictures.

The images are based on observations by the Lunar Reconnaissance Orbiter, which has been taken super-high-res images and altimetry data since it went into orbit our satellite in June 2009. The images show far more than just the lunar phase. For one thing, using the LRO altimeter data, it can calculate the lengths, directions, and positions of all the shadows of mountains, crater rims, and so on, knowing the angle of the Sun over the horizon.

After seeing it, my first thought was, "Someone should string these all together to make a video." I looked down the NASA page, et voila! They had! So I made it into a video on YouTube which I annotated. I also added music by Kevin MacLeod I rather like.

[Make sure to set it to HD for the full effect, which is mesmerizing.]

That weird rocking and tilting motion is real. It’s called libration. The Moon’s orbit around the Earth is elliptical, so sometimes it moves faster in its orbit than other times. However, the Moon’s spin is constant. The geometry of these two things add together, allowing us to sometimes peek a little bit over the eastern and western horizons. Not only that, the Moon’s orbit is tilted a bit with respect to our Equator, so we sometimes get a little peak over the north and south poles too.

I’ll note that these views of the Moon are not designed for people at different latitudes; for example, from Australia the Moon looks upside-down compared to how I’m used to seeing it in Boulder! Instead, these views show the Moon as if you are at the center of the Earth with your head pointed toward the north pole. Still, it’s an amazing thing, and well worth bookmarking. When I need to know what phase the Moon is in — and it happens several times a month for me — this is where I’ll check.

Image credit: NASA/Goddard Space Flight Center Scientific Visualization Studio. Music for the video is "Five Armies" by Kevin MacLeod.

MORE ABOUT: libration, Moon, phase

Does this perigee make my Moon look fat?

By Phil Plait | August 26, 2010 7:02 am


I’ve been posting a lot of extreme close-ups of the Moon, but sometimes you can learn something by taking a step back.

For example, I imagine if I went out in the street and asked people what shape the Moon’s orbit was, they’d say it was a circle (or, given recent poll results, they’d say it was Muslim). In fact, however, the Moon’s orbit is decidedly elliptical. When it’s closest to Earth — the point called perigee — it’s roughly 360,000 kilometers (223,000 miles) away*, and when it’s at its farthest point — apogee — it’s at a distance of about 405,000 km (251,000 miles).

That’s a difference of about 10% — not enough to tell by eye, but certainly enough to see in a picture… like this one, by the Greek amateur astronomer Anthony Ayiomamitis:

lunar-apogee-perigee-2010

[Click to emperigeenate.]

Amazing, isn’t it? The Moon is noticeably different! He took those images at full Moon, but seven months apart, when the Moon was at perigee (last January) and apogee (just a few days ago as I write this). It’s part of a project he does every year, and it’s pretty cool. He was able to get these images within a few moments of the exact times of apogee and perigee.

You might wonder how the Moon can be at apogee when it’s full one time, and perigee at another time it’s full. Read More

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
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