Moons

(International Space Station crewmember, André Kuipers, snapped this photo of the Supermoon sinking behind the Earth’s atmosphere.)

Did you get a chance to see this year’s “Supermoon“? Still confused as to what was so super about it, anyhow? Simply, the supermoon is the colloquial name for what is scientifically referred to as the perigee-syzygy moon. “The … what”, you ask? Don’t worry, it’s not as complicated as it sounds. The Moon orbits our Earth, not in a perfect circle, but in an ellipse. As a consequence of this, there are times the Moon is closer to the Earth and times it is further away. For any object orbiting the Earth, the part of its orbit that takes it furthest from our planet is called apogee. The closest point, perigee.

So now that we have perigee out of the way, “what was that other funny word again?” A syzygy,  (pronounced, Sizz-ih-gee), is a term used to refer to an astronomical event in which 3 celestial bodies form a straight line. In our case with the Moon, the bodies are the Sun, the Earth, and the Moon. You’re probably realizing that the Sun-Earth-Moon system experiences two syzygies each month; we call them the New Moon and the Full Moon.  The lunar month (29.53059 days) is defined as the period of time between two identical syzygies (Full Moon-to-Full Moon / New Moon-to-New Moon).

Putting it all together now: a perigee-syzygy Moon is the Full Moon or New Moon which coincides with its closest approach to Earth. Keep in mind, a New Moon at perigee could also be referred to as a supermoon; however, it’s unlikely to generate much attention because we can’t see the New Moon from Earth. “Well, of course. That makes sense!”

So now that we know what a supermoon perigee-syzygy Moon is, let’s talk about what a perigee-syzygy Moon does; or, more importantly, doesn’t do. There is no correlation between perigee and major earthquake activity. There is certainly no correlation between perigee and human behaviour (well, except for the fact that when people start talking about supermoons, more people are likely to take a look at the Moon on that occasion). “But what about bigger tides?” Well, yes! Tides are greatest during Full and New Moons, and there is an increase in the tides when the Moon is closer to the Earth as well. Luckily, tidal forces are weak and even the few percent increase due to the perigee-syzygy isn’t going to create anything that will cause alarm.

“But I heard the supermoon is super big and super bright!” While the perigee-syzygy Full Moon is what we can call the biggest and brightest Moon of the year, it’s such a small degree bigger and brighter that its really not noticeable. In fact, last night’s supermoon was only about 1% bigger/brighter than last month’s Full Moon. It did appear 14% larger than the smallest Moon of the year, but again, you’d have to be using some tools other than just your eyes to notice the difference.

(This image shows the difference in apparent size between a Full Moon at perigee and a Full Moon at apogee. Lined up next to each other, the difference looks quite large. In the sky by themselves, you’d be hard-pressed to notice the difference.)

Now, I purposely waited until after the Supermoon had passed to offer this explanation. Why? Because I didn’t want to discourage people from thinking they might see something special if they looked up at the Full Moon last night. It wasn’t easy to stay quiet for a couple of reasons. First of all, all of the ridiculous claims and fear that is generally associated with this event is hard to ignore — and in cases where real fear was involved, I did explain how there was nothing to worry about. The other reason it was difficult to not publish this before the event was that I didn’t want to entirely erase the hype that inevitably surrounds the “Supermoon”. Call it selfish, but I wanted people looking up at the sky last night — even if it was under some slight false pretenses. I want people looking up every night, and if some buzz on the internet can help make that happen, well then… good.

The truth is, the Moon is amazing whenever you can see it. The light of a Full Moon creates amazing shadows on our planet, and is a comforting companion to have overhead at night. Waxing and waning Moons are also beautiful, because they occur at an angle with the Sun in which the shadows and craters are much more pronounced.  And a New Moon (one we cannot see) offers us the darkest skies to observe the other billions of fascinating objects that are just above our heads.  All of which are… well… Super.

(Click to enlarge)

Earlier this month, I gave a minor overview of NASA’s Gravity Recovery And Interior Laboratory (GRAIL) mission. I had mentioned that the two mirror-twin spacecraft that make up the mission were currently — and temporarily — dubbed GRAIL-A and GRAIL-B, with official names coming later in the month. Beginning last October, NASA appealed to elementary students to come up with replacement names for the spacecraft.

Over 11,000 students, from 45 states and several territories, participated in contest, making for stiff competition.

Ultimately, it was the 4th Grade students from Emily Dickinson Elementary school, in Bozeman, Montana, who were chosen as the nationwide winners of the naming competition, with their names of Ebb and Flow. The students arrived at their name by researching what the GRAIL mission was studying and how it worked. They learned how important the Moon is to our lives on Earth, and how the Moon’s gravity causes our high and low tides. They decided on Ebb and Flow, because the names represent both the Moon’s gravity and its effects on our home.

Congratulations Emily Dickinson 4th-Graders! Not only did you come up with great contest-winning names, you came up with names that will forever exist in the historical pages of the world’s exploration of space!

For more about GRAIL, check out these links:

• The 365 Days of Astronomy podcast episode for January 20 has expanded information about the competition winners.
• The NASA Lunar Science Institute
• And both NASA’s and MIT’s Grail websites

(Click for full-size version)

NASA.gov – Flying past Saturn’s moon Dione, Cassini captured this view which includes two smaller moons, Epimetheus and Prometheus, near the planet’s rings.

Dione (698 miles, or 1,123 kilometers across) is closest to Cassini here and is on the left of the image. Potato-shaped Prometheus (53 miles, or 86 kilometers across) appears above the rings near the center top of the image. Epimetheus (70 miles, or 113 kilometers across) is on the right.

This view looks toward the northern, sunlit side of the rings from less than one degree above the ring plane. The view was acquired at a distance of approximately 67,000 miles (108,000 kilometers) from Dione. Image scale is 2,122 feet (647 meters) per pixel on Dione.

It’s been a busy few weeks and I have a lot of draft posts added to the list for publishing in the near future; everything from the origin of the Moon to NASA’s opening of its first solar-sail. In the mean-time, enjoy this wonderful video captured by JAXA’s SELENE (Selenological and Engineering Explorer) orbiter; also known as Kaguya.

(I recommend the highest HD resolution and full-screen, if your connection and hardware allows.)

The video was captured in November of 2007. After orbiting the Moon for one year and eight months, SELENE was purposely dropped out of lunar orbit and crashed into the lunar surface.

Our cratered Moon:

Photographed December 24, 2010 – 12:16am.
Technical Data:
f/5.6
1/2500sec
ISO 800
250mm

If you have clear skies, be sure to take the opportunity to view the total lunar eclipse of December 20/21, 2010. My forecast isn’t looking good, but I’m holding out hope that I’ll get a clear view and get some photographs of the event. The following image does a great job of detailing when to look, and what you can expect:

*Note, the times listed on this image are for Alaskan time, which is 4 hours earlier than Eastern time.
I got the image from Mr. Eclipse who not only explains what you’re seeing, but provides a wealth of other information, including how to photograph it.

A lunar eclipse occurs when the Moon enters the shadow of Earth. This can only happen during a full moon, but not every full moon coincides with an eclipse. Why? Because the Moon’s orbit is inclined about 5.1° to the Earth. So a lunar eclipse will occur when a full moon also happens to be on the same plane, or 0°, as the Earth.

If you’re plagued by cloudy skies, you can still watch it and participate in a live chat, courtesy of NASA/JPL.

So there you have it, no excuses. If you miss this one and reside in the North America, you won’t have another chance until 2014.

Happy observing!

Saturn’s icy moon, Mimas, has long been remarked for its large Herschel Crater giving it the appearance of the Death Star, the fictional space station of Star Wars fame.

Perhaps Mimas inspired George Lucas when creating the Death Star? Nope; Voyager was the first to give us close-up views of Mimas, a few years after ‘A New Hope’ was in theatres.

But earlier this year, Mimas revealed another uncanny secret resemblance to something out of recent pop-culture history: Pac-Man!

So what we’re seeing here is a map of temperature differences placed over a visual-light image of Mimas. If you think it’s curious that the highest temperatures seem to vary in such a way, you’re not alone:

“Even though we can’t explain the observed pattern of surface temperatures on Mimas, the giant Herschel crater is a leading suspect” “The energy of impact that created it several billion years ago has been estimated to be one-seventh of Mimas’s own gravitational energy. Anything much larger would likely have torn the moon apart. We really would like to see if there is also an anomalous temperature pattern on the other side of Herschel, which has not been observed so closely.” – Dr. Mike Flasar, composite infrared spectrometer principal investigator from NASA Goddard Space Flight Center.

The following image gives an idea of how what’s actually occurring on Mimas compared to what would previously be expected:

A leading theory is that different textures of surface materials (mostly water ice with small amounts of rock) are holding on to heat from the Sun differently, but what is still not understood is why such sharp boundaries exist between these textures — giving the Pac-Man shape. It’s possible that the impact that caused the Herschel Crater distributed the more heat-absorbent materials in that pattern, but Mimas is constantly bombarded by impacts (as can be clearly seen when viewing the high resolution image of Mimas above), which you’d expect to destroy long ago any non-uniform surface make-up.

So for now, no definite answer is available. Luckily, we have the amazing Cassini orbiter up there, collecting more data for the scientists to work with.