Monthly Archives: March 2011

astronomy, media mistakes, mis-education, Moon, perigee

The Full Moon Rising over the Carnival

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Carnival of Space, That Is

This week’s Carnival of Space — that compendium of writing by various bloggers — is now up for your reading pleasure. Take a few moments to check out stories about everything from the Japan earthquake to cataclysmic variables, density waves in spiral galaxies, comet Halley, and movie reviews over at Steve’s Astro Corner.

This enhanced image of the Moon was taken with the NOAO Mosaic CCD camera using two of the National Science Foundation's telescopes located at Kitt Peak National Observatory near Tucson, AZ. The image of the Moon itself was taken through the U-band filter at the 0.9-meter telescope. It is superimposed on a deep R-band image of the background sky taken at the Mayall 4-meter telescope. This composite image demonstrates the large field of view of the 0.9-meter telescope when using Mosaic, a view that covers more than five times the area of the Moon. It furnishes this large field of view without sacrificing high resolution - details as small as a few kilometers across can be seen on the lunar surface. Credit: T. A. Rector, I. P. Dell'Antonio/NOAO/AURA/NSF

As you’ve probably read (in breathless prose on some media sites, I’m sure), there’s a Full Moon today (March 19th).  You’ve no doubt been treated to all this hype and anguish over how it’s the LARGEST FULL MOON EVAR!!! and the CLOSEST FULL MOON IN MODERN TIMES and all kinds of other hyperbolic fulminating.

Lots of people are crowing about something that isn’t all that rare… and didn’t cause the earthquakes, thank you very much.

Here’s a sanity check on the news behind the hype.

As it turns out, tonight’s Full Moon is going to be closer to us than usual, and for that reason, it’s being dubbed a “SuperMoon”. The last one THIS big was in 1993 (as you can read here at NASA’s Science News site).

But it’s not all that an unusual thing to happen. During parts of its orbit, the Moon does sometimes come closer to us than other times.  As it happens, this is the closest one in less than three years. Yep, that’s right, the last “close” full Moon was in late 2008.  In fact, the January 2010 Full Moon was only 20 kilometers farther away than tonight’s.

The point is, this big Full Moon that lots of mainstream media (and astrologers) are hyping isn’t so rare after all.

My fellow blogger Ian Musgrave in Adelaide, Australia, did a little nosing around to find out the truth behind the hype.  He takes on some popular mythology about the Moon and all kinds of coincidental occurrences here on Earth. He also has a nice chart you can check out that shows the distances of the “close” Full Moons since 1991. There have been 21 in 20 years.

Umm… not so rare there, folks.  But, that hasn’t stopped Yahoo.com, Accuweather, and other sites I used to think were credible from spouting nonsense that appears to be based on something an astrologer wrote.  Do I need to point out (again) that an astrologer is not a scientist — not a lunar geologist, not an earth sciences person, not an astroNomer, and certainly not a credible expert on lunar orbits?

Look, think of the Full Moon in its orbit like a car going around an oval-shaped race course.  If you stand at one end of the oval, the car is going to be close to you at least once each time it goes around.  That’s called “perigee” and it’s entirely normal and nothing to start casting horoscopes over.  When the car is farthest from you in the oval, it’s at apogee.  Now, due to various conditions, sometimes the car gets closer to you during perigee than at other times during perigee.  So, imagine that in one lap it was three meters away from you. In the next lap, it might be one centimeter closer to you.  It’s perfectly normal and nothing to start reading palms about.

The Moon’s orbit is the same way, in that sometimes it’s a few percent closer to us than other times. Occasionally, that perigee time coincides with Full Moon — the phase of the Moon that occurs when the Moon is on the opposite side of Earth from the Sun, thus allowing the side facing us to be bathed in sunlight. (Perigee and Full Moon are two different things, so don’t confuse them with each other.  For a more thorough discussion of Full Moon, go here. )  They are perfectly normal and nothing to start blaming the Japan earthquake on. That temblor  and all the earthquakes that occur in Japan and around the Pacific Basin are due to the so-called “Ring of Fire” are due to Earth’s plate tectonics. These are natural phenomena and nothing to start blaming the Moon for.

I’m not sure why this is such a big deal, this SuperMoon thing.  Is it because if an astrologer says so in flowery language that somehow looks impressive but means very little (the definition of amphigory, by the way)?  If so, see the last sentence of previous paragraph.  Is it because if you put the word “Super” in front of something, that makes it all magical somehow?  It’s like putting “mega” in front of words. You see it all the time, particularly when somebody wants to sell you something (whether product or whack idea).  “MEGA-SAVINGS ON BULK ADULT DIAPERS!”  or “MEGA-SALE AT XXX AUTO DEALERSHIP!!!!!  SAVE 1000’S OF $$$”  (Try saying that last one out loud and it comes out as “Save one thousands of dollars!”  Who talks like that? Who taught the copywriter how to punctuate?)

Now, you can take my word for it that there’s nothing magical or mysterious about the closeness of this particular Full Moon.  It will look beautiful, provided you aren’t under cloudy skies. I guarantee you will (or have done so already) walk outside, look at this gorgeous Full Moon and say to yourself, “It’s wonderful, but I don’t see much difference from the other Full Moons I’ve seen.” And, you would be correct.

And, that’s the point.   Last month’s Full Moon measured 33.4 arcseconds across.  Tonight’s Full Moon will measure 33.7 arcseconds. It’s NOT a difference that you or me or anybody who looks at it with the old Mark I eyeballs are going to SEE. I defy you to tell me your eyes can discern that small of a difference.  And furnish proof, if you do.

What I will CHALLENGE you to do is go out and look at the lovely Moon.  Enjoy it. Cherish it.  That’s what its’ all about in skygazing. Enjoy what you see.  Any time you can step outside and enjoy a lovely moon rise is a life experience worth having!

Mercury, MESSENGER, NASA

Standard Mercury Orbit, Mr. Sulu

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Mercury Has a Long-Term Visitor

MESSENGER at Mercury (artist's conception). Courtesy MESSENGER Mission.

Last night I went down to the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado for a briefing and “wait-it-out” event for the MESSENGER spacecraft’s orbital insertion. The lab built one of the instruments onboard the spacecraft — the Mercury Atmospheric and Surface Composition Spectrometer (MASCS). As I was sitting there watching the folks in the control room at the Johns Hopkins Applied Physics Laboratory (by remote link), I thought about all the times we’ve seen “standard parking” orbit commands applied in shows like Star Trek. They make it sound so easy. The captain just says “Standard orbit” to the helm, the officer punches a few buttons or slides a fader or waves a hand over the console, and the ship slides into the correct spot.  What we don’t see are the ship’s thrusters firing to nudge the ship — a massive behemoth compared to a small planetary probe like MESSENGER —  from its previous course into the parking orbit around the world it’s visiting.

We didn’t actually see MESSENGER’s thruster fire either last night. What we heard was a stream of announcements that told us what the Doppler readings were from the spacecraft as its fuel tanks fed the thruster that nudged it into a parking orbit (highly elliptical at that!) around Mercury.  You can see an animation of how it might have looked here.

To see the kind of orbital trip MESSENGER has taken since its launch on August 3, 2004 , go here for an animation showing its long journey. As of today, the spacecraft has traveled 4,902,668,000 miles. That’s 7,890,000,000 kilometers, or 52.7 astronomical units. If Messenger had traveled in a straight line for that distance, it would be well beyond the most distant point of Pluto’s orbit!

MESSENGER's orbit around Mercury is very elliptical, meaning its lowest point is only about 124 miles (200 km) above the surface and gets as far asway as 9,300 miles (15,000 km) at its most distant. The closest approach of the orbit will take it high over the north pole, where there is some radar evidence of something -- possibly water ice -- hidden on crater walls. Courtesy NASA/JHUAPL.

MESSENGER is small, only about the size of a minivan, so it wouldn’t take nearly as much power to put it into “standard orbit” as a giant starship would need.  But, the principles are the same no matter what size of object you’re trying to put in orbit around another one.  The incoming object has a certain path it’s following, and it’s going at a certain speed. If you want the spacecraft to merely fly by, you wouldn’t need to deviate the probe from its path.  But, if you want it to go into orbit, you have to slow it down at the right place, the right time, and at the right rate. Once you do that, you’ve got your spacecraft (regardless of its size) at a point where the gravitational pull of the planet it’s orbiting is EXACTLY matched by the spacecraft’s speed around the planet. It’s a constant tug of war that must be balanced correctly.

Now that MESSENGER is safely orbiting Mercury, scientists are testing its systems to make sure they’re doing okay in the hot, harsh environment around the planet.  The spacecraft is subject to solar heating eleven times hotter than we experience here on Earth, and it is protected with a sunshade to protect the delicate instruments inside. As soon as they’re satisfied that all systems are working on the nominal, they’ll turn the instruments on and commence the next phase of mission science.  The first images should start streaming to Earth in the first part of April, so stay tuned!