Written by Kelly Herbst, Astronomy Curator for the Virginia Living Museum. Updated every two weeks, more or less.

Wednesday, September 28, 2011

I'll See You on the Dark Side of the Moon

There is no dark side of the Moon, really.  Matter of fact, it's all dark.

Pink Floyd had it correct, you know.  The Moon doesn't generate its own all the planets and moons of our solar system, it merely reflects the Sun's light.  But what a beautiful reflection it is.  So let's talk a little bit about the Moon.

It's pretty much the easiest thing to observe in the night sky.  It's big, bright, and details can be seen with nothing more than your eyes!  We've been looking at the Moon a long time - ever since man first raised his eyes to the skies.  Every culture around the world has seen things depicted in the patterns of light and dark rocks on the Moon...faces are common, both male and female...and numerous animals have been found cavorting across the face of the Moon.  What you see may depend on your vision, the clarity of the sky when you look, and your own imagination.

(From top) Man carrying sticks, with dog; Rabbit; Human face 1; Human face 2; "The Lady in the Moon" Attributed to Magnus Manske, Wikipedia

When scientists began investigating the Moon, the darker areas were quickly named "mare," Latin for "sea."  Indeed, early astronomers believe that the dark regions on the Moon might be water, filling the low-lying regions of the lunar landscape.  These regions were given names like "Sea of Fecundity," "Ocean of Storms," and "Bay of Love."  Even after men traveled to the Moon and found no water on the surface at all, let alone oceans, seas, and bays, the naming scheme persisted.  There seems to be a permanent connection between water and the Moon

It turns out, there actually is!  The Moon's gravitational influence is the primary reason why we have tides.  The Earth's gravity keeps the Moon in orbit around us.  The Moon's gravity tugs on the waters of Earth, forcing them to move up and down in response to its gravity.  The Sun gets in on the act too, but if the Earth had no Moon, the tides would be all but invisible to us.  Many species of life depend on the constant and regular motion of the tides...and many scientists believe that without the tides, life as we know it on Earth would not be possible.  Turns out those ancient astronomers were on the right track after all - the connection between the Moon and water is extremely important to all of us here on the Earth.

Observing the Moon is easy...just look up!  Okay, well, maybe it's not that easy.  The Moon isn't always visible in our sky - you have to know when and where to look to see itThe Moon's phases, or changes in shape, are caused by our perspective changing as the Moon revolves around us in its monthly cycle.  We see varying amounts of the daytime side of the Moon depending on where the Moon is relative to the Sun as it orbits around us.  Many people assume the best time to observe the Moon is during a Full Moon, since the entire side of the Moon facing us is lit up.  But that's actually not true, for two reasons.  First of all, a Full Moon, by definition, is exactly opposite the Sun, meaning that it rises at sunset and sets at sunrise.  This might sound great - the Moon is visible all night!  But the means that you must wait until around midnight for the Moon to be high in the south, where it is easiest to observe.  And let's face it...most of us are not quite that lunatic.  (Ha!  Fun play on words!)

First Quarter Moon.  Courtesy NASA.

The second reason why the Full Moon is not the best for observing is that during a Full Moon, the light striking the surface of the Moon is coming pretty much from directly overhead, from the lunar perspective.  That means there are virtually no shadows, and very little contrast.  Shadows give you a sense of height and depth - something that really adds to your observing as you look at mountains and craters on the surface and try to get a sense of how high or deep they are.  The best time to observe the Moon is during the First Quarter phase - the Moon is high in the south around sunset, and the dark line the runs across the face of the Moon dividing the daylight side from the nighttime side (it's called the terminator) is perfect for viewing - the shadows there are long and deep, and you get an excellent sense of depth perception when you scan along it with your telescope.

In fact, consider this an invitation to join us here at the Virginia Living Museum on the evening of October 8th.  Not only is that our regular monthly Star Party and Laser Light Night, it also happens to be International Observe the Moon Night, and we will be celebrating!  A First Quarter Moon will be gracing the skies, and, weather permitting, we'll have our telescope trained on it to give you the best view possible.  We'll have some special Moon-based crafts and activities for kids, and the folks from NASA will be on hand with their Driven to Explore exhibit...which includes a rare TOUCHABLE Moonrock!  There are only 8 lunar samples in the world that can be touched - don't miss your opportunity to touch the Moon!  The festivities begin at 6pm, and are FREE to all, except for the planetarium and laser shows ($3 for members, $6 non-members).  We'll see you there!

Until next time...
Carpe noctem!

Thursday, September 15, 2011

A Day Late and a Dollar Short


You know, I've been so proud of myself for keeping this up...even posting a day early when I know I won't be around on a Wednesday...

So imagine my shock when I looked ay my calendar and saw the "Update Blog" icon proudly displayed across...YESTERDAY!  ACK!  Talk about a good time for a time would be it!  Or even a good improbability  Well, guess I'll just have to take my lumps and admit to being a day late.  I blame it on the calendar program...I'm quite sure that banner wasn't there yesterday.

Anyway, I'm back today!  Let's talk about something spacey!  Specifically, let's talk about what's going on in the sky for this month.

The sky is still desperately clinging to more water than I would like.  I'm waiting for the final break in humidity...the one that announces in no uncertain terms, "okay, Fall has arrived!"  The autumn months are excellent for's cool, but not too cold...the sky is clearing up and visibility improves...sunsets are coming steadily earlier, giving us more nighttime to enjoy.

One of the most prominent objects in the sky right now makes its appearance in the late evening sky in the east.  It rises up, brilliant white and very steady, and more than a few people have wondered if they are seeing a UFO!  Don't worry though, it's not an alien invasion.  It is instead the regal planet Jupiter.

Jupiter is one of the brightest objects you'll ever see in our night sky; fourth behind the Sun, the Moon and Venus.  Combine that brightness with a still-soupy atmosphere and you can get some strange effects.  Normally, the planets don't twinkle.  Twinkling of stars is caused by the tiny bit of light we receive from a star getting jostled about by the moving air of the Earth - so naturally, twinkling is more intense under humid or smoggy conditions.  Planets are much closer to us than the stars, so their light tends to be stronger, and less affected by the air.  But on a humid night, even a planet can seem to fiddle, fidget, wink, flash colors, or move about slightly thanks to atmospheric effects.  Add that to our tendency to squint at something to try to "bring it into focus" and it's not hard to see why magnificent Jupiter has been mistaken for an alien spacecraft.

Jupiter.  Courtesy NASA.

Another spacecraft Jupiter (and Venus, too) is often confused with is the International Space Station.  The ISS is quite bright, occasionally even exceeding Jupiter's brightness as it crosses our sky!  However, there's a big difference between Jupiter (or any planet) and the ISS - speed.  Planets are stationary, by and large.  Oh sure, they are orbiting the Sun, just like we are, but you won't notice that motion when looking up at a planet at night.  If you stand and stare long enough (maybe an hour or two), you will notice that planets, like all other celestial objects, move slowly across our sky.  This is thanks to the rotation of our very own planet Earth - and that's why all natural objects cross the sky from east to west.  The Sun, The Moon, the stars, the planets...everybody appears to move east to west across our sky thanks to the Earth's own rotation on its axis.

 The International Space Station.  Courtesy NASA.

Spacecraft, however, move thanks to the initial kick from the rockets that got them up into orbit and the gravitational pull of the Earth.  So not only can they move in pretty much any direction we choose to set them, they can also move much, much faster than the rotation of the Earth carries objects across our vision.  The ISS, for example, circles the world in about 90 minutes, meaning that it will cross your patch of sky in about 5 or 6 minutes or so.  How can you distinguish the ISS from a plane?  Easy - planes always have some kind of blinking light.  The ISS will move fast, and shine rock steady.  The best way to be sure you're looking at the ISS is check with the excellent satellite tracking website  You'll need to tell them your location - latitude and longitude are best if you have them (try Google Earth for help) - and then they'll tell you when and where you can look up to see satellites whizzing by over your head.  If you've never done this before, be warned - it is very fun and highly addictive!

Before I go, let me share some exciting news about Jupiter for those of you with telescopes...the South Equatorial Belt is back!  Jupiter's rapid rotation for such a large planet (the gas giant is ten times the size of Earth but rotates once in under 10 hours!) causes its clouds to form into huge stripes around the whole planet.  Most of the time, these stripes are pretty constant - there are usually a couple large dark reddish belts around Jupiter which contrast beautifully with other whitish stripes.  Recently, the southern belt decided to take a vacation, disappearing from telescopic view for quite some while.  Now, whatever weather processes on Jupiter that allow such things to form have kicked back in, and the SEB is returning beautifully.  So check out Jupiter with your telescope (or even binoculars!) and enjoy the show.

Well, I guess that catches us up for now...and I promise to be on time in two weeks.
Carpe noctem!