Update: April 18, 2007

Eclipsed?

By Pam Eastlick for THE DEEP on line

Welcome to The Deep science and technology column where we cover topics from the deep sea to deep space and beyond.

I’ve caught some flack lately from several different people because I didn’t feature an eclipse in my newsletters or press releases.  This confused me because there have been no eclipses visible from the western Pacific this year. Yet these people insisted that they’d seen what was described as an almost total solar eclipse.  So what’s been going on?

An eclipse happens when three solar system bodies line up, the Earth, the Sun and our moon Luna (yes, our moon does have an official name).  (Our Sun’s official name is Sol.).  Whether we have a solar eclipse or a lunar eclipse depends on which of the three worlds is in the middle. If the Earth is between the Sun and the Moon, we have an eclipse of the Moon or lunar eclipse.  Our Moon enters the Earth’s shadow and in theory, should completely disappear because no light shines on it.  We can only see the Moon and all other solar system bodies because the Sun’s light shines on them.  None of them have any light of their own.  However, you can usually see the Moon in a lunar eclipse because your planet has air.  This air bends the Sun’s light around the Earth to shine on the Moon.  Since the air is passing through the sunrise/sunset ring the light is red and the Moon looks red in a lunar eclipse.  Lunar eclipses can only happen when it’s full Moon.

A total lunar eclipse

The other type of eclipse is a solar eclipse.  This one happens when the Sun. Moon and Earth line up with the Moon in the middle.  The Moon is 400 times smaller than the Sun, but the Sun just happens to be 400 times farther away so the Moon can hide the Sun’s light entirely.  But the Moon is so small that the band where the Sun’s light is completely hidden (called totality) is very narrow.  We have already had the best solar eclipse over Guam that will occur in your lifetime on 11 June 2002.  The path of totality for that eclipse was just south of Rota.  Solar eclipses can only happen when the Moon is new.  We don’t see the Moon at all then because the Sun’s light is shining on the side of the Moon we never see from Earth.

A total solar eclipse

Eclipses don’t happen every at every new and full Moon because the Moon doesn’t orbit the Earth in the same plane as the Earth orbits the Sun.  The Moon’s orbit is tilted 5 degrees to the Earth’s orbit.  There are solar and lunar eclipses every year, but you don’t see all of them from one location on the Earth.
There will be a total lunar eclipse (eclipse of the Moon) over Guam and the Northern Marianas this year on 28 August.  We’ll have a front row seat when the Moon rises partially eclipsed and then enters the darkest part of the Earth’s shadow.  You can sit in your yard and watch the Moon turn blood-red.  You can mark your calendars now, but don’t worry; I’ll be featuring it in all my publicity.  If you want to be sure you don’t miss it, sign up for the Planetarium newsletter by e-mailing me at stars@guam.net

We’ll see a nice partial solar eclipse on 22 July in the year 2009 and another on 9 March in the year 2016, but there will be no total solar eclipses in your lifetime over Guam.  You’ll have to travel somewhere else to see a total solar eclipse.

So if lunar and solar eclipses are totally predictable and we haven’t had any this year, what were these people seeing that had them so convinced they’d seen a solar eclipse?

Solar eclipse	Solar eclipse??

Well, have a look at these two pictures.  They look pretty similar, don’t they?  The first one is a picture of an almost totally eclipsed Sun.  The second picture has the same rim of light, but if you look closely you can see markings on the dark area of the second picture.  Although you may not be able to make out what the markings are in the picture, they’re the blotchy face of the Man in the Moon.  The second picture is a photo of what your ancestors used to call “the old Moon in the new Moon’s arms” and it’s a picture of a very thin crescent Moon.

Now if you see a sliver of light in the sky, you all know it’s the crescent Moon.  But that’s not what the second picture shows.  It shows a round object lit on one side, like the edge of a totally eclipsed Sun.  In other words, you can see the face of the whole Moon in the second picture.  So here’s the question.  If the Sun’s light is shining on the other side, what’s lighting up the Moon’s face?

Traditionally, you could only see “the old Moon in the new Moon’s arms” in winter in the mainland US.  In summer, the Moon’s face was totally black and only that lovely crescent of sunlight reflecting off the ‘side’ of the Moon was visible.  So what’s the origin of the mystery light?

The clue is winter and summer.  In winter, the ground is covered with very reflective snow.  You see a thin crescent Moon just after sunset.  Although the Sun has disappeared for you, it’s still shining on the Earth to the west of your location.  And when the Sun’s light hits all that white, highly reflective snow, it bounces back into space to shine on the black face of the Moon.  That glow is Earthshine!

We have no snow here on Guam, but virtually every thin crescent Moon here has “the old Moon in its arms”.  Why?  Because the ocean is a mirror.  It’s a much better light reflector than snow and our view of the crescent Moon almost always looks like the second picture.

Want to be a scientist and observe this phenomenon for yourself?  Would you like to see a little Earthshine in your own back yard?  Just go outside any time between 7:00 and 8:00 p.m. this Thursday evening and look in the western sky where the Sun disappeared.  You’ll see that lovely sliver thin crescent Moon but you’ll also probably be able to see the whole Moon as well, lit up by the reflected light of your own planet.  Have a look on Friday night as well.  The crescent Moon will be hanging next to that astoundingly bright star in the western sky.  That’s not a star; it’s the planet Venus.  Enjoy a little Earthshine this week!