September 27 – Totally Super!

Just some images from tonight’s supermoon eclipse. Enjoy!

“And so it begins”

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Halfway up the mountain

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Just a sliver left before totality

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That’s not Mars; it is the Moon! The red color comes from the light of every sunrise and every sunset on Earth, simultaneously. And if that ain’t cool, I don’t know what is!

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Overexposed to show the stars by the Moon.

September 25 – Look! Up In The Sky!

Today’s factismal: The technical term for a supermoon eclipse is a perigee-syzygy.

Mankind has been watching the skies for millenia. And we’ve seen our share of eclipses in that time, starting with the first eclipse in recorded history was seen over Sumeria (near modern-day Iran) in 1375 BCE and going through to the “supermoon” eclipse coming up on Sunday. During that time we’ve developed some terms to describe the event (such as syzygy, or “yoked together”) and we’ve learned some things.

The Earth-Moon system, draw to scale. Notice how the Moon's orbit is slightly elliptic.

The Earth-Moon system, draw to scale. Notice how the Moon’s orbit is slightly elliptic.

We’ve learned that eclipses are caused when the Moon blocks the Sun’s light from part of the Earth (a solar eclipse) or when the Earth blocks the Sun’s light from the Moon (a lunar eclipse like Sunday’s). We’ve learned that happens because the Moon orbits the Earth in a near-perfect circle. If the Moon’s orbit were a perfect circle around Earth’s equator, then we’d have an eclipse twice every month with a solar eclipse at new moon and a lunar eclipse two weeks later at full moon. But it isn’t and we don’t. Because the Moon orbits in a tilted ellipse where it comes as close as 225,291 mi and heads out as far as 251,910 mi, eclipses are rare; we only get between two and five solar eclipses each year, and the same number of lunar eclipses. In addition, the ellipse slowly precesses around the Earth so that the close part (what astronomy wonks call perigee) doesn’t always happen at the full moon; when it does, we get a “supermoon” where the Moon appears about 14% larger than normal.

The Sun, Earth, and Moon, drawn to scale (almost - the Moon is three times as large as it should be)

The Sun, Earth, and Moon, drawn to scale (almost – the Moon is three times as large as it should be)

This month we are exceptionally lucky. The Moon will be in the right place to have an eclipse (rare) and it will happen when the moon is at its closest approach (rarer)! The last time this happened was 33 years ago, and it won’t happen again for another18 years. All told, there have been five supermoon eclipses in the past century (counting this one). So you should definitely go out and see it!

All you will need to see the supermoon eclipse is clear skies and an alarm clock. For all of North and South America, the Moon will either be in eclipse at moonrise or will goo into eclipse shortly thereafter.  And the Moon will stay in total eclipse for a good hour or so. From the start of the eclipse (when the Moon first enters Earth’s shadow) to the end will take just over five hours, so you’ll have plenty of time to see the spectacle.For folks in the Central time zone, the eclipse starts at 8:07 PM and hits totality at 9:47 PM. So skip the Simpsons and go see something truly amazing!

The perigee-syzygy will be visible over all of the Americas (Image courtesy NASA)

The perigee-syzygy will be visible over all of the Americas
(Image courtesy NASA)

If you’d like to learn more about eclipses, including if you’ll be able to see any of the four eclipses visible nextyear, then head on over to the NASA Eclipse Web Site:
http://eclipse.gsfc.nasa.gov/eclipse.html

April 3 – In The Dark

Today’s factismal: The technical term for an eclipse is syzygy.

Imagine, if you will, that tonight is a warm summer evening in Ancient Greece. You look up and are amazed that the Moon is slowly getting darker and turning a blood red. Being a philosopher, you immediately realize what is happening. The Earth, Moon, and Sun have become yoked together and so you shout out “syzygy!” (the ancient Greek word for “yoked together”). You have just witnessed an eclipse.

The Sun, Earth, and Moon, drawn to scale (almost - the Moon is three times as large as it should be)

The Sun, Earth, and Moon, drawn to scale (almost – the Moon is three times as large as it should be)

Eclipses are one of the more interesting natural phenomena. Not only did the eclipses of the Sun and Moon help ancient Greek philosophers to reason out how large the Solar system must be and the fact that the Earth is round, but they help show both how predictable and how uncertain the Solar System is. The predictable part is easy; once you know all of the factors affecting the orbits of the Earth and Moon, you can easily calculate when the next eclipse will happen and what type it will be. More than 3500 years ago (or about 800 years before that warm summer night in Greece) Babylonian astronomers were predicting eclipses.

The uncertain part is also easy once you stop and think about the problem. The Moon doesn’t orbit the Earth in a perfect circle; worse, the Moon’s orbit is tilted away from the Earth’s. As a result, sometimes the Moon is too high or too low or too far away to create an eclipse. That’s also why some eclipses are very short (like the one tomorrow morning; it will last just 4 minutes and 43 seconds) and some are very long (like the one in 1859 that lasted 1 hour, 46 minutes, and 27 seconds), and why some years we only see two lunar eclipses and some years we see five (1879).

That variation in the Moon’s orbit also determines what type of eclipse we’ll have. If the Moon is close to the Earth, then the Earth’s shadow completely covers the Moon and we get a total eclipse. If the Moon is a little farther out then the Earth’s shadow is smaller and only covers part of the Moon, giving us a partial eclipse. And if the Moon is farther out still, then we don’t get an eclipse at all! Or at least, not an umbral eclipse.

The parts of Earth's shadow

The parts of Earth’s shadow

You see, the Earth’s shadow in space isn’t a perfect cone. Because the Sun is wide, the light from one side casts a slightly different shadow than the light from the other side. If you’ve ever looked at the shadows cast by light coming in from two nearby windows, you’ve seen this effect at work. The area in the middle is dark because no light from either window makes it into the room; this is the umbra (Latin for shadow). And the area directly in front of a window is bright because lots of light makes it in. In between the two regions is the penumbra (from the Latin for “nearly shadow”) where a little light from one window makes it in but no light from the other does. The same thing happens in space; when the Moon moves into the Earth’s penumbra, it gets about 10-30% less light and dims slightly. To an astronomer, that is the start of the eclipse even though a non-astronomer won’t call it an eclipse until the Moon moves into the umbra.

And now that you know what will happen, set your alarm clocks! Tomorrow’s eclipse will be short and sweet – don’t miss it!

October 22 – Against The Fading Of The Light

Today’s factismal: The last solar eclipse of 2014 takes place tomorrow evening at 3:30 PM EDT (assuming that you live in Alaska).

If you live anywhere in North America, get ready! You won’t want to miss the last eclipse of 2014. It happens tomorrow afternoon at 3:30 PM and will be visible across the entire continent. Though this will only be a partial eclipse, thanks to the Moon’s angle with the Sun, it nevertheless promises to be a spectacular show.

Tomorrow's eclipse (Image courtesy NASA)

Tomorrow’s eclipse
(Image courtesy NASA)

 

Local Eclipse Times
City Eclipse Starts Eclipse Ends
 Anchorage, AK  11:55 AM 2:28 PM
 Baltimore, MD  5:51 PM  6:15 PM
 Baton Rouge, LA  5:02 PM  5:59 PM
 Dallas, TX  4:48 PM  5:43 PM
 Oklahoma City, OK  4:40 PM  5:48 PM
 Portland, OR  1:37 PM  4:22 PM
 Richmond, VA  5:55 PM  6:21 PM
 Tallahassee, FL  6:09 PM  6:56 PM
 Denver, CO  3:18 PM  5:44 PM

Of course, eclipses don’t just happen in one year; we have some every year. There will be four eclipses in 2015. On April 4, before you pay your taxes, you can see a total lunar eclipse from the central US through all of Europe and Africa. On March 20, you can watch the total solar eclipse if you live in the middle of the north Atlantic Ocean (great if you are a fish). On September 15, there will be a partial solar eclipse that will be most visible if you happen to be a penguin; outside of Antarctica and parts of Australia, it won’t be visible at all. Then on September 28, there will be another total lunar eclipse; this time it is visible mostly over Asia. If you’d like to learn more about eclipses, including if you’ll be able to see any of the four eclipses visible next year, then head on over to the NASA Eclipse Web Site:
http://eclipse.gsfc.nasa.gov/eclipse.html

October 7 – This Little Light Of Ours

Tomorrow’s factismal: Tomorrow morning people on the East Coast of North America will be able to see both the Sun and the lunar eclipse at the same time!

Eclipses are one of the wonders of our world. We are fortunate that the Moon is just the right size and just far away to be the same apparent size as the Sun in the sky. And we are even more fortunate that the Moon’s orbit brings it into almost the right position to fall into the Earth’s shadow once a month. (Two weeks before or after, the Moon returns the favor by bringing its shadow to the Earth’s surface.) And the most fortunate thing of all is that the Earth has an atmosphere because that is what will make tomorrow morning’s eclipse so special.

The Earth-Moon system, draw to scale. Notice how the Moon's orbit is slightly elliptic.

The Earth-Moon system, draw to scale. Notice how the Moon’s orbit is slightly elliptic.

You see, the Moon’s orbit isn’t perfectly circular and it isn’t perfectly aligned. If the Moon’s orbit were perfectly circular and if the Moon orbited in the same plane as the Earth, then we would have a lunar eclipse every month on the full moon and a solar eclipse two weeks later on the new moon. But the Moon moves slightly closer to the Earth (a mere 225,622 mi) and slightly farther away (a whopping 252,088 mi). Because the Moon is sometimes closer to the Earth and sometimes farther away, sometimes it is close enough to be in the Earth’s shadow and sometimes it isn’t. And because the Moon’s orbit is slightly inclined, sometimes it is above the Earth’s shadow and sometimes it is below it and only every once in a while is it in exactly the right place to be in eclipse. (This is also why solar eclipses are sometimes total and sometimes just partial.)

This month is not one of those times when the Moon is in exactly the right place; instead, the Moon is just slightly too far away to be in the Earth’s shadow. So, if the Earth didn’t have an atmosphere, then there would be no eclipse this month. Instead, the Moon would stay nice and bright all night long. Luckily for us, the Earth does have an atmosphere which means that we will have a breath-taking eclipse tonight. You see, that atmosphere bends some of the Sun’s light around the Earth, creating a second, larger shadow called a penumbra (from the Latin for “almost dark”; the penumbra also owes its existence to the fact that the Sun is a big, fat star and not a tiny pinpoint of light). Like the name says, this shadow isn’t completely dark. Instead, it has the light of every sunrise and every sunset on Earth shining through it which is why the Moon turns a deep, dark red color when it passes through the penumbra.

And the Earth’s atmosphere will do us one more favor tomorrow morning. Because the atmosphere refracts light, it allows us to see things that are slightly below the horizon. That’s why the Sun takes on such a funny, squashed shape as it rises and sets. And it is also why we will be able to see the Sun rising tomorrow as the full Moon sets in eclipse. The technical term for this is a selenelion (“selene” {Moon} plus “helion” {Sun}) eclipse and it happens in about one out of every forty eclipses.

The eclipse will be visible over most of North America (Image courtesy NASA)

The eclipse will be visible over most of North America
(Image courtesy NASA)

The sunrise and moonset will be most visible on North America’s East coast from 4:15 AM (when the Moon starts to go into the Earth’s penumbra) until 7:25 AM (when the Sun rises);  though folks in the Central and Western parts of the US won’t get the selenelion effect (I told you it was rare!), they will still be able to see the blood red lunar eclipse which is still pretty darn cool. So get out of bed early tomorrow and watch one of the rarest and most wonderful things that you’ll ever see!

November 2 – Yoked Together

Today’s factismal: The last solar eclipse of 2013 takes place tomorrow morning at 7:10 AM EST.

If you live on the East Coast, then set your alarm! You won’t want to miss the last eclipse of 2013. It happens tomorrow morning at 7:10 AM and will be visible as far west as Atlanta (just barely); if you live anywhere on the East Coast, you’ll have a great view. From North America, the eclipse will appear to be a partial eclipse with the Moon taking a bite out of the Sun. But from Europe, it will be a total eclipse.

The path of tomorrow's hybrid eclipse (Image courtesy NASA)

The path of tomorrow’s hybrid eclipse
(Image courtesy NASA)

Why the difference? Consider what happens when you and your spouse are sitting on the couch and watching TV. Your eldest walks through the room and into the kitchen, grunting “hey” as he passes (must be a teenager). As he walks across the room, he completely blocks your view(total eclipse) for a moment but only partially blocks your spouse’s view (partial eclipse) because the two of you are sitting at different ends of the couch. The same thing happens in space; because the Earth, Sun, and Moon are all moving relative to each other, the amount of the Sun that gets covered changes.

An eclipse over Texas (My camera)

An eclipse over Texas
(My camera)

Of course, eclipses don’t just happen in one year; we have some every year. There will be four eclipses in 2014. On April 15, after you pay your taxes you can watch the total lunar eclipse if you live in North America, South America, or Australia. On April 29, there will be an annular solar eclipse that will be most visible if you happen to be a penguin; outside of Antarctica and parts of Australia, it won’t be visible at all. Then on October 8, there will be another total lunar eclipse; this time it is visible mostly over Europe and Africa. And the last eclipse of 2014 happens on October 23, when a partial solar eclipse is seen across most of North America. If you’d like to learn more about eclipses, including if you’ll be able to see any of the four eclipses visible next year, then head on over to the NASA Eclipse Web Site:
http://eclipse.gsfc.nasa.gov/eclipse.html

May 3 – In the Dark

Today’s Factismal: The first eclipse in recorded history was seen over Sumeria (near modern-day Iran) in 1375 BCE.

Eclipses are fascinating. If the universe were perfect, then moons would orbit in circles and we’d have an eclipse twice every month with a solar eclipse at new moon and a lunar eclipse two weeks later at full moon. But the universe isn’t perfect; instead of orbiting in a circle around the Earth, the Moon orbits in an ellipse where it comes as close as 225,291 mi and heads out as far as 251,910 mi. In addition, the ellipse slowly precesses around the Earth so that the close part doesn’t always happen at the full moon. And, just to make things even more complicated, the Moon does orbit around the Earth’s equator like a ring; instead, it shimmies up and down a bit like a hula hoop. As a result, we only get between two and five solar eclipses each year, and the same number of lunar eclipses.

The Earth-Moon system, draw to scale. Notice how the Moon's orbit is slightly elliptic.

The Earth-Moon system, draw to scale. Notice how the Moon’s orbit is slightly elliptic.

Because of their rarity, each eclipse was viewed as a special phenomenon by ancient cultures. The Sumerians made a close study of the motions of the Moon and Sun and were able to predict eclipses. They weren’t alone in that; the Maya also incorporated eclipses in their calenders, as did many other ancient cultures.

A partial solar eclipse as seen in Texas (My camera)

A partial solar eclipse as seen in Texas
(My camera)

Today, we still view eclipses as something special. And we have developed a rich vocabulary to describe them, from the penumbral eclipse where some sunlight refracts through the Earth’s atmosphere to light the Moon to the total solar eclipse where the Moon completely blocks the view of the Sun during syzygy (the moment of eclipse). If you’d like to learn more about eclipses, including if you’ll be able to see any of the five eclipses visible this year, then head on over to the NASA Eclipse Web Site:
http://eclipse.gsfc.nasa.gov/eclipse.html