Science@NASA: Annular Solar Eclipse this Weekend

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Science@NASA: Annular Solar Eclipse this Weekend

Post by bystander » Tue May 15, 2012 9:32 pm

Annular Solar Eclipse this Weekend
NASA Science News | Dr. Tony Phillips | 2012 May 15
Something strange is about to happen to the shadows beneath your feet.

On Sunday, May 20th, the Moon will pass in front of the sun, transforming sunbeams across the Pacific side of Earth into fat crescents and thin rings of light.1

It's an annular solar eclipse, in which the Moon will cover as much as 94% of the sun. Hundreds of millions of people will be able to witness the event. The eclipse zone stretches from southeast Asia across the Pacific Ocean to western parts of North America.

In the United States, the eclipse begins around 5:30 pm PDT. For the next two hours, a Moon-shaped portion of the sun will go into hiding. Greatest coverage occurs around 6:30 pm PDT.

Because some of the sun is always exposed during the eclipse, ambient daylight won't seem much different than usual. Instead, the event will reveal itself in the shadows. Look on the ground beneath leafy trees for crescent-shaped sunbeams and rings of light.

Near the center-line of the eclipse, observers will experience something special: the "ring of fire." As the Moon crosses the sun dead-center, a circular strip or annulus of sunlight will completely surround the dark lunar disk. Visually, the sun has a big black hole in the middle.

The "path of annularity" where this occurs is only about 200 miles wide, but it stretches almost halfway around the world passing many population centers en route: Tokyo, Japan; Medford, Oregon; Chico, California; Reno, Nevada; Albuquerque, New Mexico, and Lubbock, Texas. In those locations the ring of fire phenomenon will be visible for as much as 4 and a half minutes.

"The ring of sunlight during annularity is blindingly bright," cautions NASA's leading eclipse expert Fred Espenak of the Goddard Space Flight Center. "Even though most of the Sun's disk will be covered, you still need to use a solar filter or some type of projection technique. A #14 welder's glass is a good choice. There are also many commercially-available solar filters."
[img3="A "ring of fire" over China in 2010."]http://science.nasa.gov/media/medialibr ... re_med.jpg[/img3]
Many astronomy clubs will have solar-filtered telescopes set up for public viewing. Through the eyepiece of such an instrument, you can see the mountainous lunar limb gliding by dark sunspots and fiery prominences. It's a beautiful sight. Be absolutely sure, however, that any telescope you look through is properly filtered. Magnified sunlight can cause serious eye damage even during an eclipse.

A safe and fun way to observe the eclipse is to use your own body as a solar projector. For example, try criss-crossing your fingers waffle-style. Rays of light beaming through the gaps will have the same shape as the eclipsed sun.

Or just stand under that tree. The sight of a thousand ring-shaped sunbeams swaying back and forth on a grassy lawn or sidewalk is unforgettable.

Slooh: Live Feed of Annular Solar Eclipse from Japan to U.S., May 20th
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alive to the gentle breeze of communication, and please stop being such a jerk.
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Re: Science@NASA: Annular Solar Eclipse this Weekend

Post by bystander » Fri May 18, 2012 12:29 am

Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

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Hinode Mission to Capture Annular Solar Eclipse This Weekend

Post by bystander » Fri May 18, 2012 12:49 am

Hinode Mission to Capture Annular Solar Eclipse This Weekend
NASA GSFC | Hinode | 2012 May 17
On May 20-21, 2012 an annular eclipse of the Sun will be visible from within a narrow corridor along Earth's northern Hemisphere -- beginning in eastern Asia, crossing the North Pacific Ocean, and ending in the western United States. A partial eclipse will be visible from a much larger region covering East Asia, North Pacific, North America and Greenland.

During an annular eclipse the moon does not block the entirety of the sun, but leaves a bright ring of light visible at the edges. For the May eclipse, the moon will be at the furthest distance from Earth that it ever achieves – meaning that it will block the smallest possible portion of the sun, and leave the largest possible bright ring around the outside.

The joint JAXA/NASA Hinode mission will observe the eclipse and provide images and movies that will be available on the NASA website at http://www.nasa.gov/sunearth. Due to Hinode’s orbit around the Earth, Hinode will actually observe 4 separate partial eclipses." Scientists often use an eclipse to help calibrate the instruments on the telescope by focusing in on the edge of the moon as it crosses the sun and measuring how sharp it appears in the images. An added bonus: Hinode's X-ray Telescope will be able to provide images of the peaks and valleys of the lunar surface.

The orbits for NASA's Solar Dynamics Observatory (SDO), NASA's Solar Terrestrial Relations Observatory (STEREO), and the joint ESA/NASA mission the Solar Heliospheric Observatory will not provide them with a view of the eclipse.

The next solar eclipse will be the total solar eclipse on November 13, 2012.

More information on eclipses: http://eclipse.gsfc.nasa.gov/eclipse.html

To find information about the time of any eclipse in your location: http://eclipse.gsfc.nasa.gov/JSEX/JSEX-index.html
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BA: Followup: Supereclipse

Post by bystander » Sat May 19, 2012 5:43 pm

Followup: Supereclipse
Discover Blogs | Bad Astronomy | 2012 May 19
I wrote earlier about the annular eclipse happening this coming Sunday. It’s a solar eclipse, with the Moon blocking the Sun, but because the Moon is at apogee — the point in its orbit farthest from Earth — the Moon appears smaller in the sky, so it doesn’t completely block the Sun. We’re left with a ring of solar surface surrounding the Moon, the so-called Ring of Fire.

I got a couple of people asking me why this eclipse is happening at lunar apogee when we just had a "Supermoon", when the Moon was full at perigee (when it’s closest to Earth in its orbit). This is a good question! It’s not a coincidence. In fact, it must happen this way! Here’s why.

First, here’s a drawing of the Moon’s orbit, courtesy NASA:

The Moon orbits the Earth in an ellipse, so sometimes it’s closer to us, and sometimes farther. The ellipticity is exaggerated in the drawing; it’s actually about a 10% difference in distance between apogee and perigee. The Moon orbits the Earth once every 27.3 days, so it takes about 13.7 days for it to go from apogee to perigee — a little less than two weeks.

This is different than the phase of the Moon, which is how much of the Moon we see lit by the Sun. When the moon is between us and the Sun, it’s new: we only see the unlit side. When it’s opposite the Sun in the sky — when the Earth is between the two — the side of the Moon we see is lit, so we say it’s full. There are approximately 8 billion web pages describing how this works; here’s one I wrote. The time it takes to go from full Moon to full Moon is 29.5 days. That means to go from full Moon to the next new Moon takes half that time, or about 14.7 days — a little more than two weeks.

We can only get a solar eclipse when the Moon is between us and the Sun. This happens when the Moon is new (I’ll note in passing that it doesn’t happen every time the Moon is new, because the orbit of the Moon doesn’t align exactly with the Earth’s orbit around the Sun).

The phases of the Moon don’t line up perfectly with its position in the orbit because of the two different periods: 27.3 days to go around the Earth, but 29.5 days to go from full to full again (this video might help you). So sometimes full Moon happens at perigee, sometimes at apogee, and most of the time sometime in between.

Now let’s put this all together! The Supermoon is when the Moon is full and at perigee, right? That’s what happened on May 5th. On Sunday, a bit more than two weeks will have elapsed since then. That means the Moon will have moved halfway around its orbit — it actually reaches apogee on Saturday May 19th. But the phase has been changing, so it’s new on May 20, and it so happens that things have aligned for it to eclipse the Sun.

Since this happens the day after apogee, the Moon is farther away than usual, and from Earth it looks smaller. BOOM. Annular eclipse.

I think the confusion stems from folks not knowing the Moon orbits the Earth once per month on an ellipse, so it goes from perigee to apogee in two weeks. Once you get that, hopefully the rest of this makes more sense.

And because why not, I’ll leave you with this video showing the phase of the Moon as well as its apparent size in the sky as they change over the course of the year. If you want a detailed explanation of what you’re seeing, here ya go.
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor