| Solar Eclipses |
| Michael Swanson Ryukyu Astronomy Club - www.nexstarsite.com/rac.htm |
What is a Solar Eclipse?
The Moon travels once around the Earth every 29 days (approximately). A solar
eclipse occurs when the Moon comes directly between the Earth and Sun and covers
all or part of our view of the Sun. In theory this could occur once every 29
days, but in practice, the Moon's orbit is tilted as compared to our line of
site to the Sun, so eclipses happen much less frequently than that. For example,
from a specific location on Earth, it may be hundreds of years between
occurrences of a total eclipse but generally there is at least one total eclipse
somewhere on the planet each year. The path on the surface of the Earth where an
eclipse is visible is a long, rather narrow band, for example:
http://eclipse.gsfc.nasa.gov/SEmono/TSE2009/TSE2009fig/TSE2009globe1a.JPG
There are actually three types of solar eclipses:
It is NEVER safe to view a partial or annular eclipse directly or through binoculars, a telescope or a camera UNLESS you use special filters. A total eclipse can be viewed safely without filters but ONLY when the Sun is COMPLETELY covered by the Moon. If even a small part of the Sun is peaking out from behind the Moon it is NOT safe without special filters. Failure to use a safe filter will result in PERMANENT damage to your eyes.
Owners of telescopes can purchase filters or filter material (Baader Solar Film is my personal choice) from any reputable dealer of astronomy equipment. Such filters are always used over the front of the telescope, between the Sun and the optics of the telescope. This filter material can also be used over the front of binoculars and camera lenses. Welder's glass rated 14 or higher can also be used to safely view an eclipse.
A few companies make "solar glasses" which are safe for viewing eclipses or
even the full Sun. While I haven't reviewed all offerings, I can state that
these are safe:
http://www.rainbowsymphonystore.com/eclipseshades.html
Another method which almost anyone can employee is a pinhole projector.
Basically all you need is two pieces of cardboard, a piece of aluminum foil and
a pin. See here for details:
http://www.exploratorium.edu/eclipse/how.html
In addition to observing the Sun, also take time to notice the general darkening of the sky, shadows on the ground around you and possibly even bright stars and planets in the sky.
On July 22nd, 2009, a total solar eclipse will occur in a narrow band from India, passing through China, across some of Japan's southern islands and then out into the South Pacific. Local time will vary, but the Moon will begin to pass in front of the Sun at about 9:30AM, cover it to the maximum extent around 11AM and move off from the front of the Sun at about 12:30PM. In the center of the path, the totality phase of the eclipse will last approximately 6 1/2 minutes - almost as long as is theoretically possible. In fact, this will be the longest duration eclipse for nearly 100 years.
The path of totality crosses Japan from the northern tip of Amami Island up
to the islands just south of Kagoshima. As it continues out into the South
Pacific, Iwo Jima will also enjoy a view of the total eclipse. For viewers in
Okinawa, mainland Japan, Korea and the Philippines, this will be a partial
eclipse. You can determine the percentage of the Sun which will be covered in
your location using this interactive map:
http://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2009Jul22Tgoogle.html
Zoom in on your area and click the map to place a marker on your location.
"Magnitude" is the percentage of coverage after moving the decimal point two
digits to the right. For example, a magnitude of 0.934 indicates 93.4 percent of
the Sun will be blocked by the Moon.
