Monday, January 18, 2010

Partial Solar Eclipse

Last Friday (15/01) there was a partial solar eclipse. The moon passed between the earth and the sun, partially hiding it.
Warning: Observing the Sun requires special equipment. It is dangerous to observe the Sun directly. Read the safety instructions from NASA.

There are three types of eclipse:
  • Total eclipse - occurs when the Sun is completely obscured by the Moon. During any one eclipse, totality is visible only from, at most, a narrow route on the surface of the Earth, while all other observers will see a partial eclipse.
  • Annular eclipse - occurs when the Sun and Moon are exactly in line, but the apparent size of the Moon is smaller than that of the Sun. Hence the Sun appears as a very bright ring, or annulus, surrounding the outline of the Moon. Also in this type of eclipse, the Annular eclipse can be seen from a very narrow strip on Earth.
  • Partial eclipse - occurs when the Sun and Moon are not exactly in line and the Moon only partially obscures the Sun. This phenomenon can usually be seen from a large part of the Earth outside of the track of an annular or total eclipse

Friday morning started with lots of clouds which made me worried that we would not see anything. The older children went to school equipped with special filters suitable for safe solar viewing and instructions how to use them and show the eclipse to others. Me and another kid stayed and waited on our roof.
About 7:50am we were able to see the sun through some cracks in the clouds. We saw the sun for about a minute and even took some pictures of it which came out surrealistic. We were very happy that we managed to see the eclipse at all.

Then the clouds got thicker so I sent my kid to kindergarten and I continued to wait. At some point I managed to steal another peek through the clouds but it was hard to maintain and was for a very short amount of time.

At 8:30am the sky suddenly became completely clean of clouds and we could finally watch the eclipse properly. The eclipse was at its end and well after the peak (Which was very small, about 20% of the sun was covered. Such low coverage will not cause any noticeable reduction in brightness or temperature. Coverage of over 60 percent will make us feel a drop of several degrees and less brightness).
We took better pictures, too. Pay attention to the sun spots in the top of the picture. Sunspots are colder regions (500 degrees less than normal) on the surface of the sun and radiate less light, and in relation to their surroundings they look black. Actually, the light they radiate is 50 times stronger than the light of the full moon, which reminds us again how in life and especially in the universe, everything is relative.

A better eclipse (with 60% Sun coverage at the peak), will occur in the next Hebrew year (4-Jan-11),on 28 Tevet 5761 (Notice that it will be two days before the new moon of Sh'vat due to the rules of the Hebrew Calendar).

Monday, January 11, 2010

Partial Lunar Eclipse 2010

Lunar eclipse occurs when the moon passes through the Earth's shadow. Like anything, Earth has a shadow and anything in the shadow of the earth (Including all of us during the night), does not receive sunlight. When the moon is in shadow, it does not get the sunlight, so part of it disappears. Two weeks ago, the fourteenth of Tevet, was a partial lunar eclipse. In a partial eclipse, Not the entire moon is in the shadow area, so only a small part of it disappears (even in full eclipse, the moon will still be visible due to some refracted light).

The following video is a set of about 90 movies which show how the moon pass through he shade. The eclipse was very small, only 8% of the moon surface were in the shade area, but still it was very enjoyable to observe.

Taking such picture is easy. Simply photograph the moon just like any other night. The full moon is very bright so make sure not to over-expose. Only in the final stages of an eclipse (A full eclipse) the moon will become dim and require longer exposure.
Making the photos into a movie is also easy. Picasa and tons of other software can do it for you. Aligning the photos is a more difficult task which I use hugin for. Hugin is a freeware tool used to create panorama from many photos but can be used for other tasks as well.
The next full eclipse will be at 14 Sivan 5771 (15/6/2011). It is worth to wait for it.