Difference: PreguntesEclipsiSol ( vs. 1)

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Frequently asked questions

What's a solar eclipse?

A solar eclipse happens when the Moon is placed between the Earth and the Sun, thus blocking the Sun's light. Seen from the Earth, both the Moon and the Sun have almost the same apparent diameter. However, due to the distance variations between the Earth and the Moon, the latter can appear larger or smaller than the Sun, producing three different kinds of eclipses: partial, total or anular.

Which are the different kinds of solar eclipses?


A partial eclipse takes place when the Moon is not fully aligned between the Earth and the Sun. In this case, a part of the Earth will be within the penumbra of the Moon, but is never really touched by the Moon's shadow. From the Earth, we would see how the Moon disk covers part of the Sun face, but never gets to cover it completely.
All solar eclipses start this way, because the Moon moves until it reaches the right alignment.

Figure 1: Position of the Earth, the Moon and the Sun during a partial solar eclipse.


If the Moon is placed between the Earth and the Sun when it is far away from us, its shadow will not be long enough to touch the Earth (see Fig. 2). Then, an anular eclipse takes place. An observer looking from the right Earth spot will see how the Moon covers the central part of the solar disk. Around this dark central zone, he/she will still see the Sun's light.

Figure 2: Position of the Earth, the Moon and the Sun during an anular eclipse.


If the solar eclipse happens when the Moon is closest to the Earth, we will see a total eclipse (see Fig. 3). These eclipses do not only allow to see a complete occultation of the Sun, but also a series of rare phenomena, such as the so-called Baily's beads: When the Moon is about to cover the Sun completely, it is possible to observe the Sun's light reflected on the Moon valleys in the form of a series of bright spots around the dark Moon disk, ressembling a group of pearls. After that, with the proper instrumentation, it is possible to see the protuberances on the Sun chromosphere, a part of the Sun's atmosphere. Finally, when the Sun's face is completely covered by the Moon, it is possible to observe the outer atmosphere layer of the Sun, the corona. Both the corona and the chromosphere are not usually seen due to the Sun brightness, but they are perfectly visible during an eclipse. However, some modern instruments allow to block the Sun's light in an artificial way, so that astronomers can study these parts of the Sun.

Figure 3: Position of the Earth, the Moon and the Sun during a total solar eclipse.

Why is there not an solar eclipse with each new moon?

In the new moon phase, the Moon is only getting light from the Sun on the face opposite to the Earth. Thus, a solar eclipse will always happen during a new moon. However, given that the Moon's orbit is slightly tilted (5 degrees and 6 minutes) respect to the Earth-Sun plane, most of the times the new moon is placed in a different plane from the Sun and cannot block its light. Only when the new moon is placed on the Earth-Sun plane, or very close to it, a solar eclipse takes place.

How can I observe a solar eclipse?


To look directly to the Sun without proper eyes protection can produce you very serious ocular injuries (even by using sun eyeglases, or telescopes or another instrument NOT SPECIFICALLY DESIGNED to do it). You should not use X-ray plates, negatives of photographic film or smoky glass because these artifacts are unable to filter the strong UV radiation coming from the Sun, and you can result seriously injured anyway.

So, how to observe the eclipse?

  • The safest way to do it is by projecting the image of the Sun produced by a telescope over a white screen (see the figure). With this technique you also have the advantage of simultaneous observation for a group of people. But be careful: limit the amount of incoming light or you can destroy your telescope!
  • Another way to project the eclipse is by using a dark chamber. You will need a big box, and:
    1. make a small hole with a needle in one side of the box (1 in the figure). It is better if you first cover this side of the box with aluminium paper (dark zone of the figure).
    2. In the opposite side make a larger hole (2 in the figure) and cover it with translucent paper.
    The light will enter to the box by the small hole and will be projected in the translucent paper. You can also make a lateral hole to see the image with better contrast.
  • Also you can use a telescope properly equipped with high quality solar filters.
  • If you don't have a telescope try to get specific solar eyeglasses, or a very dark mask of soldering (number 14) or a piece of mylar.

From which places on Earth is it possible to observe a solar eclipse?

Contrary to a Moon eclipse, which is visible from every Earth spot provided it is dark, Sun eclipses can be observed only from particular Earth strips. That is, the eclipse will be total (or anular) only for observers placed inside a narrow strip some hundreds of kilometers wide and some thousands of kilometers long. The strip length corresponds to the cone of shadow caused by the Moon on the Earth's surface. In a broader strip the eclipse will be seen as a partial eclipse.

What are the Saros series?

Eclipses have a cyclic behaviour: Every 18.6 years, two similar eclipses take place. They are grouped in the so-called Saros series. Although this might lead to think that all eclipses belonging to a same series will be very more or less the same, this is not exactly true, given that only two consecutive eclipses are similar. As the series proceeds, eclipses evolve, so solar eclipses start as partial eclipses, then they become total or anular and then partial again. After the last partial eclipse, in a process that can take more than 1500 years, the series ends.

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