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A solar eclipse is a phenomenon caused by the interposition of the Moon between the Sun and the Earth, dimming the sun light either entirely or partially.

Eclipses are more common than you might think, but at a particular site on Earth, you can see a total solar eclipse only once every 360 years.

Why does a solar eclipse occur?

As you know, the moon, Earth and other planets and satellites spin around their axis and at the same time orbit around the Sun. The duration of the orbits varies according to the distance from the sun, so at different times of the year, the planets are in different positions.

Solar eclipses occur only if the moon is in the new moon phase.
When the moon is in the new moon phase, it is orbiting very close to the Sun from a perspective seen from Earth, and that is when a solar eclipse can happen. Strictly speaking, solar eclipses occur only if the moon is in the new moon phase, but this obviously does not mean that they can happen every month. Sun and moon eclipses would occur every month only if the moon rotated in the same plane in which the Earth does around the Sun, called the ecliptic plane.

Another important issue is that the moon is at a distance from earth that is similar in size to the sun, so it can perfectly cover the sun when it passes in front of it in the case of total eclipses.

Each year there are between 2 and five eclipses, and every 100 years occur about 240.

Characteristics of a solar eclipse

On average, a total solar eclipse occurs every 18 months and lasts no more than a few seconds or minutes. Each year there are between 2 and five eclipses, and every 100 years occur about 240. However, there are no more than two total eclipses every year.

In a solar eclipse, the umbra is the shadow projected on the Earth and produced by the moon when it completely blocks the light from the Sun; therefore the people on such area see a total eclipse. In contrast, a softer shadow product of a partially covered sun is the penumbra; evidently, people that experience the penumbra see a partial eclipse.

What are the types of solar eclipses?

There are four types:

Total eclipse.
It is only visible from a small area of ​​the Earth where the moon completely covers the Sun. People in the center of the moon’s shadow are the ones who can see a total solar eclipse since the umbra passes in that area of ​​the earth’s surface.

During this type of eclipse, you can observe the chromosphere, which is the outermost zone of the Sun, along with the solar corona and other protrusions.

Annular eclipse.
This kind of phenomenon happens when it is only possible to observe a small section of light in the form of a ring from the disk of the Sun since the Sun and the Moon are aligned, but the size of the latter is smaller than the apparent dimension of the Sun seen from the Earth.

types of solar eclipses.

Partial eclipse.
In this type of eclipse, only a part of the Sun’s disk is visible, so the crown and the chromosphere can not be seen. The shadow of the Moon passes through an area of ​​the earth’s surface, and it is called the penumbra; therefore, a person located in this area observes a partial eclipse.

Hybrid eclipse.
A hybrid eclipse is the fourth type, but it is very unusual. It happens when the eclipse is total in some regions of the terrestrial surface, while in others it is seen like annular eclipse.

IMPORTANT! You should not observe the solar eclipse directly with your eyes; A special filter must be used to protect your eyes. Otherwise, you risk damaging your retina irreversible to the point of losing your sight.

Eclipses in culture

Despite not affecting humans, solar eclipses were associated with bad omens and mythological events by some ancient cultures. For example, the Vikings believed that during eclipses wolves pursued the sun or the moon and managed to catch them. This belief of beings who ate the sun or the moon was common in many ancient cultures so that people used to bang objects hard enough to make a sharp noise that would frighten the evil creature.

One of the myths that still survive in some parts of the world is that these eclipses can be dangerous for pregnant women and their unborn children, but this belief has no scientific basis. However, it is important to remark that you should not watch the solar eclipse directly with your eyes without a proper filter to avoid eye damage.

Gamma-Ray Burst

 

Flashes of gamma-rays which are associated with highly energetic explosions are known as gamma-ray bursts. These bursts have been noticed in distant galaxies and are the the brightest electromagnetic events known to man in the universe. These bursts can last anywhere from 10 milliseconds to a few minutes. Usually, a longer-lived “afterglow” follows the first burst, which then comes in longer wavelengths.

Early discovery of gamma-ray bursts

The discovery of gamma-rays happened almost by accident. The satellites which detected the rays had been built to detect nuclear weapons testing during the time of the Nuclear Test Ban Treaty. Not sure what was causing the rays that were showing up on the satellites, the team filed the data away. After newer, more sophisticated satellites were launched, more of these rays continued to show up. After analysing the data, it became clear that the gamma-rays were not from nuclear testing or even from solar activity. The findings were published in 1973 in an article titled, “Observations of Gamma-Ray Bursts of Cosmic Origin”.

Even though astronomers and scientists have been studying gamma-rays rays since that time, they are still unable to accurately pinpoint the origin of the gamma-ray explosions. Some suggest they come from outside the Milky Way, but at this time, there is no way to be sure.

What causes gamma-ray bursts?

Because gamma-ray bursts happen so far away, it’s difficult for astronomers to be sure what exactly causes the bursts. Most are believed to be made up of a narrow beam of intense radiation which is released during a supernova. This is a high-mass star rotating at high speeds, which collapses and forms a black hole, neutron star, or quark star. While it is currently speculation, it’s possible that the entire crust of a star could shatter due to the development of a resonance between the core and crust. This is a result of huge tidal forces which stars experience in the seconds shortly before their collision.

Study of gamma-rays suggest that the blasts are not only extremely far away, but also very energetic and most likely immensely rare.

Classification of gamma-ray bursts

Unlike nova or supernova, which follow a structure of a bright burst of light which eventually fades out, the light curves of gamma-rays are unpredictable, diverse, and complex. There are no two gamma-ray bursts which are exactly the same. Some bursts have several high peaks, while others have a single peak only. Some show a very weak burst, followed by a very large burst after a short period of inactivity. Some gamma-ray bursts show highly chaotic and irrational profiles with no logical explanation.

The study of gamma-ray bursts does put them into 2 main categories: Long gamma-ray bursts and short gamma-ray bursts.

Long gamma-ray ray bursts exceed 2 seconds. Most gamma-ray bursts are in this category. A very long burst—over 2 ½ months long—was tracked, but none that long was seen since.

Short gamma-ray bursts are less than 2 seconds. It is unclear what causes these short bursts, but since 2005, the afterglow of these short bursts has been able to be studied, giving astronomers more detail on what these little bursts could be.

Effects of gamma-ray bursts

Right now, there is no danger to earth from gamma-ray bursts. They are much too far away to be of concern, though astronomers are speculating on the possibility of nearer stars colliding and the impact it could have on the earth’s atmosphere. Depending on how far or close it happens, the hypothetical effects would be devastating.

 

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