Orionids: a shower of stars created by Halley's comet

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From Sunday 20th to Tuesday October 22nd the maximum activity of the Orionids will take place, a meteor shower created by the famous Halley comet. Due to the waning moon it will be preferable to observe the shooting stars before midnight.

Waning Quarter

The Orionids take place from October 4 until November 10, approximately, reaching its maximum activity on the nights of October 20-21 and October 21-22, at which time we will be able to observe about 20 shooting stars per hour . Orionids are fast and relatively large meteors, their speeds can exceed 60 kilometers per second and usually leave yellow or green trails.

As the name implies, the radiance of this shower of stars is in the bright constellation of Orion and, more specifically, near the bright star Betelgeuse, but you do not need to know this star or this constellation to observe the meteors that may appear by either side of the celestial vault. Since the radiant is relatively close to the celestial equator, the Orionids can be observed both from the Northern Hemisphere and from the South.

On the nights of October 20 and 21, the Moon will be in its waning room, since the novilunio takes place on the 28th. Orion will reach a good height above the horizon at 11:30 p.m., but the Moon will rise an hour later and begin to light the sky background. For all these reasons, it will be preferable to observe the meteors before midnight. After that moment, it will be convenient to look away from the position of the Moon to try to locate some bright racing car.

As the activity of the meteors continues until November 10, we can try to continue observing the following nights, as the week progresses from October 21 to 27. Towards that weekend, and at the beginning of the following week, the meteors - although less numerous - will contrast on the very dark sky of the novilunio.

Fragments of Halley's comet rain

Every year, the Earth, in its translation movement around the Sun, crosses twice annular regions populated by the fragments left by the famous 1P / Halley periodic comet that visits us once every 76 years. When one of these fragments (or meteoroids) falls into the Earth's atmosphere, it is burned by friction with the air, creating the luminous glow we know as meteor or shooting star. Typically, the most common meteors that we observe with the naked eye are produced by particles of a few millimeters to a few centimeters in size that burn at about 100 kilometers in height.

In May the first passage of the Earth takes place through one of those areas where fragments of the Halley abound, thus creating the rain called 'Eta Aquarids'. Now in October, go through the second zone creating the Orionids.

The Halley is the most famous comet and one of the brightest. He received his name from astronomer Edmund Halley, although this was not his discoverer because the comet was known since ancient times. However, it was Edmund Halley who calculated his orbit in 1705 according to Newton's theory, predicting the return of the comet by 1759. Halley died in 1742 and could not witness the arrival of the comet in that year. However, the comet was received with great expectation as it constituted a spectacular triumph of Newton's theory of gravitation.

Two millennia of history

The oldest records of observations of Halley's comet date back to the 3rd century BC when it was sighted by Chinese astronomers on one of his visits. Also in China, but many centuries later, in the s. VI d. C, it was noted for the first time of a shower of stars that, most certainly, can be identified with the Orionids.

The radiant of this meteor shower was located by the British astronomer Alexander Herschel (grandson of the great William Herschel) in the 1860s. But we still had to wait another century to relate this shower of stars with the king of comets, specifically until 1983, when Canadian astronomer BA McIntosh and Slovak A. Hajduk published an article in which they unambiguously established that the origin of the Orionids was the famous Halley.

Rafael Bachiller is an astronomer and director of the National Astronomical Observatory (IGN)

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