GEMINIDS: ORIGINS, CHARACTERISTICS AND HOW TO OBSERVE THEM - ARTE - 2025

The Geminids is the name given to an extremely active meteor shower, which seem to come from a point in the constellation Gemini and are visible from early to mid-December, approximately.

The peak of this rain occurs around December 14 of each year, for that moment it is estimated to be able to observe 100 or even more meteors per hour, as long as the sky conditions are ideal: excellent visibility and a moonless night.

Figure 1. The Geminids and Comet 17P / Holmes, seen from San Francisco. Source: Wikimedia Commons. Brocken inaglory

It is therefore the most active meteor shower that can be seen today, together with the quadrantids, a shower that appears in the month of January.

This of course, unless some particular event encourages a much larger rain, as happened with the Leonids in 1833, 1866 and 1966, which went from being a shower of between 10-20 meteors / hour in previous years, to a true storm. of meteors, with 100,000 meteors / hour, but only in those years.

The event that detonated the storm was the passage of Comet Tempel-Tuttle, progenitor of the Leonids. Most meteor showers are caused by debris that comets and asteroids leave behind when the orbit brings them closer to the Sun.

The gravitational attraction that the star exerts, in addition to the intense radiation, fragments the outer layers of the comet or the asteroid. The remnants remain in orbit moving at high speed and when the Earth gets close enough, they enter the atmosphere.

Figure 2. The orbit of the earth intersects with that of the meteorids and it is then that the meteor showers take place. Source: Maran, S. 2013. Astronomy for Dummies.

The friction produced by contact with atmospheric gases causes ionization in them, manifesting as a trace of light at high altitude, while the heat totally vaporizes the meteor.

Very rarely do the fragments reach the ground. In such a case it is called a meteorite, while while they are still in orbit, they are called meteoroids. In this way the fragments are categorized, depending on whether they are outside or inside the atmosphere or have finally landed.

Origins and characteristics

The Geminids are a somewhat unusual meteor shower in origin, which is not a comet, but an asteroid called Phaeton, discovered in 1983. Almost all the showers are caused by comets.

Astronomers do not agree on the nature of this object, because it appears to have hybrid characteristics between an asteroid and a comet, although observations do not reveal the hair -comat- typical of comets in Phaeton.

The general difference between one body and the other is that the comet is usually made up of layers of ice, while the asteroid is supposed to be rocky.

There is the hypothesis that Phaeton was a comet 2000 years ago, but when it got very close to the Sun, its gravitational pull caused a great catastrophe that changed the orbit substantially and left a large amount of debris, which we know today as the Geminids.

It seems that the Geminids did not appear immediately after this event, because the first record of their appearance dates back to 1862. On the other hand, other meteor showers such as the Perseids and the Leonids themselves have been seen for centuries.

It is a fact that even when meteor showers are associated with the debris left by asteroids and comets, the debris left by the last approach is not necessarily seen every year.

The fragments that give rise to this year's shooting stars could have been produced a long time ago, and have remained in orbit ever since. But it must be taken into account that the orbits are not static, they alter due to gravitational interaction with other bodies.

Main characteristics of the Geminids

Geminids are so named because they appear to come from a point in the constellation of Gemini called the radiant.

It is nothing more than a perspective effect, since the trajectories being parallel, seem to converge at a distant point, like the train tracks. But it has served to baptize all the important meteor showers, which in this way are named after the constellation where the radiant is.

The rain begins to be visible around December 4, continuing until the 17th, with a peak of activity around the 13th or 14th.

Hourly zenith rate, zenith rhythm or THZ is the number of meteors per hour under ideal visibility conditions, which includes a cloudless and moonless sky.

Geminids have one of the highest zenith rates: between 100-120 meteors / hour, which suggests that the debris left by Phaeton has not dispersed much so far.

Furthermore, observations reveal that the zenith rate has increased slightly since the rain was discovered.

The population index measures the brightness of the trails left by the meteor swarm, which in the case of the Geminids are yellow. It depends on factors such as the mass and speed of the meteors and is denoted as r.

Its value is almost always set to 2, but in mathematical models adjusted to the behavior of geminids the value is r = 2.4 and during maximum activity it is 2.6.

For its part, the yellow color indicates the possible presence of iron and sodium in the composition of the fragments.

When and how to observe them

Geminids are seen from both hemispheres, although it is best from the northern hemisphere. There the radiant begins to be visible in the afternoon, while in the southern hemisphere you have to wait for midnight.

As with all meteor showers, the hourly rate of meteors increases as time passes and the radiant is higher in the sky. The best times to observe the Geminids and the other meteor showers are during the early morning until sunrise.

During the day the rain continues, but it is hardly appreciated, especially in the case of the Geminids, in which the speed of the fragments is not very fast: about 35 km / s compared to other rains that reach up to 60 km / s.

The best observations are made by choosing a location away from city lights, high up and without the moon in the sky, or at least waiting until it is low enough on the horizon.

During the same night, the meteors become more and more numerous: just before sunrise you can see twice as many meteors as at sunset. It is because, after midnight, the Earth is heading frontally towards them, while in the afternoon, they are the ones who intercept us from behind.

Recommendations for observing the geminids

The good thing about stargazing is that you don't need a lot of equipment. Binoculars and telescopes are not necessary because they limit the field of view.

The best way to take advantage of Geminids is to lie directly on the floor or on a chair with a folding back.

Since it is a labor of patience, you have to wear comfortable and warm clothes, since the most suitable hours are those in the early morning. For the same reason you have to add a thermos with a hot drink and if you are going to go out into the open, bring insect repellent and a flashlight.

It is not necessary to directly observe the radiant, since meteors can appear anywhere in the sky. What is important is that the sky is very dark, without the moon, clouds or objects that obstruct the view, such as trees or buildings.

Figure 3. Observing the geminids does not require special instruments. Source: Pexels.

The view should get used to the darkness well, then you can start to look around the sky.

The asteroid Phaeton

It is the subject of controversy, as it has characteristics of both asteroid and comet. After all, its orbit is quite similar to that of a comet, even though it doesn't have hair, so it could be a "dead" comet.

In addition, Phaeton has been found to reflect blue light, an unusual fact for asteroids, because almost all of them reflect shades of gray or red in the best case.

Figure 4. Phaeton's orbit takes it very close to the Sun and Earth. Source: Wikimedia Commons. Tomruen.

The color depends on the composition of the surface, there are not many blue asteroids. The asteroid Pallas is one of them and some experts believe that Phaeton could be a large fragment detached from it.

In any case, the International Astronomical Union (IAU) has called comets and asteroids with the same term: "minor bodies of the Solar System."

Phaeton's orbit is so close to the Sun that the surface heats up to 800 ° C, enough to melt and break up some of the material. In addition, it has been established that its orbit coincides with that of the Geminids. Both circumstances prove his paternity.

Apart from that, there has been a lot of speculation about the risk of collision, because among all the asteroids, Phaeton is the closest to Earth. It is no coincidence that it bears the same name as the mythological character who insisted on driving the chariot of the Sun and caused great damage by losing control.

Phaeton is believed to have its closest approach to Earth in 2093. Its distance from our planet will then be equal to about 7 times the distance between Earth and the Moon.

References

1. American Meteor Society. Major Meteor Showers. Recovered from: amsmeteors.org
2. Maran, S. 2013. Astronomy for Dummies. L Books. chap. Four.
3. POT. Geminids. Recovered from: solarsystem.nasa.gov
4. Oster, L. 1984. Modern Astronomy. Editorial Reverté. 107-111..
5. Pasachoff, J. 1992. Stars and Planets. Peterson Field Guides. 413-418.
6. Phys.org. Rare blue asteroid responsible for Geminid meteor shower reveals itself during fly-by. Recovered from: phys.org.
7. Ryabova, G. 2017. Increasing Geminid meteor shower activity. Recovered from: arxiv.org.
8. Sky & Telescope. The Best Meteor Shower in 2019. Recovered from: skyandtelescope.com.
9. Wikipedia. Geminids. Recovered from es.wikipedia.org.