July 11, 2020

Mercury walks this Monday ahead of the Sun – La Provincia

Mercury will walk next Monday ahead of Sun, for the fourth time in this century. He transit of the planet will occur this November 11, from 12.36 h. at 18.04 h., almost five and a half hours long that will be broadcasted in full and live from the Canary Observatories.

Transits of inner planets –Venus and Mercury– They are rarer than the eclipses of Sun and Moon. On average we will have 13 transits of Mercury per century and will occur in the months of May or November. The last transit of Venus was June 2012. We had transits of Mercury in the years 2003, 2006 and 2016 and the next one will not occur until 2032.

Few readers of this article will have seen Mercury, a very small planet. Ganymede, one of the four Galilean moons around Jupiter, and Titan, the largest of Saturn, are older than him. We can see it shine with the naked eye like a star at sunrise or sunset, always close to the Sun, since its orbit is quite close to our star. It is an extreme and strange planet, where the Sun can rise twice the same day, or where its surface temperature can range between 450 and -170 ° C.

Due to its small size and remoteness, until the invention of the telescope, it was impossible to observe a transit of Mercury. The first observations of the telescope were made by Galileo Galilei in the seventeenth century. Its size and brightness vary significantly depending on its position in the orbit. When it crosses in front of the Sun, we see it with its maximum size (between 10 and 13 arc seconds), while when crossing behind the Sun we see it with its minimum size (about 4.5 arc seconds). The disk of the Sun or the Moon in comparison is about 2,000 arc seconds. Our visual limit is about 60 arc seconds, so it is impossible to see a transit of Mercury if it is not with the help of a telescope. It was Johannes Kepler who first predicted that a transit of Mercury would take place on November 7, 1631. He did not live to see it, but this information was used by Pierre Gassendi to be the first to observe one of those "walks" of the planet by in front of the sun.

When it comes to observing the Sun, you cannot fail to warn of its dangers. We must never observe it, with the naked eye, much less with instruments without due caution. Observing a transit is as dangerous as directly observing the Sun, since the planet will not cover a significant part of it, and we must take precautions. An improper observation of the Sun can permanently damage our retina or even blind us. The recommended methods are observation by projecting the solar disk on a screen or by telescopes equipped with the appropriate solar filters.

The Canary Islands Observatories invite you to follow the broadcast from the GREGOR Solar Telescope (OT, Observatorio del Teide, Tenerife) the largest solar telescope in Europe operated by KIS (Leibniz Institute for Solar Physics, Germany) and from the Swedish Solar Telescope SST (ORM, Roque de los Muchachos Observatory, La Palma) operated by the ISF (Institute for Solar Physics , Sweden)

The Institute of Astrophysics of the Canary Islands (IAC) offers the following possibilities to follow the phenomenon. Through the YouTube channel IAC Videos of the Instituto de Astrofísica de Canarias. It will also be broadcast by the Nazionale Galileo Telescope (TNG), from the ORM.

The European initiative EELabs, through the sky-live.tv channel, will broadcast live all Mercury transit, connecting with the different telescopes of the Canary Observatories and explaining in detail the phenomenon in collaboration with the QuantumFracture scientific dissemination channel, to from 12:30 UT.


We call a transit to the passage of one body in front of another, so that the nearest hides a part of the surface of the farthest. For example, it is possible to observe an ISS transit ahead of the Sun. In the Solar System, only the inner planets (Mercury and Venus) can transit the Sun from our point of view on Earth.

Mercury rotates in a rather elliptical orbit, completing a return to the Sun in approximately three Earth months (88 days), during which time the Earth has moved a quarter of its orbit. Therefore, Mercury will be placed between the Sun and Earth after 116 days, that is, it is repeated about three times a year. We can try to visualize this effect thinking about the minute hand of a clock, which takes 65 minutes to reach the hour hand. Why don't we then have three transits of Mercury a year? Mercury moves in a plane that forms 7 ° with the Earth's orbital plane around the Sun and so that the three bodies are sufficiently aligned, both planes must coincide. Otherwise, Mercury will pass above or below the solar disk. To simplify, we can imagine two concentric circles that represent the orbits of Mercury and the Earth (the Sun is its center) painted on a notebook. Now let's raise the leaf slightly: that is the orbital plane of Mercury, while that of the Earth is horizontal. Both sheets (planes) are cut along a line, which will coincide with two dates of the year on the Earth's path. In the case of Mercury, May 8-9 and November 10-11; If a few days before or after that date it coincides with the passage of Mercury in front of the Sun, there will be transit. There is a certain periodicity in these phenomena, although it obeys complex rules. It is clear that it has to be a multiple of the 116 days it takes to match Mercury and Earth aligned. This usually occurs on average about 13 times per century, at intervals ranging from 3.5 to 13 years. The next transit of Mercury, after this November 11, 2019, will be on November 13, 2032.

Mercury Transit 2019

During a transit we can highlight five key moments. The first, when the planet's disk touches the sun's luminous disk (the first contact); the second, when he finishes entering. The period between them is what we call "income." The third would be right in the middle, where the distance between the planet and the center of the Sun is minimal. In an analogous way to entry, but in reverse order, the "exit" is made, a period between the inner contact of the edge of the planet with the edge of the disk of the Sun until its disappearance. The precise moments of each of these events depend on the position of the observer on Earth, and may vary within a couple of minutes. Regarding the geocentric position, these are: 12:35, 12:37, 15:19, 18:02 and 18:04 (all in Universal Time – UT. They must be corrected for each hourly use). Miquel Serra-Ricart, astronomer of the Institute of Astrophysics of the Canary Islands (IAC) comments: "The transit of Mercury is a good opportunity to organize educational activities in schools. It is a simple phenomenon to observe, but governed by fundamental laws of the Physics. It is important to remember again that the observation must be carried out following strict safety measures so that the Sun does not harm our eyes. "

"Transits in the Solar System are unusual phenomena in Astronomy. If Mercury seems rare, the rarest is Venus, which will not transit the Sun until 2117, with the additional inconvenience of not being able to observe from the Canary Islands because it will occur overnight (it will be observable from the other half of the planet), "says Alfred Rosenberg, an astrophysicist who disseminates the IAC.

But transits are more fashionable than ever. Considering that our galaxy is made up of hundreds of billions of stars, most of them with planets spinning around it, it is only a matter of time (in addition to super-powerful and precise instruments) to get to observe them. In recent years thousands of exoplanets have been discovered, planets that revolve around other stars. Of these, as of today, 2,965 planets have been detected using the transit method, of which 482 are part of multiple planetary systems. From the precise measurement of the decrease in brightness (the light curve) repeatedly we can determine the orbital period, the size of the planet and other values ​​that allow us to know the mass, volume, (density), orbital parameters, etc., which in turn allow us to establish the "habitability" of said planet. Something that looked like science fiction a few decades ago is becoming a reality: we are getting closer to finding a twin of our planet.

Seen from any other star, Mercury would hide only one in 85,000 photons of the Sun. A planet as small as Mercury would be at the limit of being able to be detected by the transit technique with current instrumentation. Somewhat larger planets, such as Earth, are detected today.

Three Spanish Supercomputing Centers, the Extremadura Center for Advanced Technologies (CETA-CIEMAT), the Consorci de Serveis Universitaris de Catalunya (CSUC) and the Instituto de Astrofísica de Canarias (IAC) will collaborate in the distribution of web portal retransmission (sky -live.tv).

EELabs (eelabs.eu) is a project funded by the INTERREG V-A MAC 2014-2020 Program, co-financed by the ERDF (European Regional Development Fund) of the European Union, under contract number MAC2 / 4.6d / 238. In EELabs work 5 centers of the Macaronesia (IAC, ITER, UPGC, SPEA-Azores, SPEA-Madeira). The objective of EELabs is to create Laboratories to measure the Energy Efficiency of Night Artificial Light in protected natural areas of the Macaronesia (Canary Islands, Madeira and Azores).

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