Fundación Galileo Galilei - INAF Telescopio Nazionale Galileo 28°45'14.4N 17°53'20.6W 2387.2m A.S.L.

Telescopio Nazionale Galileo presents:

Mercury Transit 2019 Live

11 November 2019

Telescopio Nazionale Galileo presents an afternoon dedicated to Mercury the smallest planet of the Solar System, on the occasion of its transit.

From 12:35 UT to 18:27 UT: streaming of the transit live from Roque de Los Muchachos

From 12:15 UT to 16:15 UT: a Hangout talk given from the TNG Control Room

When the inferior planets of the Solar System, Mercury and Venus, are projected onto the solar disc as seen from Earth, a transit is produced. This is a phenomenon similar to the Solar eclipse, one of the most spectacular phenomena. However, while the apparent sizes of the Moon and the Sun are almost identical (approx. 30 arcmin), the apparent sizes of Mercury and Venus are much smaller – 10 arcsec and 1 arcmin, respectively, and they can only be observed with a telescope. If the orbits of the inferior planets lay on the same plane as the orbir of the Earth, the transits of Mercury and Venus would be a very common phenomenon when the Earth, the planet and the Sun are aligned. Due to the slightly different inclination of the orbits of the inferior planets and of the Earth, however, most of the times, the alignments of the Earth with any of the inferior planets do not get projected onto the solar disc. If we want to observe a transit, the alignment must take place along the intersection line between the planet’s orbit and the Earth. This intersection line is called the node line.

Because of this, the Venus transit occurs only 5 times every 243 years following a bizzare cycle. The transits of Mercury are more frequent than those of Venus, but also quite rare (13 or 14 times per century) of which the last occurred in 2016.

For many years, the transits of Venus were the most precise method to calculate the Astronomical Unit, the semi-major axis of the Earth’s orbit. In theory, the transit of Mercury could also be used for this estimation, but due to the greater distance from the Earth to Mercury, they are more difficult to be used for the calculation of the value of the Astronomical Unit.

The transits of the planets in front of their stars represent a very important subject because they are used as a method of detection of extra-solar planets, i.e. planets belonging to systems outside the Solar System. Thanks to the use of both methods, the transit and the Doppler effect, today we have identified more than 4000 of them.

Historically Mercury, apart of being used for the determination of the Astronomical Unit, has played a fundamental role in the confirmation of the Theory of General Relativity. A century ago, prior to the publication of his “Theory of General Relativity”, Alber Einstein confirmed it by using the motion of Mercury around the Sun. It was already known for some time, that the motion of the innermost planet of the Solar System showed an anomaly considering Newton’s theory. Einstein showed that the precession of the axis of Mercury was in perfect agreement with his calculations. After more than a century after the publication of Einstein’s theory, in October 2018, ESA’s mission BepiColombo was launched towards Mercury.

Among its objectives is to carry out tests and to measure the relativistic effects close to the Sun.

Mercury Transit from Roque de Los Muchachos

A series of talks has been planned for schools and the general public from the control room of the biggest Italian optical and infrared telescope. The topics will be: The Solar System, the transits of interior planets, the estimation of the Astronomical Unit and the solar diameter; The extrasolar planets and the contribution of Telescopio Nazionale Galileo towards their characterization. The talks are going to be given remotely with interested groups and will be held in Italian and in Spanish.

At the same time, the transit will be streamed on the YouTube channel of Telescopio Nazionale Galileo.

The observations of the transit will be carried our with a solar telescope with an Hα filter and with a Maksutov telescope with a broadband solar filter.

For more information:

When/how/where to follow us

Universal Time (UT matches Canary Islands time)

  • First contact (outer contact) 12:35 UT
  • Second contact (internal contact) 12:37 UT
  • Maximum (minimum angular distance from the Solar centre) 15:19 UT
  • Third contact (internal contact) 18:02 UT
  • Fourth contact (external contact) 18:04 UT

Right: Picture of the Sun taken during the test for the Mercury transit (solar telescope with 60 mm aperture and Hα filter). Credits: J. San Juan (FGG-INAF).

  • 12:15 UT – 18:30 UT: Streaming of the transit of Mercurio in the Telescopio Nazionale Galileo YouTube channel with a solar telescope with an Hα filter and a Maksutov telescope with a broadband solar filter.
  • 12:15 UT – 12:45 UT: Talk on: the Roque de Los Muchachos and the Telescopio Nazionale Galileo; the transit of the inferior planets in the Solar System.
  • 13.30 UT – 14.30 UT: The estimation of the Solar diameter and the Sun-Earth distance using the transit of Venus.
  • 15.00 UT – 15.30 UT: The transit and the Doppler effect to discover extrasolar planets.
  • 16.00 UT – 17.45 UT: Telescopio Nazionale Galileo and the study of extrasolar planets.