One of the most awaited astronomical events of the year 2019! The transit of the planet Mercury between the Earth and the Sun will give terrestrial spectators a rare show. It repeats itself after several years, about 13 times for century.
What we will be able to see, telescopes in hand, will be a disk, a small dot (Mercury) “crossing” the surface of the Sun. Obviously equipped with appropriate sunscreens, you can observe the inner planet of the Solar system passing in front of our star. An event we can admire again only in November 2032. The last one we could see occurred on May 9, 2016. Telescopes and hand filters then!
On November 11th, little Mercury will peep out and take a walk (perspective) in front of our Sun. At 1.35pm there will be the first contact. That is the dot that we will see behind the eyepiece of our telescopes … it will be just Mercury!
The second contact will be at around 13:37 and Mercury will reach the maximum distance at 16.19. Then we will witness the slow descent of Mercury that will set with the Sun. The third contact will be in fact at 19.02 followed by the fourth at about 19.03, when the Sun will already have set and therefore no longer visible.
The protagonist of our “walk on the Sun” is the little Mercury! With its small diameter compared to the other planets, Mercury is the smallest planet in the Solar System and the innermost. It is located at 57.9 million km from our star with a diameter of “only” 4878 km. The minimum surface temperature reaches -180 °, while the maximum temperature reaches + 430 °. A year on Mercury lasts 88 days because, being closer to the Sun it revolves around it faster. This is why on Earth the duration of the solar year is 365 days, while on Mercury it is much shorter.
During his journey Mercury will give us the idea of how huge the mass of our Sun is compared to a planet. It would take 285 Mercury-diameter planets aligned to “fill” the diameter of the Sun!
• The transits of Mercury in front of the Sun can only take place in the months of May and November.
The event is so rare for one reason. The orbit of Mercury is inclined by 7 ° with respect to the orbit of the Earth, for this we witness the transit only at the precise
moments in which the Earth is aligned with the planet and with the Sun and is found at the points of intersection of the two orbits (called ascending and descending nodes). This happens in the months of May and November and about 13-14 times per century.
• During the 11 November transit, Mercury will be near the perihelion (point of minimum distance from the Sun), while in the transits that take place in the month of May it is near the aphelion (point of maximum distance from the Sun).
• The transit of Mercury is much more frequent than the transit of Venus. The first is in fact closer to the Sun and faster orbit.
• The simultaneous transit of Mercury and Venus in front of the Sun is an exceptionally rare event.
• Astronomers identified many of the extrasolar planets discovered thanks to their transit in front of their parent star. This is the case of HD 209458 b, the extrasolar planet nicknamed Osiris, discovered thanks to the transit technique, orbiting its parent star (HD 209458) in the Pegasus constellation.