A few days ago, on Nov. 11 2019, a rare astronomical event took place which will not occur again for another 13 years. The small, rocky and innermost planet of our solar system- Mercury- crossed directly in between the sun and the Earth while on its 88-day orbit around the star. The event, called a 'transit', lasted for roughly 5.5 hours and was visible to much of the world.. so long as you had the proper equipment to observe it safely.
https://cdn.mos.cms.futurecdn.net/x5...PxG-650-80.jpg
(Mercury in transit, visible as a small dark spot to the upper left against the face of the sun, as seen from Turkey on 11 November 2019)
At first thought, one may have the assumption that transits such as this should occur on a regular basis given the fact that all planets in our solar system orbit around the sun at the center. While that is true, the physics behind the orbit of the planets is a little bit more complicated than that. In a nutshell, the orbit of Mercury around the sun is inclined (or tilted) by around 7 degrees relative to the plane of Earth's orbit around the sun. That means that from Earth, the orbit of Mercury appears to shift above and below the sun throughout the year. Only when Mercury is in the part of its orbit that crosses through the same horizontal plane of Earth's orbit is it possible to witness this event. However, depending on where Earth is in its orbit is also important to be able to witness this alignment.
http://lasp.colorado.edu/~bagenal/10...luto_orbit.gif
(Diagram of the 'Ecliptic Plane', showing the tilted orbits of Mercury and Pluto relative to the rest of the major solar system bodies. Only when Mercury crosses through the center point of the diagram is it possible to witness as a transit across the face of the sun, assuming Earth is also in the right place at the right time, such as it was on Nov. 11 for only 5.5 hours)
Like Mercury, the same phenomenon can also occur with the planet Venus, although those transits occur much more rarely. The last transit of Venus visible from Earth was in June 2012, and will not occur again until December 2117.
A short but sweet video of the 2019 transit of Mercury, as observed by NASA's Solar Dynamics Observatory (SDO).
https://youtu.be/0yNzSwlnQ2Q
Did anybody get to view this event first-hand? Many observatories and amateur astronomers around the world setup special solar-filtered telescopes to view the transit without searing anyone's corneas, and invited the public to come take a look. Super cool stuff!
