A Great conjunction is a conjunction of the planets Jupiter and Saturn. Great conjunctions occur regularly (every 19.6 years, on average) due to the combined effect of Jupiter’s approximately 11.86-year orbital period and Saturn’s 29.5-year orbital period and due to the proximity of the orbits of the planets. The upcoming Great conjunction will occur on 21 December 2020.
Conjunctions occur in at least two coordinate systems: equatorial and ecliptic. The conjunctions in first system are measured in right ascension, along the celestial equator. The second system is based on the ecliptic, the plane of the Solar System. When measured along the ecliptic, the separations are usually smaller. Conjunctions are characterized by angular distance between planets and elongation (angular distance from Sun). The visibility of the exact moment of a conjunction depends on the observer’s location.
The upcoming Great conjunction will occur on 21 December at 13:30 UTC (in right ascension). At this time Jupiter will be 0.1 degree (6 arcmins, the one fifth of Moon diameter) south of Saturn and 30.3 degrees east (on the left) of the Sun. The closest approach of the planets will be at 18:25 UTC, elongation at this moment will be 30.1 degree. This Great conjunction will be the closest since 1623. This means that in telescopic field of view, both planets will be visible simultaneously. And also they will be distinguishable from each other without optical aid.
The Great conjunction will occur in the constellation of Capricornus. After sunset, the two planets will be visible at the southwestern part of the horizon, low above it. From mid-northern latitudes, the planets will be less than 15 degrees in altitude, one hour after sunset.
Check if the Great conjunction 2020 can be seen in your location using WinStars 3.
Source: Wikipedia (redacted version by Sergey Telukhin)
On July 30, a powerful AtlasV rocket left Earth with the Perseverance rover and the Ingenuity drone on board. The Mars 2020 mission is designed to operate until 2030 and should help NASA and ESA to reach important milestones in the exploration of the Red Planet.
It will begin with a planned landing on February 18, 2021 near the Jezero crater, which presents an interesting profile for the quest of traces of past life. We now know that this crater was a lake several billion years ago.
Mars 2020 is in fact the first step in an ambitious project consisting of three missions designed to bring samples back to Earth for further examination. The rover will carry out drilling cores that will be carefully stored before their return to Earth. The Sample Retrieval Lander (SRL), built by NASA, and the Earth Return Orbiter (ERO), developed by the European Space Agency (ESA), are scheduled to launch in a few years to retrieve these precious samples from the Martian soil.
You can follow the itinerary of Mars 2020 in W3 by downloading the module of the same name. The trajectory of the probe is directly taken from the Horizons server of the Jet Propulsion Laboratory.