I have a doubt about planetary conjunction.
These days, we can see Saturn, Mars, Jupiter and the Moon close to each other.
I mean if Saturn, Mars, Jupiter and the Moon were in conjunction with each other, last February, 19th, 2020.
Is this a conjunction or is it an alignment?
Strictly speaking, a conjunction is when two objects appear at the same right ascension or ecliptic longitude. These are not exactly the same but are usually close since the major planets remain near the ecliptic.
When Venus or Mercury is in conjunction with the Sun, we distinguish between inferior (near side) and superior (far side) conjunction. The outer planets can have another type of alignment, opposition, in which they are 180° away from the Sun around the equator or ecliptic.
When two solar system objects appear only a few degrees apart, it's fair to say they are near conjunction. If they don't quite reach conjunction, their minimum angular separation is called an appulse.
Mars is in conjunction with Jupiter on March 20 and with Saturn on March 31. Other planet-planet conjunctions are listed here. On 2020-12-21 Jupiter and Saturn will appear only 0.1° apart at conjunction and should be interesting to see together in a telescope shortly after sunset.
A conjunction is when two objects have the same Right Ascension (ie the same longitude in the sky) When planets have conjunctions they will be close to each other, since they follow the ecliptic. The time of conjunction might not be the time of closest alignment. A conjunction is a moment in time you can only have two planets in conjunction, not three or more.
An alignment is a less precise term meaning "in a line". There can be several planets roughly in a line.
There are some conjunctions this spring: Mars passes Jupiter (on 20 March) and Saturn (on 31st March) in the morning sky, close to the sun. Because Jupiter and Saturn move slowly, they won't reach a conjunction with each other until December. Again this will be too close to the sun to be observe easily.
There will be times when Mars, Jupiter, Saturn and the moon are all roughly aligned in the morning sky this spring. The planets are going to remain roughly aligned, and the moon moves quickly so will pass through. But as the sun is also nearby, it won't be much of a spectacle.
Be aware that in some news reports and so on "conjunction" is used less formally. A close alignment can look quite impressive, and so may be reported in non-specialist media. But, for example, the moon has a conjunction with each of the planets every month (and there was a conjuction between a crescent moon and Venus at the end of Feb 2020). Conjuctions are not themselves rare.
This is probably not helpful, but, if you visit https://eclipse.gsfc.nasa.gov/SKYCAL/SKYCAL.html (check all boxes) and set timezone to MST, you get the below which shows the Moon conjuncts Mars, Jupiter, and Saturn on March 18th.
Of course, this is timezone dependent, but should be the same day for all contiguous 48 states US time zones, though not for GMT (the Saturn conjunction occurs 4 minutes past midnight) or time zones further east (including Guam), and also not for time zones further west than the Pacific Time Zone (such as Hawaii and Alaska).
