If you’re hoping for a discussion of UFOs, you can stop here…
Not uncommonly, two celestial objects appear close to one another in the sky. These events involve the Sun, Moon, and/or the planets (and, once in a while, comets), since all of these objects appear to move in the sky against the background of the distant stars, as seen from Earth.
With the exception of comets, all objects that move in our sky, relative to the background stars, closely follow an invisible line called the plane of the ecliptic (the path that the Sun appears to travel as the Earth orbits it). When two objects have the same right ascension (essentially, when they are due north or south of one another), they are said to be in ‘conjunction.’
Technically, two objects can be in conjunction and still not appear to be as close as they can get to one another. The term for when two objects are closest to one another is an ‘appulse.’ The difference between when two objects are in conjunction and when they are an appulse is slight. Conjunction is the term most commonly used to describe two objects appearing close together in the sky, so I’ll use that term here.
Most conjunctions we observe in the night sky involve the Moon since the Moon makes an entire circuit of the ecliptic in only about 28 days. The Moon’s high apparent speed against the background stars causes the Moon to frequently approach and pass other celestial objects (sometimes the Moon actually passes in front of another object, ‘occulting’ it). Less commonly, one planet will be in conjunction with another planet or nearby star.
In the half year, we’ve been treated to a number of close conjunctions. The highly anticipated conjunction of Jupiter and Saturn occurred in December, when the two largest planets appeared so close to one another that they could be captured in the same field of view in a telescope or, as in the photo below, the zoom lens of a camera.
Jupiter (below) made its closest approach to Saturn on December 21, 2020. This photo was taken with a camera and telephoto lens. In my telescope, not only could I see the two planets in the same field of view, but I could see the four Galilean Moons of Jupiter and the two brightest moons of Saturn. That’s eight solar system objects in one field of view!
This is what Jupiter’s close encounter with Saturn looked like with the unaided eye. Jupiter is below and to the left of the more distant, dimmer Saturn, as they set together between the Sandia Mountains and Grand Central Mountain in the Cerrillos Hills.
Below are several examples of other close encounters that have recently occurred in our skies.
An almost full moon is in conjunction with the planet Mars (top right) in October 2020. Seeing conditions were particularly excellent that night.
As Jupiter pulled away from Saturn (after their December conjunction), Mercury joined the action, to the left of Grand Central Mountain (partially obscured by the house) and Cerro de la Cosena.
In March, the red planet Mars (lower left), had a close encounter with the blue-white Pleiades star cluster in Taurus.
This past Wednesday (May 12), the Moon and Venus made a nice pair in the west, above Tetilla Peak (left foreground) and the Jemez Mountains. The waxing crescent moon was only 1.5% illuminated.
The following evening (Thursday, May 13), the Moon passed Mercury at a somewhat greater distance than the Moon’s recent close encounter with Venus.
Since celestial objects visible to the unaided eye that appear to move against the background of the distant stars can be counted on two hands, conjunctions and appulses are not every night occurrences.
However, if you have binoculars or a telescope, the opportunities to observe close encounters increase substantially since there are many asteroids orbiting the Sun that can be in conjunction with another object. And, if you include man-made satellites in Earth orbit, conjunctions of one kind or another are virtually nightly events.
FYI, tonight (Saturday, May 15), the Moon will pass close to the planet Mars in the constellation Gemini. There’s always something happening above us in our silent night skies.
Mars is twice the size of the Moon, but appears as a mere dot near the left edge of the photo since it’s currently about 200 million miles farther from Earth than the Moon.
Please avoid unnecessary lighting, so we can all enjoy the show.