Jupiter reaches its climax of observability in the night of May 8 for America, May 9 for Europe.
Here it is, rising after darkness falls. By midnight it will be highest, in the south
At the picture’s time and location – the central time zone of North America – the planet is more or less exactly at opposition, that being close to 0h Universal Time.
As you see if you are able to see the picture at fairly large scale and look closely, Jupiter in the present part of its orbit is traveling a little north of the ecliptic. So it passes just north of what I mark as the “anti-Sun,” which could be called the shadow of the Earth (where the Moon, when it passes exactly enough, is eclipsed).
Jupiter does not vary greatly in apparent brightness and size, because its orbit is not very far from circular. (The orbit’s eccentricity is about 0.05, which is much less than for Mercury and Pluto, though not as near to circular as those of Venus and Neptune.) Jupiter was at aphelion in early 2017, so it is still in the more distant part of its orbit. Its magnitude at opposition (-2.5) is not as bright as it will be (-2.9) around 2023 when it will be at perihelion.
What varies much more in the great planet’s 12-year cycle is how far north or south it is in the sky. Here is a chart for about a quarter of the cycle. I may have to show this broad chart in more than one piece.
The chart is ecliptic-based; the more familiar lines of right ascension and declination are added, slanting in relation to the ecliptic. The planet’s course is shown in gray when it is in the morning sky, between Sun-conjunction and opposition.
During these approximately three years,Jupiter moves across a quadrant of the celestial sphere – what I would call the third quadrant, from Virgo to Sagittarius. The quadrant begins at 12h right ascension (180° longitude), where the ecliptic descends through the celestial equator and the Sun appears at the autumn equinox; and reaches to 18h (270°), the ecliptic’s southernmost part, home of the Sun at midwinter.
So Jupiter was in eastern Virgo in 2017; is in Libra in 2018; and in 2019 will be in Ophiuchus (the constellation that has stolen most of that part of the zodiacal band from Scorpius). In 2017-2018 it is at middling latitude in the sky; in 2019-2010 it is low for us, high for people in the southern hemisphere.
Each year, the planet as we overtake it seems to perform a retrograde loop, a backward swirl toward us in space, centering on the moment of opposition. And in a multiple-year chart like this you can compare these loops: they flatten as they get progressively nearer to the ecliptic, from Jupiter’s maximum latitude above the ecliptic at the end of 2016 toward its descending node in early 2020.
Guy, thanks for the in-depth look at Jupiter’s movements over this recent and near-future span of years. I do enjoy looking at Jupiter in a telescope, especially the various phenomena of the satellites such as shadow transits, but the naked-eye view of its changing orientation against the stars and planets is just as interesting. I’m looking forward to, and looking forward to reading your upcoming description of, Jupiter’s 2020 conjunction with Saturn and what sort of patterns emerge when looking at a longer time-span of the 20-year separated Jupiter-Saturn conjunctions (the last was in 2000 in Taurus, I believe). The one before that was in 1980 or 1981, in Leo or Virgo, if I remember your AstCal correctly. According to my planetarium software, the next one after 2020 will be in Virgo in 2040.
In the course of looking ahead to 2040 for how Jupiter and Saturn will interact (of course, I was hoping to discover a cool triple conjunction, but did not), I did stumble across a rather amazing conjunction or appulse of all 5 naked eye planets in the evening sky of early September 2040. For example, on 8 September 2040, Jupiter will be lowest on the western horizon, 20 degrees elongation from the Sun, and Mars will by 9 degrees to its upper left. Mercury, Saturn, and Venus will be between them. That’s got to be pretty rare! Hope I’m still around to see it, and have some clear skies LOL. We have no idea what the state of humanity or our societies will be then, but the night sky is always there to provide continuity and constancy amid the chaos.
Hey Guy,
At age 72, it was an effort to drag my telescope out from storage, but well worth it. At 22:30 EDT, in Western New York, USA, I observed Jupiter. Io was nearly touching Jupiter’s image. Observation was made with my 6″ reflector. Sometime this summer, I plan to repair the mount for my 12″ reflector.
You are an inspiration… keep on going, Guy.
Joseph