In this seemingly endless summer, a couple of celestial events have popped up to vie for our attention, a welcome distraction from other news that need not be mentioned here. The splendid comet designated C/2020 F3 NEOWISE (an acronym for Near-Earth Object Wide-field Infrared Survey Explorer, the NASA space telescope that discovered it) has transitioned from pre-dawn to after sunset and now ascends the early evening sky under the bowl of the Big Dipper. If you haven’t seen it yet there’s still time – grab a pair of binoculars and have a look at the northwest skies on a clear night after sunset.
As alluring as the comet is, two other celestial wonders are now making their presence known in the southern sky in early evening. A smart phone astronomy app would be a good way to quickly find these planets, and they are bright enough that they stand out even in our light pollution- compromised skies. The great Jovian planets Jupiter and Saturn – gas giants! – both reach opposition in mid to late July; that’s when they’re at their closest position to earth in their orbits, which happens once a year due to earth’s orbit. Jupiter and Saturn themselves have orbital periods of 10 and 11 earth-years. This is also why they transit near midnight right now, meaning that they reach their highest altitude in the sky and cross the celestial meridian at midnight (the meridian is the line joining both poles with the zenith point). In addition, you’ll notice Jupiter and Saturn have reached their brightest, with magnitudes -2.7 and 0.1, respectively. In fact, Jupiter is brighter than any star or planet in our skies, except Venus when it is at the far side of the sun relative to earth. The magnitude unit is a scale worked out centuries ago, with the brightest to dimmest stars seen by naked eye ranging from magnitude 1 to 6, each magnitude number being 2.5 times brighter than the next so that 6 magnitudes spans ~100-fold difference in brightness.
Both Jupiter and Saturn are great sights if you’re lucky to have a small telescope; both show surprising detail even with binoculars if held steadily enough. For instance, you can see the 4 Galilean moons of Jupiter, discovered by Galileo himself in 1609 using a small telescope, which had been recently invented. Notice how the positions of the 4 moons relative to each other and the planet change, even in the course of a couple hours in the same evening. If you had a big enough telescope to see the details of the surface of Jupiter you’d notice the surface changing in the span of a few hours as well. Amazingly, Jupiter rotates on its axis once every ~10 hours! Under good conditions you will notice the “stripes”, prominent bands of different shades of yellow in the hydrogen atmosphere. There is also the famous Great Red Spot, a violent storm that has been observed on Jupiter for over 300 years and can be seen under very good visibility conditions in a small scope.
A few degrees to the left (east) of Jupiter you’ll see Saturn, brighter than other stars in the sky at this time, though much dimmer than Jupiter because it is twice as far away. Imagine the line between them: this is an arc along the ecliptic, the plane in which all the planets’ orbits lie. (Except Pluto, one of the reasons it was demoted from planet status a few years ago). Saturn’s rings are visible through binoculars and especially pronounced in even a small telescope. Galileo was the first to see Saturn’s rings, though he thought they were moons on either side of the planet. The rings are actually made up of solid material, largely water ice, aggregated over millennia into discs around the planet due to Saturn’s immense gravity and dynamics. Their angle of inclination, or tilt, toward earth changes in the course of its orbit around the sun. While viewing Saturn, that other bright point of light you may see in the scope is Saturn’s largest moon, Titan. Well-named, as it’s the largest moon in our solar system, Titan was once hypothesized to be a possible place for life, though the current thinking is that this is highly unlikely and that it is an inhospitable place, suitable for science-fiction scenes but not likely biological ones.
The photo attached to this article was taken from my back yard in Titusville using a small telescope and specialized astronomy CCD camera. If you’re interested in learning more about astrophotography (or just want to gaze at some deep sky objects!) visit my website at www.rexparkerpixels.com. If you’d like to get more involved in astronomy activities, including lectures on the Princeton University campus and our Observatory at Washington Crossing State Park (note: public observatory nights are suspended during the time of COVID), check out the Amateur Astronomers Association of Princeton at www.princetonastronomy.org.
Submitted by Rex Parker, PhD, who is the Director of the Amateur Astronomers Association of Princeton and lives in Titusville NJ.