« Larry Niven and Gregory Benford on Designing an Alien Megastructure: Bowl of Heaven | Main | SpaceX/NROL-108 Launch, Second Attempt »

Friday, December 18, 2020

THE HAPPENING WORLD: Jupiter and Saturn in One 300 mm Frame

Jupiter and Saturn, 2020-12-18

Tonight provided the first opportunity to observe the conjunction of Jupiter and Saturn from Fourmilab. Weather this time of year tends to be foul, with dense ground fog which often doesn't clear until the time the giant planets are setting. At 16:33 UTC on 2020-12-18, which is well before the end of nautical twilight (16:58) at this location, and an hour before the end of astronomical twilight (17:58), both planets were easy naked eye objects. Clouds threatened to obscure the planets (and carried out that threat a few minutes after I took this picture). I set up my Nikon D600 camera with its “do-everything” 28–300 mm zoom lens and tried to get some pictures showing both planets in the same 300 mm frame. With the clouds rolling in, I didn't have as much time as I'd have liked to experiment with ISO sensitivity and shutter speeds, and since I had to extend the centre pillar on the tripod to its maximum to dodge a pesky tree branch, the camera tended to be jiggly, even using the mirror lock-up feature (which I always employ for astrophotography). I ended up with a lot of squiggles and potato-shaped gas giants: this is the best of the lot. The apparent sizes of Jupiter and Saturn can be discerned, along with Saturn's more yellow colour, and with a little imagination you can glimpse a hint of Saturn's ring structure. This is a straight crop from the original camera image with no processing other than a little contrast stretch and sharpening. Even three days before the conjunction, the planets really are that close together with respect to their apparent sizes! This is a 1/15 second exposure at ISO 400 with the lens wide open at f/5.6 and a focal length of 300 mm.

If the above picture was devoid of trickery, that can't be said of the one below. I've superimposed the picture of Jupiter and Saturn on a shot of the crescent Moon taken a few minutes before with the same lens and focal length, sloppily focused and blurred by being viewed through a thin cloud. But what you can see is that Jupiter and Saturn are closer already than the apparent diameter of the Moon, which was 0.5144 degrees when this picture was taken.

Jupiter and Saturn superimposed on the crescent Moon

Posted at December 18, 2020 17:06