Tonight, December 21, is the “Great Conjunction” of Jupiter and Saturn. This is the closest they have been in 397 years. Look in the southwest sky at dusk. Jupiter/Saturn will be the brightest thing you see.
Finding Jupiter and Saturn
Jupiter and Saturn will appear in the sky in the southwest at dusk. At first they will be quite faint. In the photo above they are in the middle of the frame, left to right, and about 1/4 of the way down from the top of the frame As they sky gets darker they will be much more obvious (photo below). You might see one bright object instead of two. More about that later
If you want a computer simulated preview of tonight’s sky, download Stellarium (it is free, link below) and install it on your computer. Pick the nearest town to you in the software’s database and use that is your default location. Or can add your own GPS coordinates as your default location. You can set the date and time to any date and time of your choosing. Start with 5 pm this evening and run the clock forward, minute by minute, to see what happens. You have a limited time window before Jupiter and Saturn set in the southwest. Stellarium will tell you how much time you have.
Another option is to check out the information at “Earth and Sky” and “Time and Date” at the links below.
If it is cloudy tonight, go out tomorrow night or the next night. Jupiter and Saturn will still be close together in the sky and much closer than they will be any time between now and 2040. You still have a few more nights to look before they get so close to the sun that they will be lost in the glow of sunset.
Visual Observing
Jupiter passes Saturn only once every 20 years in the night sky, so this won’t happen again until 2040. But this time is extra special. They will only be 6.1 arc minutes apart. That is 0.102 degrees. The last time they were this close was 1623, just 14 years after Galileo made his first telescope.
How close is 6.1 arc minutes? There is a double star in the middle of the handle of the Big Dipper. Mizar (2nd magnitude) and Alcor (4th magnitude) are a naked eye double star that are 11.8 arc minutes apart, roughly twice as far apart as Jupiter and Saturn will be tonight. Mizar and Alcor have long been a test of visual acuity. Some people can see them as two stars, and some people as one. And as our eyes age, its gets harder to see them as two stars. Which means you may or may not be able to see Jupiter and Saturn as two separate objects. Take binoculars out with you. Binoculars will easily separate Jupiter and Saturn.
If you know how to use a telescope, you know what to do. If you aren’t a telescope user already, don’t go out today and buy a cheap telescope at a big box store. First, the quality will be poor, and second, it will be an exercise in frustration. You will be much happier using binoculars. They are a much better choice for the first time observer.
Photography
To take pictures, first, you need to know how to focus focus your lens at infinity and do it at night. Autofocus will not work, and manual focus at night is tricky at best. Plus zoom lenses focus past infinity so it is not just a matter of turning the focus ring until it stops. For suggestions, read the first two articles in the links section.
A 300mm or longer lens can capture Jupiter, it’s 4 Galilean moons, and Saturn. Focus carefully in manual mode. With a long lens try ISO 3200, f/5.6, and a range of shutter speeds between 1/60 and 1/8 second. The image immediately above, cropped from the image at the top of this article, will give you an idea what is possible at around 300mm.
If you are using a normal lens to get Jupiter/Saturn, the evening sky, and the landscape (a lake would be nice) all in one image, start as soon as Jupiter is visible, meter the night sky and bracket generously in one stop increments on either side of the camera meter reading.
Despite lots of clouds last night, I went out to photograph Jupiter and Saturn yet again. Most of the time they were totally hidden behind clouds, but for a few minutes they appeared behind hazy, wispy clouds. They were dimmer than usual. You can see just a hint of Saturn’s rings, which gives Saturn an oblong shape. Thanks to the thin clouds, Jupiter’s moons were not visible most of the time. But there was a moment I could faintly see one of the moons and clicked the shutter. This photo is the result. I picked up 3 of the 4 Galilean moons. The inset in dark blue is from the computer program Stellarium. I set Stellarium to the approximate time of the photo, zoomed in on Jupiter and Saturn and did a screen capture. You can see Ganymede in my photo, and Io and Europa are there but very faint. I don’t see Callisto in this photo. Without the thin clouds all four moons would stand out. My 400mm lens was on a Canon 7D Mark II which has a cropped sensor, so the 35mm equivalent focal length was 640mm. The exposure was 1/8 second at f/8 with an ISO of 6400.
How To Links
How To Focus Your Lens at Infinity for Night Photography
How To Get Critical Focus in “Live View” Mode with a Magnified Image
Free Software Link
Information Links
Time and Date: the Jupiter/Saturn Conjunction
Earth and Sky: Jupiter and Saturn’s Great Conjunction