Monday, October 18, 2021

What stars you might see during the eclipse


NASA has produced a poster that shows that the sun (and moon) will be in the constellation Leo, very close to its brightest star, Regulus, during the eclipse Monday, and Jupiter, Mars, and Venus will all be in the field, with Mars being very close to the eclipse.

Star chart at the moment of the eclipse (NASA/Goddard Space Flight Center)

To get an idea just how close these solar system objects are in the (daytime) sky on August 21, take a look at the rise and set times of these objects at Carbondale, Illinois, which is about 20 kilometers away from the point of greatest duration:

Solar System Object Apparent Magnitude Rise (CDT) Set (CDT)
Venus (in Cancer) –3.9 3:30 AM 5:53 PM
Mars (in Leo) –?? 5:36 AM 7:22 PM
Moon (new) –2.5 6:02 AM 7:48 PM
Sun (uneclipsed) –26.7 6:17 AM 7:41 PM
Jupiter (in Libra) –1.8 10:30 AM 9:52 PM

Since celestial objects rise in the east and set in the west, Venus will be the first of these objects above the horizon and will have been up for about two hours when Mars rises. Venus is about 34° ahead of the sun. Next comes the moon and, 15 minutes later, the sun. At this point, the sun will brighten the entire sky and nothing else will be visible—until the eclipse, that is.

Jupiter rises above the horizon in Carbondale four hours after the sun. That makes the angular distance between our solar system’s largest planet and the eclipse about 51°. If you have a wide enough lens on your camera, it might be possible to catch all three planets—Jupiter on the east, Mars near the eclipse, and Venus on the west—in the same shot. There’s a challenge.

The angular distance between Jupiter and Venus will be about 85°, with the eclipse in the middle, near Mars and Regulus. A 50mm lens has an approximate angle of view of 39°, so you’ll need a much shorter lens than that. Try a lens with a 19mm focal length.

(Note that if you’re west of Wyoming, you won’t be able to see Jupiter during totality, because it will not have risen yet from the southeastern horizon.)

This might be an opportunity for you, especially if a 35mm or 50mm lens is your shortest one, to use the technique of “stitching” to piece together a photo of the sky, as on a mosaic. Sure, the sky will move a little as you pan the camera from Jupiter to Venus, but not that much.

Some photographers recommend, to get the planets with mid-twilight lighting during totality, using a tripod for an f/2.8 lens and a 6-second exposure time (experiment a little). I would recommend setting the ISO sensitivity to about 400.

Note that these calculations are approximate, based on the Earth’s rotation of 24 hours. Some corrections are necessary, given Carbondale’s location on the globe, the flattening of the ecliptic across the sky during the eclipse, and other factors. If you can supply these, please post a comment here with a reference link.

Paul Katula
Paul Katula is the executive editor of the Voxitatis Research Foundation, which publishes this blog. For more information, see the About page.

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