Gazing to the eastern sky

Guest blog, Michael D. Edmiston Ph.D. '72,
Professor of chemistry and physics

Perhaps you have heard this is a good time to view Jupiter in the eastern sky. It is a good time for Jupiter, and maybe also Uranus.

I have been waiting for a good night to set up some telescopes for viewing Jupiter. We want clear sky, no moon, and Jupiter high enough in the sky at a reasonable time of night. Tonight and the next week-or-so should be pretty good.

Tonight (Wednesday, Sept. 29) Jupiter rises at 7 p.m., but will not be high enough for good viewing until about 8:30. The last-quarter moon does not rise until 11 p.m. Therefore we have a window from about 8:30 until 11 to view Jupiter without much interfering light from the moon.

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For those of you near campus, I am going to set up several telescopes on top of Shoker this evening. I will have them ready to observe by about 8:30, and will probably stay out until 10:30.
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With a small telescope having 40 or 50 magnification, you can easily see the same four moons that Galileo saw almost exactly 400 years ago. You can also barely see them with binoculars, except it is very difficult to hold the binoculars steady. The four moons are Io, Europa, Ganymede and Callisto. Jupiter's moons are fun to watch because they orbit so fast that they look different each night.

Tonight Io, Ganymede and Callisto will be on the true-left side of Jupiter, and Europa will be on the true-right. Using a telescope it is likely that right/left will appear reversed, and that's why I said true-left and true right. In the telescope, the three moons will appear on the right with one on the left. Binoculars give a true view. The moons and Jupiter all appear approximately on a straight line from Earth's vantage point.

Tomorrow night (Thursday, Sept 30) is especially interesting because at 8:30 p.m. Ganymede and Callisto will be on the left, Io on the right, and Europa not visible because it will be behind Jupiter. However, around 9:50 p.m. Io will begin to disappear behind Jupiter (on the true-right side), and Ganymede will begin to reappear on the true-left side. By 10:30 Io will be gone, and Callisto, Ganymede and Europa will all be on the true-left side. For those who want to stay out late on Thursday night, by about 12:36 a.m. Friday morning, Io will reappear on the true-left, and therefore all four moons will be visible on the true-left side

As an added bonus... the planet Uranus is very close to Jupiter, and should be visible as well. On a dark night you can see both Jupiter and Uranus with your eyes alone, but probably not from Shoker because of the lights. If you do see Uranus with your eyes (without a telescope) you probably will not distinguish Uranus from a star. With a telescope Uranus will appear small, but will have an observable cyan (blue-green) color. If you can hold them steady, you might be able to distinguish Uranus with binoculars.

For the next few nights, Uranus is only 1.30 degrees away from Jupiter. If Jupiter is at the center of a clock face, Uranus will be in the 10:00 position at 8:30 p.m., and in the 11:00 position by about 10:30 p.m.. The field-of-view (FOV) for typical binoculars is about 7 degrees, so Uranus and Jupiter are well within the same FOV with binoculars, that is, you can see them at the same time. The FOV for most small telescopes is about one degree, so Uranus will be just outside the FOV if Jupiter is inside the FOV. You only have to move the scope a tiny bit left and up to get to Uranus once you have found Jupiter. Remember, you are looking for something star-like, but through binoculars or a telescope it will not be as small of a point as a star, and it will have a pale cyan color.

For reference the width of your little finger, held arm's length, is about one-degree. Therefore, once you have found Jupiter, hold your left little finger at arm's length, and tilted toward 1:00 on a clock-face, and put Jupiter just visible on the right side of your finger, and Uranus should be roughly just on the left side of your finger.

For those of you too far away to come to Shoker... At 8:30 p.m. tonight, Jupiter will be in the low slightly-south-of-east sky, about 16-degrees above the horizon. By 10 p.m. it will be in the east-south-east, about 30-degrees above the horizon. By 11 p.m. it will be in the south-east about 40-degrees above the horizon. The moon will rise in the east at 11: p.m. but will not be high enough to see over trees until about 11:30 p.m.