First sight of the Great Red Spot is a high point for any amateur astronomer. Few tire of the sight of this massive and ancient storm in Jupiter’s upper atmosphere. But while it looks fine in photos, it’s surprisingly hard to see in a small telescope. Here are three tips to increase your chances of seeing the “GRS”, and a few words about this swirling vortex that’s large enough to swallow several Earths.
Tip 1 – Make sure the GRS is visible. The spot rotates, more or less, as Jupiter rotates. So every 10 hours the spot makes a full rotation around the visible disk of the planet. You’ll get your best chance of seeing the Red Spot as it crosses the central meridian… the imaginary north-south line that bisects the planet’s disk. Even if the GRS is an hour before or past the meridian, you can get a good view.
So when the the Great Red Spot cross the meridian? Your best bet to get this information is to go to Sky and Telescope’s transit table here…
This page lists all transit times over the next few months. Times are listed in Universal Time (or Greenwich Mean Time). You can determine UT relative to your local time with this website…
So for example, the Sky and Telescope table shows transit of the GRS on December 1 at 8:17 and 18:13, and on December 2 at 4:08 and 14:04 UT. In my timezone (Eastern Standard), this means there are transits at 3:17 a.m. and 1:13 p.m. and 11:08 p.m. on December 1, and 9:04 a.m. on December 2. Of course, I’ll only see the GRS when the sky is dark, so the transits at 3:17 a.m. and 11:08 p.m. are my best bets.
Tip 2 – Make sure you have steady sky. The GRS appears quite small, even at 150-200x. So you need good steady sky to see it. If the stars are twinkling madly, or if you see the limb of the planet rippling, the seeing is poor and your chance of seeing the spot is reduced. Steady sky in which the stars barely twinkle is nearly essential. And you can try a light-green color filter (a #56 or #58) on your eyepiece to make the spot appear darker against the planet’s disk.
Tip 3 – Try hard! Don’t just take a quick peak and give up. If takes effort to see fine detail in a telescope. Look carefully, rest your eyes, and look again. It takes time for the detail to register in your brain. And you may need to wait for brief moments of steady seeing.
Here’s a quick review on how to see fine and faint detail in a telescope.
And here’s a time-lapse of the spot in action…
It’s worth a try to see the Great Red Spot. This massive storm, which packs winds of more than 400 km/h, may have been first seen nearly 350 years ago, and may be much older. The storm is just south of Jupiter’s equator, and rotates counter-clockwise as seen from Earth. It measures about 30,000 km across at its long point, and half as much at its shorter axis, though the spot has become less elongated in the past 15 years. No one knows why. Nor is anyone sure what causes its red color. It may be a colorful brew of complex organic molecules in the planet’s upper atmosphere.