Source: NASA/JPL-Caltech
Published: November 1, 2019
Historical Date: November 1, 2019

Highlights of the November sky include how to watch as Mercury transits the Sun on Nov. 11, plus how to observe the regular dimming and brightening of the "Demon star," Algol, with your own eyes

Details and Sky Charts


What's Up for November? Mercury transits across the Sun, and the dimming of the "Demon star," Algol.

On November 11 we're in for a rare treat, as the innermost planet, Mercury, passes directly in front of the Sun for a few hours.

This event is called a transit, and for Mercury they happen only about 13 times in a century. (Transits of Venus are even more rare.)

The event will last about five and a half hours, during which Mercury's path will take it right across the middle of the Sun's disk. For observers in the Eastern U.S., the transit begins after sunrise, meaning you'll be able to view the entire thing. For the central and western U.S., the transit begins before sunrise, but there's enough time left as the Sun climbs up the sky for you to catch a glimpse before Mercury makes its exit.

Now remember, you should never look directly at the Sun without proper protection, as it can permanently damage your eyes. If you have a pair eclipse shades, those are okay for viewing the Sun, but Mercury is so small in comparison that it can be next to impossible to see a transit without magnification. Your best bet is a telescope with a certified sun filter, but other options include solar projection boxes and sun funnels. Plus, NASA's Solar Dynamics Observatory spacecraft will be sharing near-realtime images during the transit. Whatever method you choose, be safe when observing the Sun!

The next Mercury transit that will be visible in the U.S. isn't until 2049! So if you're in the States, you might want to make the effort to catch this special celestial event.

A more frequent type of transit you might want to check out is the regular dimming and brightening of the "Demon Star," Algol.

Found in the constellation Perseus, Algol is actually two stars orbiting each other, and they're oriented nearly edge-on such that, from our perspective, the smaller star regularly passes in front of the larger, brighter one, causing it to dim for about 10 hours at a time. This happens like clockwork, every 2 days, 20 hours, 49 minutes. You can find tables of these "minima," as they're called, in lots of astronomy magazines and websites.

To observe Algol's eclipses, find the date and time of a predicted minimum and start observing maybe an hour or two before that time. Take a look about every half hour (binoculars are really useful for this). Over a few hours following the minimum, Algol will slowly brighten back to its normal state.

At its normal brightness, Algol appears about as bright as the nearby star Almach, while at its minimum, it dims to around the brightness of its neighbor Gorgonea Tertia. So these two stars provide a helpful way to compare Algol's brightness throughout the night as you observe.

Here are the phases of the Moon for November.

Phases of the Moon for November: 1st quarter, Nov/ 5
Credit: NASA/JPL

You can catch up on all of NASA's current and future missions at

I'm Preston Dyches from NASA's Jet Propulsion Laboratory, and that's What's Up for this month


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