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The Mercury Transit Explained

by Zachary Singer

Diagram of a transit of Mercury.
Diagram of a transit of Mercury.

(All illustrations © Zachary Singer.)

If you’ve heard about the November 11 Transit of Mercury (visible 6:39 AM – 11:04 AM, Mountain Standard Time, here in Denver), you may have a simple question: “What is it, and why is a transit a rare event?” The “what” is quick to answer; the “why” takes a bit longer, but isn’t hard to understand.

During a transit of Mercury, we see Mercury’s silhouette pass across the face of the Sun. It’s very much the same idea as a solar eclipse (when the Moon passes in front of the Sun), except that Mercury is so much farther away that it hardly covers the solar disk—all we see (through a telescope set up for safe solar viewing) is the planet’s “little black dot” move across the Sun over several hours.

If we could watch this event while looking down from a vantage high above our solar system, we’d see Mercury, the Earth, and the Sun arranged in a fairly straight line, with Mercury between the Earth and Sun (see Chart 1, below). Continue reading “The Mercury Transit Explained”

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Brilliant ISS Pass over Denver, 10-8-19!

Chart of ISS path across Denver, Colorado sky, 7:30 PM, 10-8-19
Chart of International Space Station (ISS) pass through Denver, Colorado’s local sky on Tuesday, 10-8-19. The ISS will be directly overhead around 7:34 PM. Click on image to enlarge. (Image plotted in SkySafari, and optimized in Photoshop.)

If you’re in the Denver area Tuesday, October 8, 2019, get outside and look for the International Space Station (ISS) just after 7:30 PM. We’ll have a brilliant, close pass as the ISS flies almost directly overhead, about 250 miles above us.

The space station will rise in our northwest at 7:29, becoming visible shortly after. It gains height above our horizon slowly at first, appearing just 14° up at 7:32, Continue reading “Brilliant ISS Pass over Denver, 10-8-19!”

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Looking for the “Monthly Skies”?

If you’ve been reading my monthly column here for the last year, or for the last several years on the Denver Astronomical Society’s site, you might have noticed that I’ve taken a break…

Don’t worry–while the planets move across the sky from week to week, the stars keep more or less the same positions from each other year after year (you’d need some expensive astronomical instruments to tell the difference). That means that if you’re looking for good targets in August (or September, or October…), you can hit the Astronomical Society’s archived pages.

You’ll find four years of columns, from 2015 to 2019, so there will be four “Augusts” for you to peruse (and of course, four Septembers, and so on…). There’s enough material there for a book. (As it happens, I’m working on that right now!)

The archived PDF files from 2015 to the end of 2018 are linked HERE.

More recent, WordPress-based articles, from January 2019 to May 2019, are HERE. (I recently edited noted astronomy writer Jeff Kanipe’s article on observing in the Southern Hemisphere, “Five Nights in the Magellanic Clouds,” and you’ll find that there, too!)

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March Skies 2019

by Zachary Singer

In March, we have a relatively quiet month for planets: Most of them are now early-morning objects, but they are at a greater angle from the Sun, allowing better observing. In the “Stars and Deep Sky” section, we’ll look at two stars in the constellation Cancer—the first is a wonderful binary, and the other, a lesser-known carbon star.

Continue reading “March Skies 2019”