Thinking Outside the Classroom: The transit of Mercury |

Thinking Outside the Classroom: The transit of Mercury

By Astro Mark Laurin
Thinking Outside the Classroom

The Earth’s orbit around the sun is what gives us our four seasons, some longer than others. It’s also what gives us an ever-changing night- and daytime sky. At Keystone Science School, we often use the ever-changing night sky to teach about Earth and space science. We don’t just teach facts about the night sky but encourage our students to be curious learners. We want each student to look up and wonder. The night sky can be enjoyed with high powered telescopes, simple tools such as a pair of binoculars or even the naked eye.

Astronomical events are often thought to be enjoyed at night, but that’s not always the case. The rising and setting sun is an awe inspiring astronomical event, but there are other events that are viewable during the day. One such event, the transit of Mercury, can be viewed from 6:43-11:02 a.m. Monday, Nov. 11.

What is the transit of Mercury?

Every so often, a planet (or a moon of a planet) lines up in a way that blocks out part of the sun’s rays from reaching Earth. This is called a transit. A planetary transit happens when one planet crosses the face of its star and aligns with another planet as it passes through an orbital intersection. For us here on Earth, our solar system’s two innermost planets — Mercury and Venus, which reside between us and the sun — are planets we can see transit the sun. If you lived on one of our outer planets, (Mars, Jupiter, Saturn, Uranus or Neptune), you could see a transit of Earth across the sun.

Transits of Mercury happen at regular intervals about 13 times a century. Currently, those alignments occur only within a few days of May 8 and Nov. 10. The May transit is when Mercury is farthest from the sun, known as aphelion, and the November transit is when it is closest to the sun, known as perihelion. The transits of Mercury are gradually shifting to later in the year. Centuries ago, Mercury’s transits were in April and October, but the opportunity to see a transit of Mercury will always be six months apart. The November transit is important and special as it is the last one visible from the Americas until 2032.

How to view the transit of Mercury

The first thing to know is that you should never look directly at the sun with the naked eye. You should only attempt to view the transit using special solar filters on glasses, telescopes or binoculars. Attempting to view the transit without proper filters can cause permanent vision damage.

If you still have the eclipse glasses you used in August 2017, give them a try. It’s doable, but realize that without magnification, Mercury is going to be quite small and hard to see. A white light filter is the cheapest option to turn your existing telescope into a solar telescope. If you want to get more sophisticated, hydrogen-alpha telescopes are made for solar observing. Those telescopes excel at viewing the chromosphere, solar flares, prominences and transits.

  • 6:43 a.m. For residents in Summit County, the transit already will be happening at sunrise. Since the sun is near the horizon at this time, it’s best at a high point or an unobstructed area with free sight to the east-southeast
  • 8:20 a.m. Mercury is closest to the center of the sun as seen from Summit County.
  • 11:02 am. Mercury is starting to leave the sun’s edge. Watch for the “black drop effect,” which is an optical illusion that appears to connect Mercury’s disc to the sun’s edge.
  • 11:04 am. Mercury leaves the sun’s edge and concludes the transit.

You can also view the transit of Mercury from 8-10 a.m. Monday at the Frisco Marina with Keystone Science School. There will be a collection of solar telescopes along with staff members and volunteers to help attendees understand the transit of Mercury.

Astro Mark Laurin is a Keystone Science School volunteer.

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