Mercury —  the innermost planet in our solar system —  crossed the sun’s path on Nov. 11, a rare celestial event. This occurrence won’t happen again until 2032.

Students, staff and the surrounding University of New Mexico community gathered at the University Campus Observatory Monday morning to witness the event.

Although the time between Mercury's transits across the sun varies, it only happens 13 times in a century, according to the Jet Propulsion Laboratory at NASA. Mercury is only 1/194 the size of the sun when observed from Earth. Observers need binoculars or a telescope with a certified sun filter to see it.



Mercury’s journey across the sun was a five and a half hour event, starting at 5:36 a.m. Mountain time and ending at 11:04 a.m., according to EarthSky.

Ylva Pihlström, the director of the Campus Observatory, said Mercury has an inferior orbit to Earth, meaning the angle of its rotation around the sun varies by several degrees compared to Earth’s degree variation.

"Mercury’s orbit is every 88 days, so one could imagine that this would happen more often, but it doesn’t do that because of the plane of the orbit that Mercury has. (Mercury) has an inclination of seven degrees to Earth's orbit," Pihlström said. "So sometimes when Mercury should pass in front of the sun, it is actually above or below the sun."

Venus’s orbit also transits the sun —  an event even rarer. The last time this happened was June 5, 2012, and it won't happen again until Dec. 11, 2117, according to Space.com.

Pihlström said the transit of Mercury and Venus helps prove the heliocentric model of the Solar System, as well as calculating the size of the Solar System. Using basic trigonometry, Pihlström said the distance between the Earth and Mercury can be calculated, giving astronomers an absolute scale of the Solar System.

Dilys Ruan, a senior in the physics and astronomy program, said the telescope that the UNM Observatory uses tracks with the celestial sphere. This means they use celestial coordinates, rather than what they have locally. This makes the telescope much more accurate, Ruan said.

The lense on the telescope has a neutral density filter, which makes the sun less bright and doesn’t burn people’s eyes.

"With this new telescope, we can see so many more new things, or at least it’s much better resolution than we had before, so we’re lucky to have it," Ruan said.

Whenever there is a special event, like the transit of Mercury, the Campus Observatory is open to the public for viewing. Pihlström said the next big event will be an annular solar eclipse, when the moon passes in front of the Sun, on Oct. 14, 2023.

The Observatory is also open to the public every Friday night from 7 p.m. to 9 p.m., weather permitting.

Caitlin Scott contributed writing and reporting to this article.

Amanda Britt is the photo editor at the Daily Lobo. She can be contacted at photo@dailylobo.com or on Twitter @AmandaBritt__