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New Mexico State University

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NMSU to host viewing event of rare transit of Venus, June 5

Just on the heels of the visually stunning "ring of fire" solar eclipse, another rare, astronomical phenomena is about to occur; on June 5, a dark circular shape will move across the sun in what is known as a transit of Venus. This event will not happen again until 2117.


The New Mexico State University Department of Astronomy will host an event to view the transit of Venus from 5-8 p.m. on June 5, at the Mesilla Valley Mall in Las Cruces. Astronomers will be set up in the parking lot in the southwest corner of the mall, near the recycling bins. The department will have several telescopes equipped with solar filters to enable the public to safely view the event.

"We want to encourage the public to stop by and take a look through our telescopes so they can view this rare event, but we also want to emphasize that this will be a less visually dramatic event than the solar eclipse that took place on May 20," said Nancy Chanover, an associate professor of astronomy at NMSU. "Venus will appear as a very small black dot that slowly makes its way across the disk of the sun."

The transit will still be going on when the sun sets and will be visible across the United States.

The orbit of Venus is inclined, or tilted, by several degrees relative to Earth's orbit, Chanover said. This means that when Venus passes between the Earth and the sun (which takes place every 584 days), it usually does not result in a transit because Venus is usually slightly above or below the sun as seen from Earth.

Venus transits occur at regular intervals of eight, 105.5, eight, and 121.5 years. The last one occurred in 2004.

"Since the advent of the telescope in 1610, there have only been seven transits," Chanover said. "The next Venus transit, which will occur on June 5, will be the last opportunity to see a Venus transit in our lifetimes."

Besides being a visual experience, Venus transits played an important role historically by giving astronomers a way to calculate the size of the solar system, Chanover said. By observing a transit from two widely separated locations on Earth, timing how long it took Venus to cross the disk of the sun, and using trigonometry, the Earth-to-sun distance can be calculated. Early observations of a Venus transit revealed that Venus had a "halo" around it, which turned out to be the first indication that Venus is surrounded by a thick atmosphere.

Today, the Earth-sun distance is known very accurately and there are spacecraft that have observed Venus' atmosphere up close. However, a Venus transit is still of great interest to astronomers because currently, this same technique of observing transits is being used to discover planets around other stars. By watching how much a star's light "dims" as a planet transits in front of it, astronomers have been able to discover many planets in other solar systems.

"The general public will have the opportunity to view this rare event and appreciate this special alignment of the Earth and Venus," Chanover said.

On June 5, NMSU astronomers will have special hand-held solar viewers and glasses for people to use or purchase at the mall. They will be sold for $1 each, and will be sold on a first-come, first-serve basis starting at 5 p.m. No more than five pairs will be sold per person.

It is not safe to stare directly at the sun and could cause lifelong damage to eyes. NMSU astronomers caution that regular sunglasses do not provide adequate protection to look safely at the sun.

People can safely view the Venus transit by looking at the sun through a piece of welder's glass but, it has to be number 14 or higher, Chanover said. Anything less than 14 is not safe to view the sun through. You can also make a pinhole projector by poking a small hole through a piece of cardboard and projecting an image of the sun through the pinhole onto the sidewalk or another piece of paper.

Both of these options do not provide any magnification, so Venus will barely be visible as a tiny black dot against the disk of the sun. If you do not have appropriate eyewear, the best way to view the event is through a telescope, said Chanover.

For more information on the transit of Venus event, contact the Department of Astronomy at 575-646-2567.