By Edwin Vega
For the Fort Bend Star
On Aug. 21, 2017, more than 300 million people in the United States could potentially view a total solar eclipse.
A partial eclipse will be visible in every state, however, a total solar eclipse – which is when the moon completely covers the sun – will occur across 14 states in the continental United States along a 70-mile-wide portion of the country.
The total solar eclipse will occur near Lincoln City, Ore., at 10:15 a.m. PDT, 1:15 p.m. EDT. Totality ends at 2:48 p.m. EDT near Charleston, S.C. The partial eclipse will start earlier and end later; however, the total eclipse itself will take about one hour and 40 minutes to cross the United States.
“Total solar eclipses offer scientists the rare opportunity to observe and study the outer atmosphere of the sun, or corona,” said Andy Shaner, of the Lunar and Planetary Institute. “Studying the sun’s corona is important because the corona is the scene of explosive, high-energy events, such as solar flares and coronal mass ejections (CMEs). When released from the sun, CMEs and solar flares affect the entire solar system including the Earth. These phenomena can, and have, caused major disruptions to spacecraft in Earth orbit and power grids on the ground.”
“They’re interesting because total solar eclipses don’t happen that often and it’s a neat phenomenon that people can see once in a while,” said Van Eric Mayes, of the college of science and engineering at the University of Houston-Clear Lake.
Calculating solar eclipses can be done using Besselian elements, which are a set of values used to calculate and predict the local circumstances of occultation for an observer on earth.
The basic idea is to compute the motion of the moon’s shadow on a plane that crosses the earth’s center. Then, the shadow cone of the moon can be projected on the earth surface.
“You have to be able to calculate when the moon is going to be directly in front of the sun,” Mayes said. “The plane that the moon orbits in is actually inclined at a five-degree angle to the plane the earth’s orbit around the sun is in, meaning eclipses only happen when the two planes intersect and that only happens once in a while. If they were orbiting in the same plane, they would be happening all the time, like once a month.”
The sun’s diameter is 400 times wider than the moon’s, but it is also 400 times farther away. The result is that the sun and the moon appear to be the same size from the perspective on earth. When they line up perfectly, the moon can conceal the sun’s entire surface, creating a total solar eclipse. This line-up occurs once every 12 to 18 months. Partial solar eclipses, on the other hand, occur when the alignment is such that the moon blocks only part of the sun and these can occur more frequently.
“Other factors that you have to take into account are the fact that the orbits are elliptical, not circles,” Mayes said. “So for the moon to block out the sun, the apparent size has to be same as the sun in the sky and so if it’s further away, it doesn’t quite block the sun entirely. This is called an annular eclipse.”
Compared to a total eclipse, in an annular eclipse, the moon is further away from the earth. This gives the appearance of the moon being smaller in the sky; however, it does not completely cover the sun.
Viewing an eclipse without using proper equipment can be hazardous to the eyes; therefore, it’s important to take viewing safety tips into consideration.
It is dangerous to stare directly at the sun with your naked eyes because there is a high risk of permanent vision damage; however, with special-purpose solar filters, such as eclipse glasses or a handheld solar viewer, you can safely look directly at the sun.
“Never look directly at the sun,” said Shaner. “If they are made available at an event near you, use special eclipse viewers or observe the eclipse through a telescope that utilizes a proper solar filter. If you are unsure about the safety of a certain product, always be cautious and reach out to an expert. Chances are, there is an amateur astronomy club in your area you can contact. Number two, because the eclipse this year is in August, please also make sure you take the proper precautions to stay hydrated and avoid sunburns.”
Eclipse viewing glasses and handheld solar viewers should meet all the following criteria: Have certification information with a designated ISO 12312-2 international standard, have the manufacturer’s name and address printed somewhere on the product, not be used if they are older than three years, or have scratched or wrinkled lenses, and not use homemade filters, or be substituted for ordinary sunglasses, not even very dark ones because they are not safe for looking directly at the sun.
An alternative method for safe viewing of the eclipse is with a pinhole projector. With this method, sunlight streams through a small hole, such as a pencil hole in a piece of paper, or even the space between your fingers onto a makeshift screen, such as a piece of paper or the ground. It’s important to only watch the screen, not the sun. Never look at the sun through the pinhole.
The Lunar Planetary Institute will be helping Houstonians witness this historical event by providing viewing glasses at two locations, Levy Park and Clear Lake City-County Freeman Branch Library. Scientists and educators will be at both locations on Aug. 21, from noon to 2 p.m.
The general public will also have the opportunity to view the eclipse at the Houston Museum of Natural Science, where volunteers will be setting up solar telescopes at both campuses in Hermann Park and in Sugar Land. Each telescope will be filtered to offer a safe view of the sun.
The Burke Baker Planetarium will offer a special schedule on Aug. 21, featuring six 15-minute shows about the eclipse. These will run at noon, 12:20 p.m., 12:40 p.m., 1 p.m., 1:20 p.m., and 1:40 p.m. Tickets are $4.
Brazos Bend State Park will offer a viewing program at 12:45 p.m. at the Nature Center, but the George Observatory located within the park belonging to the Houston Museum of Natural Science will not be open.