On Sunday, the moon will be completely obscured by the earth’s shadow making a total lunar eclipse.
On Sunday the moon will become rusty red as a lunar eclipse occurs over several hours. The peak viewing time is 11:11 p.m., according to NASA. Credit: NASA Ames Research Center / Public Domain

San Antonians may get a chance to see a blood moon this weekend, weather permitting.

If the sky is clear, those looking into the night sky Sunday evening will be able to see a total lunar eclipse, which will color the moon from its usual white to a rusty reddish hue.

While blood moon is a common term, there are other names for it. NASA writes in its May-June full moon guide that the Maine Farmer’s Almanac began, in the 1930s, to publish Native American names for the full moons of the year. According to this almanac, the Algonquin tribes called this the Flower Moon for the flowers that are abundant this time of year.

The eclipse starts at 8:32 p.m. Sunday and lasts until about 1:50 a.m. Monday, reaching peak viewing time at 11:11 p.m. Sunday, according to NASA’s website. Folks can watch from their yards, or join a viewing party to view the eclipse through a telescope. NASA will also stream the eclipse on its YouTube channel.

A total lunar eclipse takes place when the earth passes directly between the sun and the moon, casting the earth’s shadow onto the moon, said Angela Speck, professor of astrophysics and the chair of the Department of Physics and Astronomy at the University of Texas at San Antonio.

As the earth’s shadow moves into place over the full moon, it appears as if the moon has had a bite taken out of it, Speck said. During this process, the moon still looks white.

“That’s one of the reasons we’ve known the earth is round for a really long time,” Speck said. “But as the moon gets completely eclipsed, we see it’s basically the light that is passing through the earth’s atmosphere.”

Once the moon is completely in shadow the sun’s light bends around the earth and reflects off the moon’s surface, then bounces back, visible to those on the planet’s night side. The reflected light refracts through the earth’s atmosphere like a prism, and gives the moon a reddish coloring, Speck explained.

“You’re only seeing the sunlight that’s going to the edges of the earth,” she said. “Most of the solid earth is in the way of the light … so you’re basically seeing the light of gray every sunset and sunrise on the planet, reflected off the moon.”

While about two solar and two lunar eclipses take place every year, not everyone is in the right place on the planet to view each one, Speck said. So while the U.S. will get to witness the lunar eclipse this weekend, half the world won’t, because it will be daytime, Speck said.

While a solar eclipse, such as the partial one San Antonio saw in 2017 or the total one that parts of San Antonio could see in 2024, cannot be stared at directly due to the strength of the sun’s rays (which can cause eye damage), lunar eclipses are safe to look at directly since they are a reflection of the sun’s light.

Speck said she encourages everyone to experience eclipses when they can, especially if they’ve never seen one before, because “it’s really cool.”

For those interested in watching the event and learning more about eclipses among fellow amateur astronomers, both the Scobee Education Center at San Antonio College and the Curtis Vaughan Jr. Observatory at the University of Texas at San Antonio will be hosting watch parties.

The Curtis Vaughan Jr. Observatory’s viewing party will take place at 8 p.m. Sunday at McAllister Park, and the Scobee Education Center’s will begin at 7:30 p.m. on the rooftop of SAC’s Parking Garage 1. Parking at SAC will be available at parking lot number 16, next to the parking garage and on lower garage levels. 

Danielle Rappaport, a local astronomer and outreach programs coordinator for the San Antonio Astronomical Association, said she and other members of the association are very excited to bring their telescopes out to the viewing at SAC so people will be able to get a closer look at the rare sight.

“You won’t need a telescope to be able to see it and enjoy it, but it’s definitely cool to see it up close with one,” Rappaport said.

Lindsey Carnett

Lindsey Carnett is the Science & Utilities reporter for the San Antonio Report.