Mar. 13 -- Look west and see the sun set. Look east, the full moon rises.
Seeing this phenomenon is impressive, but not unique, according to the Journal's astronomy expert, Kevin McKeown. In April, September, October and December a supermoon offers up the next easy chances. Stay tuned to the end to understand why.
The eastern plains of New Mexico, where it is so flat that you can almost see the back of your head when you stare into the distance, is the perfect place to experience this event, as is west Texas just east of Muleshoe National Wildlife Refuge, where we experienced it in 2019. Or Chaco Canyon National Historical Park.
Full moon was reached at about 10 p.m. March 20, 2019. There was no lunar eclipse.
Astronomical events are based on the actual positions of the sun and moon in the sky. The spring equinox is the precise moment the sun crosses the celestial equator, heading north.
"Nothing rare about seeing a full moon (full on the same day) rising in the east, with the sun setting in the west," says McKeown, who writes the daily Sky Watch column on the Journal weather page.
"Two things facilitated your very nice photos: First, the moon was nearing its major lunar standstill (December 2024), and running high. This placed the moon about 3 degrees north of the anti-solar point on the ecliptic. Secondly, atmospheric refraction was working for you. This 'lifts' both the sun and moon higher up above the horizon.
"Now, a lunar eclipse occurring at the exact time of the equinox will rise just as the sun sets," McKeown said. "It must be a partial eclipse to see this, since it's a difficult, but dramatic observation."
On, March 20, 2019, the sun crossed the equator. This is the vernal equinox, the intersection of the ecliptic and the equator. Four hours later, the Worm Moon was exactly full. But since the full moon was running high along this stretch of the ecliptic, sunset and moonrise were visible at once. As you watched the moon rise, the sun illuminated your back.
The Chacoans understood the phenomenon of major and minor lunar standstills, which are caused by the 5.2 degree inclination of the moon's orbit to the ecliptic. Major lunar standstills occur every 19 years.
"At the time of the vernal equinox, the sun's motion northward is at its greatest pace," he said. "You'll notice how fast days get longer."
Note: a very clean horizon is needed to see these sunset-moonrise events.
Be like the people of Chaco Canyon and look up and appreciate the sky.