Red alert — lunar eclipse may be colorful

A dramatic eclipse of the harvest moon is coming Sunday evening, and as it rises in the eastern sky fully darkened by Earth’s shadow, it may take on colorful hues — perhaps as deep as coppery red.

It will be the last in a rare series of four total lunar eclipses — a tetrad, astronomers call it — that began with the first one on April 14 last year.

If skies are clear, Sunday’s eclipse will be easily visible to Bay Area viewers, and total eclipse will come early enough so that even the kids can stay up to watch it.

The moon will rise in near total eclipse at 6:57 p.m., will be fully darkened at 7:11 and remain

visible in that state for an hour and 12 minutes — until 8:23 p.m.

To celebrate the ending of the tetrad, the San Francisco Amateur Astronomers will hold a public viewing party, starting before dark Sunday evening, at the end of Pier 15 on the Embarcadero, in the pier’s public access area next to the Exploratorium.

There the sky gazers will have set up an assortment of telescopes for anyone who wants to see the eclipsed moon’s surface in clear detail.

The local astronomers will fold up their telescopes at 9 p.m.

Total eclipses of the moon occur when the sun, Earth and the full moon form a nearperfect lineup in space so that Earth’s shadow falls completely on the moon’s face.

“It’s a nicely democratic event because no special equipment is needed to see it, plus this year it’s nicely in the early evening,” said Andrew Fraknoi, chairman of astronomy at Foothill College in Los Altos Hills.

Fraknoi offered this advice: “This eclipse will start very low in the eastern sky, so make sure your observing location has a really unobstructed view toward the eastern horizon.”

Because the moon is full this late summer season, it’s often called a harvest moon, and because its orbit carries it a bit closer than usual to Earth, some observers are calling it a super-moon. But that just makes the full orb appear about 14 percent larger than normal — nothing ordinary observers would notice, Fraknoi said.

Although the path and timing of eclipses are predictable, what can’t be predicted is the color that the moon’s face will show during totality. The sun will be shining through a small edge of the Earth’s atmosphere, and that faint light will still reach the shadowed moon, Fraknoi said.

Its color will depend on the gases in the earthly atmosphere, influenced by pollution levels or high clouds or volcanic dust from eruptions anywhere in the world. The color shining on the face of the eclipsed moon Sunday could range from yellow to orange to red or copper to black.

NASA’s eclipse tables say the next tetrad of lunar eclipses won’t start until 2032.