Today's full moon is expected to be the largest and brightest in almost 20 years, said an astronomer with the Chabot Space & Science Center.
The moon will be about 15 percent bigger and brighter than most full moons because it will be about 50,000 miles closer than its farthest point, said astronomer Ben Burress.
The moon has an elliptical orbit around Earth and comes into perigee -- the part of its orbit closest to the planet -- every month. It only reaches that point as a full moon once every 18 years or so, Burress said.
A full moon at perigee is often called a supermoon, and Burress said the last one was visible in 1993.
The National Weather Service said today's forecast is mostly cloudy, but Chabot will host a free telescope viewing if it's clear.
The science center is open on Friday and Saturday nights and holds telescope viewings from 7:30 p.m. to 10:30 p.m. when conditions are favorable.
Burress said the best time to view the moon is during its rise at sunset.
An optical illusion tricks most people into thinking the moon is larger when it's lower in the sky, he said.
Burress said the supermoon was only expected to raise tides by about an inch.
The moon is typically about 240,000 miles from Earth, he said.
Bay City News