Peninsula residents will have the chance to see Venus travel in front of the sun on Tuesday, June 5 -- an event that won't occur again for more than 100 years.
The observatory is open to the public while Foothills Park is open to Palo Alto residents only.
People should only look at the sun using filters specifically designed for that purpose, and both viewing sites will have telescopes with white light and hydrogen alpha filters that allow for direct viewing of the sun.
Peninsula Astronomical Society board member William Phelps said Venus will look like a tiny black disc traveling across the sun.
Phelps will be at Vista Hill with his homemade hydrogen-alpha telescope, which is two meters long and weighs almost 400 pounds. Hydrogen-alpha telescopes view a very narrow portion of the light spectrum and allow people to see the chromosphere, the outermost layer of the sun where solar prominences and flares occur.
In a prominence, solar material leaves the sun's surface and returns, while flares eject material out into space.
"Sometimes it's a little scary ... because of the scale," Phelps said. "They're massive, huge amounts of energy. We've had several magnetic pulses from the sun shut down power grids."
According to the Peninsula Astronomical Society's website, astronomers in previous centuries used transits to help them calculate the distances between the sun and the Earth, known as Astronomical Units.
Pairs of Transits of Venus occur approximately every 100 years, with eight years separating the first and second events of the pair.
According to NASA's website, this transit will be viewable from all of North America.
But the last transit in 2004 wasn't visible on the West Coast, so Phelps traveled to the eastern tip of Long Island to view the event with other astronomers and astronomy enthusiasts.
"I got the prize for ... traveling the furthest," he said.
NASA will also be presenting a live webcast of the event.
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