Facts about Venus Transit
A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and Earth, becoming visible against (and hence obscuring a small portion of) the solar disk.
Is this rare?
Transits of Venus are among the rarest of predictable astronomical phenomena. They occur in a pattern that repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 years and 105.5 years.
When does it start? End?
In northern California, the 2012 transit starts at 3:06pm
There are five important moments of time related to the transit.
Ingress Exterior: 3:06pm This is the moment the edge of Venus touches the edge of the Sun. The transit begins.
Ingress Interior: 3:24pm This is the moment the entire disc of Venus is within the disc of the Sun.
Transit Center: 6:27pm This is the halfway point in the transit across the surface of the Sun.
Egress Interior: 9:29pm This is the moment the disc of Venus touches the edge of the Sun.
Egress Exterior: 9:47pm This is the moment the edge of Venus stops appearing on the disc of the Sun. The transit is complete.
It will be barely noticeable until 3:10 and is easily recognizable after 3:25. The transit ends after sunset so we won't see egress.
How big are Venus and the Sun compared to Earth?
The diameter of the Sun: 1,391,000 km
The diameter of Venus: 12,103 km
The diameter of Earth: 12,756 km
The Sun is 115 times the diameter of Venus.
The mass of the Sun is 409,000 times the mass of the Venus.
The Sun is 109 times the diameter of the Earth.
The mass of the Sun is 333,000 times the mass of the Earth.
The Sun is huge! To get an idea, imagine it's the size of an exercise ball, about 650mm. Venus and the Earth are almost the same size. Compared to the Sun, they are the size of a 6mm ball bearing.
How far away are Venus and the Sun?
The average distance from the Venus to the Sun is 108 million km (~.72AU).
The average distance from the Earth to the Sun is 150 million km (1AU).
Venus is about 42 million km from the Earth during the transit.
The distances in space are enormous! If the Sun is the size of an exercise ball, on the day of the transit Venus would be 31 steps from Earth and the Sun would be 93 steps from Earth.
Enjoy the Transit of Venus!
Clear skies and warm toes!