Oranges and Distance and the Transit of Venus

Venus is said to be our sister planet: about the same size, mass and density as Earth; and just 30% closer to the sun. Venus has an atmosphere filled with CO2, and, because of the heat trapping properties of this greenhouse gas, averages over 400 degrees C on a good day – hotter than Mercury, which is closer to the sun…. I’d still go … to either. Anyway: the Transit of Venus is a rare astronomical event. It happens in pairs: there was one in 2004 and 2012 and the last pairing was in 1874 and 1882. Historically, we measured the size of our solar system by observing this and similar events. Now, we have the Hubble Space Telescope, the Kelper Spacecraft  and others to get similar and other interesting measurements. The Transit of Venus won’t happen again until 2117. On June 5, 2012, Venus crossed between us and the sun. Something the whole world could marvel in. I went to witness.

Samuel Nigro

Samuel Nigro

Samuel Nigro

Transit of Venus

Transit of Venus

This was an exciting event and got me to think about many things. Too many for a single post. However, I will elaborate on the issue of distance.  The simplest analogy of the vastness of our solar system and the universe that I have come across was stated by Sir Martin Rees in his book  Just Six Numbers, p. 81-82

Suppose our star, the Sun, were modeled by an orange. The Earth would be a millimeter-sized grain twenty meters (65 feet!) away, orbiting around it. Depicted to the same scale, the nearest stars would be 10,000 kilometers away (about 6,214 miles!): that is how thinly spread matter is in a galaxy like ours.

Try to visualize that one: Earth, Sun, the next closest Star; a grain of sand, 65 feet, over 6,0oo miles! He goes on, but … You know what? I’m gonna give you the rest of the quote, because it blows me away even though I have a difficult time imagining it. It has to do with understanding why the universe’s expansion is not slowing down because of gravity, like we initially thought, but expanding. I this. Have fun, or just skip to the end:

But galaxies are, of course, especially high concentrations of stars. If all  the stars from all of the galaxies were dispersed through intergalactic space, then each star would be several hundred times further from its nearest neighbor than it actually is within a typical galaxy – in our scale model, each orange would be millions of  kilometers from its nearest neighbor. If all the stars were dismantled and their atoms spread uniformly through our universe, we’d end up with just one atom in every ten cubic meters. There is about as much again (but seemingly no more) in the form of diffuse gas between the galaxies. That’s a total of 0.2 atoms per cubic meter, twenty-five times less than the critical density of five atoms per cubic meter that would be needed for gravity to bring cosmic expansion to a halt.

OK: Vast, Huge stuff.

The other major issue that I though about
when viewing the Tranist of Venus is
The Iconic Geometry of the Circle.
That’s for a future post.

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Filed under Astronomy, Story

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