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Short Essays

Another Earth

Blue Shift

Bright Star

Star Distance

Proper Motion

Earth Daze


Farthest Naked Eye Object

Faster Than Light

Time Travel

More Time Travel

Visible Planets

Loose Ends

Maintained by suitti@uitti.net, Stephen Uitti
At my astronomy club, it was suggested that we have some astronomy trivia prepared, in case a talk finished early. It hasn't happened yet, and seems unlikely. I have this game, Good Heavens, which is an astronomy trivia game. One of the cards asked, how far away is the nearest star to the Earth? Immediately, I thought of Proxima Centauri, thinking about light years. I looked at the answers, and was stunned. 93,000,000 miles. Of course, they meant the Sun. Doh!

President Bush, like his father, has proposed that the US embark on a mission to Mars. Since then I've at least twice heard people state that Mars is the closest planet to the Earth. Even the other year when Mars had it's closest opposition in over 70,000 years, Venus gets much closer.

I've also heard it said that Pluto is so far away that the Sun would just look like a bright star from there. The math suggests otherwise.

The average distance from Pluto to the Sun is 39.5 AU, or 39.5 times farther than the Sun is to the Earth.

Due to the inverse square law of light, the Sun is 1/(39.5 * 39.5) as bright from Pluto as from the Earth. That makes it 1/1560.25 as bright.

A magnitude is a measure of brightness. Negative numbers are brighter, positive numbers are dimmer. A magnitude is the 5th root of 100, or about 2.512. A star that is one magnitude brighter than another shines about 2.512 times as much energy. 1,560.25 times as dim in magnitudes is ln(1560.25) / ln(2.512) = about 8 magnitudes.

The Sun's apparent brightness is about -26.75 from the Earth. So, the Sun should be about magnitude -18.75 from Pluto. Now, the Moon's apparent brightness, when full, is about -12.6. So, the Sun, from Pluto, is about 6 magnitudes brighter than the full moon - or about 250 times brighter. For me, anything brighter than the Moon, which is visible during the day most of the time, fails any comparison to a star I might make. (And yet, this is a discussion about looking at a star.)

It has been suggested that the Sun would blind you from Pluto. For one thing, the ultraviolet rays would likely make it to the surface of Pluto with minimal interference from Pluto's thin atmosphere. Sure, it would take longer to be blinded than from Earth, but it seems likely, for the persistent. This might include most people making the attempt. It's going to take some mighty patient people to make it out to Pluto.

The Hubble Space Telescope observations show that Charon is bluer than Pluto. How do we cheer it up?