Sadistic nerd humor

My sister forwarded this email to me...

"First time in recorded history that Mars will be this close! It will be centurys before this happens again, so make sure your kids don't miss it! (Would make a great school project for later years!) It will rise in the East and will appear as large as the moon. Note or photograph any color and size changes.

Brent,
Any truth to this?"

This was my response...

"Yes and no.

Every 26 months, Earth passes Mars, so every 26 months we get close - a point in time called "opposition", when Mars is closest to Earth and opposite the Sun in the sky. Typically it's about 50-60 million miles away at opposition.

All plants have an elliptical (not circular) orbit, and "perihelion" refers to that point in the orbit when a planet is closest to the sun. Every 15 years or so, Mars and Earth meet in a "perihelic opposition" that brings us much closer than average. These always happen between July and September.

In August of 2003, we had a perihelic opposition that brought us to within 35 million miles of Mars. This was the closest such encounter in thousands of years, and while Mars wasn't as big as the moon, in a telescope it was much larger - about 25 arcseconds (an arcsecond is a unit of measurement for objects in the sky; the full moon is typically 1800 arcseconds in diameter) - than it has been during a typical opposition.

This particular email is probably left over from that event. These things tend to have a life of their own.

The next opposition with Mars - in January 2010 - will be an "aphelic opposition". Aphelion is the opposite of perihelion, i.e., the planet is furthest from the sun. So, Mars will be considerably smaller when viewed through a telescope - about 14.1 arcseconds.

No, I didn't have all of this off the top of my head, but I did know what I was looking for; a few minutes with Google helped with the details.

Feel free to send this explanation back to the source. This particular email was innocuous enough, but I'd hate to think that someone would be standing outside at night expecting Mars to rise like the moon.

Then again, you could always keep this to yourself and let them believe it's true. Think of it as sadistic nerd humor.

;-)

Brent"