Astronomy

An arcsecond is a measure of apparent size from your perspective point. A very large object that is far away might appear the same size as a close object that is smaller, and in this case, their width measured in arcseconds would be equal.

1 arc second is 1/60th of an arc minute (just like a second is 1/60th of a minute), and an arc minute (which is the same as minute of arc, abbreviated to MOA) is simply 1/60th of a degree. So an arc second is 1/3600th of a degree.

Incidentally the combined accuracy & precision of firearms is also expressed in terms of MOA. If a firearm is rated to be "1 MOA" it means that, if you fire 10 shots at a target 100 meters away, the grouping will have a maximum distance of 1 inches from the intended target.

Actually that's technically wrong, it would have a maximum distance of 1.1452 inches, because if you use trig you will see that is tan(1/60)*100 converted into inches.

I think Mars was at its closest to Earth around that time in 2005! Looking at Mars its getting alot smaller now, its currently 3.6 arc seconds ( a sixtith of a sixtith of a degree). Versus say Jupiter which is 33.2 arc seconds on the 15 Septenber.

Mars actually reached its closest point in 2003, but the email announcing it is still circling the internet (I got it again this year because too many people forward stuff without verifying it). Here is a picture: Hubble image of Mars, August 2003

Here is an explanation of magnitude, in case you still want to do a unit on astronomy.

Yep, my parents sent me the same email back in July.

Re: Astronomy




Mars and earth pass by each other roughly every two years.

Because the orbits are not perfectly circular however, the closeness of the passage also varies each time. In 2003 it was much much much closer than average. I think we were closer than average in 2005, but nothing like it was in 2003.


Magnitude is how bright something looks in the sky. The lower the number, the brighter it is. -2.9 is the near the brightest Mars can possibly get, so I'd guess you saw something from a 2003 news release.

Arc seconds are a measurement of a fraction of a circle. You probably know there are 360 degrees in a circle. Arc seconds are just fractions of a degree. What they were referring to was how much of the sky the disc of Mars actually covered at that time.

Re: Astronomy
This graphic shows the positions in their orbits for recent oppositions:



The pictures of Mars for each opposition are scaled to show how its apparent size differed each time.

You can see how 2003 looks larger than the others.