[petuniasevan]

Vacation Announcement

I will be on vacation from June 2nd through June 9th.
If anyone would like to volunteer to post APOD during that time, please FReepmail me.
Otherwise the APOD will not be posted as I will be visiting relatives in California.

On the night of August 26-27, Mars will be close to Earth. The centers of the two planets will then be only 55.758 million kilometers (34.646 million miles) apart. At that time Mars will shine at magnitude -2.9 in the constellation Aquarius. You can't miss it. The only bright star in that area is Fomalhaut at magnitude 1.15.

Right now Mars is in Capricorn at magnitude 0 (about as bright as the star Vega). Look to the southeast in the wee hours of the morning for a reddish non-twinkling "star".

Notice that the planets don't twinkle? That's because they are not "point sources" as stars are; rather they are visually "disks". For instance, Mars right now has an angular size of 10 seconds of arc. For comparison, the Moon subtends an angle of 30 minutes of arc. The planets' apparent size cancels out Earth's atmospheric effect on point source images. For an overview of the "twinkling" phenomenon, see the 25 July 2000 APOD

[petuniasevan]

[MikeD]

For those of you who don't want to do the math, that means that the Moon is 180 times wider in the sky than Mars.

MD

[xJones]

Warmer temperatures and a higher surface pressure once made it possible for liquid water to exist on the surface of Mars. When the water existed and where it went are just two of the questions being studied today.

Okay, why did Mars cool off and lose surface pressure? Was that all that caused it to lose it's surface water?