Star Points for August, 2003; by Curtis Roelle
Mars: Now more than ever

Last month I mentioned that Mars is currently closing in for a favorable observing season due to it's relative proximity to the Earth. Later in this article I'll tell you where you can go to see Mars live through a telescope with your own eye.

In August Mars inches closer every day until it reaches its nearest point to us on August 27. On that day earth and Mars will only be 34,646,418 miles (55,758,006 km) apart according to the U.S. Naval Observatory. the two worlds were separated by 42 million miles (67 million km) at the previous opposition in June 2001 (source: Star Points June 2001).

How does the current opposition compare with past and future? Sky and Telescope magazine reports that the last time the planets were closer than this month may have been in 57,617 B.C. But the difference is small - only 25,000 miles (40,000 km). The next time they will be closer has been calculated by astronomer Jan Meeus. However, the specific year varies by source. Sky & Telescope says Meeus came up with 2287, but Guy Ottewell (Astronomical Calendar 2003) says the year Meeus determined is 2729! Perhaps Meeus has modified his prediction over the years.

The closer Mars comes the larger it appears in a telescope. At closest approach its angular diameter will subtend 25.1 "arc seconds." By comparison, the full moon has an average angular size of 31 arc minutes. There are 60 arc minutes per degree, so the moon's diameter is about 1/2 degree across.

Likewise, there are 60 arc seconds per arc minute. If you could make copies of the planet Mars and lay them side by side, it would take 74 Mars "pearls" to span the diameter of the full moon.

To put it another way, when closest Mars will be the same size as a dime viewed 243 feet away.

The most prominent feature on Mars is currently the southern polar cap. Use a good telescope and a moderate power (100x-200x) to see it.

One disadvantage with close oppositions like this one for observers in the northern hemisphere is that Mars is located in the southern constellation Aquarius. Thus, it never gets very high above the horizon during the night. Haze and clouds can easily interfere and make it difficult to see fine detail on Mars' surface.

However, at opposition Mars will be up all night, rising at sunset and setting at sunrise. It is highest in the sky, and best placed for viewing, around midnight.

Astronomers are also keeping a close eye on the martian weather. As the weather warms on Mars, the polar cap melts and dust storms kick up. Dust storms can intensify to global proportions casting a pale pall over visible surface features for weeks or months.

A good chance to view Mars live during its approach will be at the Bear Branch Nature Center (BBNC) on Friday, August 8. Members from the Westminster Astronomical Society (WAS) will have telescopes set up (weather permitting) for a public star party coinciding with planetarium programs. The star party begins at 08:00 p.m. and is free. For planetarium ticket information, please call BBNC at 410-848-2517.

If the BBNC event does not work out for you, WAS members will have their telescopes set up near the tennis courts at Piney Run Park in Eldersburg between 08:00 p.m. and midnight on Saturday, September 6. There is no cost for this event. Although it will be past opposition, Mars will be closer than at the earlier BBNC star party.

Moon & Mars As mentioned last month, Mars and the moon had a close encounter on July 17. The author imaged the pair from his back yard observatory near New Windsor.