June 2001, Observer's Notebook

Discovering Mars

by John Rummel

As summer approaches, we close out an excellent season of planet watching. All winter, Jupiter, Saturn, and Venus dominated the evening and nighttime skies. Now as spring slowly turns into summer, all three have disappeared into the glare of the sunset. Jupiter and Saturn will return to evening skies this November. Venus won't return to evening skies until next March (all three can soon be seen in the early AM hours before sunrise though).

Planet watchers are quite excited about this summer though, because Mars is back. In fact, Mars will reach its closest approach to Earth this month (and thus best viewing) since 1988.

Mars is generally an insignificant orange disk in most amateur telescopes. But for a couple of months every two years or so, the planet Earth "laps" Mars in an event called opposition. During opposition, Mars rises at sunset, is up all night, and is very bright. Though its opposition date is June 13th, its closest approach to Earth is not for another week, on June 22nd. Though this seems odd, the reason is actually quite straightforward. Mars' orbit is quite eccentric - or off center from the sun. After opposition date (see diagram), Earth and Mars continue to get a little closer until the speedier Earth begins to pull away again after June 22nd. Though Mars reaches opposition every 26 months, some oppositions are better than others. Depending on where Mars is in its orbit when the Earth laps it, the distance between the two planets can vary by as much as 28 million miles, making some oppositions significantly better than others.

The next opportunity to view Mars under conditions this favorable will be August of 2003, when it will be even closer to Earth. In fact, the 2003 Mars event will be the best since 1924. Mars watchers, mark your calendars.

Mars will be large enough for excellent telescopic observation well into August, though the best times are obviously closer to the middle of June when it's closest to Earth.

Of the naked eye planets, none undergoes more dramatic changes in appearance than Mars. After lurking in relative obscurity for nearly two years, it brightens by more than a factor of 30 around opposition date, is visible all night, and then fades into obscurity again. During the same period of time, its apparent size when viewed through a telescope goes from a pinpoint 3.6 arcseconds up to a maximum (this year) of 21 arcseconds (roughly half the size of Jupiter as seen through a telescope).

Observing Tips

Mars is a challenging object for amateur astronomers. Its small size coupled with its dazzling brightness make it challenging to see the surface detail that is obtainable with modest viewing equipment. Add to that the fact that, appearing this year in the southern constellations of Ophiuchus and Sagittarius, it never gets higher than about 20 degrees above the horizon as seen from Madison (that's about the width of your hand held at arm's length). That means atmospheric turbulence will cause the planet to shimmer and waver, especially at the higher magnifications you'll want to bring to bear on this planet. Be patient and use the highest power you can. Mars will reward you with some wonderful views.

 

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