Observing Mars
with Barry Adcock, General Meeting 10 March 1999

So you think you know all about Mars? You have watched its size waxing and waning from a minimum of 4" to a maximum of 26" diameter. You have read Rod Brown’s article “Mars Opposition - April 1999" in February-March Crux, showing its 18̊ retrograde path in the sky during the next three months. You have seen pictures taken with the Hubble Space Telescope in detail and clarity beyond anything an earthbound telescope could ever achieve. You have seen the Rover on the surface of Mars giving a panoramic view of the boulder-strewn landscape in stark realism. What could possibly be left to observe about Mars, the red god of war with his two chariot horses Phobos (fear) and Deimos (panic)?

But Barry has a few surprises! Barry Adcock fits the image we all have of a typical college Professor. Even his mannerism, whether by nature or purposely adopted for effect, portrays the overworked, distracted academic who can never find his notes, can’t remember where the switch of the overhead projector is located, or forever loses the laser pointer. I have long ago learned to appreciate these subtle hints by which Barry catches your attention and passes on his information.

Mars now approaches Earth at over a million km per day, its picture changing rapidly. April 24 will provide the best view since 1990, and this will not be met again until August 2003, at the peak of its 15 year cycle. Mars is about 60% the size of Earth, yet the Martian day is about 40 min longer than here, which means it takes about a month to observe every point on Mars at the same Earth-time.

With its 25̊ tilted axis and an inclined orbit to the ecliptic (a pronounced ellipse), the edges on Mars are continuously changing. The polar ice cap leaning towards Earth is often visible and can be monitored. The changing pole caps, as well as the cloud composition is still a great mystery. Noted as early as 1680 by Christian Huygens, these features of Mars have challenged man’s ingenuity for centuries. Percival Lowell spent the better part of his life trying to prove that the faint density markings he noticed in his observations were artificial “canals”. He may have been wrong about the canals, but he certainly succeeded in raising the profile of planet observations.

Stressing the importance of colour filters in astronomical observing, Barry demonstrated the effect of various filters in the light beam of a diffraction-grating. Red and orange filters show off Martian surfaces best. As you move towards the blue you see less of the surface and more of the atmosphere and the clouds. For consistency of records and for the validity of your data it is important to use only calibrated filters, such as the Wratten (W) series. Standardised forms to record these details and mark up your observations or sketches are a big help and are readily available from your astronomy centre.

With our knowledge of Mars increasing daily, our awareness of the gaps within that knowledge also grows. Amateurs perform a vital function filling-in that picture by observing subtle changes, which will compliment the detailed mapping done by satellites such as NASA’s new Mars Global Surveyor.