June General Meeting Report
“The Best Ever Opposition of Mars”
Barry Adcock, Director Lunar and Planetary Section
Right from the opening sentence it became clear where Barry’s love and his veneration lay. For him astronomy started with the invention of the telescope; the age when the celestial objects in the night sky became more than mere pinpricks of light in a black sea of eternity. When planets took on shapes and distinguishing features: Overnight (literally) Saturn had “ears”, Venus had crescent phases and Jupiter had moons. Before long, surface features were noticed on the planets Jupiter and Mars. That’s when astronomy started to get interesting. Forget about Stonehenge, Thales, Hipparchus and the epicycles of Ptolemy. 1610, for Barry Adcock, was “the birth of Astronomy”.
Even though the first telescopes were of very poor quality compared with today’s standards and (due to chromatic aberrations) very limited in objective size, early sketches of Mars already show recognisable surface features. (See attached sketch by Huygens in 1659 and Herschel on August 16 1830) Huygens in 1659 discerned the nature of Saturn’s Rings, the “ears” that had so puzzled Galileo back in 1610. Sketches like these provided the most important record in those times. Experimentation with telescopes flourished then (come to think of it, it still does), and focal length was one way to compensate for the lack of quality glass for lenses. Johannes Hevelius (of Selenographia fame) had a 150ft long tubeless setup reaching high above the roofs of Gdansk. Together with his 6ft solid brass sextant he achieved resolutions down to one arc minute. Not much planetary observing was done at that time. The difficulty of having one’s observations confirmed may have compounded the problem. A well-known cryptic message between Galileo and Kepler says: “The mother of lovers [Venus] imitates the shapes of Cynthia” [Moon]. For the early users of astronomical telescopes, a telescope was merely a device that allowed a star to be sighted more easily and positioned with far greater precision than had ever been possible with the naked eye. Kepler found a way to increase the field of view, Christian Huygens developed a better ocular and Newton in 1669 the reflector telescope; Dolland in 1758 overcame colour aberration by using a combination of different composition glasses for the objective lense. But it was Herschel who started the dramatic increase in reflector size from 15cm diameter to 120cm by 1789.
Mars, Earth’s outer neighbour, is the most publicised of the planets. The planet is well placed for amateur astronomy observation when in opposition, shows seasonal changes and, before the coming of space probes, surface features were tantalisingly close to the limit of visibility. Important investigations of the planets were made in the 1890s at the Lowell Observatory in Flagstaff Arizona, although Percival Lowell is now mainly remembered for his fanciful interpretation of Schiaparelli’s 1879 canali markings on Mars as ‘canals’. Things have changed a lot in the last few years. The Mariner 4 fly-by in 1965 brought the first pictures of Mars from space; Mariner 9 became the first craft to orbit another planet, circling Mars twice a day for a whole year. It finally put an end to any hope of finding life on Mars. The Global Surveyor entered Mars orbit on September 12, 1997. It has since returned an unprecedented amount of data regarding Mars' surface features, atmosphere, and magnetic properties. (Barry had a CD running in the background during Supper, showing the progressive surface scan of the planet.) Pathfinder in 1997and its Sojourner Rover gave us some of the most popular pictures of Mars. In 2003 the twin probes Spirit and Opportunity with their six-wheeled Mark-2 Rovers will try to settle once and for all the long-standing controversy over water on Mars.
Due to the greater eccentricity of the Mars orbit, which takes some 687 days (a bit under 2 Earth years), oppositions occur approximately every 780 days, and favourable oppositions occur when Earth and Mars line up during the Mars perihelion, once after every 15 to 17 years. Barry Adcock showed tables of data highlighting the statistical figures and the cycle of closest approach between the two planets, and with an animated computer graphic their relative positions and angles. In a novel way he demonstrated his computer calculations on the screen by writing over the relevant images much like scribbling on the back of an envelope. On August 28 this year Mars will be “only” 55,758,006km (0.373AU) from Earth, closer than it has ever been for the last 100,000 years -and will be until the year 2284. It’s disk will have an angular diameter of 25.1 arcsecond and a magnitude of minus 2.9. As the title of the talk says, it will be the best opposition of Mars – ever.
And what to look out for? Mars will, as always during opposition, be in the retrograde loop during this August and not moving very far. But, Barry advises, with the likelihood of bad weather in August you may not get many viewing chances. So use every opportunity, and plan ahead by using the yearbook to work out from the central meridian what you will see on Mars at any given time. Record the size of the pole caps, watch for frost-glint, monitor dust storms. And experiment with filters to bring out specific details.
It was a fascinating talk, by a man who knows what he is talking about. A winner of the 1990 Berenice Page Medal for services to planetary astronomy; a man who designed a special telescope for disabled observers and helped build the Ballarat observatory, a past ASV President, Section Director and lecturer at Swinburne. A man whose name brings up over 20 references on the Internet and whose home address is familiar to everyone in the ASV even remotely interested in the Solar System.