[Talk given c. 1983]
As you may gather, this talk is about Mars as seen from Earth using earth based equipment, especially that used by amateurs. I shall not be discussing the Viking or other space shots, as this may be the subject of another talk, nor , with the title Mars, shall I reads out something else, as happened on one occasion !
I will start with some slides showing drawings, alas, no photographs, made by observers since the arrival of the telescope. The fact that Mars was not a normal star was known to the Egyptians, who called it the Red One. The Babylonians and Greeks also knew it was not normal and studied its path, but all studies were simply positional.
By 1610 Galileo had pointed his telescope at all the planets and made startling discoveries. Two planets puzzled him : Saturn, which appeared to have ’ears’ which disappeared and returned, and Mars. Mars did not seem to be circular, and although no detail was visible the fact that the phase was slightly bulbous puzzled him. It was not an easy thing to see so he wrote to a friend, P. Castelli, concerning the aberration.
In 1636 Francisco Fontana produced the first known sketches of the planet’s surface (Slide1) accompanied by a description : “ The form of Mars was spherical. In the centre was a dark cone in the form of a very black hill. The disc was of many colours but appeared to be flaming in the concave part. Except for the Sun, Mars is much the hottest of all the stars.” Of course the early drawings reveal more about the telescope used than the planet, but they are at least a try.
We next come to Huygens, who drew Syrtus Major in 1659. Not only was he the first to see it but used it to deduce the rotation period. (Slide 1). The telescopes used were the ultra long focal length refractors of smallish aperture, supported by strings and masts, and a small army of volunteers.
Then, in 1719 Miraldi was one of the first observers to make drawings of the newly discovered polar caps. (Slide 2).
During the 1780’s Hershel measured the diameter of Mars, using home made small reflecting telescopes rather than the large 48 inch ones. He fixed the rotation to within a few seconds, and tried to determine the extent of the atmosphere on Mars by means of a Mars / star occultation. From this he concluded correctly that the Martian atmosphere was very thin.
Around the end of the 18th century John Schroter added detail to the Martian surface, though he could not always make up his mind as to which were permanent surface ones and which were cloud. (Slide 3). Shroter’s observatory was unfortunately destroyed in 1813, during the Franco / German war, and French soldiers carried off the brass telescopes, allegedly thinking they were gold.
Beer and Madler, two more German observers, made a serious attempt to map Mars in the 1830’s. Although the detail is fairly simple, (Slide 4), it has to be remembered that their instrument was a 3.75 inch refractor. They had already produced a Moon map, which was in use for 50 years. Bigger and better telescopes and spectroscopes were now coming into use, and the subsequent Mars maps improved with the optical progress. Examples of good maps are those produced by the British observer R.A.Procter, in 1867 and the Frenchman, Flammanon. In 1876 .(Slide 5). There was intense rivalry between British and French observers, who accused each other of inaccuracies, and that the British selected names for features biased in favour of British as opposed to French astronomers and personalities.
Now we come to 1877, and the famous Italian astronomer, Giovanni Schiaparelli. He used a fine 8.75 inch refractor (the equivalent of one of today’s 12 inch reflectors), and , with Mars perfectly placed (opposition on 5th Sept. 1877), he decided to make a new Mars map.(Slide 6). This was beginning to compare with modern maps, save for one striking feature that everyone knows about - the canals ! If the discovery was startling the implications were even more so, and he published his work after the next opposition in 1879, after which Mars was not going to be well placed until 1886. Then, observers using the 30 inch refractor at Nice again saw canals, as did Percival Lowell, using a 24 inch refractor in the climatically ideal area of Flagstaff, Arizona. Lowell wrote a book in 1906, suggesting that the canals were built by advanced Martians, trying to conserve water from the polar caps. He also noted a ‘wave of darkening’ spreading from the melting polar caps.
It was only after Lowell’s death in 1916 that the existence of canals were seriously questioned. A Greek astronomer, Eugene Antoniardi, who used the 33 inch refractor at Meudon, France, and found the canals were little more than line of sight effects caused by rows of dots (Slide 7). Antoniardi had, in 1911, been the director of the Mars section of the B.A.A. Even earlier, in1901, he and Flammanon had made another map of Mars (Slide 8), in which canals are implied if not precisely expressed., but Antoniardi’s maps are as accurate and detailed as any produced before the space probe era.
Apart from the last two or three instances mentioned above, the historical observations were made with telescopes no better and often far smaller and inferior than, say, the 12 inch amateur instrument of today. The next part of the talk is devoted to how the well equipped amateur can do interesting, satisfying, and useful work on Mars, and what you can really expect to see, though for the English observer it is a challenge ! Mars is, to be honest, a pretty frustrating object, but don’t let that put you off.
From Earth, the best oppositions (and rarest) can bring Mars within 35 million miles, giving apparent diameter of 25.7 seconds of arc, or nearly that. However, only about 1 opposition in 7 is like this (Slide 9). As any oppositions are at least 2 years apart it means that the best ones occur only every 15 years. Of the 6 oppositions that occur between, about 2 would show Mars’ angular diameter of about 16 to 20 seconds of arc, while the other 4 would show a maximum of 14 to 15. So, for every opposition that shows Mars at its best we have 6 in which Mars appears to be little more than half the diameter it could be. At its furthest conjunction the diameter goes down to 3.5 seconds.
Mars’ orbit is highly elliptical, and ellipses rotate only very slowly. Because a good opposition depends on Mars being on the closest to the Sun section of orbit at the same time Earth is overtaking it on the inside, this means that first class oppositions always occur at the same time of the year. This happens to be the end of August. Of course most Augusts have no opposition at all, but the rare first rate ones are always in August - early September. This is bad news for English observers, not only because the evenings are still quite light, but the planets tend to be very low in the southern sky at this time of year.
For some idea of what the telescope has to achieve, scaling Mars down to the diameter this 6inch globe, the best opposition would bring it to 4000 feet on the same distance scale. A normal , indifferent opposition would be equivalent to viewing this globe from 7000 feet. And, if the Earth and Mars were on opposite sides of the Sun, the distance between them at this scale would be about 30,000 feet. So, with a good opposition, and a good 8 inch (or more) telescope, on 200 times magnification Mars should appear in the telescope like this globe, viewed 20 feet away.
One of the principle features is SYRTUS MAJOR (Slide 10), the V-shaped dark area extending from the equator into the northern hemisphere (downwards when viewed through an astro telescope). To the west of this landmark is the ochre region of AERIA and ARABIA, and to the east is ISIOIS PLANITIA, where Viking 2 landed, and LIBYA..
To the south of Syrtus Major is HELLAS. Circular, and variable in brightness, at some oppositions it can approach polar brightness, at others it is hardly recognisable, due to cloud and mist in the basin. Between Hellas and NOACHIS is the dark region HELLESPONTUS
Extending from Syrtus Major and Libya to the east are two more dark regions, TYRRHENA PLANUM and MARE CIMMERIUM, separated by HESPERIA PLANUM.
To the north of the Tyrrhena - Cimmerium streaks is TRIVIUM CHARONTIS, a prominent dark patch once thought to be the centre of a system of canals.
Back to the equator we find SINUS MERIDIANI. This area is at 0 degrees longitude. It has two dark forks pointing north, and has been called Davies forked bay.
To the west is SINUS MARGARITIFER, shaped rather like Syrtus Major, but less prominent.
Due north is ACIDALIA PLANITIA, the principle dark region in the northern hemisphere.
THARSIS is a volcanic area, containing Olympus Mons, Pavonis Mons, and Arisa Mons, none of which can be seen with normal telescopes.
TITHONIUS LACUS is a sometimes prominent dark region where Lowell showed a canal called The Coprates. Mariner 9 revealed it to be a giant chasm, the Valles Marineris.
A large dark area in the north polar region is the VASTITAS BOREALIS and over the south pole the smaller MARE AUSTRALE. The best known features of these regions are, of course, the polar caps.
The mapping of Mars has now been taken over by the Martian probes but the amateur can still do useful work in two fields. Firstly, in detecting any colour variations in the different regions. Although now known to have no life seasonal changes do occur. As the polar caps melt a wave of darkening happens, probably due to moisture.
Secondly, is the observation of any dust storms. People watch out for TLP’s extremely concientiously while transient Martian phenomena really do happen. Granted dust storms are rare, but isolated mist and fog patches at dawn on Mars do occur more often.
When making a survey using the telescope the observer should sketch details, but not forget the phase that can go down to as little as 85%. Pre-cut discs can help here. After drawing in the polar caps and principle dark areas note the time (GMT 24hour clock). Then sketch in the small detail through the highest useful power, using the already sketched main features as reference points. This is important because Mars is rotating fairly fast. Note anything unusual, especially clouds, and add the following data :- Date. Time. Observers Name. Type and Aperture of Telescope. Magnification. Visibility Conditions. Longitude of Central Meridian. ( Visibility or seeing ranges from 1, perfect; to 5, very bad).
Longitude of the central meridian can be found in books such as the BAA Handbook, where it gives the longitude for 0 hours GMT. For every hour before or after 0 on that NIGHT, subtract or add 14.6 degrees to the meridian angle given in the book for that particular night.
Those who have cameras can try some Martian photography. This striking photograph (Slide 11) was taken using only a camera and clock mount, while these photos of Mars (Slides 12 - 16) were taken using the ‘famous’ GQ (“Galactica Quinnash”) telescope, featured in the Astrophotography talk a few weeks ago. A close look just reveals Syrtus Major.
[ This large telescope was made by Paul and John Nash and set up in its observatory in the back garden of Nash’s council house, at 9 Tavistock Road, BS4 1DL. What became of it after Nash moved to Cornwall is unknown to me, NQ].
Finally, don’t expect vast detail of Mars from a cheap, small aperture telescope, no matter how elegant the instrument looks in the shop window. To see much, Mars needs at least a 3 inch refractor or a 4inch or 6 inch reflector. However thesesorts of telescopes are available on loan within the Society, and many members have instruments much larger than this. If one cannot draw, telescopes can be adapted to take cameras and, as you have seen successful photographs can be taken.
Having heard all that, I am pleased to tell you that although the next opposition, in May, 1984, is only moderately good, the one in July, 1986, will be good, and that in September, 1998, will be excellent.