Last touched 2001 December 4
Originally published in M-111, the Newsletter of the Richland (Ohio) Astronomical Society
Reflections in the Eyepiece
by Robert Bunge
Most of you probably believe that all I ever observe are deep sky objects. However some people who observed with me in 1988 know better. I also like to observe planets -- especially Mars. And Mars is about to return for another show!
The red planet reaches its largest size on November 20, 1990 during its closest approach to Earth. Opposition occurs seven days later when the planet is located 178 degrees away from the sun. Opposition happens after close approach because the orbits of Earth and Mars are not perfectly round.
While Mars will not achieve the large size that it did in 1988, it will be placed higher in the sky... 25 degrees higher than in 1988. There it will not be subject to as much of the Earth's turbulent atmosphere that prevents you from seeing detailed views of the planet.
I first warmed up for Mars during the red planet's first apparition, the one in 1986. In late 1985, for about $70, I constructed a high performance 4 1/4-inch F/10 newtonian that was specifically designed for planetary observing. Using a $30 Jaegers mirror, a $14 "second" optical window from Edmund, a super-tiny 1/2 inch diagonal and a crude but simple dobsonian mount I was able to make a very effective telescope that would return its cost in short order. I used that telescope at home to develop observing skills that would later allow me to push the 31-inch to its limits.
You see, planetary observing and deep sky observing have something in common. They are both an acquired skill that is best gained by practice. Deep sky observers have to learn how to use averted vision. Planetary observing requires extreme patience and careful attention to detail. In many respects, I consider planetary observing to be the harder, more challenging of the two.
During the summer 1986 apparition of Mars, from my apartment in Columbus, I started to observe as soon as it got larger than 10 arcseconds in diameter. Since this was at the beginning of the apparition, the planet was rising in the east during the early morning. I was able to set the telescope out in the evening and than get up before work to make the observation. This gave the telescope plenty time to cool off and equalize with the outside air temperature.
It seemed that each night I could see a little more detail. At first I thought this was because the planet was growing larger in apparent size. However, since I was seeing more detail each night, I soon realized that it was because I was becoming better at seeing fine detail! As this happened, I started to pick up little tricks that helped the process.
I learned to focus the telescope on a fairly bright star before trying to observe the planet. This assured me that the telescope was in focus and I wasn't seeing a fuzzy image.
I picked one small section of the planet and just stared at it. In the course of a few minutes, a moment of good seeing would come about and I would see a wealth of detail for an instant. After drawing what I had seen, I picked another section of the planet and waited. I naturally learned to divide the planet into a grid system and observe each grid during a moment of good seeing.
I used lots of different magnifications. Often I started at 170x, and later then tried higher and lower powers. A few nights of trying this soon taught me that some nights let me use higher powers and others lower. Along the same line, some detail is seen better at different powers.
In the beginning, I used color filters to help see the different details on Mars. Several different lists of what filters allow you to see what details have been published in magazines and observing handbooks. But, for me, I soon learned how these different details appeared in white light -- without the filters. I'm guessing because I have years of training and experience in gauging the color of photographs, it was easy to me to pick out different colors.
When conditions allowed it, I made trips up to Warren Rupp to use the 31-inch. In 1986, many of these trips were made in company with Brent Archinal. With both of us up on the mit-e-lift, we normally traded off in five or ten minute sessions. While not at the eyepiece, I normally sat on the floor of the lift and either rested or watched for meteors outside the slit.
One of the first things to know about the 31-inch and planetary observing is seeing conditions. My 4-inch was rarely limited by the seeing. The 31-inch is almost always limited by the seeing. It was a rare night that seeing conditions allowed us to take advantage of the 31-inch's superior resolving power. But, when that great night of outstanding seeing came along, we would quickly cancel all other plans for the evening and stay on Mars.
One such night was July 3rd, 1986. The seeing was terrific. The planet was as steady as it gets. The normally large, ill-defined dark patches on the red planet would suddenly break-up into tens or even hundreds of highly defined detail. At times, as the seeing came and went, the details would merge together to form streams and lines of details that stretched from one side of the planet to the other. All of a sudden, we could see Lowell's canals! They really aren't there, but it sure was easy to see how observers of the time could be confused by them!
It was on that night that Brent first noticed Phobos. The tiny moon that orbits Mars in six hours would appear on one side of the planet for only a few minutes at a time. It was almost buried in the haze and shine from the planet, and we found it helped to just put the planet out of the field of view.
By the time the 1988 apparition rolled around, I felt that my planetary observing skills were at an all-time peak. In the year since the last Mars opposition, I had been practicing on Jupiter and Saturn. I had learned tricks about using the 31-inch for planetary work. Some of them follow:
* Always give the observatory time to cool off. While that wonderful piece of fused quartz may not change its shape too much with temperature, the heat soaked up all day by the dome and surrounding concrete takes hours to radiate away. In almost every case that we had a long period of great seeing, it was in the early morning hours -- sometime after 1 a.m..
* It didn't take me long to figure out that observing planets low in the southwest usually didn't offer good results. Heat from the concrete observing platform and from the clubhouse radiate an incredible amount of heat in the evening.
* Not only did I learn to use different magnifications, but also different apertures. I made a 9-inch off-axis mask for the 31-inch. This effectively allowed me to use a 9-inch F/22 refractor that was free of any chromatic aberration. Some nights were better with the smaller aperture, others were better with full aperture. Details in the darker sections of Mars were easier to see at 9-inches, and lighter detail was easier to see at full aperture.
* In general, the 31-inch collects too much light for planetary work. During the time around opposition, Mars shines at a magnitude of -2. The use of neutral density filters or a variable polaroid filter often increased the amount of detail that could be seen on the planet surface by dimming the image and reducing glare and internal reflections in the eyepiece.
* Experience showed that the seeing improved if there was no more than two people in the dome at the time. People walking around on the floor below the telescope either stirred up air currents in the dome or contributed heat currents that would rise through the open tube of the telescope and disrupt the seeing. (This is a good reason to wrap the telescope in some type of light material and mount small "muffin" fans at the mirror end of the tube.)
* Observe when you least expect it. Because Mars is bright, I often went Mars observing when the moon was up. It sounds crazy, but yes, I drove an hour and a half just to look at Mars. Under these conditions, you may be the only person at the observatory. For safety reasons, (like stepping off the mit-e-lift and breaking a leg) I always find an observing partner.
* I developed a system for gauging the seeing conditions. On a scale of one to ten, ten was perfect seeing and one the worst. Sometimes the image would shimmer quickly, with a few, very short moments of good seeing. On these nights it was sometimes possible to see more detail on Mars with the smaller telescopes outside.
Because of the above observations, I have always preferred to do my planetary observing with the 31-inch sometime after midnight when the planet is either in the east or near the meridian. The later is preferred because it means the planet is as high as it gets and isn't degraded by the Earth's atmosphere. This means I do most of my observing BEFORE opposition. This is because when the planet is at opposition, it rises about the time the sunsets, and by the time the observatory cools off the planet is located in the southwest.
If I was with another person, we would trade off 15 or 20 minute periods alone in the dome so the observer would be the only source of heat. When I wasn't at the eyepiece, I pulled a chair out of the dome and tried to see how many meteors I could see with a full moon in the sky!
Attention to all of the above details often rewarded me with great observations of Mars in 1988. I'm looking forward to doing the same thing later this fall.
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