Star Points for June, 2001; by Curtis Roelle Prominent Mars Arrives On Summer's Coattails The bright orange colored "star" in the southeast after twilight has ended this month is the planet Mars. This month is the best opportunity we have had to view the planet in the past 13 years, since 1988. Mars is the next planet out from the sun beyond the earth. Since our planet is closer to the sun we travel faster along our orbital path and so are now catching up to Mars. On June 21, the first day of Summer, the two planets will be at their closest, or 42 million miles (67 million kilometers) apart. After that the distance will slowly increase as the earth races past slower Mars. What this means for telescopic viewers is this: Mars will be at its maximum apparent size for the current encounter with an apparent diameter of 20.8 arcseconds. Mars will have the same apparent size as a dime 1,200 feet away. So even at its closest Mars is still a small disc. Luckily next time around in 2003 Mars gets even closer when its apparent diameter swells to 25.1 arcseconds. Because of its small apparent size high magnification is critical for seeing detail on the Martian surface. How much "power" is needed? With 100x the most prominent features will be visible on the small disc. To see them well though you will need 200x and up. Magnification alone will not suffice. A small telescope with a small opening (aperture) will yield a very fuzzy unpleasing image at high power. The larger the aperture the more light is gathered and the brighter the magnified image. A telescope with good quality optics in the 4- to 6-inch aperture range with a focal length of 48 inches or more is a good start. From there bigger is better. With telescopes there is no such thing as too much aperture, although there are other factors to consider such as portability, set-up time, and price. Mars' most visible attributes are the dark "albedo features" -- brown patches on Mars' salmon pink disc. The most prominent of these is called Syrtis Major. There are also lighter patches such as the one known as Hellas. Other features may be more transient. Hazes and clouds may appear in the thin Martian atmosphere and yellow dust storms occur from time to time. One tool often used by planetary observers are colored filters. Some colored glass filters are threaded and can be screwed directly into the eyepiece barrel. Glass filters can be purchased from companies such as Orion Telescopes (telescopes.com). Other forms of filters include hand held cut strips of colored gelatin sheets available at photo stores. Which colored filters are best for viewing Mars? For many years astronomy magazines would ask professional astronomers this very question. The answer always seemed to be the Wratten 25 red. So once upon a time I bought one and found it was too dark to see any details through it. Then one year I used the red (W25) on a telescope with 20 inches of aperture and it was awesome. Obviously they had been asking the wrong persons about filters. The filters used by professional astronomers were for large telescopes. Amateur telescopes are smaller and their filter needs and results also differ. For amateur observations, the orange (W21) has gained in popularity in recent years. Even among amateurs the choice of filter often depends on telescope size. One filter that I especially enjoy using is the green (W58). Speaking of Mars, in May I completed construction of a domed observatory in my back yard. Marstown Observatory took its name from the village of Marston, located less than one mile away. The observatory structure was originally owned by Carroll County amateur astronomer Ron Smith. Ron disassembled his observatory and delivered it to our new home near New Windsor in 1998 with each piece labeled in kit form. There were sections of floor, walls, and ribs for the dome. Ron offered tips for refurbishing the building and was instrumental in making many improvements over the original design. Other persons played major and minor parts in the project as well. One of my neighbors, Gary Hann, loaned me his auger which I attached to my tractor, using it to dig the post holes and carve out the pit for the pier. Cal Richards of Marston just happened to stop by one day as I was loading the telescope tube into a van for transport to the construction site and lent a helping hand. Checked it out last night and both observatory and telescope are working well. In the future there may be updates from under the dome in this column. In the meantime, keep your eyes on Mars. If you'd like to learn more about Mars, come to the Bear Branch Nature Center (BBNC) for the planetarium program scheduled for 7:30 p.m. on Friday, June 29. Please call the nature center at 410-876-9234 to make reservations. Carroll County Parks & Recreation charges a nominal fee for the programs. BBNC members do receive a discount, however. Weather permitting after the show the Westminster Astronomical Society (WAS) should have telescopes set up at BBNC for viewing Mars. Maybe I will see you there in one of the telescope lines.