A great challenge that will enhance your understanding of Mars is to find and draw what you see through your telescope of the albedo features. A Mars albedo map will aid you in identifying these features.
Note that not all features noted on the map are visible to an observer at any one apparition/opposition as it depends upon the hemisphere of the planet that is pointing towards the earth (Northern Hemisphere during aphelic oppositions and Southern Hemisphere during perihelic oppositions) as well as the presence of dust and clouds over the surface of the planet over time. The darker albedo features shown are typically visible during the majority of apparitions/oppositions.
The North and South Polar Caps (NPC and SPC) will change in size according to the current martian season over that hemisphere. The canal-like albedo features are due to a contrast effect between the light and dark zones over the surface.
Observing Equipment
The tools and techniques applied by astronomers using quality instruments and accessories is vital to be able to detect low-contrast albedo features across the surface of the planet Mars and other extended celestial bodies (Moon, planets, and nebulae).
An observer hoping to detect faint detail over the surface or atmosphere of the planet Mars must prepare beforehand to have a successful observation. The prospective Mars observer needs to be using an instrument that is diffraction-limited (1/4 wave peak to valley surface error allowable of a lens or mirror), properly collimated, and cooled to ambient temperature before being able to detect the fine albedo features over the red planet.
Many excellent telescope designs are available for high-resolution observation and imaging of the planets that include refractors (doublet (achromatic) or apochromatic (triplet) lenses), reflectors (multiple mirrors of different configurations and surface figures), and catadioptric ( a combination of lenses and mirrors).
The refractor employing a doublet (achromatic) or extra-low dispersion (ED) triplet lens is considered by many to be the classic planetary instrument. The design using a lens that is properly figured (diffraction-limited), centered, and baffled (placed within the tube to reduce stray light from affecting the final image) will produce the sharpest and highest contrast image possible for the observer.
The refractor, unfortunately, becomes very expensive as the lens diameter exceeds 4 inches/10.2 cm that will require a larger and heavier mount to sustain it unless using a short-focus ED triplet lens. The view of Mars under good seeing (atmospheric) conditions in a 4 to 6 inch (10-15 cm) refractor is impressive and memorable.
Reflectors come in many designs but the most popular one is the Newtonian reflector that was created by the eminent English scientist Sir Isaac Newton (1643-1727) in 1668. The Newtonian reflector employs a primary parabolic mirror at one end and a small flat secondary mirror at the other end of the tube that the deflects the reflected light to the side of the tube in order to observe the object.
A well-constructed Newtonian reflector with a diffraction-limited primary and secondary mirrors and with the secondary mirror’s diameter being no greater than 20 to 25% of the diameter of the primary mirror may provide outstanding images of the moon and planets. Some of my best views of the moon, planets, and deep sky objects have been through quality made Newtonian reflectors.
The catadioptric reflector employees both a lens and a mirror to form the final image. An example of the catadioptric design is the Gregory Maksutov-Cassegrain reflector developed by Russian/Soviet optical designer and amateur astronomer Dmitry Dmitrievich Maksutov (1896-1964) in 1941.
A popular type of Maksutov-Cassegrain telescope is the Gregory or “Spot” Maksutov-Cassegrain that uses all-spherical surfaces and have, as secondary, a small, aluminized spot on the inner face of the corrector. This design allows “fixing” of the secondary mirror (typically an aluminized spot on the inner surface of the weakly-negative lens corrector) and eliminates the need for a spider that would produce diffraction spikes.
The difficulty in building the Gregory Maksutov-Cassegrain is that the full aperture lens corrector that is required it becomes large and heavy and more expensive as the aperture increases. The full aperture corrector lens also requires extra time for cooling down to ambient temperature which depending upon the aperture of the instrument will take a significant amount of time to do so. Maksutov-Cassegrain designs are typically not built larger than 180 millimeters (7 inches) in aperture due to these constraints.
Another popular catadioptric telescope design is the Schmidt-Cassegrain telescope that includes the Celestron Schmidt-Cassegrain (developed by Thomas “Tom” J. Johnson (1923-2012) of Celestron Pacific in 1970) and the Meade Schmidt-Cassegrain (developed by John C. Diebel in 1972). The Schmidt-Cassegrain reflector is a very popular instrument that is used by amateur astronomers around the world for observation and imaging of the moon, planets, and deep sky objects. Whatever telescope design instrument that the planetary amateur astronomer is going to use must be diffraction-limited, collimated, and allowed to reach the ambient temperature at the observation site.
Eyepieces for Observing Planets
Aluminum foil/Filter (Deep Blue or Violet)/Cardboard/Wire Occulting Bar. Occulting bar occludes Mars to show Martian moons at elongation.
About the author:
Ambassador Carlos Hernandez has contributed his planetary observations to worldwide organizations including The Association of Lunar and Planetary Observers (ALPO, United States), British Astronomical Association (BAA, Great Britain), Oriental Astronomical Association (OAA, Japan), and many other excellent planetary amateur astronomer groups over many decades.