Preparing for Mars Opposition
Preparing for Mars opposition includes thinking about your observing location and what you can do to maximize the clarity of your view. Since the planets are nice and bright, you don't have to worry about city lights but you do need to think about the some other aspects of your location and equipment.
Now let's talk about “seeing”. Seeing is a measure of the stability of the air layers above and around your telescope and also in your telescope. Everyone has probably seen the heat waves rising above a hot road in the desert.
In reality, heat waves are rising around us from our driveways, rooftops, chimneys and observatory buildings. The rising heat causes air turbulence that blurs the light from the object we are viewing and can greatly reduce the clarity of our views. On a macrocosm scale, changing weather related to passing cold fronts and warm fronts causes poor seeing. You can quickly assess your local seeing by noting how much the stars twinkle. When the stars are steady then seeing is good! There are lots of websites with more information on seeing and the 1-5 rating system frequently used by astronomers. There are also websites/apps that predict seeing for the next 24-48 hours based on weather patterns near your location. Don't be afraid of warm hazy nights as they may provide very good seeing for planetary viewing! Here are some links of interest:
More locally and within your control, setting up your telescope in the center of a green lawn provides better local seeing than the middle of your cement driveway. Seeing is also likely to be better when you're looking over a gap in the neighborhood houses, rather than directly over the neighbor's roof. Seeing over lakes is typically good and I've found seeing in the mountains to be unpredictable.
The air within your telescope can also be turbulent and reduce it's performance. A telescope stored in a warm house or garage needs time to adjust to the outdoor evening temperature before it will perform to its full capability. Closed-tube telescopes like Maksutovs and Schmidt Cassegrain Telescopes (SCTs) are very popular and can benefit from a few layers of inexpensive Reflectix insulation wrapped around the telescope tube. Even open truss-tube designs can have turbulent air located just above their large warm mirrors. These scopes can benefit from a “boundary layer” fan. I recommend doing some web research! You can learn a lot from the Cloudy Nights Forums.
So what kind of telescope is best for planetary viewing? Well, there are lots of opinions on that! A traditional answer is refractor telescopes of good quality (ED or APO) since they are unobstructed and rarely need optical adjustment. Maksutov and SCTs are also capable of excellent views and are probably even better suited for planetary photography than refractors since they can provide larger aperture (more resolution) and longer focal lengths (larger image size in your camera).
Regardless of your telescope type, it needs to be in good optical alignment (collimation). If you're not sure how to align yours, seek the advice of a fellow astronomer in your local astronomy club.
Eyepieces are important, too! Traditional Orthoscopic eyepieces are excellent for viewing the planets, but almost any quality eyepieces will do well. Keep them clean since dust and eyelash oil can blur your views. You might notice that using high power to view the planets can reveal the annoying floaters within your own eye. Binoviewer attachments that allow viewing with both eyes helps your brain “process-out” those floaters and make them much less noticeable.
Even a modest, low-cost binoviewer is adequate for the planets and will probably help you see more detail with relaxed eyes.
We're lucky this year that Jupiter and Saturn are currently well placed in the evening sky and provide us great views and the observing practice we need before Mars reaches it's best in October. Get ready!
About the Author
John McVey is a recently retired electrical engineer and R&D manager. He's been interested in astronomy since he received a 40mm Tasco Refractor for Christmas at age 10. Classically a visual observer, he has enjoyed many telescopes including a 6” APO Refractor and a 16” Dobsonian reflector. More recently he has focused on casual astrophotography of the planets and the deepsky.