Q: What are the best conditions for observing?
A: Good or poor viewing is not always determined by the optics of a telescope. There can be external factors determining the quality of an image. The blanket of air surrounding the earth is constantly in motion. This shifting and swirling of the atmosphere causes a poor image especially at higher powers. This constantly changes so some nights may be better for viewing than others.
Optical distortions made by the rippling of air currents emitting above a heated surface or area can cause a poor image. Objects are more distinct when viewing straight up because you are only viewing through an atmosphere of about 10 miles thick. This is opposed to an atmosphere 15 miles thick at 45 degrees, and over 100 miles thick near the horizon.
Light pollution: If possible avoid using your scope around lights (street lights. house lights. etc.). A high magnifying telescope is very sensitive to light, resulting in a washed out image or an annoying glare. The effects of bright light become more obvious near cities. Many of the stars seem to disappear near the city horizon.
Moonlight can be another factor. The harsh glare from a full or bright moon can dim nearby stars and planets. The moon itself is best viewed during the phases near the area dividing the darkness and sunlight.
Avoid viewing through an open window (never view through a closed window). The air currents caused by the inside/outside temperature, especially during the cold season makes quality observation impossible.
A bank of clouds is impossible to view through. Fortunately these are constantly moving. When stars twinkle rapidly, this is a result of the warm and cool air mixing. This results in poor viewing. Try to observe on nights when the stars have a steady 'burn' like the planets. A heavy haze causes poor viewing but a faint haze usually means a still atmosphere and good viewing may be possible. Stars always appear as pinpoints of light. They are at such great distances that any discernible size difference between very low and high magnifications within the telescope is impossible. The light gathering power of the telescope allows you to see stars and planets that your eyes would not normally see within the solar system.
Most telescopes give their widest field of view at lowest power - usually not more than 1-1/2 degrees. This means it is frustratingly difficult to find anything in the sky with the telescope alone. A small telescope called a finderscope is mounted parallel on the side of the main scope to get around this problem. The low powered finderscope with its four to six degree field of view and central crosshairs permits precise aiming before you look through the main body of the telescope.