Mars is the planet that most rewards timing and most punishes impatience. For most of its cycle it is a small featureless orange dot, and for a few months every twenty six months it is one of the finest sights in the sky.
Why opposition decides everything
Mars and the Earth orbit at different speeds, so the distance between them varies enormously. Near opposition Mars can be over 20 arcseconds across; at its worst it is under 4, which is smaller than Uranus. Aperture cannot compensate for that: the same telescope that shows polar caps and dark markings at opposition shows an orange dot two years later.
What is visible when the timing is right
At opposition in a 130mm instrument the polar cap is obvious as a white spot and the larger dark regions show as grey-green patches that rotate out of view over a couple of hours. A 200mm instrument on a steady night adds finer markings and, in a dust storm year, shows the surface features disappearing altogether, which is its own kind of observation.
Saturn as the reliable alternative
Where Mars is an event, Saturn is dependable: the rings are unmistakable in any telescope in this index and the view barely changes across the year. The ring tilt varies over its 29 year orbit, which means some years show the rings wide open and others nearly edge on, and both are worth seeing.
Questions people ask about telescope
What telescope do I need to see Mars?
Any of them at opposition. Between oppositions no aperture will show useful detail, because the planet is simply too small and too far.
What does Saturn look like through a telescope?
A pale yellow disc with a clearly separated ring system, unmistakable at 50x. The Cassini division in the rings appears in about 100mm of aperture on a steady night.
When is the next good time to observe Mars?
Oppositions come roughly every 26 months and vary in quality with the planet's distance. A planetarium app for your date will tell you the apparent diameter, which is the number that matters.