Things you can see with a telescope based on its aperture

60-70 mm refractors, 70-80 mm reflectors:

• binary stars with angular separation of over 2", e.g. Albireo, Mizar, etc.;
• faint stars (up to 11.5 stellar magnitude);
• sunspots (with an aperture filter);
• phases of Venus;
• lunar craters (8 km in diameter);
• polar ice caps and maria on Mars during oppositions;
• atmospheric bands on Jupiter and the Great Red Spot (GRS) under ideal conditions, four moons of Jupiter;
• rings of Saturn, Cassini Division under ideal conditions, pink atmospheric band on the planetary disk;
• Uranus and Neptune as stars;
• large globular, e.g. M13, and open clusters;
• almost all of the Messier objects (not detailed).

80-90 mm refractors, 100-120 mm reflectors, 90-125 mm catadioptric telescopes:

• binary stars with angular separation of over 1.5", faint stars (up to 12 stellar magnitude);
• structure of sunspots, granulation and solar flares (with an aperture filter);
• phases of Mercury;
• lunar craters (5 km in diameter);
• polar ice caps and maria on Mars during oppositions;
• clearer view of atmospheric bands on Jupiter and the GRS, shadows cast by moons onto the planetary disk;
• Cassini Division in the rings of Saturn and 4-5 moons;
• Uranus and Neptune as small disks with no details;
• tens of globular clusters, bright globular clusters are resolved into cosmic dust at the edges;
• tens of planetary and diffuse nebulae and all Messier objects;
• brightest objects from NGC;
• some details are resolved on the brightest and largest objects;
• details are not resolved during observations of most galaxies.

100-130 mm refractors, 130-150 mm reflectors and catadioptric telescopes:

• binary stars with angular separation of over 1", faint stars (up to 13 stellar magnitude);
• details of lunar highlands and craters (3-4 km in diameter);
• spots in the atmosphere of Venus may be seen with a blue filter;
• numerous details on the surface of Mars during oppositions;
• features in the atmospheric bands of Jupiter;
• atmospheric bands on Saturn;
• plethora of faint asteroids and comets;
• hundreds of clusters, nebulae and galaxies;
• spiral features of the brightest galaxies (M33, M51);
• a large number of objects from NGC (features may be observed on most objects).

150-180 mm refractors, 175-200 mm reflectors and catadioptric telescopes:

• binary stars with angular separation of less than 1", faint stars (up to 14 stellar magnitude);
• lunar features (2 km in diameter);
• Clouds and dust storms on Mars;
• 6-7 moons of Saturn, planetary disk of Titan may be observed;
• Spokes in the B ring of Saturn, at the peak of visibility;
• Galilean moons as small disks;
• at such apertures, resolution is more dependent on viewing conditions, rather than practical power;
• some globular clusters are resolved into individual stars;
• with minimal light pollution most features of a number of galaxies and nebulae may be observed.

200 mm refractors, 250 mm reflectors and catadioptric telescopes (and beyond):

• binary stars with angular separation of 0.5" (under ideal conditions), faint stars (up to 15 stellar magnitude);
• lunar features (less than 1.5 km in diameter);
• small clouds and features on the surface of Mars, at times Phobos and Deimos may be observed;
• a large number of features in the atmosphere of Jupiter;
• Encke Gap in the rings of Saturn, planetary disk of Titan;
• Triton, moon of Neptune;
• Pluto as a faint star;
• viewing conditions have a great effect on the quality of produced images;
• thousands of galaxies, star clusters and nebulae;
• almost all of the NGC objects, faint colors may be observed in the brightest nebulae;
• finer details on many NGC objects.