I’m new to observing; this is my attempt to summarize a useful distinction I’m learning.
Sometimes the view is bright enough, but it won’t look sharp. Stars seem to shimmer, planet edges look soft, and higher magnification makes the softness more obvious. This is usually seeing. People often describe it as “mushy seeing,” or say “the seeing settled for a minute and then broke again.” The idea is: the air is turbulent, so the image keeps being slightly blurred and shifted.
Other times the view is steady, but faint things don’t show up. The sky background looks grey or milky, faint stars drop away, and nebulae/galaxies lose contrast. This is usually transparency. People say “transparency is hazy tonight,” or “transparency is great; the faint stars are popping.” Here the air is acting more like a filter: haze, humidity, dust, or aerosols scatter and absorb light, so faint detail gets drowned out.
A useful split is sharpness versus faintness/contrast. The same object can stay the same while the appearance changes, because what shows up at the eyepiece is “object + conditions,” not the object alone. So the view works better as evidence about the night than as a verdict about skill or equipment.
Once the limit is clear, the plan becomes clear too: poor seeing favors lower magnification and blur-tolerant targets (open clusters, wide doubles, bright nebulae, Moon at modest power), while poor transparency favors bright targets (Moon, planets, bright clusters) and postpones faint galaxies and nebulae.
I’d love to hear how others judge seeing and transparency in practice.