What is the difference between “seeing” and “twinkling”?

Answer 1

The term seeing describes how objects appear to the astronomer through a telescope during different atmospheric conditions. Excellent seeing means at high magnification you will see fine detail on planets. In bad seeing, planets might look like they are under a layer of rippling water and show little detail at any magnification, but the view of galaxies is probably undiminished. Bad seeing is caused by turbulence combined with temperature differences in the atmosphere. A seeing forecast attempts to predict turbulence and temperature differences that affect seeing for all altitudes. Based on this description, the twinkling effect of stars is the result of bad seeing, so the degree of twinkling and degrees of seeing are essentially synonymous.

Bad seeing can occur during perfectly clear weather. Often good seeing occurs during poor transparency. It's because seeing is not very related to the vater vapor content of the air.

The excellent-to-bad seeing scale is calibrated for instruments in the 11 to 14 inch range.

Note also that you may observe worse seeing though your telescope than what a perfect seeing forecast would predict. That is because tube currents and ground seeing mimic true atmospheric seeing. You may also observe better seeing than predicted when observing with an instrument smaller than 11 inches.

Answer 2

Seeing refers to the impact of atmospheric effects on the quality of telescopic viewing, while twinkling generally refers to the naked-eye impression of those effects.

Seeing is measured in a variety of ways, depending on the type of observing being done. The 10-point Pickering scale is based on the appearance of a star's diffraction image, and is often used by double-star observers. The five-point Antoniadi scale describes seeing in terms more applicable to planetary observing. Astrophotographers are apt to measure seeing in arc-seconds, by the diameter of star images produced in their cameras.

Strong twinkling often indicates bad seeing, but the relationship is not locked in. Sometimes what looks like strong twinkling to the naked eye shows only a slight drifting of an otherwise very sharp image in the telescope. On the other hand, when the jet stream is overhead, you may see a heavy and rapid blurring in a telescope while the naked-eye view can be quite steady.

Answer 3

Seeing is a term that describes the condition of the atmosphere at the time of observation, that is, whether is turbulent or steady. For example, good seeing means you can see more details in your telescope because the atmosphere is steady. You can make an estimate of seeing either at night or in daytime, for example before you start observing sunspots. So, there is scientific value to it.

Twinkle I heard it only for stars at night. All stars twinkle because they are point sources in the sky, as opposed to planets that are not. Twinkle, as a concept, shows that layers in the atmosphere are not steady.