Observation Techniques for Lunar Eclipse
Many observers find it easier to detect the penumbra by viewing the dimmed Moon with a Moon filter, which used to dim the Moon’s dazzling appearance, attached to their telescope’s eyepiece. Others detect the penumbra by sweeping their telescopes back and forth across the Moon’s surface at moderate power.
The penumbra influences the appearance of surface features, especially the brighter areas, such as craters’ ray systems. Nothing is changed in the crater itself and the rays lose much of their brightness as the eclipse progresses.
A modest-sounding task often proves daunting because it can be quite impossible to predict exactly the end of penumbra and the start of the umbra. Hence, it often determined with vague boundary.
We have to know exact time to judge the times of contact .
As with contact timings, crater timings are best done with small apertures telescopes, neutral-density Moon filters, and magnifications of 100x or less. These objects can mark the shadow’s passage over the center of the crater to within an accuracy of at least six seconds as the shadow moves very quickly across the Moon.
Small-aperture telescopes can give better results of the time because the greater light-gathering power of larger instruments makes the Full Moon overwhelmingly bright, making the distinction between the umbra and the penumbra difficult. A neutral-density Moon filter can enhance shadow contrast further.
Another popular alternative method is to videotape the eclipse through a telescope for later analysis, using a small video camera or a lightweight camcorder. The shortwave radio is positioned near the camera’s microphone so that the time signals will be recorded on the audio track as the video captures the disappearing Moon.