You can’t control the weather, but by being aware of what’s occurring in the atmosphere you can prepare for the night ahead
The sky often looks ideal for stargazing, but looks can be deceiving. Amateur observers describe viewing conditions using terms such as ‘transparency’ and ‘seeing’. Transparency is straightforward: observing a sky with poor transparency is like trying to look through a dirty window, but in this case the dirt is high, in thin clouds, atmospheric dust or moisture, or even aircraft contrails.
Seeing describes how steady or turbulent the atmosphere is and it can be estimated by observing brighter stars with the naked eye. When the seeing is poor, stars appear to twinkle more. Weather forecasts for astronomers can be helpful for anticipating observing conditions (try en. sat24.com or www. clearoutside.com) – if good conditions coincide with a dark new Moon period, the view should be outstanding.
Ambient temperature also plays a role, which is why telescopes need time to acclimatise when you take them outside – allowing an hour of cooling before you start observing really helps. Even so, a target that looks poor one night may be spectacular the next. A worthwhile experiment is to observe a bright lunar limb (the visible ‘edge’ of the Moon) at high magnification and note how the view appears to wobble. This is the effect of the seeing. Lingering on the view a few minutes will reveal patches of improved seeing, letting more detail shine through. Experienced observers will take their time over each target and keep coming back to favourite objects over the years.
Focus on the bright limb of the Moon to gauge how good or bad the ‘seeing’ is