BBC Sky at Night Magazine
Steve’s top tip
Do I need to let my telescope cool down before observing?
When you take your telescope outside for an observing session, the column of air within the telescope generates a micro version of atmospheric disturbance, in the form of tube currents, as it tries to reach temperature equilibrium with the air outside. These tube currents distort and diffract the light from celestial objects, robbing your view of fine detail and giving stars distorted and smeared shapes.
To stop this from happening, it is important to set up your telescope outside some time before you intend to start observing to allow it to cool down to the temperature of the surrounding air.