Steve’s top tip

Do I need to let my telescope cool down before observing?

Just as unstable air in our atmosphere warps and distorts the light reaching our eyes from celestial objects, so too does the air inside a telescope tube have the propensity for spoiling the view. The column of air within your telescope generates a miniature 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, destroying fine detail and giving stars odd smeared shapes, so allowing time for your telescope to cool down is an important part of the pre-observing routine.

Steve Richards is a keen astro imager and an astronomy equipment expert