# Observe stars with a cloudy sky

Is there any way to view the stars even in a cloudy sky? For example by using a particular camera, or a particular UV filter in front of the camera, and so on.

• How far away from visible light can the wavelength be? Because radio telescopes routinely observe on cloudy days. – probably_someone Sep 11 '18 at 20:31

Have a look at the liquid water absorption spectrum across a wide wavelength range:

As long as you are not observing from from space, there is always some water vapour along the line of sight to a star. Depending on the thickness of the cloud cover and the brightness of the stars, it may be possible to view some of the stars.

Relevant Wikipedia article.

• More important is the variation of the cloud. With a perfect uniform and constant cloud we could observe a star if any tiny amount of signal gets through. In reality the variation in the cloud makes this difficult. In the near IR there is always a varying bright background due to light from O-H bonds which makes even a 'clear' sky challenging – Martin Beckett Sep 11 '18 at 22:26

for a cloudy sky, Mie scattering is playing the role. to see a star you have to use larger wavelength :

but the ordinary cameras are not sensitive in IR ($\lambda$ >900 nm) as a rule of thumb, the larger the wavelength the easier way to image through the particles.

• probably you mean shorter, why longer? For example, a RADAR can see through clouds because the wavelengths are much shorter than visible light. – CipherX Sep 12 '18 at 12:02
• Radars use longer wavelength than visible light (cm to meter). its simple, shorter wavelength means in a specific length there are more electric field than the longer wavelength. and this means there are more interaction and more scattering and wave can not propagates simply. – Persian_Gulf Sep 12 '18 at 12:27