Galactic Dust and Nebulae

How does the interstellar medium affect astronomical observations?

The interstellar medium is, of course, itself a target for astronomical study. However, it can also complicate astronomical observations substantially. Think about sunsets on Earth. For some reason, the Sun looks much redder when it is setting than it does during the middle of the day. That is because when the Sun is low in the sky it shines through dustier air; the dust in the sky tends to absorb proportionately more blue light and allow proportionately more red light to shine through. This effect of dust is called extinction, and it both changes the observed colors of astronomical objects and obscures them from view.


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