In general, as the temperature of an object cools, it shows up more prominently at farther infrared wavelengths. Moving away from visible light towards longer wavelengths of light we enter the infrared region. In the near-infrared region, the hot blue stars seen clearly in visible light fade out and cooler stars such as red dwarfs and red giants come into view. The near-infrared is also the region where interstellar dust is the most transparent to infrared light. As we enter the mid-infrared region of the spectrum, the cool stars begin to fade out and cooler objects such as planets, comets and asteroids come into view.
Planets absorb light from the sun and heat up.
They then re-radiate this heat as infrared light. Warm interstellar dust also starts to shine as we enter the mid-infrared region. This dust surrounds newly forming stars as well as stars going through their final phases. In the far-infrared, the stars have all vanished. Instead we now see very cold matter.