Effects of Earth's Atmosphere on Astronomical Observations

Effects of Earth’s Atmosphere on Astronomical Observations

Atmospheric Extinction

  • Atmospheric extinction is the scattering and absorption of electromagnetic radiation by the atmosphere which diminishes the intensity of celestial objects.
  • Objects at different altitudes are affected by extinction in varying degrees - those near the horizon more so than those at the zenith, due to the increased length of the atmospheric path.

Refraction

  • As light from celestial objects enters the Earth’s atmosphere, it bends due to a phenomenon known as refraction.
  • Refraction makes the object appear higher in the sky than it actually is.
  • This effect is more pronounced when the object is closer to the horizon, since light travels through more atmosphere.

Scintillation (or Twinkling)

  • Scintillation is the fluctuation in star brightness caused by the Earth’s atmosphere.
  • Caused by pockets of air at slightly different temperatures, it results in stars appearing to “twinkle”.

Skyglow

  • Skyglow refers to the brightening of the night sky caused by artificial light pollution.
  • This significantly hampers visibility of faint celestial objects.

Astronomical Seeing

  • The term astronomical seeing refers to the blurring and twinkling of astronomical objects, which is caused by the turbulence in Earth’s atmosphere.
  • Rapid changes in air density create an effect like viewing objects through a rippling pool of water.

Atmospheric Windows

  • Atmospheric windows are specific wavelengths or ranges of electromagnetic radiation that can penetrate the Earth’s atmosphere.
  • Visible light, some ultraviolet (UV) light, and some infrared (IR) light can reach the ground, whereas most other forms of electromagnetic radiation are absorbed.

Weather and Observations

  • Weather significantly impacts astronomy. Clouds can obscure objects, winds can cause telescopes to vibrate, and humidity can form droplets on equipment.

Radiowaves and Atmosphere

  • The Earth’s atmosphere is largely transparent to radiowaves, which means data at these wavelengths can be received at ground-based observatories.