Categories
Astronomy

Impact of Earth’s Atmosphere on Optical Telescope Observations

The importance of visibility when making observations with an optical telescope may be an obvious consideration, but it can also be easy to discount the challenges faced in acquiring a clear image. One of the most potent barriers to optical telescope viewing is the atmosphere of the Earth (Chaisson & McMillan, 2011). Any astronomical observation is subject to the effects of the atmosphere as radiation must pass through it before it can be registered by an Earth-bound telescope. The air acts as a lens that prevents light from reaching an optical telescope at a flat angle and therefore distorts the image from any source outside of the atmosphere. Some common atmospheric effects include blurring and variations in brightness known as twinkling. This problem has been a target of research for much of the existence of optical telescopes, though it took the relatively recent development of launching telescopes into space to escape the effect in totality.

            The deformation of measurable object diameters is the most devastating effect of the atmosphere on observations made through an optical telescope. Diameter has historically been a key variable in the identification of celestial objects and the atmosphere causes refractive distortions that threaten the ability to reliably record such values. The primary cause of atmospheric refraction is the presence of turbulence and the resultant mixing of air components. Turbulence causes sections of air to flow in a way that impacts adjacent streams, resulting in apparent ripples throughout the atmosphere. These alterations can result in the blurs and twinkles that are common problems when making observations with an optical telescope.

            The degree of distortion caused by atmospheric turbulence is variable based on location and time. Accordingly, optical telescopes have been consistently placed in areas that are thought to be the least impacted by the atmospheric factor, such as those with low humidity like deserts and mountain peaks. The latter example has two qualities that are helpful in this cause as high altitudes reduce the amount of atmosphere that light must pass through before reaching the telescope. Additional steps have been taken to minimize this issue in the form of complicated techniques and tools known as advanced optics. However, not even these innovations are immune to the effect on a full-time basis. The development of the Hubble telescope helped to circumvent the confounding influence of the atmosphere completely, though deploying instruments outside of the atmosphere is not a simple task and thus will not be a widely available solution for some time.

            The atmosphere has had such a dramatic impact on astronomic optical imagery that humans have been forced to abandon the planet in order to achieve a desirable quality of representational accuracy. Though space bound telescopes like the Hubble offer the best image, there are several other techniques that allow for a much improved reliability in optical telescope viewing. However, these tools are similarly expensive and difficult to implement. It is possible that the most efficient approaches to the atmospheric problem will come from interferometry and its associated concepts. Turbulence in the air is a form of interference because it is essentially a pressure wave that is interacting with electromagnetic waves. Instruments called interferometers have been developed from this perspective and address the issue by observing the waves from multiple reference points that can then be used to deduce and reduce the impact of interference on visible waveforms.

Reference

Chaisson, E., & McMillan, S. (2011). Astronomy: A beginner’s guide to the universe. (6th ed.).             Benjamin-Cummings Pub Co.