Techniques of Observational Astronomy
AST3722C

Basic Astronomical Optics

Astronomical observation requires the use of a variety of optical principles, both geometrical and physical.Here we will briefly outline those optical effects most important to understand the operation of astronomical instruments.

Geometrical Optics

Refraction

Light, traveling from one transparent medium into a second will be refracted at the interface. The change in path is given by Snell's Law.

Total Internal Refraction may occur in the denser medium if the angle of incidence exceeds the critical angle.

Dispersion results because the index of refraction is wavelength dependant.

Application to Parallel Plate

• can be used to provide small displacements of a beam
• results in an extension of a focal point
• can cause astigmatism

Application to Prism

Generally a prism should be used at its angle of minimum deviation since then small changes in the incoming angle result in nearly identical changes in the outgoing beam.

Simple Lenses

The rules for simple lens apply to thin lenses and paraxial (close to the axis) rays. In general, the basics of image formation can be illustrated within these restrictions.

• Rays parallel to the optical axis will pass through a focus
• Rays through the center will be undeviated

Reflection

Useful References

A great deal of useful information can be found on the web. Try a Google search for your topic. Some good specific sites follow:

Edmund Scientific http://www.edmundoptics.com/techsupport/optics.cfm

This page was last edited September 9, 2003 7:28 PM