Telescopes

Telescopes

General Information

• Telescopes are instruments for collecting visible light or other forms of electromagnetic radiation.

Key Terms and Definitions

1. Aperture

   • Diameter of the primary lens or mirror of a telescope.

2. Chromatic Aberration

   • Distortion that causes an image to appear fuzzy when each wavelength coming into a transparent material focuses at a different spot.

3. Detector

   • Device sensitive to electromagnetic radiation that makes a record of astronomical observations.

4. Eyepiece

   • Magnifying lens used to view the image produced by the objective lens or primary mirror of a telescope.

5. Focus (of Telescope)

   • Point where the rays of light converged by a mirror or lens meet.

6. Primary Focus

   • Point in a telescope where the objective lens or primary mirror focuses the light.

7. Reflecting Telescope

   • Telescope in which the principal light collector is a concave mirror.

8. Refracting Telescope

   • Telescope in which the principal light collector is a lens or system of lenses.

9. Adaptive Optics

   • Systems used with telescopes that compensate for distortions in an image introduced by the atmosphere, resulting in sharper images.

10. Resolution

    • Detail in an image; specifically, the smallest angular (or linear) features that can be distinguished.

11. Seeing

    • Unsteadiness of Earth's atmosphere that blurs telescopic images; "good seeing" means the atmosphere is steady.

12. Charge-Coupled Device (CCD)

    • Array of high-sensitivity electronic detectors of electromagnetic radiation, used at the focus of a telescope (or camera lens) to record an image or spectrum.

Advanced Techniques

Interference and Interferometry

13. Interference

    • Process in which waves mix together, allowing their crests and troughs to alternately reinforce and cancel one another.

14. Interferometer

    • Instrument that combines electromagnetic radiation from one or more telescopes to achieve a resolution equivalent to what would be obtained with a single telescope with a diameter equal to the baseline separating the individual telescopes.

15. Interferometer Array

    • Combination of multiple radio dishes that effectively works like a large number of two-dish interferometers.

16. Radar

    • Technique of transmitting radio waves to an object, then detecting the radiation reflected back to the transmitter; used to measure distance to, and motion of, a target object or to form images of it.

17. Concave Mirror

    • A curved mirror that reflects light inward to a single focal point.

18. Flat Mirror

    • Reflecting surface that redirects light hitting it at the same angle of incidence.

19. Objective Lens (Telescopes)

    • Lens that gathers light to create an image.