Telescopes – Vocabulary List (9/2/2024, 9/8/2024, 9/16/2024)

Vocabulary flashcards covering telescope terms and definitions from the lecture notes.

astronomy

the study of all matter and energy in the universe.

universe

everything that exists to the best of our knowledge.

reflection

the redirection of a beam of light off a surface when it strikes the surface.

refraction

the bending of a beam of light as it passes from one material into another.

refracting telescope

a telescope that uses lenses to form an image.

reflecting telescope

a telescope that uses mirrors to form an image.

catadioptric

a telescope that uses both lenses and mirrors to form an image.

objective

the main mirror or lens of a telescope.

focal point

the point to which a central parallel beam of light from a distance point source is brought by the objective of a telescope.

focal plane (or image plane)

the plane to which several beams of parallel light from a distance extended object are brought by the objective of a telescope.

focal length

the distance from the objective to the focal point inside a telescope.

eyepiece

a lens placed after the image plane of a telescope to create parallel light so that the human eye is capable of focusing it.

magnification

the focal length of the telescope objective divided by the focal length of the eyepiece used.

Formula: magnification = focal length of obj. ÷ focal length of eyepiece

chromatic aberration

the failure of the different color components of visible light to form a common focus when using a simple biconvex lens.

crown glass

a low-density glass. Solution to chromatic aberration.

flint glass

a high-density glass. Solution to chromatic aberration.

achromatic doublet

a lens formed by cementing crown glass and flint glass back-to-back to solve the chromatic aberration problem.

spherical aberration

the failure of light striking the edge of a spherically shaped optic (a mirror or lens) to form a common focus with light striking closer to the centerline.

The first image shows a correct lens

The second image shows a lens whose curve is incorrect.

Schmidt-Cassegrain telescope

a telescope that uses a spherical objective mirror and a corrector plate lens to solve the spherical aberration problem.

Cassegrain focus

when the focal plane of a telescope is located through a hole behind the objective mirror.

Airy disk

the actual pattern of light that is created at the focal point of a telescope by light from a distant point source.

resolution

the minimum angular separation between two distant point sources of light that can clearly be separated as such by a telescope.

north celestial pole

the imaginary point in the sky to which earth’s rotational axis points.

alt-azimuth mount

a telescope mount that uses two axes (one perpendicular and one parallel to the horizon) of tracking to compensate for Earth’s rotation.

equatorial mount (or polar mount)

a telescope mount that uses a single axis of tracking that is parallel to earth’s rotation axis to compensate for Earth’s rotation.

convection

the upward and downward movement of a fluid due to density differences caused by temperature differences between regions of the fluid.

seeing

a measure of the lack of twinkling (or lack of convection or lack of turbulence) of stars in the night sky when viewed from the earth’s surface.