Chapter 6.1-6,2 Flashcards
Telescopes
The basic tool of astronomers. Working over the entire range from gamma rays to radio waves, astronomical telescopes collect and concentrate electromagnetic radiation from celestial objects.
Resolution
How close two points can be to each other before we can no longer distinguish them.
Refracting Telescopes
A telescope that uses objective lenses to collect and focus incoming electromagnetic radiation to form an image.
Reflecting Telescopes
A telescope that uses mirrors to collect and focus incoming electromagnetic radiation to form an image in their focal planes the size of a reflecting telescope is defined by the diameter of the primary mirror.
Aperture
The clear diameter of a telescopes objective lens or primary mirror.
Refraction
The redirection or bending of a beam of light when it crosses the boundary between two mediums having different refractive indices
Objective Lens
The primary element in a telescope or camera that produces an image of an object
Focal Plane
The plane, perpendicular to the optical axis of a lens or morrow, on which an image is formed.
Focal Length
The optical distance between a telescope’s objective lens or primary mirror and the pane on which the light from a distant object is focused.
Eyepiece
The lens that is closest to the eye in a telescope. Changing the eyepiece will change the magnification of the image in the telescope.
Chromatic Aberration
A detrimental property of a lens in which rays of different wavelengths are brought to different focal distances form the lens.
Dispersion
The separation of rays of light into their component wavelengths
Compound lens
A lens made up of two or more elements with different refractive indices, the purpose of which is to minimize chromatic aberration.
Reflection
The direction of a beam of light that strikes but does not cross the surface between two media having different refractive indices.
Diffraction
The spreading of a wave after it passes through an opening or beyond the edge of an object.
Diffraction limit
The limit of a telescope’s angular resolution caused by diffraction.
Astronomical Seeing
A measurement of the degree to which Earth’s atmosphere degrades the resolution of a telescope’s view of astronomical objects
Adaptive Optics
Electro-Optical Systems that largely compensate for image distortion caused by the earth’s atmosphere.
Arcsecond
1/3600 of a degree of arc.
Magnification=-
Telescope focal length/eyepiece focal length.
What are the limitations of a refraction telescope?
1) Physical size limits due to the weight of the lens.
2) Chromatic Aberration
3) Need a large focal length to produce a large image.
Who made the first reflection telescope?
Sir Isaac Newton. It used a copper primary mirror and a secondary mirror angled at 45 degrees. The secondary mirror angled the light towards the eyepiece.
What makes a good location for an observatory?
1) High. 2) Dry. 3) Dark.
Integration Time
Time interval during which the eye can add up photons. Approximately 30 ms.
Quantum efficiency
Determines how many responses occur for each photon received. For the human eye 10 photons must strike a cone within 100 ms to activate a single response. So our eyes have 10 percent efficiency.
How were early astronomers limited by the human eye?
Because of the integration time and quantum efficiency of the eye. Even large telescopes created images which were very faint and hard to discern using the human eye.alone?
Photographic Plates
Used by astronomers. Had 1-3 percent efficiency and used long esposure times to capture an image.
Charged Coupled Device
Created by bell laboratories. Linear capturing devices which electronically record images. Efficiency of up to 80 percent at some wavelengths. Photons strike pixels which creates small electrical charges within the silicon.
Spectroscopy
The study of an objects spectrum
Spectrographs
Instruments that take the spectrum of an object and record it.
Diffraction Grating
Used in modern electrocardiographs. Uses engraved closely spaced lines in glass to disperse incoming light into its constituent wavelengths.
What are the three most important elements of a telescope?
1) Light gathering power.
2) Resolution
3) Magnification
Focus
Where the light comes together in a telescope to produce an image.
Spherical Abbe-ration
Light through a lens come into focus at different points.
Angular Resolution
Separation of objects in terms of angle. wavelength/diameter of telescope.
Light Gathering Power
pie/5 (D^2)
