Slide 1
A curved mirror collects and focuses faint light
A reflecting telescope uses a curved mirror to gather light and bring it to a focus. Its central job is to collect information from a small patch of sky.
More to Read
The main mirror is called the primary mirror. Additional mirrors can redirect the focused light toward an instrument, so the detector need not sit directly in the incoming beam.
Slide 2
A wider aperture collects more photons
The aperture is the width of the light-collecting opening. A larger mirror can collect more photons from the same object during an equal exposure.
More to Read
For unobstructed circular mirrors, collecting area grows with diameter squared. Doubling the diameter gives four times the area, before accounting for losses from coatings, obstructions and detector efficiency.
Slide 3
Sensitivity and sharpness answer different questions
Sensitivity is the ability to detect a faint signal. Angular resolution is the ability to distinguish nearby objects or details in the sky.
More to Read
At a given wavelength, a larger ideal aperture can also resolve finer detail. Atmospheric turbulence and optical imperfections can prevent a real telescope from reaching that theoretical limit.
Slide 4
Detectors and instruments turn light into measurements
A detector records the arriving signal. Filters or a spectrograph can separate parts of the light to answer different questions about an astronomical object.
More to Read
An image maps where light arrives, while a spectrum separates it by wavelength. The same telescope can therefore support different investigations by feeding different instruments.
Slide 5
Magnifying cannot restore detail that was never collected
Enlarging a telescope image does not restore information that was never collected. Aperture, observing conditions and instrument quality shape the useful result.
More to Read
A longer exposure can improve the detection of faint sources, but it does not automatically overcome atmospheric blur. Choosing an observing strategy begins with the kind of information the question requires.
Sources
- Telescopes
OpenStax, Rice University
- Observations outside Earth’s Atmosphere
OpenStax, Rice University