Astronomers use different techniques to extract information from the light that they detect with detectors Celestial objects emit light (different wavelengths) Telescopes are used to see these distant celestial objects Detectors (like CCDs) are used to record information about the light (what type of information is dependent on the astronomical technique used)
These methods are used to establish the properties of the celestial object that is under study What a celestial object is made of What the intensity of a celestial object is in different wavelengths Where the celestial object is so others can study it and confirm others observations Shape of the celestial object What the magnetic field of the celestial object is And many more properties
Spectrometry (Spectroscopy) Element identification and other important information Using Spectrometer Prism (splits light) Diffraction Grating Images: Wikipedia and NASA
Spectroscopy There our many spectroscopy techniques in science; here we are referring to Atomic Spectrometry (or Atomic Spectroscopy ) Spectroscopy is the study of how light interacts with materials Atomic spectroscopy is the study of elements from the light they emit or absorb (spectrometry is the actual measurement really not a recognized difference today) Thermal infrared spectroscopy is also used by astronomers. There are dozens of different types of spectroscopy Chemistry, Physics, Biology, and Engineering all use spectroscopy
Spectroscopy Is it spectroscopy or spectrometry? Spectrometry is the actual measuring where spectroscopy is the study (science), but for all intensive purposes today they mean the same thing Technically there are three different things: spectroscopy, spectrometry, and spectrography Spectroscopy is the study of light and matter interaction Spectrometry is the technique of measuring this interaction Spectrography is the photographic measurement of the spectrometer (spectroscope): not really used as much now Same idea as photometry, and photography (there is no photoscopy however there is a photoscope)
Spectroscopy Using a grating or slits the spectrum is split (like a prism does) into its component parts Two results might appear (emission or absorption) Hydrogen spectrum seen here (example of an emission spectrum)
Gratings Diffraction Grating Multiple slits Uses interference of light
Reflection Grating
Photometry Intensity of stars Magnitude Logarithmic scale UVB magnitudes U ~300nm-400nm B ~370nm-550nm V ~480nm-700nm
Astrometry Measures position of stars in the sky RA,Dec Absolute position Relative position (separation) Transit telescope Uses rotation of the Earth Altitude circle has microscopes on them
Polarimetry Measures polarized light Polarized light gives us information on the shape of an object Birefringent polarizers Reflection polarizer
Magnetometry (Zeeman magnetometry) Measures magnetic fields using the Zeeman effect (splits spectral lines) Many celestial objects have magnetic fields Emission lines change due to magnetic fields There are other magnetometry techniques; this is just one specific one
Some astronomical techniques are used to improve or increase the performance of the collection of the light to be studied The method can be used to make a telescope act as a large telescope without increasing its actual size Or a portion the view can be obscured in order to improve the performance of the detector Or a detector might be operated in such a way as to improve light collection (I do not discuss that here)
Interferometry Constructive interference Michelson Stellar Interferometer Intensity Interferometer In essence makes a bigger telescope
Astronomical Technique Gravitational Lensing Uses enormous gravitational objects as a sort of telescope Example is the red Lynx Arc Microlensing (stars still being developed)
Gravitational Lensing Another example Blue images
Studying the Sun Can't look at it directly Herschel wedge, eyepiece projection, or full aperture filter Herschel wedge is the least expensive
Using a Coronagraph to study the sun Uses a disk to block the bright part of the sun Sort of like an artificial eclipse SOHO
Coronagraph Occulting disk Lyot Spot helps to fix problems produced by the occulting disk (fringing)