Physics 📚📌

• The above observations are only valid when the distance between the slit and the screen is large
• Spectrograph


  An instrument used to obtain and record an astronomical spectrum by splitting or dispersing the light from an object into its component wavelengths
• Ways to split or disperse light into a spectrum

  • Using a prism
  • Using a diffraction grating
• Most astronomical spectrographs use diffraction gratings rather than prisms
• Diffraction gratings


  • Consist of thousands of narrow, closely spaced parallel slits
  • Due to interference, the intensity of the light travelling through the slits depends on the wavelength and direction of propagation
• Diffraction gratings are more efficient than prisms, which absorb some of the light passing through them
• Every incident photon is precious when trying to get a spectrum from a faint source, so scientists prefer using a diffraction grating
• The response of a diffraction grating is linear, whereas a prism disperses the blue light much more than the red part of the spectrum
• Main components of a modern slit spectrometer

  • Slit
  • Collimating mirror
  • Diffraction grating
  • Detector
• The slit allows only a small portion of incident light required for the spectral analysis to enter the spectrograph, and helps to filter out any stray light
• The collimator focuses the light onto the diffraction grating
• The diffraction grating splits the light into its constituent colours
• The spectrum is finally captured by a detector or a camera lens and fed into a computer for further analysis
• Figure 9.32 shows the schematic diagram and the main components of a slit spectrograph used for spectral analysis of the light from the stars