what happens to the light that is missing in an absorption spectrum

Continuum, Absorption & Emission Spectra

• A given atom will absorb and emit the SAME frequencies of electromagnetic (E-M) radiation.
• A gas of hydrogen atoms will produce an absorption line spectrum if information technology is betwixt you (your telescope+spectrograph) and a continuum light source, and an emission line spectrum if viewed from a different angle.
  • If you were to observe the star (a source of white light) directly, you would see a continuous spectrum, with no breaks.
  • If yous find the star through the gas (telescope to right of gas cloud, points towards star through deject), you volition run into a continuous spectrum with breaks where specific wavelengths of energy accept been absorbed by the gas cloud atoms and so re-emitted in a random direction, scattering them out of our telescope axle. Nosotros call this an absorption spectrum (continuous + dips).
  • If you detect the gas merely not the star (telescope below gas cloud, points through gas but abroad from star), y'all volition only see a portion of the scattered low-cal being re-emitted by the gas. The continuum radiation from the star volition not fall into our telescope axle, considering we are pointed away from the star. This is called an emission spectrum (just peaks, not continuous).
  • The Due east-M radiations frequencies absorbed and emitted match the immune energy levels in the atom.
  • The allowed energy levels in an atom depend mostly on the electric field configuration. Hydrogen, with one proton in the nucleus, has a dissimilar field configuration than does Helium with two protons – this is why the two atoms accept a different energy levels and different characteristic absorption and emission lines.

  [NMSU, N. Vogt]

  
  

• Continuum spectrum: A gas can exist collisionally excited. Imagine a hot gas. The atoms are flying effectually, bumping into one some other and sometimes the energy of motion during the collision will bump an electron into a higher energy level (or completely ionize the cantlet, freeing the electron completely). When this electron drops back downwardly to lower free energy, a photon is emitted. This conversion of kinetic energy into radiant free energy cools the gas.
• There is a connection betwixt emission lines from a gas and the continuous spectrum from a solid. As y'all crowd atoms together (as in a solid), the allowed free energy levels in ane atom start to become distorted due to the influence of the electric field of neighboring atoms. Distort an free energy level difference a footling bit and y'all go a slightly unlike frequency emission/absorption line. A distribution of distortions leads to a distribution of lines than eventually blend into a continuum.
• Here we see the fashion that a spectrum fills in every bit the density of our medium increases (from gas to solid) by clumping particles together.

  [NMSU, Due north. Vogt]

• Absorption spectrum: What do stellar spectra wait like (the low-cal observed from stars)? Stars take absorption line spectra. We can recall of stars every bit a hot continuum source with a "absurd" temper of absorbing gas. The wavelengths that get absorbed depend on the chemical make upwardly of the gas in the stellar atmosphere.
• In the 1800's the light from the Sun was dispersed and it looked more-or-less like a Planck spectrum (a blackbody bend) with some missing light, or assimilation lines at certain wavelengths.

  [NMSU, N. Vogt]

• Stellar blackbody spectra have a characteristic shape, with a steep rise, a superlative in or nearly to the visual passband, and a slow decrease in the infrared. Hotter stars take higher peak amplitudes, and peak at shorter wavelengths. Blackbody curves are shown for three stars in the figure beneath, with temperatures ranging from 4,000 K (a cool, carmine star) to vii,500 K (a hot, violet-blue star). Small arrows mark the peak wavelength for each star.

  [NMSU, N. Vogt]

• Emission spectrum: The wavelengths with missing low-cal in a stellar spectrum turned out to be very interesting and important. Their importance was realized after emission line spectra were discovered and investigated by chemists.
• If a gas is heated to the bespeak where it glows, the resulting spectrum has calorie-free at discrete wavelengths that plough out to match the wavelengths of missing lite in stellar spectra. So past studying the spectra of various elements in a laboratory here on Globe, we can determine the composition of the distant stars!

  [NMSU, North. Vogt]

---

Thanks to Mike Bolte (UC Santa Cruz) for the base contents of this slide.

collinsthout1961.blogspot.com

Source: http://astronomy.nmsu.edu/geas/lectures/lecture19/slide02.html

Share this post