Star spectrum
If light (especially sunlight ) is allowed to fall through a narrow slit onto a prism or onto a diffraction grating , the light beam is broken down into its individual color areas - the so-called spectrum .
As a star's spectrum , the spectrum of is point-like appearing orb called. Its generation does not necessarily require a slit diaphragm, because the light beam falling into the astronomical telescope is practically parallel, but it is advantageous to fan out the light beam to the side (see also collimator ). By attaching a flat prism in front of the lens , one obtains short star spectra of an entire star field , which allows a rough determination of the “ spectral classes ” (color temperature) of the stars photographed.
A well-resolved star spectrum can be viewed not only as a colored band, but also as a mathematical function that describes the intensity of the observed light as a function of the wavelength . A range of information about the star can be extracted from such an accurate spectrum:
- the surface temperature
- by comparison with the ideal curve of a black body radiation
- from the strongest wave range of light (see Wien's law of displacement )
- the abundance of chemical elements in the star's upper (radiating) layer - which follows from its line spectrum
- the luminosity through the relative line intensity of certain spectral lines. The luminosity (absolute brightness) together with the apparent brightness enables the determination of the distance of a star (spectroscopic parallax )
- the speed of rotation (also for other celestial bodies) - from the broadening of the spectral lines compared to the line width expected based on the surface temperature . For this, at least the approximate radius of the star is required.
- the radial velocity - from the shifts of the spectral lines due to the Doppler effect
- as well as indications as to whether the star is in a double star system (see spectroscopic double star )
- There can also be references to extrasolar planets because the star then orbits around the barycenter (common center of gravity of the star system ).
The spectroscope (visual) and the spectrograph (photographic) serve as measuring instruments for observing star spectra . Newer instruments can also record the spectra (i.e. the frequency-dependent light intensity) digitally .