A Transiting Planet is detected by the change
in the light from its star, being reduced while
the planet passes in front of the star, producing
a curved graph (Exoplanet Eclipse Light Curve)
if light is plotted against time.
This Light Curve offers information about the planet.
- The amount of reduction is related to the relative sizes of the planet and star, and to the degree that the size of the star can be determined, the planet's can as well.
- Viewing the transit with filters or with a Spectrograph and comparing with the starlight before/after the Transit reveals Photometry and Transmission Spectroscopy information about the Atmosphere.
- When the planet is in position to reflect the star's light, photometry or Spectroscopy of the light reflected can be determined, revealing characteristics of the material on the surface of the planet.
- At the beginning and end of the transit, the increase/decrease of light reveals information about the thickness of the planet's atmosphere and its density at different levels.
- Changes in the length of the period of reduction reveal information about the planet's orbit.
Getting spectrographic data requires Differential Spectroscopy,
comparing the spectrum at different points in the planets orbit
including before, during and after the eclipse. This use
of spectroscopy is known as Occultation Spectroscopy.
The transit of the planet across the star is also called
the Primary Eclipse. The Secondary Eclipse, the
planet passing behind the star, also produces light curves
revealing information about the planet, by watching which
Wavelengths are reduced, when, and by how much.