Slide 1
A planet can block a little starlight
A transit occurs when a planet crosses its star from our viewpoint. The star’s measured brightness briefly falls because the planet blocks part of its light.
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Most planetary orbits are not aligned to produce a transit as seen from Earth. A star without observed transits can still have planets whose paths never cross its visible disk for us.
Slide 2
A light curve records the dip
A light curve plots measured brightness against time. Repeated dips with a consistent pattern can indicate an orbiting body passing across the star.
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Other events can also change brightness. For example, two stars can eclipse each other and create a similar dip. Astronomers check its shape, timing and other observations before confirming a planet.
Slide 3
The depth helps estimate relative size
A larger planet generally blocks a larger fraction of its star’s light. Transit depth therefore helps estimate the planet’s size relative to the star.
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If the star’s visible disk were equally bright everywhere, the blocked fraction would be approximately the square of the planet-to-star radius ratio. Real analyses account for brightness variations across the star’s surface.
Slide 4
Repeated transits reveal an orbital period
The interval between successive transits can reveal how long the planet takes to orbit. Several observations help distinguish a repeatable cycle from an isolated event.
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Long-period planets require longer observing campaigns before repeated transits can be seen. A survey’s duration therefore affects which kinds of planetary systems it is most likely to detect.
Slide 5
A radius is only part of the description
Transit measurements constrain planetary size, but size alone does not determine mass or composition. Other observations supply complementary information.
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Combining a radius with an independently measured mass gives average density. Different interiors can have similar overall density, so this limits the possible compositions rather than showing the interior directly.