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Astronomy & optics

Simplified exoplanet transit depth

Estimate the relative dimming during the full transit of a dark planet across a uniformly bright stellar disc.

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01

Your inputs

The starting values are an example.

Decimals: 12.5 · Thousands: 1,234.56. Follow the field instructions for lists.

02

Your result

Enter your values and select Calculate.

Your calculation will appear here.

Your result will include the relevant values and units.

Understand the calculation

Formula and example

How it is calculated

Relative light loss ≈ (planet radius/star radius)²

Worked example

If the planet’s radius is one tenth of the star’s radius, the model gives a light loss of 1%, or 10,000 ppm.

Things to check

  • Both radii must use the same length unit. A radius ratio is sufficient.
  • The model assumes a full transit. Limb darkening, a grazing transit and additional light in the measurement field change the actual depth.