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Planet Orbiting a Star

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Summary of Current Information
A. The Parent Star
B. The Exoplanet
Photometry Observational Data

The graph plots the un-calibrated signal minus the average signal from the instrument. When a planet passes in front of the star (making a transit across the star), the total light output drops accordingly. This causes the larger observed dips in the graph.

Note #1: If desirable, the plot may be printed so that the data may be measured more accurately. Simply click on the graph and then print the resulting web page.

Note #2: If no transits are observable in the data, then go beack to the previous page and select a different star.

I. Calculating Orbital Information from the Observational Data

A. Period of the Exoplanet

From the graph above, calculate the average time between transits of the planet across the star face. (Find the day of the first and last transit and divide by the number of time intervals between these transits.) Then enter this period in days in the formula below.

  Period = days (1 yr / 365.25 days)

Period = yr
(Press the calculate button to convert the period of the exoplanet from days into years.)

B. Distance of the Exoplanet from Its Parent Star

The third law of planetary motion derived by Johannes Kepler (and modified by Isaac Newton) connects the orbital period of a planet in our solar system, the mass of the Sun and the planet's average distance from the Sun.

Astronomers have been able to estimate the mass of a star if it is a main sequence star (on the H-R diagram) and if its spectral type is known. See the table.

Stellar Masses (in units of solar masses)

Spectral Type 05 B0 B5 A0 A5 F0 F5 G0 G5 K0 K5 M0 M5
Stellar Mass 40 17 7.0 3.5 2.2 1.8 1.4 1.07 0.93 0.81 0.69 0.48 0.22

Locate the spectral type for this star and read off its mass. Then enter this number in the appropriate empty box below.

Kepler's third law can be written as:

  p2    M    =    a3
  ( yr)2 sol. mass. = (AU)3
(Press the calculate button to find the average distance the exoplanet is from its star.)


Press the "Next Page" button to continue your analysis.


Notes on the Photometric Observations

Notes on Kepler's Third Law

Hints (Reminders)

More Info

Simulation Authors: Richard L. Bowman (Bridgewater College) and David Koch (Kepler Mission)

Maintained by: Richard L. Bowman rbowman@bridgewater.edu (2002-04; last updated: 19-Apr-04)