Journal of Physics & Astronomy

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Refining Planetary Radius Calculations by Exploring the Geometry of Transit Photometry


Affiliations
1 Department of Physics and Astronomy, University of Waterloo, Canada
 

This paper has altered what appears to be the common equation taught and used to calculate the radius of an extrasolar planet, by way of transit photometry. The standard equation is: RPlanet = RStar√B


Where RPlanet is the radius of the planet, RStar is the radius of the star and B is the percentage of light blocked by the planet during a transit, expressed as a decimal.

RPlanet = RStar√B(1-a/dstar)

Where, a is the semi-major axis of the planet’s orbit (i.e. its orbital radius) and dStar is the distance from the observer to the star. There are also two additional derivations in this manuscript, which allow for calculation of the radius using angular measurements. In previous versions of this paper, author has labelled the variables in the equation differently. This is only important for those who have read or intend to read Versions 1 and 2 of this manuscript.

The additional factor in the parentheses does not always make the most significant difference, considering the fraction evaluates to nearly zero in most exoplanetary cases, but it could make a difference considering other calculations depend on an accurate radius calculation, such as volume and density, for example.

This aim of this equation and of this paper is to improve astronomical calculations that make use of exoplanetary transits and transit photometry. The previous, more common equation does not take into consideration the distance of the planet from its parent star. That is what this paper seeks to fix.


Keywords

Photometry, Astronomy, Star.
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  • Epp RJ. Introduction to the Universe. Uni of Waterloo. Phys. 2017; 175.

  • Ratra PA. Refining transit photometry. 2017. Waterloo ON.

  • Ratra PA. A more accurate method to determine the radius of an extrasolar planet by refining the use of transit photometry. 2017.Waterloo ON.

  • Baird CS. Since one satellite can see half of the earth. why do we need more than two satellites in a given network? 2017;28.

  • [No authors listed]. Angular Diameter. 2017;27.

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  • [No authors listed]. Is the Yellowstone Supervolcano About to Erupt. IFLScience (nd). 2017.


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  • Refining Planetary Radius Calculations by Exploring the Geometry of Transit Photometry

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Authors

A. R. Pranav
Department of Physics and Astronomy, University of Waterloo, Canada

Abstract


This paper has altered what appears to be the common equation taught and used to calculate the radius of an extrasolar planet, by way of transit photometry. The standard equation is: RPlanet = RStar√B


Where RPlanet is the radius of the planet, RStar is the radius of the star and B is the percentage of light blocked by the planet during a transit, expressed as a decimal.

RPlanet = RStar√B(1-a/dstar)

Where, a is the semi-major axis of the planet’s orbit (i.e. its orbital radius) and dStar is the distance from the observer to the star. There are also two additional derivations in this manuscript, which allow for calculation of the radius using angular measurements. In previous versions of this paper, author has labelled the variables in the equation differently. This is only important for those who have read or intend to read Versions 1 and 2 of this manuscript.

The additional factor in the parentheses does not always make the most significant difference, considering the fraction evaluates to nearly zero in most exoplanetary cases, but it could make a difference considering other calculations depend on an accurate radius calculation, such as volume and density, for example.

This aim of this equation and of this paper is to improve astronomical calculations that make use of exoplanetary transits and transit photometry. The previous, more common equation does not take into consideration the distance of the planet from its parent star. That is what this paper seeks to fix.


Keywords


Photometry, Astronomy, Star.

References