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Explanation of How the Coordinates of an Object are Defined

-- George Papagiorcopulo | February 7, 2021

Question:

I am writing a sci-fi novel and I know very little about astronomy/ I have a Master’s degree in Engineering, so I understand everything on your site, but feel unable to explain it to somebody else.
My question is this: What is the equivalent of “coordinates of an exoplanet” please? Put differently, if you found a new exoplanet, what “unique” information would you give me to direct me to it?

Background to my question: In my novel, the main character has discovered an exoplanet hundreds of light years away and there is a lot of public interest in his discovery after he announces his discovery. But he doesn’t want to say where it is. Normally, if his secret location was on Earth, I would write that he is keeping its “coordinates” secret. What is the equivalent of “coordinates” or “location” of an exoplanet please?

-- George Papagiorcopulo

Answer:

There are a number of different coordinate systems that astronomers use to define the positions of objects in the sky. The most common is called Right Ascension (RA) and Declination (Dec), which are projections of the longitude and latitude coordinates that we use on Earth. RA corresponds to east/west direction (like longitude), while Dec measures north/south directions, like latitude. As you might expect, then, the celestial equator is the part of the sky that is directly over the Earth’s equator. Normally RA is measured in hours, minutes, and seconds, while Dec is measured in degrees, arcminutes, and arcseconds.

-- Jeff Mangum

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