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HD 189733 b.

How would it be if instead of ‘Manreet’, I was given a name something like what is mentioned above? Strange, huh! Imagine being called HD 189733 b by your teacher and saying “Present Miss”. Then probably, your siblings would be named something like HD 189733 c, HD 189733 d, HD 189733 e and so on. And you will be friends with HAT-P-11 b and Kepler-1004 b. Well, well, well! Why would someone even name me or anybody like that? But that is not always the case. Not ‘somebody’ but ‘some buddies’ up there in the sky are named like that. HD 189733 b, HAT-P-11 b, and Kepler-1004 b are names of the exoplanets as listed in NASA’s Exoplanet Catalog.

In a previous blog, Naming the Heavens, I talked about the traditional or the ancient naming system for the stars and the Bayer designations which were based on the apparent brightness of the star. In this blog, I will be talking about a few other stellar designations, star catalogs and finally, why the exoplanets have these weird names. The simplest and apt answer to this is that they are thousands in number. 4,292, to be precise, is the number of confirmed exoplanets as of October 9, 2020 as mentioned in one of NASA’s websites. So, they cannot be given ‘good names’ like yours or mine and later I will talk about what these weird names actually mean.

Credit: Kepler-22b | Space.com

Star Catalogs

Designating the stars, is a very simple, practical and organized way of naming or labelling the stars. Just like Alpha Cygni is a Bayer Designation for the brightest star in the constellation Cygnus- Deneb, 50 Cygni is its Flamsteed designation. John Flamsteed, in the 1700s, cataloged around 2500 stars and numbered them based on the increasing Right Ascension (RA). More about the Right Ascension (RA), Declination (Dec) and other celestial coordinate systems can be known here.

Alternative designations for Deneb are HD 197345 in Henry Draper Catalog, SAO 49941 in SAO Star Catalog, HIP 102098 in Hipparcos Catalog, BD+44 3541 in Durchmusterung Catalog, 777 in FK5 Catalog and ADS 14172 in Aitken Double Star Catalog.

The Henry Draper Catalog gives the Stellar Classifications of 359,083 stars covering the entire sky. The Smithsonian Astrophysical Observatory (SAO) Catalog numbers are given to the stars based on the RA and Dec. The Hipparcos Catalog was made by HIgh Precision PARallax COllecting Satellite (HIPPARCOS) mission of European Space Agency (ESA). This primary goal of the mission was to accurately measure the position of celestial objects in the sky. This mission resulted in high precision measurements of the motion of the stars. It is a catalog of more than 118,200 stars.

Credit: Gaia | NASA Solar System Exploration

Not just these, there are various other catalogs like the Gould Catalog, General Catalog (GC) of Boss, Bright Star Catalog (HR for Harvard Revised Photometry) aka Yale Bright Star (YBS) Catalog, Positions and Proper Motions (PPM) Catalog etc. Various star catalogs are also released, based on some satellite mission or a sky survey like the Gaia Catalog and Hipparcos Catalog based on the Gaia and HIPPARCOS satellites respectively.

Naming the Exoplanets

NASA’s TESS and Kepler missions are the two most popular exoplanet hunters. Kepler has confirmed over 2600 exoplanets whereas TESS has confirmed 79 exoplanets until now. These exoplanets are given weird names based on their stars which are in turn named based on the mission/survey/catalog that discovered them. For example, 51 Pegasi b which was the first exoplanet to be discovered has been named as follows:

‘51 Pegasi’ is the name of its host star as in Flamsteed’s Catalog and the lowercase alphabet ‘b’ specifies that it was the first planet to be discovered revolving around its host star.

Credit: Kepler Space Telescope | NASA

The lowercase alphabets are used for the planets whereas the uppercase alphabets are used for the stars in the system (in case the system is a multiple star system). The brightest star in the system is given the designation ‘A’, the next brightest star ‘B’ and so on. As for the exoplanets, found revolving around these stars, ‘b’ is used for the first planet discovered, ‘c’ is used for the second planet discovered around the host star, ‘d’ for the third and so on.

Another example, Kepler-1004 b, is the name given to the first planet discovered revolving around the 1004-th star discovered by the Kepler Telescope.

Now, suppose, if 3 exoplanets are discovered orbiting around a star at the same time, then they are designated based on the order of their orbits from the star. The planet which is revolving closest to the star is designated as ‘b’, the next one ‘c’ and the one in the farthest orbit as ‘d’. Later, if an exoplanet is discovered between the orbits of ‘b’ and ‘c’ then irrespective of the order of its orbit, it will be designated as ‘e’.

And now, if you want to name yourself like an exoplanet then, here is an activity and so, you can call me MK 110300 b. I would also like to read your Exoplanet Names in the comments below.

Credit: NASA


[1] “Deneb – α Cygni (Alpha Cygni) – Variable And Double Star in Cygnus.” Variable And Double Star in Cygnus | TheSkyLive.com, theskylive.com/sky/stars/deneb-alpha-cygni-star.

[2] “Exoplanet Catalog – Exoplanet Exploration: Planets Beyond Our Solar System.” NASA, NASA, exoplanets.nasa.gov/exoplanet-catalog/.

[3] “How Do Exoplanets Get Their Names? – Exoplanet Exploration: Planets Beyond Our Solar System.” NASA, NASA, exoplanets.nasa.gov/faq/20/how-do-exoplanets-get-their-names/.

[4] “International Astronomical Union.” IAU, www.iau.org/public/themes/naming_stars/.

[5] “Kepler Space Telescope.” NASA, NASA, 24 Sept. 2020, exoplanets.nasa.gov/keplerscience/.

[6] “Transiting Exoplanets Survey Satellite (TESS) – Exoplanet Exploration: Planets Beyond Our Solar System.” NASA, NASA, 24 Sept. 2020, exoplanets.nasa.gov/tess/.



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