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With star names like 2MASS J05551028+0724255, it might seem like astronomers are not so great at naming things. But if you know the code, these names can actually help you find the star in the sky.

Hosted by: Reid Reimers
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Sources:
https://www.iau.org/public/themes/naming_stars/
https://simbad.cds.unistra.fr/simbad/sim-id?Ident=HD+39801
https://cds.unistra.fr/cgi-bin/Dic-Simbad?BD%2b07
https://ui.adsabs.harvard.edu/abs/1995yCat.1122....0A/abstract
http://vizier.u-strasbg.fr/viz-bin/VizieR-3?-source=I/122/bd
https://solarsystem.nasa.gov/basics/chapter2-2/
http://astro.unl.edu/naap/motion1/cec_units.html
https://www.britannica.com/science/right-ascension
https://skyandtelescope.org/astronomy-resources/right-ascension-declination-celestial-coordinates/
https://heasarc.gsfc.nasa.gov/W3Browse/all/bd.html
https://www.iau.org/administration/about/
https://cdsweb.u-strasbg.fr/Dic/iau-spec.html

Images:
https://commons.wikimedia.org/wiki/File:Betelgeuse_captured_by_ALMA.jpg
https://commons.wikimedia.org/wiki/File:Orion_Head_to_Toe.jpg
https://www.gettyimages.com/detail/illustration/orion-constellation-royalty-free-illustration/1203038669?phrase=betelgeuse&adppopup=true
https://www.gettyimages.com/detail/photo/great-ocean-road-at-night-milky-way-view-royalty-free-image/498309616?phrase=stargazing&adppopup=true
https://commons.wikimedia.org/wiki/File:AxialTiltObliquity.png
https://www.gettyimages.com/detail/photo/orion-kenidjack-castle-cornwall-uk-royalty-free-image/1381725810?phrase=betelgeuse&adppopup=true
https://www.gettyimages.com/detail/illustration/high-detailed-sky-maps-vector-set-royalty-free-illustration/859199494?phrase=star%20map&adppopup=true
https://commons.wikimedia.org/wiki/File:Simple_Constellation_Map.png
https://commons.wikimedia.org/wiki/File:Al-Sufi%27s_Orion,_1125_Baghdad_copy,_Doha_Museum_of_Islamic_Art_Ms_2._1998._SO.jpg
https://commons.wikimedia.org/wiki/File:Dunhuang_Star_Atlas_-_Orion.jpg
https://www.gettyimages.com/detail/photo/star-map-of-northern-hemisphere-royalty-free-image/157280056?phrase=star%20map&adppopup=true
https://commons.wikimedia.org/wiki/File:Orion_IAU.svg
https://www.gettyimages.com/detail/illustration/orion-constellation-vector-illustration-with-royalty-free-illustration/1061064662?phrase=betelgeuse&adppopup=true
https://svs.gsfc.nasa.gov/20339
https://commons.wikimedia.org/wiki/File:Eta_Cassiopeiae.jpg
https://commons.wikimedia.org/wiki/File:South_Celestial_Pole.ogv
[♪ INTRO] They might not want to admit it, but astronomers can be pretty bad at naming things.

Take the star Betelgeuse. Sure, that’s a funny name, but astronomers also call it this.

Or one of over forty other names that look just as confusing. Like, seriously? There’s math in that name.

But to astronomers, those letters and numbers are a clearer name than Betelgeuse. That’s because they provide information about the star…for those who know the code. And I’m here to help you join that not-so-exclusive club.

Often, a star’s name, like our own names, will have two or three parts to it. John Michael Green has three parts to his name, and this name for Betelgeuse does too. While the BD comes first, it works more like a family name.

It’s an acronym that stands for Bonner Durchmusterung, a catalog of stars that was first compiled between 1859 and 1903. For those of you who don’t speak German, it’s basically equivalent to the name Bonn Observatory's Survey of Stars. In other words, this part of the name tells us who’s naming the star in the first place.

Now about those numbers. The John Michael of it all. Here’s the good news.

Those numbers aren’t telling us to do math. They’re telling us where Betelgeuse is in the sky! Which makes sense, right?

Having a name that tells you a location is super handy if you’re an astronomer, or anyone who would rather not memorize where every single star is. When we look at the sky, we see all of 3D space collapsed onto the 2D surface of a sphere. And drawn onto that sphere, extending from the Earth’s equator, is an imaginary line called the celestial equator.

The “plus seven” in Betelgeuse’s BD name tells us the star can be found seven degrees north of that equator. It’s a value referred to as declination, and it serves the same role as latitude does on the Earth’s surface. So we’re narrowing down Betelgeuse’s location.

If you look seven degrees above the celestial equator, you’ll see a band of space that wraps all around the sky. But we haven’t pinpointed it yet. There are loads of stars in that band.

Just like there are loads of John Greens that aren’t the man we’re talking about. That’s where the last set of numbers comes in. Like a middle name, it adds specificity.

Now, a sensible astronomer would provide the celestial equivalent to Betelgeuse’s longitude as the second number. But in the BD catalog, astronomers upheld their reputation of being terrible at naming things. So to understand that 1055 value, we have to lay some groundwork.

If declination is like latitude, then Right Ascension is like longitude. But instead of degrees, it uses the term “hours.” And just like zero degrees longitude is arbitrarily set to go through Greenwich, England, zero hours Right Ascension is arbitrarily decided, too. On a map of the sky, it’s here…going through the constellations Pisces and Pegasus.

So the BD in Betelgeuse’s name tells us the list of stars in the so-called family. The plus seven tells us to look only at stars in one band around the sky. And the 1055 means that you start at zero hours Right Ascension, and then start counting stars as you move east until you hit the 1,055th star.

But you have to make sure you only count the stars that are in the BD survey. More modern catalogs can simplify the task further. Like these names for Betelgeuse tell you both the Right Ascension and the Declination, but the one with more digits is a little bit more precise.

Phew. We’re done, right? Now all of those outrageous names should make sense?

Unfortunately, just like different cultures have different ways they come up with names for people, astronomers don’t always follow the same rules for naming celestial objects, either. So humanity has spent millennia renaming the exact same objects according to different rules. Even when those names still hint at their positions.

For example, in one Chinese naming scheme, astronomers assign a star’s name based on which star pattern it’s a part of, plus a counting number starting with one. Betelgeuse is known as Shēn Four. I guess it’d be like naming John Michael Green “Indiana 9,002”.

So sometimes a star’s “family” name tells you the survey catalog it’s found in, like BD. And sometimes it tells you the place in the sky you can find it, like Shēn. But the goal is the same: helping astronomers get at least a vague idea of where a star is without having to know any other information.

There are even names that provide other information, too. For example, the Bayer naming scheme developed in the 17th century bases part of a star’s name on how bright it appears to be relative to other stars in a given constellation. In that catalog, Betelgeuse goes by the name Alpha Orionis.

So if all these naming schemes exist for a star we all just call Betelgeuse, what’s the point? Why isn’t anyone sitting every astronomer down and forcing them to agree on one name, for every star? Well, there is an organization that’s doing that…kind of.

It’s called the International Astronomical Union, or IAU. It was founded in the early 20th century in part to try and establish rules for how to name things in space, including how to format catalog names, and consolidate names that already existed. Like for Betelgeuse, they finally got everyone to use the same spelling.

But for the most part, they’re letting astronomers keep their collection of catalog names. And with new telescope missions launching every however many years, the many names of Betelgeuse are only likely to grow in number. But the IAU is working to assign stars proper names that us non-astronomers might actually have a chance at pronouncing without having to think about math!

That includes putting in effort to make sure those names are more culturally representative, too. So some things in space have far too many names, and most are not what you might consider pronounceable. But that wasn’t the intent when astronomers named them.

Often, they’re just trying to help their colleagues out, and make it easier to find an object in the sky. In that way, some of these terrible names aren’t so terrible after all. But, yeah.

Betelgeuse certainly is more fun to say. Thanks to Patreon patron Jim Canday for asking the question that set this video in motion. If you have burning questions like this one, you can ask us on Patreon too!

Visit Patreon.com/SciShow for all the details. [♪ OUTRO]