# Question about stellar classification and names **URL:** \ **Category:** Factual Questions\ **Created:** [November 5, 2013, 4:47am UTC](https://boards.straightdope.com/t/question-about-stellar-classification-and-names/673128 "2013-11-05T04:47:45Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![wevets](https://avatars.discourse-cdn.com/v4/letter/w/e9a140/32.png) [@wevets](https://boards.straightdope.com/u/wevets)\ **Post date:** [November 5, 2013, 4:47am UTC](https://boards.straightdope.com/t/question-about-stellar-classification-and-names/673128/1 "2013-11-05T04:47:45Z")
Hi any astronomers out there - I’m trying to write some science fiction for NaNoWriMo, and I’ve been thinking about setting an alien civilization on a fictitious planet circling a star that might be known as Gliese 364 (it might also be known as I Hydrae according to [this page](http://www.atlasoftheuniverse.com/50lys.html)) a little less than 50 light years from here. I have two questions if anyone can help me out: Are Gliese 364 and I Hydrae both names of the same star? (I’m confused because [this other page](http://www.astrostudio.org/xhip.php?hip=47522) identifies I Hydrae as a different star 500+ light years away.) I’m also wondering about the classifications - one of these stars is classified G0V, and the other is F9IV… I gather from [wikipedia’s stellar classification article](http://en.wikipedia.org/wiki/Stellar_classification) that G0V would be hotter that the sun but still main sequence, while F9IV would be both much hotter than the sun and much larger… is that right? What else could we know from the classification? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 5, 2013, 3:55pm UTC](https://boards.straightdope.com/t/question-about-stellar-classification-and-names/673128/2 "2013-11-05T15:55:42Z")
The Sun is a G2V, so while a G0V would be a bit hotter, it’d still be basically Sunlike. As for the specific star or stars you’re asking about, I’m not really finding anything resembling consistent information on them, and one of the top Google hits is a paranormal site. ---
**Author:** ![wevets](https://avatars.discourse-cdn.com/v4/letter/w/e9a140/32.png) [@wevets](https://boards.straightdope.com/u/wevets)\ **Post date:** [November 5, 2013, 5:05pm UTC](https://boards.straightdope.com/t/question-about-stellar-classification-and-names/673128/3 "2013-11-05T17:05:38Z")
Which one is a paranormal site? Was it one of the ones I linked to? At least I could avoid anything from there. ☹ Are there any good star atlases available online? If I can at least find a source that should be reliable, I can stick with it instead of the random crazies convinced UFOs are the reason their text messages never go through. ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [November 5, 2013, 5:12pm UTC](https://boards.straightdope.com/t/question-about-stellar-classification-and-names/673128/4 "2013-11-05T17:12:04Z")
Why not use the Kepler data here –\> [http://kepler.nasa.gov/Mission/discoveries/](http://kepler.nasa.gov/Mission/discoveries/) You would (if you’re looking for earth like conditions) want the Stellar effective Temp and Stellar Mass and Metallicity to be roughly on par with Sol. Earth and Jupiter are both listed so Sol is already in to help with the comparison. I should add that the table is for confirmed planets which is only a part of Kepler’s output - you could dig around in the candidate lists. ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [November 5, 2013, 5:23pm UTC](https://boards.straightdope.com/t/question-about-stellar-classification-and-names/673128/5 "2013-11-05T17:23:04Z")
You could also go to the Gliese catalog at Heidelberg University : [ARICNS 4C00756](http://wwwadd.zah.uni-heidelberg.de/datenbanken/aricns/cnspages/4c00756.htm) Gliese 364 comes up as [ARICNS 4C00756](http://wwwadd.zah.uni-heidelberg.de/datenbanken/aricns/cnspages/4c00756.htm) that has RA 09 42 14 and DEC -23 54.9 That lines up HD 84117 in Hydra [HD 84117 - Wikipedia](http://en.wikipedia.org/wiki/HD_84117) RA 09 42 14 and DEC -23 54 and sits 50 odd light years out. HA! HD 83953 is also called I Hydrae and sits at RA 09 41 17 and DEC -23 35 and is 500 light years distance. Looks like that might be the confusion. ---
**Author:** ![wevets](https://avatars.discourse-cdn.com/v4/letter/w/e9a140/32.png) [@wevets](https://boards.straightdope.com/u/wevets)\ **Post date:** [November 5, 2013, 5:30pm UTC](https://boards.straightdope.com/t/question-about-stellar-classification-and-names/673128/6 "2013-11-05T17:30:36Z")
How about this one: [Uranometria: Stars and Astronomy: Near Star Catalogue](http://uranometria.blogspot.com/p/near-star-catalogue.html) Does that seem like a relatively reliable source? The star in question is given as N16 Hya, a “Variable Designation” of 175 G., a “Gliese Catalog” of 364, and a “Bright Star Catalog HR number” of 84117… This is all pretty confusing - do astronomers have a universal systematic naming arrangement for stars, or does each compiler/catalog give its own designation, resulting in multiple identifies for an individual star? ---
**Author:** ![wevets](https://avatars.discourse-cdn.com/v4/letter/w/e9a140/32.png) [@wevets](https://boards.straightdope.com/u/wevets)\ **Post date:** [November 5, 2013, 5:31pm UTC](https://boards.straightdope.com/t/question-about-stellar-classification-and-names/673128/7 "2013-11-05T17:31:44Z")
Oh, didn’t see your post before I posted, **Grey** - that’s very helpful, thanks! 🙂 ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 5, 2013, 6:46pm UTC](https://boards.straightdope.com/t/question-about-stellar-classification-and-names/673128/8 "2013-11-05T18:46:19Z")
> [@](#): > > …or does each compiler/catalog give its own designation, resulting in multiple identifies for an individual star? Mostly this. The lists tend to have different depths, and you generally use the name from the shortest list that works. ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [November 6, 2013, 2:34am UTC](https://boards.straightdope.com/t/question-about-stellar-classification-and-names/673128/9 "2013-11-06T02:34:18Z")
Note: F class stars are hotter than G class stars. The order is OBAFGKMS. The nmemonic to remember this is “Oh Be A Fine Girl, Kiss Me Smack!” There are some oddball categories not provided here, but they would not main sequence stars. Also, I forget if “S” is really a main sequence class, or also an oddball class, at best. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [November 6, 2013, 7:46am UTC](https://boards.straightdope.com/t/question-about-stellar-classification-and-names/673128/10 "2013-11-06T07:46:59Z")
> [@Jinx](#): > > Note: F class stars are hotter than G class stars. The order is OBAFGKMS. The nmemonic to remember this is “Oh Be A Fine Girl, Kiss Me Smack!” There are some oddball categories not provided here, but they would not main sequence stars. Also, I forget if “S” is really a main sequence class, or also an oddball class, at best. S is more of an oddball class. The sequence is now OBAFGKMLTY, where L and T are for brown dwarfs and Y is for objects too cold to be those. Y objects are generally around 300 to 400 kelvins (note that 300 kelvins is about room temperature). But equally important is the Roman numeral after the spectral class. A V there indicates a main sequence star such as the sun. An IV is a subgiant, which is a star that’s no longer on the main sequence but has moved off it on the way to being a giant. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 6, 2013, 5:47pm UTC](https://boards.straightdope.com/t/question-about-stellar-classification-and-names/673128/11 "2013-11-06T17:47:23Z")
I’ve also seen the sequence as OBAFGKMRNS. I can’t remember what sorts of objects are described by R, N, and S, but they’re apparently not considered as important as the L, T, and Y categories nowadays. In any event, everyone agrees on O through M. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [November 6, 2013, 6:45pm UTC](https://boards.straightdope.com/t/question-about-stellar-classification-and-names/673128/12 "2013-11-06T18:45:58Z")
> [@Chronos](#): > > I’ve also seen the sequence as OBAFGKMRNS. I can’t remember what sorts of objects are described by R, N, and S, but they’re apparently not considered as important as the L, T, and Y categories nowadays. In any event, everyone agrees on O through M. R and N are [carbon stars](http://en.wikipedia.org/wiki/Carbon_star). [Class S](http://en.wikipedia.org/wiki/S-type_star) has unusual elements in its atmosphere. They all look redder than they would based just on their temperature, so they were placed after M. The spectral classes were originally based on the color of the star but are now based on temperature.