Star color
- details

Mitchell Charity <>
  > What color are the stars?
  >   > Star color - details
  >   > Star color - data comparison
  >   >   > Star color - data plots
  >   > Star color - blackbody approximation
  >   > What color is the Sun?
  > What color is a blackbody?

This colorized datafile (.txt) has my second cut at unification.


Sources of model spectra and blackbody Teff's
KuruczKurucz Model Spectra
SilvaSilva Digital Stellar Spectra
PicklesA Stellar Spectral Flux Library (1998)
GunnStrykerGunn & Stryker 1983, ApJS 52, 121. 175 spectra, broad types/classes.
HandbookHandbook of Space Astronomy and Astrophysics (pp 68-70)
TokunagaTokunaga's Effective Temperatures And Intrinsic Colors for [...]

My colors for the sources are compared on Star color - data comparison,
and plotted on Star color - data plots.
Blackbody Teff's are explored on Star color - blackbody approximation.

These colors were calculated using the CIE 1931 2 degree Color Matching Functions as modified by Judd (1951) and Vos (1978) , and the sRGB's color space primaries and gamma correction, and a D65 whitepoint. Using my blackbody color tool hack. (Note particularly the discussion of white-point impact.)


Here is a draft star color datafile (and a colorized version).

Coverage of stellar type/class is clearly partial. If there turns out to be interest in this page, I will likely dig up spectra, and/or perhaps interpolate, to fill in the gaps. It would also be nice to have a principled approach to substituting a similar type/class for a missing one.

All these numbers are approximate!

These are not magic values for pixel color. Each time I change the details of how things are handled, and then regenerate these web pages, different colors fall out. Quite similar, but different.

The choice of white point (D65 vs D50) makes a big difference. I.e., is the Sun bluish or pinkish. sRGB and Rec.709 both use D65.

The choice of gamma correction (sRGB vs Rec.709) makes some difference. And the chromaticities I derive from the various sources are not very tightly clustered. And I may well be making mistakes.

For each type/class, I am blindly averaging (in XYZ space) together the chromaticities of the spectra I have available ( Kurucz, Silva, Pickles ), or of the blackbody chromaticities ( Handbook, Tokunaga ) if I have none. This approach unfortunately creates color discontinuities as one jumps among data sets. I am also missing data on assorted class/types.

What are possible improvements? There are few enough class/types that one could hand craft a set of colors. I am unlikely to do this. One might interpolate missing class/type colors to get a more complete set. Look more carefully at the spectra to determine the sources of variance. Get more complete spectra sets (Kurucz comes to mind). Provide ranges of colors rather than single points (solves a different problem). Broaden the set of class/types covered.

Unless I receive feedback to the contrary, I am likely to leave the current color selection approach, and worry about other things. Like adding D50 colors.


White Dwarf stars use a completely different spectral classification system from the one given above. A white dwarf's spectral class always starts with a capital "D", which stands for Degenerate. The letter after the D is either an A, B, C, O, Z, or Q, which indicates whether certain elements are present in the star's spectral lines at all. After this second letter comes a number from 0 to 9, which indicates its surface temperature -- 0 being the hottest at about 50 000 Kelvins, 9 being the coolest at around 10 000 Kelvins. It is this number, rather than the D or the second letter, which is your best indicator as to the white dwarf's color.

Color indices: The relative brightness of this star between certain frequency filters, or "colors", of light. A star's magnitude isn't just measured in the visual (yellow-centered) portion of the spectrum; it can also be measured in the blue-centered end of the visible spectrum, or in the red-centered end, or in the near ultraviolet, or in the near infra-red. There are standardized frequency-range filters that are used to measure a star's brightness in some portion of the spectrum. These filters are given one-letter names: U is ultra-violet, B is blue, V is visual (yellow), R is red, and I is near infra-red. The difference between a star's magnitude in two adjacent filters -- U minus B, B minus V, R minus I -- can then be used to determine the star's color, and thereby its "color temperature." The lower the magnitude difference, the brighter the star is in the higher of the two frequency-range filters, because a higher magnitude means a dimmer light source. For example, our sun has a B-V index of +0.65, while the much hotter star Sirius has a B-V index of +0.00, and the very cool star Proxima Centauri has a B-V of +1.83. For cool class M stars, R-I gives the best precision as to what color and temperature the star is; for hot class A, B, or O stars, U-B is a better color temperature indicator.
[from Internet STELLAR DATABASE - fields]


White dwarfts...
D?0 100000 K #9bb2ff
D?1 50400 K #9fb5ff
D?2 25200 K #a8bdff
D?3 16800 K #b3c5ff
D?4 12600 K #c0cfff
D?5 10080 K #cfdaff
D?6 8400 K #e0e6ff
D?7 7200 K #f3f3ff
D?8 6300 K #fff7f5
D?9 5600 K #ffefe1
using Teff = 50400 / temperature_index. [a src]
I've not run white dwarf model spectra.

-0.40  113017 #9bb2ff 0.25   7483 #eeefff 0.90   5052 #ffe8ce 1.55   3892 #ffd29c
-0.35   56701 #9eb5ff 0.30   7218 #f3f2ff 0.95   4948 #ffe6ca 1.60   3779 #ffd096
-0.30   33605 #a3b9ff 0.35   6967 #f8f6ff 1.00   4849 #ffe5c6 1.65   3640 #ffcc8f
-0.25   22695 #aabfff 0.40   6728 #fef9ff 1.05   4755 #ffe3c3 1.70   3463 #ffc885
-0.20   16954 #b2c5ff 0.45   6500 #fff9fb 1.10   4664 #ffe2bf 1.75   3234 #ffc178
-0.15   13674 #bbccff 0.50   6285 #fff7f5 1.15   4576 #ffe0bb 1.80   2942 #ffb765
-0.10   11677 #c4d2ff 0.55   6082 #fff5ef 1.20   4489 #ffdfb8 1.85   2579 #ffa94b
-0.05   10395 #ccd8ff 0.60   5895 #fff3ea 1.25   4405 #ffddb4 1.90   2150 #ff9523
-0.00   9531 #d3ddff 0.65   5722 #fff1e5 1.30   4322 #ffdbb0 1.95   1675 #ff7b00
0.05   8917 #dae2ff 0.70   5563 #ffefe0 1.35   4241 #ffdaad 2.00   1195 #ff5200
0.10   8455 #dfe5ff 0.75   5418 #ffeddb 1.40   4159 #ffd8a9
0.15   8084 #e4e9ff 0.80   5286 #ffebd6 1.45   4076 #ffd6a5
0.20   7767 #e9ecff 0.85   5164 #ffe9d2 1.50   3989 #ffd5a1
[Used B-V -> Te calculation from here (Javascript).]

Main Sequence ( Class V )
B0 -0.30 26500 K #a7bcff
B5 -0.16 13800 K #bbccff
A0 0.00 9850 K #d1dbff
A5 +0.14 8260 K #e2e7ff
F0 +0.31 7030 K #f7f5ff
F5 +0.43 6400 K #fff8f8
G0 +0.59 5900 K #fff3ea
G5 +0.66 5660 K #fff0e3
K0 +0.82 5240 K #ffead5
K5 +1.15 4400 K #ffddb4
M0 +1.41 3750 K #ffcf95
M5 +1.61 3100 K #ffbd6f
Supergiant Stars ( Class I )
B0 -0.27 21000 K #acc0ff
B5 -0.10 11500 K #c5d3ff
A0 +0.01 9400 K #d5deff
A5 +0.11 8300 K #e1e7ff
F0 +0.19 7500 K #eeefff
F5 +0.37 6800 K #fcf8ff
G0 +0.70 5800 K #fff1e7
G5 +1.01 5100 K #ffe8d0
K0 +1.12 4900 K #ffe5c8
K5 +1.62 3750 K #ffcf95
M0 +1.63 3660 K #ffcd90
M5 +1.62 2950 K #ffb866
Giant Stars ( Class III )
G5 +0.92 5010 K #ffe7cc
K1 +1.10 4580 K #ffe0bc
K3 +1.30 4210 K #ffd9ab
M0 +1.55 3660 K #ffcd90
M3 +1.60 3300 K #ffc37c
[ Odenwald's Can the B-V colors of stars be used to estimate their temperatures? ]
Note you must know a star's luminosity class to get a good B-V to Te mapping.
"For example, [...] a K5 Supergiant with B-V = +1.62 has T=3750 , but a main sequence star with the same B-V would be an M5 star with T=3100 , a difference of 650K." [private communication]

Some very rough additional colors...
The FAST data isn't yet online (as of 2001-Jun-15), but I yanked very low resolution spectra from the gif images of the spectra graphs. And mishandled them into these colors. All very crufty. The main thing I take away from this is that planetary nebula are still the most colorful things I've encountered.

Pre-main sequence FUOri type TTauri type N0 N4 N7 R2 R5 R8 S S5 WN6 Wolf-Rayet WC8 WC5 WN3 WN9 C White dwarfs, unknown luminosity class :( DO? (H and He features) DC? (featureless continuum) DQ? (carbon features) Supernova Type II Supernova Type Ia another another Supernova SN99cb

Again, don't believe these colors.

Excerpts from correspondence with a reader...

   > > > Descriptions of stellar types often say things like "yellow".

   > > Those 'yellow' stars are white, and what are usually termed 'red' stars are 
   > > yellow to yellow-orange. Stellar types are defined using for calibration the 
   > > blue star Vega, which provides an extremely simple spectrum at the '0' 
   > > magnitude. The colors assigned stars were never intended to have any 
   > > relationship to reality, but simply showed the temperature relative to Vega. 
   > > Thus we have the seeming absurdity of our overwhelmingly, brilliantly white 
   > > Sun being called a 'yellow' star.

   > Fascinating.  What an unfortunate naming scheme.
   > I wonder if it started out fully qualified ("Vega-yellow", "yellow
   > relative to Vega"), and then degraded, or whether correct interpretation
   > always presumed domain knowledge.  At this point, judging by some of the
   > colors used in stellar type tables by astronomers teaching intro
   > astronomy classes, this context is sometimes forgotten even within the
   > profession.  And outside...  what a mess.

  It did [presume domain knowledge], but that 'domain' was originally
  comprised of astronomers doing photometry who would presumably
  understand the system.


Color Index and Temperature Conversion - interactive B-V to Teff conversion.
Libraries of stellar spectra - very nice.
The FAST Stellar Spectral Atlas
Spectra Converter - there are also alternate versions - the site is currently (2001-Jun-23) in flux.

Comments encouraged - Mitchell Charity <>

  Red shift shows up as movement along the blackbody curve.
    I suspect some of these datasets may not be redshift corrected.
  Pickles has some interesting values.

  Mention redshift issue in body.
  Describe D65 vs D50 vs Sun as white.
  Move the individual colorized datafiles online.
  Believe Pickles' outliers?
  vanilla/metal-{rich,poor} table.
  Fill in type/class gaps.
  Add R N S W L T etc stars.  RNS obsolete?
  Try for a better set of integrated values.
  Yass. (yet another spectra set)
  Interactive conversion from assorted color indexes and Teff to Teff and pixel.
  Add (sp xy rgb src alldata) table.
  Add full Kurucz grid.
  Explore BV->K values.  Other color indexes.

  2002-Nov-11  Fixed links broken by CVRL move.
  2002-Jan-02  Added excerpt of old correspondence re Vega "whitepoint".
  2001-Jun-23  Added white dwarfs.
  2001-Jun-22  Edited to reflect Jun-15 combination approach.  Oops.
  2001-Jun-15  New dataset combination approach.   FAST hack colors.
  2001-Jun-13  Added D, color-index notes.
  2001-Jun-08  Added GunnStryker (sortof).
  2001-Jun-07  Added Odenwald B-V table.  Added Pickles.
  2001-Jun-05  Added B-V table.
  2001-Jun-04  on-line