Star Colors

Stars are seen as points of light and it is difficult to see the color of a point, so the techniques I used to better portray the colors of the various stars is to either defocus the star image while I am taking the exposure and/or to allow the star to trail across the camera sensor with the turning motion of the sky. In the images that follow you will see a static image, similar to what you see at night by looking up, followed by images of the same constellation that better reveal the colors of the component stars.

Several Constellations of the evening winter skies

After you finish with all the illustrations on this page, come back to these two images to see what constellations you can identify on this wide angle view (taken with my 14mm lens). The two images are the same; I let the diurnal motion (the movement of the sky) track the stars across the camera chip for 55 minutes for the second image.

For several constellations which follow, I have inverted all the colors to create colored negatives which shows dark stars in bright skies. I have labeled some of the brightest stars in these images with their names, their spectral classes and luminosity classes, their distances in light years, and their temperatures in degrees Kelvin. An explanation of the symbols used is given at the end of this web page.

Cassiopeia

Gemini

Orion

Orion taken through 50mm "regular" lens.

Orion taken through 28mm to 200 mm telephoto lens, at a setting of approximately 35mm.

Taurus

Notice the Pleiades is the tight group (a cluster) of stars in the constellation Taurus, near the top of the frames. I used a 28 mm to 200 mm telephoto lens, set at about 35 mm, to take this image.

Pleiades

I used a telephoto lens (28 mm to 200 mm, lens setting near 200 mm) to produce these images of the Pleiades star cluster, which also appeared in the previous set of images.

Explanation of symbols used, based in whole or part on the book A Spectroscopic Atlas of Bright Stars: A Pocket Field Guide by Jack Martin.

Spectral Type - major characteristics of optical spectrum. Each spectral type (OBAFGKM) is subdivided into 10 numeric catagories (0123456789), so our sun is a G2 spectral type star and Sirius, the brightest star in the sky, is an A1 spectral type star.

O --- singly ionized helium (HeII) in emission or absorption

B --- neutral helium (HeI) lines in absorption

A --- neutral hydrogen (HI) lines in absorption

F --- once ionized calcium (CaII) lines in absorption

G --- neutral metallic lines and once ionized calcium (CaII) lines in absorption

K --- metallic lines in absorption

M --- some molecular bands of TiO in absorption

Spectral Type - temperature of stellar atmosphere (and color of star):

O --- 28,000 - 50,000 degrees K (color: blue)

B --- 9,900 - 28,000 degrees K (color: bluish white)

A --- 7,400 - 9,900 degrees K (color: white)

F --- 6,000 - 7,400 degrees K (color: yellowish white)

G --- 4,900 - 6,000 degrees K (color: yellow)

K --- 3,600 - 4,900 degrees K (color: orange)

M --- 2,000 - 3,600 degrees K (color: red)

C-R --- 2,800 - 5,100 degrees K (carbon star of G/K) (color: deep red)

C-N --- 2,600 - 3,100 degrees K (carbon star of K/M) (color: deep red)

Luminosity Class

Ia --- Bright supergiants

Ib --- Supergiants

II --- Bright Giants

III --- Giants

IV --- Sub Giants

V --- Main Sequence

VI --- Sub dwarfs

VII --- White dwarfs

Luminosity class suffixes for emission lines:

e --- Emission line star

em --- Emission by metal lines

ep --- Pecular emission

eq --- P Cygni emission

er --- Reversed emission

f --- Helium and Nitrogen emission

Other suffixes:

k --- Interstellar lines

m --- Strong metallic absorption

n --- Nebulous diffuse lines

nn --- Very diffuse lines

p --- Chemically pecular spectrum

s --- Sharp lines

si --- Silicon star

v --- Variation in spectrum

wk --- Weak lines