Some Examples using Sharpless 308

Making a color image from astronomical data

The color image of Sharpless 308 is really a composite of 2 images that were taken with different filters using the Mount Laguna 1m telescope. Below I show the color composite image adjacent to a black and white negative of these two images. The first black and white image was taken by placing a filter in front of the camera which transmitted a small portion of the optical spectrum around the H-alpha emission line (wavelength=6562 Angstroms, a photon with this wavelength is emitted when an electron in the 3rd excited state of a hydrogen atom drops to the 2nd excited state). A positive version of the H-alpha image was used to scale the value in the red channel of an RGB image.

The second black and white image was taken with the same instrument as the first image but the filter was changed to one which transmits a small portion of the optical spectrum around the [O III] emission line at a wavelength of 5007 Angstroms. A positive version of the [O III] image was used to scale the value in the green channel of the same RGB image.

Note that this image is not a "true" color image but a "false" color image. There are many reasons for this: 1) while the hydrogen emission line is emitted at a red wavelength, and the oxygen emission line observed is at a green wavelength, the images are displayed to show the nebular features in each image and not so that the relative amount of emission in each image are correctly proportioned, 2) there is no blue image, 3) the emission lines are only in a small portion of the the total spectum and therefore do not show the contribution of continuum emission from the gas and stars at wavelengths outside the range the filters transmit.

The Physical Structure of a Wind-Blown Bubble

Just the images so far here...

Last Updated: December 7, 2000