Calculating the Magnitude of the ISS

[moon1989]

Hi All,

I have a photo of the ISS and i wanted to calculate its absolute magnitude and compare it to the predicted mag when the photo was taken

I've found the pixel value for a point on ISS and i have also found the pixel value for an identified star in the background.

How would I calculate the ISS absolute magnitude and apparent magnitude from the pixel values. I have the apparent/absolute mag of the known star.


thanks
D

 

[omoplata]

I'm no expert at this but I asked someone who is.

He says you have to do aperture photometry for the two stars (assume the ISS is a star for a moment), get their relative instrument fluxes, and compare them. The instrument flux is just the photon count of the 'blob' the star makes on your digital image (I have no idea how to do it for an analogue image). Aperture photometry is, you just mark the perimeter of the blob (usually a circle) and count the number of photons that hit inside that perimeter.

Since the two blobs are on the same image and therefore from the same instrument, the ratio between the instrument fluxes are equal to the ratio between their real fluxes.
You can use the formula $m_{1} - m_{2} = -2.5 \log_{10} \left( \frac{f_{1}}{f_{2}} \right)$ to calculate the magnitude of the ISS.

 

[Andy Resnick]

Hi All,

I have a photo of the ISS and i wanted to calculate its absolute magnitude and compare it to the predicted mag when the photo was taken

I've found the pixel value for a point on ISS and i have also found the pixel value for an identified star in the background.

How would I calculate the ISS absolute magnitude and apparent magnitude from the pixel values. I have the apparent/absolute mag of the known star.


thanks
D

Interesting question. The ISS reflects sunlight, so a simple estimate would only involve the size and reflectivity of the ISS. More precise modeling would require details about the projected area and how the reflectivity varies with the material and (possibly) angle of reflection.

Or just look it up:

http://heavens-above.com/PassSummar...54&lng=-92.46094&loc=Unspecified&alt=0&tz=CET

http://science.nasa.gov/science-news/science-at-nasa/2002/16oct_spaceships/