Calculating the Magnitude of the ISS

In summary, the pixel value for a point on the ISS corresponds to the absolute magnitude of the ISS. The apparent magnitude of the ISS can be calculated by subtracting the absolute magnitude of the known star from the pixel value for the point on the ISS.
  • #1
moon1989
1
0
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
 
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  • #2
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 [itex]m_{1} - m_{2} = -2.5 \log_{10} \left( \frac{f_{1}}{f_{2}} \right)[/itex] to calculate the magnitude of the ISS.
 
  • #3
moon1989 said:
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/
 

1. How is the magnitude of the ISS calculated?

The magnitude of the ISS is calculated by measuring the amount of light reflected by the space station and comparing it to the brightness of known stars. This is known as the apparent magnitude method and is commonly used for calculating the brightness of celestial objects.

2. What factors affect the magnitude of the ISS?

The main factors that affect the magnitude of the ISS are its distance from the observer, its orientation in space, and the angle between the observer and the sun. Weather conditions and the amount of light pollution in the area can also impact the perceived brightness of the ISS.

3. Does the magnitude of the ISS change over time?

Yes, the magnitude of the ISS can change over time due to its orbit around the Earth. As the space station moves closer or further away from the observer, its brightness can appear to fluctuate. Additionally, changes in the ISS's orientation can also affect its magnitude.

4. What is the typical magnitude of the ISS?

The typical magnitude of the ISS varies depending on its position in orbit and the observer's location. On average, the ISS has a magnitude between -1 to -3, making it one of the brightest objects in the night sky. However, it can appear brighter or dimmer depending on the factors mentioned above.

5. How can I calculate the magnitude of the ISS myself?

To calculate the magnitude of the ISS yourself, you will need to know its current position and orientation, as well as the observer's location and the current weather conditions. There are online tools and mobile apps available that can help you calculate the magnitude of the ISS based on these factors. You can also learn how to use the apparent magnitude method to estimate the brightness of the ISS using known stars as reference points.

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