Three Fathoms Observatory
Stewart Yeung








Current Special Feature       

Special Feature on 5 August 2008 : Interpretation of Satellite Track Image


The astrophoto of M13 shown below was taken in 2 minutes at an image scale of 0.63"/px.

Incidentally this image captured a satellite track.



It happens that the Paramount ME has a gear system with a period of about 2 minutes.

So what can be deduced from the zip zap shape of the satellite track ?


        My interpretation : The zip zap records the periodic error. A ballpark estimates in Iris indicates a less than 4 pixels deviation from a straight line,

which amounts to 4 x 0.63" = 2.5" . Hence the periodic error of my Paramount ME is less than 2.5".


I've posted this deduction question to the SBIG discussion group and feedback will be gathered.

This special feature will be updated as the feedback comes along.


Thanks to R. Hamlett and Chris Peterson for their feedback.

Update on 6 August 2008 :

1.    My interpretation is simplistic and downright wrong. Obviously the satellite moved much faster than 7.5"/second

 (across the 15'  vertical FOV during the 2 minutes exposure). So the length of the satellite track doesn't correspond to a complete worm period at all.

2.    One valid deduction from the satellite track is that the system is slightly out of focus as evidenced by the double pattern of the track.

3.    A more remote conjecture, arising from the  slight broadening of the track at one end, is that the image plate is slightly tilted.

However, fluctuation due to changing seeing conditions may have equally caused this broadening .