How Do You Calculate Telescope FOV Using Earth's Rotation?

[trina1990]

a problem from an olympiad

"A student tries to measure field of view (FOV) of the eyepiece of his/her
telescope, using rotation of the Earth. To do this job, the observer points the telescope
towards Vega (alpha Lyr., RA: 18.5h , Dec: +39° ), turns off its "clock drive" and measures
trace out time, t=5.3 minutes, that Vega crosses the full diameter of the FOV. What is the
FOV of this telescope in arc-minutes?"


may i apply the formula
TFOV( IN ARC MINUTES)=DRIFT TIME IN SECONDS X COS ( DECLINATION) X 0.250684462

I got it to be 61.9 arc minutes...is it ok?

 

[Filip Larsen]

Looks OK to me.