11. Mathematically this is defined using limits as the area and solid angle tend to 0. 12. A small object nearby may subtend the same solid angle as a larger object farther away. 13. The peak area-solid angle product response function of each telescope ranges from 0.04 to 0.015 cm2-sr. 14. The ARGUS detector was a hermetic detector with 90 % coverage of the full solid angle . 15. But what solid angle are we talking about? 16. :There is more than just the 360?too, it is actually 4 pi steradians of solid angle . 17. Mathematica : Planck intensity ( energy / sec / area / solid angle / wavelength ) is: 18. :: : : Conveniently that portion is 0, since " straight forward " is zero solid angle . 19. Note that the angle and solid angle are included in this list but are actually dimensionless quantities. 20. Taking an angle of 20 milliradians gives a solid angle of W = 1.3 * 10-3 steradian.