Observational Astronomy and Instrumentation
Core concepts
Know telescope optics (refracting versus reflecting, focal ratio, plate scale), resolution limits from diffraction and seeing, detector characteristics (quantum efficiency, read noise, dark current), and photometric systems and filters. Understand spectroscopy basics: dispersion, resolution R = λ/Δλ, and line broadening. Cover calibration, signal-to-noise, and the magnitude system.
Traps
Do not confuse angular resolution with sensitivity; a larger aperture improves both but for different reasons. Remember the magnitude scale is inverted and logarithmic. Watch for confusion between resolving power and dispersion. Distinguish seeing-limited from diffraction-limited performance.
Worked example
A 2 m telescope observes at 500 nm. Diffraction limit ≈ 1.22 λ/D ≈ 1.22 × 5×10^-7 / 2 ≈ 3×10^-7 rad ≈ 0.06 arcsec. If atmospheric seeing is 1 arcsec, the actual resolution is about 1 arcsec. Rule of thumb: at 500 nm, the diffraction limit in arcseconds is roughly 0.12 divided by aperture in meters.
Rule of thumb
A magnitude difference of 5 corresponds to a brightness ratio of 100.