Announcements. This weeks lab: SDSS DR7 Advanced Projects Hubble Diagram Next week: Monday is Veterans Day …no class Week after (Nov 19): last two Observing Nights. Monday 11/19 and Tuesday 11/20. Set-up starts at 6:15pm Homework: Chapter 7 # 1, 2, 3, 4 & 5
We will be concerned mostly with just the visible window
One airmass is defined as the amount of atmosphere directly overhead. If we include Earth’s curvature, the airmass, X, is given by
Rayleigh scattering affects the shorter wavelengths more than longer wavelengths. Ozone absorption is almost entirely in the UV. Dust absorbs all wavelengths uniformly
The extinction coefficient, k, is the slope of the magnitude versus airmass plot. It is wavelength dependent and varies from night to night. Because of this, absolute photometry is extremely tedious. Many astronomers use differential photometry.
ml is the measured magnitude and ml0 is the magnitude that would be measured above the Earth’s atmosphere
Where C is the color index of the star under observation
Atmospheric dispersion causes rainbows for bright objects at high zenith distances
Changes in the density of the air above lead to an effect similar to the light and dark patterns at the bottom of a pool of water
The simplest AO systems use a tip-tilt mirror. More sophisticated systems use a deformable mirror.
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Since there isn’t always a bright star near the target, large observatories use a laser generated artificial star
The SBIG AO8 is a tip-tilt mirror system that attaches to most CBIG CCD cameras
While not as dramatic an improvement as the professional systems, amateur AO systems can definitely improve the image quality