Definition of AOD (Aerosol Optical Depth) Atmosperic aerosols are microscopic liquid and solid particles suspended in the atmosphere. Aersols can both absorb and scatter light - the combination of which is called extinction. The higher the concentration of aerosols the less star light reaches your telescope. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite collects AOD data each day. The National Oceanographic and Atmospheric Administration (NOAA) makes this information available on its web site at http://www.star.nesdis.noaa.gov/star/smcd.php From Clear(er) Skies Ahead, Phillip J. Creed, Sky & Telescope, August 2008 "Aerosol optical depth (AOD) ... (is) the best indicator of overall atmospheric clarity. The higher the AOD, the hazier your sky will appear. "So what should you look for as a stargazer? An AOD of 0.05 to 0.1 means crisp skies that deep-sky enthusiasts crave. This is the type of night to target challenging deepsky objects like the Horsehead Nebula. "... summer time AODs ... typically rise to 0.3 or 0.4. Clusters are still worthwhile, but nebulae and galaxies lack detail. The haziest nights feature an AOD of 0.5 or greater ..." |
The Bellcroft Observatory |
A private outreach venture serving Southern California |
Definition of AOD (Aerosol Optical Depth) Atmosperic aerosols are microscopic liquid and solid particles suspended in the atmosphere. Aersols can both absorb and scatter light - the combination of which is called extinction. The higher the concentration of aerosols the less star light reaches your telescope. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite collects AOD data each day. The National Oceanographic and Atmospheric Administration (NOAA) makes this information available on its web site at http://www.star.nesdis.noaa.gov/star/smcd.php From Clear(er) Skies Ahead, Phillip J. Creed, Sky & Telescope, August 2008 "Aerosol optical depth (AOD) ... (is) the best indicator of overall atmospheric clarity. The higher the AOD, the hazier your sky will appear. "So what should you look for as a stargazer? An AOD of 0.05 to 0.1 means crisp skies that deep-sky enthusiasts crave. This is the type of night to target challenging deepsky objects like the Horsehead Nebula. "... summer time AODs ... typically rise to 0.3 or 0.4. Clusters are still worthwhile, but nebulae and galaxies lack detail. The haziest nights feature an AOD of 0.5 or greater ..." |
