Atmospheric Seeing

Q.  What is astronomical or atmospheric seeing in relation to observatories?
- Published on 16 Aug 16

a. High frequency temperature fluctuations of the atmosphere
b. Reduced visibility due to cloud cover
c. Reduced visibility due to solar flares
d. The capacity of an observatory to see the moon as a reference

ANSWER: High frequency temperature fluctuations of the atmosphere
  • Seeing is high frequency temperature fluctuations of the atmosphere, and the mixing of air parcels of different temperatures/densities.
  • This behaviour of the atmosphere is seen at the eyepiece as a blurred, moving, or scintillating image.
  • There are roughly 3 main areas where Atmospheric turbulence occurs. Near ground seeing (0 – 100 metres or so.) central troposphere (100m – 2km), and High troposphere (6-12km.) Each area exhibits different characteristics.
  • Hanle in Ladakh has been identified as one of the potential alternate sites for the Thirty Meter Telescope (TMT).
  • Hanle site has lower seeing values of 0.9-1.2 arc sec as compared to the alternate sites in Chile and Canary Islands of Spain (La Palma) which have seeing values of 0.55 arc sec. Thus, scientifically, Hanle has less advantageous characteristics for hosting a mega telescope like the TMT in comparison to the other alternate sites.

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