Encore - Sun Size and Altitude
February 13, 2016
Today, and every Saturday Earth Science Picture of the Day invites you to rediscover favorites from the past. Saturday posts feature an EPOD that was chosen by viewers like you in our monthly Viewers' Choice polls. Join us as we look back at these intriguing and captivating images.
Astronomers are frequently asked why we have our observatories on high mountain tops. A big part of looking into deep space has to do with atmospheric transparency and freedom of particulates along with heat that causes blurring. A simple but effective understanding of this seeing is to put a finger at arm’s length in front of the Sun and observe the aureole that’s produced. Held at arm’s length, a finger tip subtends about one-half of a degree of sky – nearly the same amount of space that both the Sun and Moon take up. At sea level, observing is often compromised by the build up of heat, dust, moisture, haze, pollution, and aerosols that include ash and even salt. Higher up, there’s less of this to deal with since there’s less atmosphere to peer through. These three photos were taken on the Hawaiian island of Maui at (left to right) Baldwin Beach, Kula and Haleakala Observatory, respectively. The disk of the Sun is completely hidden by my index fingertip at 10,000 ft (about 3,050 m). Note, I can positively verify that my finger didn’t increase in size as a result of the thinner air.