Zodiacal Light Observed Over Tibet

September 21, 2015

Zodiacal light before dawn_1200

Photographer: Jeff Dai 
Summary Author: Jeff Dai; Jim Foster
Shown above is the zodiacal light as observed from Tibet, China. The zodiacal light results from sunlight scattered off dust particles in the inner solar system -- sunward of Jupiter. Because the particles are likely rather large (0.001 - 0.300 mm in diameter) compared to visible wavelengths of light they scatter sunlight more strongly in the forward direction. So the zodiacal light is brightest in the vicinity of the Sun's position -- but the Sun must be at least about 18 degrees below the horizon.  Note that a long exposure time (25 seconds) was used to enhance the zodiacal light on this photo.
The faint, triangular patch of light can be seen throughout the year but is more noticeable about 90 minutes before dawn in the east during late summer and early autumn, in the Northern Hemisphere, and again in late winter and early spring in the west after the Sun has set. During these times the ecliptic (zodiac) forms a steeper angle with the horizon and thus the wedge-shaped band is slightly more pronounced. Photo taken before dawn on July 16, 2015, from the mountain top of Namtso, 15,750 ft (4,800 m) above sea level.