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The Gegenschein

 

The Gegenschein

 

Move your mouse over the image above to get a version with constellation lines and labels drawn.

The gegenschein is visible as faint patch of light at the center of the image. On September 23, 2006, it was located in the constellation Pisces, just to the left and below the right-hand fish.

Gegenschein means "counterglow" in German. It is a faint and diffuse brightening of the night sky around the antisolar point, which is located directly opposite the sun. The gegenschein is sunlight reflected by interplanetary dust, just like the zodiacal light. Most of the dust particles are orbiting the sun in about the ecliptic plane. The gegenschein is so faint that it cannot be seen if there is any moonlight or light pollution, or if it falls in the vicinity of the Milky Way. It appears as a softly glowing oval region a few degrees wide and 10°-15° in length, oriented along the plane of the ecliptic.

If you look closely at the image above, you may see a faint band of light crossing the image from just below the upper left corner to slightly above lower right corner, the gegenschein is just the brightest part of this band. The band marks the ecliptic plane and is caused by the same dust particles causing the Gegenschein. Scattering works best directly opposite the source of light, the sun in this case, because each dust particle is seen in full phase, and because the back-scattering geometry leads to constructive interference, which is why the gegenschein appears with more intensity.


Exposure Data

  • Instrument: Nikkor 28-70 mm DX Zoom Lens set to 31mm
  • F/stop: 5.6
  • Exposure: 2 x 10 minutes
  • Camera: Nikon D70 with Baader UV-IR-Cut-Filter
  • Sensitivity: ISO 1600
  • Exposure start: 3:16 MESZ
  • Date: September 23, 2006
  • Location: Edelweißspitze, Salzburg
  • Conditions: Visual limiting magnitude 6.7 mag, seeing 6/10, temperature 6.5°C, no wind, low to moderate dew
  • Autoguider: Meade Pictor 216 XT, max. error 2" (RA) / 2" (Dec)
  • Enhancement: Basic data reduction, combine, background flattening, logarithmic curves, noise filtering, crop
  • Notes: Photo taken during my stay at the Großglockner-Hochalpenstraße in September 2006. See an Observation Report of this event (in German).

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© 2010 Walter Koprolin