Tuesday, April 22, 2014

Zodiacal Light: Oft Ignored Astronomical Phenomena?

Even though it seems to longer register in the consciousness of most amateur astronomers, are they missing out on observing one of the most interesting astronomical phenomena?

By: Ringo Bones 

Although no prominent astronomers – amateur or otherwise – had been recently talking about it, are first time amateur astronomers missing out one of the most interesting astronomical phenomena that can even be seen by the naked eye. But why does it ever seldom if ever even mentioned at all?

The zodiacal light or the zodiacal band is a faint glow of light seen along the ecliptic just after sunset or before sunrise is another manifestation of the interplanetary meteoric material. This “zodiacal light” is caused by the reflection of sunlight from the meteoric grains moving in interplanetary space. A still fainter diffuse luminous spot called the gegenschein or “counter glow”, found directly opposite the sun in the sky and the false “F corona” of the sun seen during total eclipse are the two other phenomena caused by this interplanetary material. Although such material is slowly spiraling into the sun, it is continually replenished by the destruction of comets.  

The zodiacal light appears as a large, faint pyramidal glow whose base is the horizon after the twilight glow has faded. This form is best seen on spring evenings and mornings in October. A fainter incarnation of zodiacal light stretches clear across the sky along the ecliptic – as in the orange line in our sky maps. Because urban light pollution overpower the glow, the vast majority of amateur astronomers will only get a chance to see the zodiacal band at a star party located at a rural location devoid of most urban light pollution – where the skies are usually quite dark - as in Class 1 to Class 4 - in the Bortle Dark Sky scale. Though urban regions that register as Class 5 in the Bortle Dark Sky scale will provide adequate Zodiacal Light observations for non demanding amateur astronomers. 

Observing the zodiacal band is one of those funny things. You don’t generally notice it until someone points it out, then – under a dark sky – it is fairly straightforward to see. Keep in mind that the zodiacal light is a magnitude or two fainter than the Milky Way.

One way to detect the zodiacal band is to watch for the sky background brightness to change as you slowly scan up from the horizon. Initially you’ll see a brighter horizon haze followed by darkness, then the sky will brighten a bit – this is the zodiacal band – only o fade as you look higher. You might have to block the light from Jupiter with your hand – it’s that dim.

Once you recognize this faint belt, you’ll notice that Saturn clearly lies beneath it as shown on the Path of the Planets map if you are on the northern hemisphere.

1 comment:

VaneSSa said...

Zodiacal Light - still of fascinating interest for the amateur astronomer, even if he or she lives in a lousy light-polluted urban night sky conditions on the Bortle dark sky scale.