The Ghostly Glows of a Truly Dark Sky
A truly dark sky isn’t dark. It is filled with glows both subtle and spectacular.
Last night, March 10, I drove up into the heart of the Gila Wilderness in southern New Mexico, to a viewpoint at 7,900 feet in altitude. I was in search of the darkest skies in the area. I found them! There was not a light in sight.
The featured image is a 180° panorama showing:
– the Zodiacal Light (at right in the west)
– the Milky Way (up from the centre, in the south, to the upper right)
– the Zodiacal Band (faintly visible running from right to left across the frame at top)
– the Gegenschein (a brightening of the Zodiacal Band at left of frame, in the east in Leo)
The Zodiacal Light, Zodiacal Band, and the Gegenschein are all part of the same phenomenon, glows along the ecliptic path – the plane of the solar system – caused by sunlight reflecting off cometary and meteoric dust in the inner solar system.
The Gegenschein, or “counterglow,” can be seen with the naked eye as a large and diffuse brightening of the sky at the spot exactly opposite the Sun. It is caused by sunlight reflecting directly back from comet dust, the scattering effect greatest at the point opposite the Sun.
The Zodiacal Light requires reasonably dark skies to see, but the fainter Zodiacal Band and Gegenschein require very dark skies.
Now is prime season for all of them, with the Moon out of the way, and the Zodiacal Light angled up high in the western as twilight ends. In March, the Gegenschein is now located in a relatively blank area of sky in southern Leo.
The Milky Way is much more obvious. Along the northern winter Milky Way here you can see dark lanes of interstellar dust, particularly in Taurus above and to the right of Orion. Red nebulas of glowing gas also lie along the Milky Way, such as Barnard’s Loop around Orion.
– Orion is at centre, in the south, with Canis Major and the bright star Sirius below and to the left of Orion. Canopus is just setting on the southern horizon at centre. It barely clears the horizon from 32° North latitude.
– To the right of Orion is Taurus and the Pleiades star cluster at the top of the Zodiacal Light pyramid.
– Venus is the bright object in the Zodiacal Light at right, in the west, while fainter Mars is below Venus.
– At far right, in the northwest, is the Andromeda Galaxy, M31.
– Jupiter is the bright object at upper left, in the east, in the Zodiacal Band, and near the Beehive star cluster.
– The Zodiacal Light, Band and Gegenschein all lie along the ecliptic, as do Mars, Venus and Jupiter.
Glows on the horizon are from distant SIlver City, Las Cruces and El Paso. The brighter sky at right is from the last vestiges of evening twilight. Some green and red airglow bands also permeate the sky.
It was a stunning night, clear, calm, and silent. Just me under the ghostly glows of a truly dark sky.
NOTE: I first published this March 11 but had to republish this blog March 15 after WordPress deleted the original post in a software bug. Thanks WordPress!
– Alan, March 11, 2015 / © 2015 Alan Dyer / http://www.amazingsky.newt