Clouds and Haze Can be Your Friends
Clouds are the bane of night sky photographers, who generally long for crystal clear skies. Yet sometimes a thin cloud layer can add interest to a starry picture, depending on the effect you want. Especially if the main subject is a constellation.
For those fortunate enough to photograph from a dark sky location, there can be so many stars recorded by the camera that the patterns of major constellations get lost in the sea of stars. I’ve noticed that when there is a high, thin layer of clouds, sometimes not fully visible to the naked eye, it tends to slightly obscure the dimmer stars and create halos around the brightest stars in the photograph, making it easier to spot familiar patterns.
This happened on a September trip to Chaco Culture National Historical Park in northwestern New Mexico. The park preserves ancient structures at a site where there once was a thriving civilization starting around 1100 A.D. In the pre-dawn sky one morning, I decided to do some deep sky imaging with a Nikon 70-200mm lens set at 200mm on a Sony A7S camera, all attached to an iOptron SkyTracker Pro. The tracking mount allowed relatively long (30 seconds) shutter speeds without any star trailing.
The first frame showed “halos” around the bright stars while the fainter stars and objects faded slightly into the background haze. Although this ended my deep sky imaging attempts, I pointed the camera at the constellation Orion as the main section nicely fit in the frame with the lens at 70mm. I used an exposure of ISO 12,800, 30 seconds, f4.
The picture produced was a classic look at the shape of the Hunter. The major stars stood out brilliantly from the background while enough of the fainter stars were recorded to provide context. The “belt” and the “sword” patterns are easily seen in the photo. Betelgeuse glows orange, revealing its nature as the red giant star it is. Rigel shows as a big white disk. At a focal length of 70mm, the distinctive shape of the Orion Nebula, M42, is easily resolved.
Another byproduct of the clouds or haze is the accentuation of the colors of the stars, especially with Betelgeuse. Rigel’s blue-white classification shows as mainly white while the remaining stars in the constellation appear bluish.
During the October AAA North South Lake observing trip, we had similar conditions. The second photo is a view to the east just after 1:00 am. Many of the thin clouds show up in this photo, reflecting lights from nearby towns, which the camera picks up more easily than the human eye.
Orion is seen rising between the trees on the right. Castor and Pollux, the twins of Gemini, are on the left above the trees. Bright Capella is at the upper left, the Pleiades about level with Capella on the right, and orange Aldebaran can be seen between the Pleiades and Orion. It’s a nice look at the winter/spring sky with the bright stars really standing out in the photo.
For this image I used a Nikon D800 with a 14-24mm lens, ISO 3200, 15 seconds, f2.8, also on the iOptron SkyTracker Pro to minimize the star trailing. This is a cropped version of the original.
While clouds aren’t necessarily the most welcome feature in the night sky for astrophotographers. Don’t put your camera away if you see a few up there. The diffuse effect created by the clouds can enhance your photos.