Star trail photography has gained popularity in recent years. What are star trails?
The earth rotates around its axis at about 1/4-degree per minute causing an apparent movement of the stars overhead by the same amount. If we leave a camera in a fixed position and point upwards, open the shutter in bulb mode and let the earth rotate under the stars, we will create an image with star trails. Similarly we could take shorter exposures and superimpose (stack) the images with image processing software. Most images of star trails taken in the Northern hemisphere show a pattern similar to the one below taken in Arches National Park, Utah, in Spring of 2016.
The location of the North Pole can be clearly seen; the star close to the center is Polaris.
Naturally, we would expect a similar image for the South Pole, and this is indeed the case. There is one important difference: When looking southwards in the Southern hemisphere we can also see the Milky Way, best observed from March to about late August. The star trail image below taken at the Siding Spring observatory in New South Wales, Australia, late April (total of 1250 images @ 30s each, from dusk to dawn) shows circumpolar rings :
The image seems to have lost all the beautiful details of the Southern Milky Way, although when looking towards the center there are clear traces of red, indicating the smear of the Eta Carina nebula in a circumpolar pattern. Can this be improved?
Let's take a look at a time lapse sequence in one hour intervals. The apparent rotation around the South Pole of the Milky Way from the early evening at 7 pm to the early morning at 5 am is spectacular.
What makes the Southern Sky so attractive is the fact that Sagittarius rises in the East (left side) and then reaches the Zenith in the early morning hours in late April. This region is heavily populated with nebulae and well known objects and it is also where the center of our own galaxy is located - the galactic center - home to a massive black hole. Curiously Saturn was clearly visible in this region end April 2017.
When we take another look at the rotating Milky Way animation we can spot the Large Magellanic Cloud diving below the horizon in the late evening and the Small Magellanic Cloud rising in the early morning hours. In the Northern hemisphere Sagittarius is well visible at lower latitudes but we cannot see location of the South Pole.
We could possibly further improve the sequence with better image processing such as color correction and levels - it looks nice but that's it - one of many time lapse clips published widely. Where is the spark?
We need some novelty, so how about superimposing the above sequence into one image? Let's give it a try:
The result above is surprising: The distinct colorful objects of the Southern Sky such as the Eta Carinae Nebula, the Large and Small Magellanic Clouds, as well as the thick bright dust patches of the Sagittarius region clearly become visible as the Milky Way paints a clock-like pattern across the sky - resembling a large cosmic clock. Curiously the pattern at the location of the South Pole is artistic, with fractal dimensions.
As we increase the interval between successive images of the sequence from minutes to hours, we can watch the Milky Way paint discrete patterns.
Interval between images: 5 min
Interval between images: 10 min
Interval between images: 30 min
Interval between images: 60 min
Interval between images: 120 min
Interval between images: 240 min
There are so many beautiful patterns in nature just waiting to be discovered. Share my passion.
About the author:
Christian's passion encompasses both eagle photography and astronomy. His academic background, particularly his knowledge of optics and the physical properties of light, has shaped his photography. He is interested in capturing how different lighting conditions affect the colors and patterns around us, paying special attention to the way that they reflect, refract, diffract and transmit light.
His Facebook page has over 110k followers - mostly eagle photography. He also runs Sky Tours where he guides live viewers through the Southern Sky with a remote telescope. He also has a YouTube channel.
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