Astro-magic: Photograph a celestial object that is barely visible?
Photographs of celestial bodies have many advantages over direct observation. They record a single moment in time. As such, objects can be studied in detail when the observation is over. The information remains in a database, it can be processed and adapted to research needs and many more.
And more important than all of that is that they have recorded details that cannot be seen with the naked eye.
Sometimes we only see the brightest part of a nebula through a telescope. And sometimes we don’t really see anything.
Why is that so?
Well, because of the long exposure!
A ray of light enters our eye, which is then transmitted by the optic nerve to the brain for processing, and then it is filtered and leaves some trace only in memory.
But when that ray falls on photographic film or, in modern times, on a chip, it leaves a permanent mark.
Now comes the interesting part because photons on the photo emulsion and the chip can be accumulated. They agree and thus reinforce each other. Fun, isn’t it?
One weak ray may not leave any trace, but if it is added to new rays – in the end it is amplified so much that it remains recorded!
So, you can get an object with a lot of details in the photo. The point is, therefore, in the exposition – that is the length of the brightness of the film, i.e. chip.
While some photos were created after exposure of a few minutes perhaps (which is often the case with amateurs), there are still photos that are the result of exposure to light for ten, twelve or even many more hours.
But how can you film a celestial object for several hours, when the whole dark night hardly lasts that long, especially in summer?
In addition, clouds often appear during the night, or the object sinks to the horizon, and it is not worth taking pictures of objects that are less than 20 degrees above the horizon. This is due to the dense layers of the atmosphere near the horizon.
So how do we still get past these obstacles? Well, by using a trick.
You simply take pictures multiple times. You know where the object is located – which is easy with modern devices, so you also know the coordinates of your observation point and when you set up the telescope and photo equipment according to those parameters, just let the camera work.
It is clear, and every observer knows that, during the night, the entire firmament moves, but today that is not a problem either, because the mechanisms holding the telescope are capable of canceling the Earth’s rotation with the help of motors and keeping the object in focus as long as possible.
Therefore, an object is recorded several times, even several hundred times, and all the recordings are combined into one image with specific software.
The author of the photo has at their disposal a number of possibilities to process the photo, to extract the details needed, to enhance or perhaps delete elements from the image etc. The possibilities are endless and novel applications for the extracted information is growing daily!
