One of the night photographs that most impacts when we see it is the one that captures the trajectory of the stars . There are many types of photographs of moving stars, however, one of the most impressive is the one that takes the Pole Star as a reference point . Why? Because the Earth rotates on itself on an imaginary axis that points North. In this way, by taking the Pole Star as a reference point, we will make the other stars that appear in our photograph move circularly around it. Here we explain step by step how to get it:
The first thing we need is a camera that allows you to manually control the exposure time , this is to have a Bulb mode . The most commonly used type of camera is SLR. The second thing we need is a remote trigger that will allow us to press the shutter button without having to touch the camera. The last thing we need is a tripod to fix our camera in it long enough.
Once we have these three things we will go to a place where there is not much artificial light such as, for example, the field or the mountains, and always at night. Once we mount the camera on the tripod , making sure we have the same battery fully charged , we will have to locate the North Star , one that more shine on the sky, and aim our goal to her.
Determining the exposure time depends on several factors. The first and most important is the type of camera . To capture 15 degrees of the star's spin, one hour of continuous exposure is required. However, we can capture several 15-minute photos and then stitch them together with an editing program. Other parameters to take into account are ISO (camera's sensitivity to light) and aperture. For the latter we will opt for a low (f / 2.8 or f / 4) . For its part, the value assigned to the ISO will vary depending on the exposure time (the longer, the less ISO). Once we have determined these factors, we press the shutter button and, without moving the tripod, we wait for the time that we have decided based on the total degrees of rotation that we want to capture.
Finally we will have to process all these photos thanks to an editing program . Although it can be done in Photoshop, it is much more advisable to use applications created especially for this purpose, such as Startrail.
Some very useful tips to keep in mind are: on the one hand, do tests to see how it looks and make sure that the settings are correctly selected. On the other hand, photography of moving stars is a type of photography that requires many hours , so we recommend that you go with some kind of distraction , be it friends or a good book and a flashlight. Finally, looking for a point of attention on Earth , such as a mountain, a lake or a tree, will make the photo take on much more force.
It is not a difficult technique, however it requires a resistant camera and, above all, a lot of patience . However, the result is worth it.