Easy Astro-photography: How to shoot Milkyway Galaxy?

Astro-photography is an art that is dependent mostly on the aspects which are not controlled by the artist himself such as weather, light pollution, and air pollution. With respect to the gear, to start off with shooting the Milkyway core, any entry-level professional camera is sufficient. The dark sky where the light pollution is very less is important in order to do astrophotography. A rural place, away from the city lights is the ideal place to shoot. It is not possible to shoot in the presence of the moon as well due to the moonlight.

The Milky Way galaxy contains billions of stars, including our own Sun. It is shaped like a spiral, with arms stretching out from its core, but from Earth appears only as a band of cloudy light to the naked eye. The Milkyway galaxy is 100 light-years thick. To take the full image of the Milkyway galaxy, the camera has to be placed far away which is beyond the reach of current technology. In the above image I clicked, the center of the Milky Way (the core) is seen along with the interstellar gas and dust that is blocking the light. At its heart and the dominant force in that area of the galaxy is a 1 million-solar-mass black hole named Sagittarius A which is responsible for the emission of light due to accelerating the motion of the matter around it. The current state of the Milkyway is not known because of the time taken by the light to travel. We will have to wait for 27000 light-years for that. So when you look at this image, you look 27000 years into the past! With our own eyes, the Milky Way looks nowhere near as detailed or colorful as the above picture. Our eyes don't do a good job of resolving color in the dark, so the Milkyway instead appears as pale/milky patches, instead of a colorful object in the night sky. A camera can see a lot more under dark conditions than the naked eye if the camera is rightly set. The same principle of setting the camera to capture more information is the basis of deep-sky astrophotography.

Shooting basics:

Mainly there are three parameters in an entry-level professional camera: Shutter speed, aperture, ISO(camera sensor light sensitivity). Every picture is captured with the combination of all these parameters. Manual mode in the camera gives control of all three parameters to the user. The right combination of these parameters is necessary to shoot deep sky bodies. Hence the first step is to shoot in manual mode. It is better to shoot the image in RAW format instead of JPEG format which compresses the image.

• Shutter-speed:
It's the speed at which the shutter of the camera closes while capturing the image. A fast shutter speed creates a shorter exposure (the amount of light the camera takes in) and a slow shutter speed leads to longer exposure of the subject. For the following case of shooting Milkyway, more light is required, hence slower shutter speed has to be set for longer exposure. With longer exposure comes the risk of shaking the camera while the shutter is still open causing ghostly images. So, a stable surface/tripod is required to avoid shaking caused by the hand while clicking the image. Longer exposure might also lead to the star trails(movement of stars is registered on the image) due to the rotation of the Earth. An expensive way of canceling the effect of the rotation of Earth is to use star trackers. The easy way of solving it is by choosing the shutter speed based on the focal length of the lens being used, using the 500 rule i.e if the focal length is 50mm, then the slowest shutter speed that could be set is 500/50 = 10 seconds. Therefore, the wider the lens, the slower the shutter speed, longer the exposure. But a single image might not give a better result. In order to make an image look better, more data is necessary which is achieved by the stacking process. In that process, the images are stacked to improve the Signal Noise Ratio. For instance, a tracked image using a tracker taken with exposure 5minute is equivalent to an untracked(stacked) image worth 10 images with an exposure of 30seconds. But untracked version involves stacking 10 images using the software. The stacked image might not be as good as a tracked image due to the few additive noises that can't be removed with stacking. Nonetheless, the stacking of images is a better way to start instead of using expensive trackers. It will be helpful to learn to stack images that can still be used with the combination of tracked images(later, if you decide to get a tracker) leading to the best result.
• Aperture:
Aperture is the amount of opening of a lens's diaphragm. It is denoted by f/stops. Aperture does affect the depth of field: The lower the f/stop - the larger the opening in the lens - the less depth of field - the blurrier the background. The higher the f/stop - the smaller the opening in the lens - the greater the depth of field - the sharper the background. Although more exposure is required i.e by having a larger opening in the lens, it has to be noted that the desired subject has to be focused properly(to infinity in our case) making everything else blurry due to the depth of field effect. In order to focus properly, for a given focal length, set the focus to manual, point to a bright star/planet, rotate the focus ring until the bright star/planet appears as a point source. Once properly set, changing the focal length leads to a shift in focus. So the lens setup should not be changed in any part of the shooting process.
• ISO:
ISO indicates the sensitivity of the camera sensor to the light. The higher the ISO value, the more sensitive is the camera sensor. Shooting in the dark demands the artist to use a higher value of ISO. Although the camera offers a wide range of ISO, large values won't lead to good images. The electronic noise is the reason behind avoiding the usage of the higher value of ISO. But one should look at the maximum value of ISO that could be set without largely affecting the image. The effects on the image due to high ISO are indicated by the grains in the image shot.

Pre-requisites:

• Dark sky:
It is difficult or impossible to view/shoot Milkyway from cities or during full moon night due to the light pollution.
• Milkyway season:
Know when and where to look at the sky using any star tracking mobile applications. The Milkyway season varies depending on the location.
• Entry-level professional camera:
Camera that has the capability to capture data for a longer period of time.
• Stable platform/tripod:
To avoid distortion caused by shaking of the camera while shooting.
• A computer for post-processing (Optional but mostly needed for better result):
For stacking and post-processing using Photoshop.
• Trackers (Optional and not necessary):
Expensive tools that will nullify the rotation of the Earth avoiding star trails in the image.

And finally, may the weather lords be with you!

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