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Knowledge Base

At Slate Sky, we are making our star maps with the greatest possible attention to scientific accuracy. We use the Bright Star Catalog from Yale University as our main source of celestial data, among several other astronomical databases. It contains galactic coordinates of all the stars visible from Earth with the naked eye. These coordinates place each star in a galactic coordinate system. When creating a map, we process six high precision data points of over 9,000 stars.

For the position of a star in the sky at a particular place and time on Earth, we calculate the azimuth and elevation of the star, based on the geolocation and time coordinates from that special moment chosen by you. The complex astronomical calculus involved in celestial mechanics ensures high fidelity and uniqueness of each map.

Once we have the position of each star in the sky, we draw a projection of the celestial hemisphere with all the visible stars.

What if the stars were not visible on the day/time I picked? Stars are still around us when the Sun is up, they are just not visible to us because their dim light being superseded by the light of Sun scattered on air molecules - that makes the blue sky. So they don't really disappear, they are just "hiding". Astronomers have been able to predict the movement of the stars in the sky for thousands of years, and we have become very good at it over the last centuries. This works even when they are not visible with the naked eye. Thanks to the method we have created for charting the stars, you can be certain that your star map will accurately reflect the sky looked like when your special moment was taking place.

To map the celestial hemisphere, there are dozens of other projection techniques such as stereographic projection etc. As we have found that most historical star charts use it or something very similar. The point being, choosing a map projection and its parameters is mostly a question of "taste" as well as utilitarian considerations of the map creator. Based on projection surface chart may appear mirrored. (North -> East -> South -> West or North -> West -> South -> East) Please refer the below pictures to get an idea. Both projection is true, but the aspect is different.

Here's a very crude illustration of typical stereographic celestial projections:

Sometimes we get questions about the accuracy of our star charts. Most of our customers are not astronomers by profession, so it might be hard to verify if the constellations of a custom-made star map really represent the sky above you at the moment you selected.

Below, there is a detailed explanation of a real-life example.

It might seem like the stars do not change as you change the time or location. In order to explain why, we think it’s best if we give you a practical example:

We created 2 maps, one from Winnipeg, the other from Yellowknife (about 1600 miles from W), for the exact same time.

Then we compared them with an image comparing software, there might be differences between the images, but these are not very significant. The explanation simply put is that while Winnipeg and Yellowknife are relatively far from each other on the map, on a global scale they are pretty close and so they both look up to a very similar sky. Here's a picture of both locations on the globe to get an idea:

This is called parallax. You can observe it when driving in the night and look at the moon - it seems to move with you. It's because it's far from Earth and so distances on Earth don't make a big difference in the perceived location on the sky. The same thing happens with the stars, except that the closest star to us (that is not the Sun), Proxima Centauri is approximately 104,430,223 (~hundred million) times farther from us than the Moon. Here's a demonstration (naturally not-to-scale):



So are all star maps the same?

No. Even with huge stellar distances like this, there are differences between the maps as you have seen in the picture above because you see a slightly different portion of the sky. Real big differences occur in time or between the Southern and Northern hemisphere, simply because of how to Earth moves and where it's located in the galaxy.

It gets even more exciting when the difference is not only North-South but also West-East (e.g. Canada vs New Zealand).

We try to be as transparent as we can with our customers. All stars maps made by any company are third party verified. what do we mean by third party verification? Well it means that one have to ask a expert to audit the star chart. 

Yes, we know there are companies which prints a paper and give the line "verified Nasa and so and so..". We personally think it's marketing gig and bit misleading to customer. Let's consider this example, if a product is ISO certified you see a ISO logo on it, if a food product has fssai license you see fssai logo on it, so do you see Nasa stamp or logo on those certificate? No. right! The reason is there's no organization in public or private domain which provides such services as of now. We use reliable and authentic sources and algorithm to make our star maps but we chose not to include certificate for above reason. We hope you get our point, feel free to reach out to us with any doubts.
e.g. Companies like under the lucky stars, positive prints does not include the certificates as well for same reason.

No, we do not provide star naming service, we just simply make the accurate star map from the details (date, time, location) provided by you.

Technically you can't name a star, even if you do via any company out there such names are not valid. And it's fair to say that such names are not legally binding and not recognized by astronomical community. 

Please refer the below video to get clear idea. As mentioned in the video and in experts articles, only IAU (International Astronomical union) can do it.

IAU article link: