How accurate is a star map? How your sky is created
Is a personalised star map astronomically accurate or mainly just beautiful decor? The honest answer is: it can be both, if it's calculated properly. What matters is whether place, date and time are really translated into a night sky, and whether the design explains what you're actually seeing. Here you'll find out how your sky is created, why every hour produces a different sky, and what a star map deliberately does not show.
The star maps on stellarto.com are calculated using the ESA's Hipparcos catalogue. They use 8,870 stars down to magnitude 6.5. That's roughly what you could see with the naked eye under a perfectly dark sky. If you want, you can also show the constellation lines for all 88 constellations, the Milky Way and a coordinate grid, all of which can be turned on and off. So this is not a fantasy graphic, but a calculated snapshot of the sky for a specific place and a specific moment in time.
What exactly is calculated
A star map always depends on three pieces of information together: place, date and time. The sky rotates by about 15 degrees per hour. That's why the sky at the same place looks different at 9 pm than it does at midnight. You enter the local time, and the matching time zone and daylight saving time are determined automatically from the coordinates. That's important because even a small shift in time changes the visible section of sky.
The precession of the Earth's axis is also calculated. That means the map is accurate not only today, but for every year, including before 1900. So if you want to create a sky from 1950 or an even earlier time, that's astronomically consistent. You can verify it yourself with an astronomy app like Stellarium by entering the same place and time there and comparing the star positions.
How the map represents the sky
A star map is not a road map, but a view upward. The zenith, the point directly above you, is in the centre. The edge of the circle shows the horizon. North is at the top, east on the left. That can feel unusual at first because it's reversed compared with a classic map. But that's exactly right if you imagine lying on your back and looking straight up at the sky.
Another important point: the map shows the stars that were above the chosen place, whether you could actually see them or not. Clouds, city lights or daylight do not change the astronomical calculation. Even during the day, stars were above you, they were simply outshone by the sun. So the star map shows the sky that was there, not necessarily the sky you perceived with your eyes.
Suitable maps and formats
What is not on the star map
Planets and the moon are not included on the star map. That is not a mistake, but a deliberate choice. The map focuses on the starry sky. If you would also like to capture the moon phase of a specific night, there is a separate moon phase poster with an astronomically calculated phase. This keeps a clear distinction between what a star map shows and what it does not.
How you can check the accuracy yourself
If you want to know whether your map is correct, you can easily check it yourself. Open Stellarium, enter the same place, the same date and the same time, and set the view so that north is at the top. Then compare the most recognisable constellations and the bright stars. If you like, you can also display constellation lines or a coordinate grid. That is exactly what these aids are for: not as decoration, but as a clear translation of a real sky.
The live preview in the browser also follows the same calculation as the final print file. So what you see there is exactly what will be printed or delivered as a digital star map. In terms of design, you can then choose from 12 colour styles, decide between a circle or a heart, and add up to three lines of text. If you prefer to print it yourself, the digital file comes as a PNG in 5906 × 8268 pixels, suitable for 50 × 70 cm at 300 dpi.
If you want to turn the sky into a gift
Alongside astronomical accuracy, what also matters in the end is how well the map fits into your everyday life. It is available as a poster, as a canvas on a stretcher frame, or framed in black or white in 30 × 40 and 50 × 70 cm. Available sizes are 30 × 40, 50 × 70, 60 × 90 and 80 × 100 cm, with 50 × 70 cm being the most popular choice. Each piece is printed individually to order in the EU. For Germany, delivery time is 4 to 5 working days.
Frequently asked questions
Why is east on the left on the map?
Because the design matches the view when you look up at the sky. North is at the top, the zenith in the middle and the edge of the circle is the horizon. So the view appears reversed compared with a road map, but it is correct for the sky.
Are planets or the moon shown on the star map?
No. The star map shows the calculated stars in the sky. Planets and the moon are not included. For the moon, there is a separate moon phase poster with the astronomically calculated phase of your night.
Is the map also accurate for 1950 or even earlier years?
Yes. The precession of the Earth's axis is calculated, which is why the map is accurate for every year, including before 1900. You can check this yourself with an astronomy app like Stellarium.