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Guide

How accurate is a custom star map?

What a real star map calculates for your date, time and place, which star and Moon data it uses, and how to tell a real map from a template.

Try it with your dateShort answer

Short answer

A real custom star map is as accurate as the catalogue and the time you give it. Sigastra places 5,044 stars (every star bright enough to see with the naked eye on a dark night, from the Yale Bright Star Catalogue and the HYG database), the planets and the Moon for your exact coordinates and minute, and draws the Moon from NASA's maps, lit for its true phase. The biggest source of error is the time: the sky turns about 15 degrees an hour.

Updated 10 November 2026 · Sigastra Gifts

What is calculated

Stars (5,044)

Source
Yale Bright Star Catalogue and HYG database (via d3-celestial)
Placed for
Your latitude, longitude and minute

Constellations (88)

Source
Constellation line figures from d3-celestial
Placed for
The same sky

Planets

Source
astronomy-engine, the models observatories use
Placed for
Your date and minute

Moon phase and look

Source
NASA SVS CGI Moon Kit (LRO LROC and LOLA)
Placed for
Lit by the Sun of that date, turned as seen from your place

Natal chart

Source
Swiss Ephemeris
Placed for
Your date, minute and birthplace

How much the time and place matter

  1. 1Time: the whole sky turns about 15 degrees an hour. An evening you remember is close enough for most people; the stars of that date stay the same.
  2. 2Place: moving a few hundred kilometres north or south changes which stars are overhead and which never rise. Two cities on the same night give two different maps.
  3. 3Date: from one night to the next the sky shifts a little; across months whole constellations come and go. The Moon changes visibly every night.

How to tell a real map from a template

  1. 1Change the city in the editor: the stars must move.
  2. 2Change the hour: the sky must turn.
  3. 3Look for the Moon: it should be in the phase it had that night, not a stock crescent.
  4. 4Check the coordinates printed on the map against the place you chose.

On the wall

Real rooms with a real print in them: change the date and the place in the studio and these frames show yours.

A star map in a thin gold frame leaning on a dark stone sideboard by a brass lamp
A star map in a thin gold frame leaning on a dark stone sideboard by a brass lamp
A moon phase print in an oak frame with a white mat above a bed with white linen
A moon phase print in an oak frame with a white mat above a bed with white linen

Questions

Anything else? Write to hello@sigastra.gifts.

Sources

The positions come from standard star catalogues and planetary models and are placed for your coordinates and minute. It is a faithful picture of the naked-eye sky, drawn for print, not a navigation chart.

It shows every star bright enough to see on a dark night. City lights, clouds and the horizon would have hidden some of them that night.

Because it was not full that night. The Moon is lit by the Sun of your date, so you see the real phase and how much of it was lit.

We use the evening (9 pm local time). The stars of that date and place stay the same; only their height in the sky changes.

Keep reading

All guides

The stars were there. Now they can stay.

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How Accurate Is a Custom Star Map? · Sigastra Gifts