The Science Behind Nosso Céu Star Maps
How we create astronomically accurate maps of the night sky
Over 20,000 Maps Created with Scientific Precision
Since 2018, Nosso Céu has created over 20,000 personalized star maps for customers throughout Brazil and worldwide. Each map accurately represents the night sky exactly as it would appear from a specific location and moment in time.
But how do we ensure each map is astronomically correct? On this page, we explain the science and methods we use to create our star maps.
Complete transparency: We believe our customers deserve to understand how their maps are created. This page details the scientific methodology behind each personalized map.
What Makes Our Maps Astronomically Accurate
We create maps that are true representations of the sky. Here are the pillars of our precision:
• Professional data: We use the Yale Bright Star Catalog, the same catalog used by NASA missions
• Astronomical calculations: We apply internationally recognized scientific formulas (IAU, IERS)
• Cartographic projection: We use stereographic projection, the standard for hemispheric celestial maps
• Temporal precision: Our maps are accurate for any date and time you choose
• Geographic precision: Valid for any location on Earth, from the poles to the equator
Our Astronomical Data Sources
Yale Bright Star Catalog: The Professional Standard
For the stars in our maps, we use the Yale Bright Star Catalog (5th Edition) – the same catalog used by professional astronomers and NASA space missions. Specifically, we use an optimized version with 2,887 stars up to magnitude 5.5, which are the brightest and most easily visible to the naked eye.
The catalog contains data on the brightest stars visible to the naked eye, including:
• Precise position: Celestial coordinates (Right Ascension and Declination)
• Brightness: Apparent magnitude of each star (from 0.03 to 5.5)
• Characteristics: Data on temperature and stellar type
Why magnitude 5.5? This is the practical limit of visibility under normal observing conditions. Fainter stars (magnitude 5.5 to 6.5) generally require very dark skies and adapted eyes, and are rarely noticed by casual observers. Our selection focuses on the stars you would actually see at the special moment of your map.
Why This Catalog is Special
The Yale Bright Star Catalog has impressive credentials:
• Used by NASA: Hubble Space Telescope and TESS mission (Transiting Exoplanet Survey Satellite)
• Used by Kepler mission: From 2010 to 2018 for target star selection
• Academic standard: Reference at universities and observatories worldwide
• Continuously validated: Over 100 years of refinement since the first edition in 1908
Our Choice: Magnitude 5.5
The complete Yale BSC catalog contains 9,110 stars up to magnitude 6.5. We use an optimized version with the 2,887 brightest stars (up to magnitude 5.5). This choice is deliberate and based on observational reality:
• Practical visibility: Magnitude 5.5 is the realistic limit in normal urban and suburban conditions
• Visual experience: Stars between 5.5 and 6.5 are extremely faint and rarely noticed
• Map quality: Fewer very faint stars result in cleaner, more readable maps
• Authenticity: Better represents what you would actually see at that moment
In summary: If the catalog is reliable enough for NASA to choose which stars to observe with multimillion-dollar space telescopes, it is certainly reliable for creating your personalized star map.
How We Calculate Star Positions
Knowing where stars are cataloged isn’t enough. We need to calculate where they appear in the sky as seen from your specific location at the exact moment you chose. This involves several stages of astronomical calculations:
Step 1: Astronomical Precession
Earth doesn’t always point in the same direction. Its rotation axis performs a slow precession motion – like a spinning top – with a period of approximately 26,000 years.
This means star coordinates change gradually over the years. Our code applies the IAU (International Astronomical Union) precession formulas to transform coordinates from the catalog (referenced to year 2000) to the date you chose.
Practical result: Your map from 1990 will show a slightly different sky than a map from 2020, reflecting this real motion of Earth.
Step 2: Earth’s Rotation
Earth completes one rotation every 23 hours and 56 minutes (a sidereal day). This means the sky changes constantly throughout day and night.
We calculate the Local Sidereal Time (LST) – essentially “what time it is” for the stars – for the exact moment you specified. This uses IERS (International Earth Rotation and Reference Systems Service) conventions, the international standard.
Practical result: Your map at 8 PM will show different stars than a map at 11 PM, even on the same date and location.
Step 3: Your Location on Earth
The sky you see depends on where you are on the planet. Someone in Brazil sees different stars than someone in Europe, and both see different stars than someone in Australia.
We transform celestial coordinates to horizontal coordinates (azimuth and altitude) specific to your latitude and longitude. We use spherical trigonometry formulas recognized in astronomy.
Important detail: We only include stars above the horizon – the ones you could actually see from that location.
How We Transform the 3D Sky into a 2D Map
The sky is a sphere around you, but your map is flat. How do we represent a sphere on a plane without distorting everything? We use stereographic projection.
What is Stereographic Projection
The stereographic projection is the standard method used in astronomy to create night sky maps. Think of it as projecting the celestial vault onto a plane while maintaining correct angular relationships.
Why this projection is special:
• Preserves angles: Constellation shapes remain recognizable
• Circles remain circles: Important for representing the horizon and altitudes
• Ideal for hemispheres: Perfect for showing the entire visible sky at once
• Standard in astronomy: Used by planetariums, astronomy apps, and celestial atlases
How It Works in Our Maps
In our maps, the center represents the zenith – the point directly above your head at that moment. The circular edge represents the horizon.
Stars near the horizon appear close to the edge, while stars high in the sky appear near the center. It’s exactly how you would see it if you lay on the ground and looked up!
Planets, Moon, and Deep Sky Objects
Beyond stars, our maps can include other visible celestial objects:
Planets
Planets move through the sky (hence the name “planet” comes from Greek for “wanderer”). Their positions are calculated using Keplerian orbital elements and Kepler’s Equation, which describe the elliptical orbits of planets around the Sun.
Our code solves this equation with an accuracy of 10⁻⁶ radians (about 0.0006 degrees), which is more than sufficient for accurate visualization.
Moon
The Moon is especially complex because it orbits Earth, not the Sun. We calculate its position using a simplified lunar theory that includes the main periodic terms of its motion.
We also calculate the Moon’s phase (new, crescent, full, waning) for the chosen moment, with an accuracy of approximately 10 arcminutes – excellent for decorative maps.
Deep Sky Objects
Beyond individual stars, we include more distant and extensive objects:
• Nebulae: Clouds of gas and dust where new stars are born
• Galaxies: Other “island universes” containing billions of stars
• Star clusters: Groups of dozens to millions of stars
How Precise is “Precise”?
When we say our maps are “astronomically accurate,” what does that really mean? And are there simplifications we make? Let’s be completely transparent:
What We Include
Our calculations include all effects observable to the naked eye:
• ✓ Precession: 26,000-year motion of Earth’s axis (up to 1.4° per century)
• ✓ Earth’s rotation: Continuous change in sky orientation throughout the day
• ✓ Geographic location: Different sky for each point on Earth
What We Don’t Include (and Why)
There are some astronomical effects we don’t include. But here’s the important part: all of them are smaller than the limit of human eye perception.
• Nutation: Oscillation of ~18 arcseconds (~0.005°) – imperceptible
• Proper motion: Changes over decades – negligible for nearby dates
• Parallax: Maximum annual displacement of 0.004° – much smaller than visual resolution
• Aberration of light: Effect of ~20 arcseconds (~0.006°) – imperceptible
Historical Context
To put this in perspective: Tycho Brahe (1546-1601), considered the greatest naked-eye observer in history, could perceive differences of only 0.02° (72 arcseconds). All the effects we omit are significantly smaller than this historical limit of human perception.
Technical Specifications Summary
For those who like technical details, here’s a summary of our maps’ characteristics:
| Component | Specification |
| Star Catalog | Yale Bright Star Catalog – 2,887 stars up to magnitude 5.5 |
| Scientific Standards | IAU and IERS formulas (international standards) |
| Reference System | J2000.0 equinox with precession applied |
| Cartographic Projection | Polar stereographic (astronomical standard) |
| Planetary Precision | Kepler’s Equation (10⁻⁶ radians) |
| Lunar Precision | Lunar theory (~10 arcminutes) with phase |
Why Precision Matters
You might be wondering: “Why does all this science matter for a decorative map?” It’s a good question, and the answer is simple:
Authenticity. When you choose a special moment – a child’s birth, a wedding, an important achievement – you deserve a map that is truly faithful to that moment. Not an approximation, not an artistic guess, but the real sky as it was.
Over 20,000 customers have trusted us to preserve their special moments with scientific precision. Each map isn’t just beautiful – it’s astronomically correct.
