Sky data & credits

Star and constellation GeoJSON files: Olaf Frohn’s d3-celestial, distributed with its BSD-3-Clause license. The repository attributes its star catalogue to XHIP (Anderson & Francis, 2012) and constellation line data to IAU resources, with modifications by Olaf Frohn.

Solar System ephemerides and the J2000-to-horizontal coordinate rotation use Astronomy Engine 2.1.19 by Don Cross, vendored locally with its MIT license in astronomy.js. The browser applies precession and nutation, computes topocentric planet and Moon positions (including lunar parallax, light-travel time, and aberration), and projects the geometric above-horizon sky with an azimuthal equidistant projection in the circle layout, or a cylindrical altitude–azimuth panorama in the horizon layout. Moon illumination and phase are geocentric calculations; the phase icon is a conventional diagram, not a local lunar-limb orientation model. In the circle layout, north is up and east is left, as for a sky viewed overhead.

Known limitations: no stellar proper motion, atmospheric refraction, local terrain, daylight visibility, or weather. Solar System bodies are plotted only above the geometric horizon. Uranus and Neptune usually require optical aid. Symbols are enlarged and are not to angular scale. In the sky panel, the Moon is hidden when it is below the horizon. The separate lunar study shows its phase independently of horizon visibility. The optional Sun is also drawn only above the horizon. Production use requires independent astronomical validation, data-rights review, and a print-proof pipeline. Supported prototype dates: 1900–2100.

City, landmark, and street-address search uses the public Photon/Komoot geocoder with OpenStreetMap data. Search text is sent on explicit search only, without the dedication, event date, or names. Results require user selection. The prototype uses the shared demo endpoint with modest, throttled requests; production needs a managed or self-hosted service. Timezone detection runs locally with @photostructure/tz-lookup 11.7.0 (CC0-1.0; see TIMEZONE-LICENSE.txt). Its compressed boundaries are approximate; the detected timezone is shown and can be corrected under Time settings. Browser timezone rules handle the event date and daylight saving. Ambiguous fall-back times use the earlier occurrence and disclose this in the editor.

The homepage gallery uses actual calculated sample artworks in illustrative frames; it is not a photograph of manufactured samples. The live chart is calculated from catalogue data, not generated by AI. Prices and product finishes are proposals, not offers for sale.

Fonts: DM Serif Display and DM Sans via Google Fonts, with system fallbacks.

Constellation names and label anchors are supplied by d3-celestial. Only above-horizon anchors with non-overlapping label space are named. At 12 × 16 inches the constellation type is 12.1 points; planet names are 13.8 points. SVG proofs carry physical dimensions and scalable vector artwork. PNG proofs are rasterized at 300 pixels per inch, with 300-PPI pHYs metadata. Fonts are rasterized into PNG; SVG font substitution remains possible on other systems. These are design proofs, not supplier-certified production files. Final bleed, font outlining, color conversion, substrate, and printed line reproduction require provider-specific preflight and a physical sample.

Composition & selected times

The Open horizon layout is a cylindrical altitude–azimuth panorama: north appears at both edges, the horizon is its base, and the zenith is its top. It distorts shapes near the zenith; it is not a landscape photograph. Zodiac emblems are custom vector strokes and decorative, not astrological placements.

When the event time is unknown, the editor asks whether to include the Moon. It samples the local date every 15 minutes, preferring the highest Moon while the Sun is below −6°. If only daylight or twilight placements exist, it discloses that. If the Moon never rises, it is hidden. Without a Moon preference it chooses the darkest sampled time. Selected times are marked on the proof as compositions, not recorded event times. Moon visibility here means geometrically above the horizon; terrain, atmosphere and daylight affect actual visibility.

Constellation name check

All 88 constellation identifiers were compared with the IAU constellation list on 7 October 2026. The catalogue variant Corona Austrina was normalized to Corona Australis. Serpens Caput and Serpens Cauda label the two parts of the single constellation Serpens. Labels use projected catalogue anchor points and small collision-avoidance offsets; they are not official boundary markers. Connecting figures are conventional illustrations, not IAU-standardized line patterns.

The celestial collection

The three artworks are the sky, lunar phase, and solar study. An optional Earth study makes four. Each exports separately at the chosen size; a ZIP contains the complete set. Small names and dedication are shared across the prints. The Moon study shows a conventional geocentric phase diagram at the selected instant, without surface detail or local limb rotation. The Sun disc is illustrative, not a solar photograph. Its lower curve samples geometric solar altitude every 15 minutes across the selected local date; gaps and repeated daylight-saving hours are not joined. The dot marks the selected time and the dotted baseline is the geometric horizon. These separate studies do not place a hidden body on the sky map.

Earth & weather

Coastline geometry is Natural Earth public-domain data, rendered as a regional atlas or hemisphere centered on the selected location. The optional outer ring encodes local estimated cloud percentage, not the spatial distribution of clouds. Optional weather uses Open-Meteo’s historical API: hourly temperature, cloud cover, wind, and precipitation at the preceding UTC hour, explicitly labeled as local model estimates. Grid resolution varies with the selected historical model (roughly 9–25 km); it does not describe conditions at an individual building. Data is CC BY 4.0. Weather data: Open-Meteo. Values are rounded for display. Credits are kept off the print face and included in the accompanying About-your-print.txt file when you download a weather print. SVG weather summaries also retain source information in accessible metadata. Weather requests pass through this store’s server and are enabled only when the commercial weather service is configured; the free public endpoint is not used. The prototype accepts archive dates from 1940 to approximately six days ago. It sends selected coordinates and the UTC date only after an explicit lookup.

Dated satellite imagery

Optional regional imagery comes from NASA GIBS MODIS/Terra Corrected Reflectance True Color. We acknowledge the use of imagery provided by NASA GIBS, part of EOSDIS. Availability begins 24 February 2000, with variable coverage. These are daily UTC composites; the date matches the calendar-date selection but not necessarily the event instant or local observation date. Source colors, cloud cover, and missing data are retained. The requested 3,456 × 3,456 raster is embedded in SVG and PNG proofs; source spatial resolution remains approximately 250 m at its finest and may be coarser. Display styling does not add authentic surface detail. Missing pixels remain blank against the print background. The regional crop is about six degrees of latitude and excludes latitudes beyond 75° or crops crossing the date line. Requests send date and regional bounds to NASA only when selected. No radar data is used.

Solar light and Earth layers

The Sun panel responds to solar elevation and bearing at the selected time: daylight, low warm light, twilight, or night. Its enlarged disc is clipped by a level geometric horizon. Colors and disc size are artistic; terrain and refraction are not modeled. When event time is unknown, the displayed selected time also applies to this study.

The Earth panel offers a regional azimuthal-equidistant map or an orthographic hemisphere, centered on the selected place. Natural Earth 50m coastlines are contemporary and generalized, not street maps or historical boundaries. Regional maps span 2,000, 4,000 or 8,000 km. A cartographic overlay can be added to dated NASA imagery. Weather is a local estimate, represented by a cloud-fraction ring and numeric details, not spatial radar or cloud imagery. Open-Meteo selects its historical model blend; precipitation is the preceding hour total and other values are at the selected preceding hour. Imagery and weather have distinct timestamps.

Projection library: D3 Geo (ISC; dependency notices included with the license). License. Google Maps imagery is not used: its published guidelines exclude retail posters.

Combined compositions

The design gallery offers eight designs, each representing one print. Under the Same Sky combines sky and Moon; The Complete Moment combines sky, Moon, Sun and a regional Earth view. Small labels are simplified in these compositions, and every subject is calculated from the same selected moment. A combined panel uses cropped artwork windows and a clear regional map. Satellite and weather layers apply to standalone Earth designs; combined prints omit these layers.