The measure
of timeזמן

Countdown is available only before a selected event, according to your device's current clock—not the observatory's playback slider. An opened window keeps its chosen event, location, time zone and method even if the map or settings change. Its hours:minutes:seconds:milliseconds are display resolution, not guaranteed clock synchronization or astronomical accuracy.

Standard Hanetz and the observer sunrise have a dedicated night-to-day scene. Stars, illustrative constellations without connecting lines, and galaxies fill the sky before the selected method's calculated Alot hashachar; horizon light grows from Alot. The sun begins to emerge eight minutes before Hanetz. The approaching sky stays reddish, then changes immediately to bright, soft warm gold at zero as a clear arrival signal visible from a distance—the scene's one intentional abrupt color change. Stars fade completely by zero, the sun retains its gentle, eased upward motion after arrival, and blue sky develops from five minutes after arrival. Each opened window keeps its selected Alot and target times. If no valid earlier Alot is available, the ordinary animation remains. Other events keep their five-minute symbolic sunrise and fixed arrival background.

After zero the timer counts negatively. The window closes one hour after the event, or when you close it. If your browser blocks popups, the same countdown opens inside the page. Suspended or background windows may not update on every frame; when execution resumes, the current clock is checked and an expired window closes. The scenes are decorative, not an actual star chart, physical sky-brightness prediction or the actual Sun's position.

Proportional-hour zmanim inherit the ranges of their actual endpoints. Repeated endpoints are combined before interval propagation: GRA Shema is ¾ sunrise + ¼ sunset, not three independent uncertain quantities. Negative coefficients and the later-of-two mincha safeguard are propagated conservatively. Nearby-location differences likewise allow unknown correlations; shared errors might cancel, but no cancellation is assumed.

This is not a 68% or 95% interval, nor a guaranteed total ±. Coordinate and height errors, limb-radius and distance errors, UTC≈UT1, modeled ΔT errors, and validation of the angular target are not quantified. No live IERS corrections or JPL ephemeris replacement have been added. Dates far from the present especially inherit unquantified time-scale uncertainty. Directions, distances, illumination, solar transit, conjunctions and seasons need separate error models and are labeled unquantified rather than given invented ± values. Exported readings preserve the limits and assumptions.

Pressure, refraction, horizon and named halachic endpoints are fixed conventions in this scenario. They are not randomized to predict a personally visible sunset. A separate observational prediction would need different inputs. USNO's event definitions; NIST on reporting uncertainty and its basis.

Sunrise and sunset use the upper edge of the solar disk. The apparent radius varies with distance. The horizon model adds 34 arcminutes of standard refraction, scaled by the entered pressure and temperature, and the horizon dip from eye height. It subtracts the entered obstruction angle. Moonrise and moonset use the Moon's corresponding apparent radius and topocentric position; a crossing does not itself establish crescent visibility.

The instant-by-instant “apparent altitude” uses an altitude-dependent refraction model. It is a different readout from the conventional constant-at-the-horizon correction used in the rise/set equation. Halachic angular dawn and nightfall use the geometric solar centre without a second refraction correction.

The ephemeris accounts for its modeled difference between terrestrial time and Earth-rotation time. The browser supplies UTC, used approximately as UT1. ZAMAN does not download live Earth-orientation corrections or future leap-second decisions. Historical and distant future results inherit the model and clock conventions used here.

When the required crossing does not occur on the selected local date, the result is unavailable. In polar regions, alternative religious conventions require their own definition; an invented sunrise would not improve the astronomy.

Height above the local ground is not the same as elevation above sea level. Metres, feet, and amot are alternative ways to enter the same physical height; a smooth, open-horizon dip remains a model assumption, not a measurement of nearby mountains or buildings. One international foot is exactly 0.3048 metres. NIST's definition.

Amot binyan uses six tefachim; amot kelim uses five. These selectable scales expose Rabbi Yehudah's distinction in Kelim 17:10. Rabbi Meir disagrees, and Bartenura there follows Rabbi Meir: five tefachim must not be read as the universal rule for every vessel.

The 8 cm tefach gives 48 cm for binyan and 40 cm for kelim; 9.6 cm gives 57.6 cm and 48 cm. The six-tefach sizes correspond to the commonly cited R. Chaim Naeh and Chazon Ish scales. The five-tefach values are arithmetic conversions, not an attribution of Rabbi Yehudah's vessel ruling to those later authorities. A custom tefach length is available. Peninei Halakha, Shabbat 30:1, note 1.

Negative sea-level elevation is supported, down to −500 m. An outdoor location below sea level still has a local horizontal plane. Underground depth is a different input and cannot be used as the symmetric negative of an elevated observer.

For a spherical open horizon, dip = acos(R / (R + h)). At positive height h, a line of sight can be tangent to Earth. For negative h, the ratio exceeds 1 and there is no real tangent solution. A pit instead needs its opening or rim geometry—for a simple rim, its elevation angle depends on depth divided by horizontal distance to the rim. Depth alone cannot determine it. This is a geometric deduction from the published elevation formula, not a new halachic ruling.

Being in a dark room does not alter this workbench's fixed-standard Shema calculation. Halachic treatments of elevation do differ; ZAMAN preserves the declared preset instead of inventing an underground adjustment. Documented elevation alternatives; Chabad's specified astronomical endpoints.

A building or house match is more specific than a street, neighbourhood, or city match, but its coordinate is not guaranteed to be your exact observing point. The address search uses Photon’s OpenStreetMap records. Select the intended result, then refine the pin on the detailed map or enter known coordinates. A long address or many decimal places does not itself prove rooftop accuracy. Photon documentation.

The default map uses a locally hosted MapLibre GL JS renderer. Zoom from the world to streets, click to place the observing point, drag the pin, or choose the center of the view. The pin is also keyboard accessible. The coordinate fields retain nine decimal places for adjustments; these are representation digits, not a measurement guarantee. North/east/south/west steps of 10 cm, 1 m, and 10 m use a spherical-Earth destination calculation. A mapped building outline is not a surveyed position.

The standard OpenStreetMap raster source stops at native tile zoom 19. MapLibre uses a 512-pixel camera world and these tiles are 256 pixels, so enlargement begins above camera zoom 18. Camera zoom can continue to 22 to aid pin placement, but no new map detail is added. Street tiles do not cover the polar caps beyond approximately 85.05° latitude; direct coordinate entry and the celestial globe remain available there. Maps do not supply eye height, elevation, terrain, or a measured skyline.

The sourced dawn is 72 seasonal minutes before sunrise. The earlier Magen Avraham Shema and the GRA four-hour tefillah are deliberately distinguished. Geonic nightfall at 13½ seasonal minutes is an early nightfall calculation, not a universal Shabbat-release time. Dawn; prayer distinctions; nightfall and additional Shabbat margin.

The cited Yalkut Yosef teaching places plag 1¼ proportional hours before tzeit. Its precise hour and endpoint conventions matter. ZAMAN currently shows explicitly labeled GRA and selected-day arithmetic comparisons; it does not present those as a complete implementation of Rav Ovadia's plag, mincha, or Shabbat rulings. Plag discussion.

Internal netz amiti and shkiah amiti use the geometric solar centre at −1.583°. They define the proportional hour, Shema at 3 hours, tefillah at 4, mincha gedola at 6½, mincha ketana at 9½, and plag at 10¾. Chatzot in this profile is the midpoint of those internal boundaries. Ordinary observed sunrise and sunset keep their separate upper-limb definitions.

Dawn uses −16.9°, misheyakir −10.2°, and ordinary tzeit −6°. On Saturday the additional Shabbat-end row uses −8.5°. A separate mincha safeguard shows the later of proportional mincha gedola and 30 fixed minutes after the midpoint, reflecting Chabad's recommendation for short winter days. ZAMAN leaves absent polar crossings unavailable and does not impose a midnight substitution. Chabad's own calculation definitions.

Halachic presets use an unobstructed, sea-level standard baseline: 1010 hPa and 10°C. The prominent observer sunset and sky readouts respond to the entered horizon settings. That distinction allows examination of a real-world horizon without silently changing each halachic convention.

Solar transit is the Sun's upper-meridian crossing, not necessarily the exact midpoint of sunrise and sunset. GRA mincha gedola is displayed as sunrise plus 6½ daylight hours; an additional 30-minute minimum is not silently imposed on that comparison. Outside the Baal HaTanya profile, misheyakir at 11° is a separately labeled comparison. Friday candles use the entered fixed-minute offset, which is a local custom rather than one universal time.

The displayed boundaries are 3 days, 7 days, half a mean lunation, and 15 days after the traditional molad. They are elapsed durations, unaffected by a daylight-saving clock change. Half a mean lunation is 14 days, 18 hours, 22 minutes, and 1⅔ seconds.

These are raw boundaries, not automatically adjusted to a suitable night with a visible Moon. The observatory's Hebrew date advances at its supplied local sunset as a display convention; twilight remains a distinct halachic interval. With no sunset, the transition is marked unknown. The local civil date line is used, without selecting an alternative halachic date-line ruling.

Chiron (2060) uses a bundled NASA/JPL Horizons numerical ephemeris (solution JPL#171, dated June 5, 2026). Calculations run locally for civil dates from 1600 through 2400, including time-zone boundary padding, using interpolated barycentric positions, light travel time, first-order stellar aberration, and the existing Earth and coordinate models. Your location and date are not sent to JPL.

Tests compare withheld samples and independently requested geocentric vectors; their small numerical residuals are not a bound on the object's physical position. Orbit uncertainty and time-model uncertainty grow away from observations. This display does not include a total Chiron uncertainty estimate, gravitational light deflection, or a brightness model. The source record and limitations and reproducible data generator accompany the source download. Chiron does not change the classical-seven aspect list or any zmanim calculation.

This sequence follows the GRA recension of Sefer Yetzirah, chapter 5. Both Adars retain the Adar correspondence in a leap year.

Retrograde means the computed geocentric ecliptic longitude decreases across the sampled 24-hour interval. The aspect list compares the classical seven at 0°, 60°, 90°, 120°, and 180°, allowing a 3° difference from each exact angle. These are transparent geometric labels.

Modern astrological aspect names do not establish one universal Jewish interpretation. Letter-to-planet mappings also vary between textual recensions. This instrument exposes positions and sourced correspondences; it does not generate personal predictions, auspiciousness scores, or claims about destiny.