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Glossary

The words the instruments and the readings use, defined once. The same definitions appear in the chart’s tooltips.

Altitude: Height above the local horizon, from 0° on the horizon to 90° at the zenith; negative below the horizon. Values here include atmospheric refraction.
Angular separation: The true angle between two bodies on the sky, along a great circle, including their latitudes. It is the same in every zodiac.
Apparent magnitude: Brightness as seen from Earth. Lower is brighter: Sirius is −1.46, the faintest naked-eye stars about +6.
Apparent place: Where the body appeared from Earth at that instant: corrected for light-time and aberration, and referred to the true equator and equinox of that date (precession and nutation applied).
Applying / separating: Whether the orb was shrinking (applying, moving toward exact) or growing (separating) at the moment, from the bodies' motions.
Aspect: A traditional angle between two bodies measured along the ecliptic: conjunction 0°, sextile 60°, square 90°, trine 120°, opposition 180°, and minor ones between. An aspect counts while the measured angle is within its orb.
Astrometric J2000: Right ascension and declination on the mean equator and equinox of J2000 (the ICRF frame star catalogues use), corrected for light-time.
Ayanamsa: The angle between the vernal equinox and the sidereal zodiac's zero point. Precession makes it grow by about 50″ a year (one degree in about 72 years). Each sidereal tradition fixes the zero point differently, so the ayanamsa is always named.
Azimuth: Direction along the horizon, measured from north (0°) through east (90°), south (180°) and west (270°).

Celestial equator: Earth's equator projected onto the sky. Declination is measured from it; the Sun crosses it at the equinoxes.
Chart angles: Where the ecliptic crosses the local horizon (Ascendant in the east, Descendant in the west) and the meridian (Midheaven above, IC below). These are measured geometry, not a house system.

Declination: Angular distance north or south of the celestial equator (the projection of Earth's equator onto the sky). It is the same in every zodiac.
Declination difference: How far apart two bodies are north–south of the celestial equator. Near 0°, on the same side, they are parallel; at equal distances on opposite sides, contra-parallel.
ΔT: The difference between Terrestrial Time, which runs uniformly, and Universal Time, which follows Earth's slightly irregular rotation. It was about 57 seconds in 1990 and about 69 seconds in 2020.
Distance: Distance from Earth's centre in astronomical units (1 AU ≈ 149,597,871 km, the mean Earth–Sun distance), with the light-time: how long its light took to reach Earth.

Ecliptic: The Sun's apparent yearly path around the sky — the plane of Earth's orbit seen from Earth. The zodiacs are 30° divisions of it; the planets stay close to it.
Ecliptic latitude: Angular distance north or south of the ecliptic, the Sun's apparent yearly path. Zodiac labels ignore it; the true separation between two bodies does not.
Ephemeris: The mathematical model of the Sun, Moon and planets that the positions come from. This app uses astronomy-engine and checks it against JPL Horizons.
Epoch: The instant a coordinate system is referred to. 'Of date' coordinates use the equator and equinox of the moment itself; J2000 coordinates use those of 1 January 2000, 12:00 TT.
Equinox: The instant the Sun crosses the celestial equator (about 20 March and 22 September). Day and night are then close to equal everywhere, and astronomical spring or autumn begins, depending on the hemisphere.

Frame: The reference a coordinate is measured in: tropical, sidereal, star-fixed, equatorial or horizontal. Every value on this site carries its frame's badge, so two frames are never mixed silently.

Hour angle: How far a body has turned past the local meridian, in hours: 0 h is culmination (highest), negative before it, 12 h the lowest point.
House system: A convention for dividing the sky around the observer into twelve sectors. Different systems divide space or time differently; none is objectively correct, so the system is always named.

IAU constellation: The constellation region containing the body, using the International Astronomical Union's 1930 boundaries. The boundaries are a convention, not physical objects; constellations have unequal sizes and do not match the 30° zodiac signs.
Ingress: A body's entry into a new sign. Because the tropical and sidereal zodiacs are offset by the ayanamsa, the same body enters a given sign on different dates in each; every ingress here names its zodiac.

Local sidereal time: The right ascension on the local meridian: a clock that follows the stars rather than the Sun. It fixes which part of the sky is rising, culminating and setting.
Longitude difference: The difference of the two ecliptic longitudes, folded to 0°–180°. Traditional aspects are defined on it; it ignores latitude, so it can differ from the true separation.
Lunation: One cycle of the Moon's phases, from new Moon to new Moon: 29.53 days on average (the synodic month). The phase follows the Moon's angle from the Sun, its elongation.

Naked-eye visibility: A documented heuristic, not a photometric model: the object must be at least 3° above the horizon and brighter than the limiting magnitude for the sky's darkness (−3.5 by day, 1 in civil twilight, 3 nautical, 5 astronomical, 6 at night).

Obliquity: The tilt of Earth's equator to the ecliptic, about 23.44°. It is why the Sun's declination swings through the year.
Orb: How far a measured angle may differ from an exact aspect angle and still count. Orbs are a convention, so the profile in use is always shown.
Out of bounds: A declination beyond the Sun's greatest (the obliquity of the ecliptic, about 23.44°): the body is farther north or south than the Sun ever goes.

Parallel / contra-parallel: Two bodies at nearly the same declination on the same side of the celestial equator (parallel), or on opposite sides (contra-parallel).
Perihelion and aphelion: Earth's closest (early January, about 0.983 AU) and farthest (early July, about 1.017 AU) points from the Sun. The distance changes by only 3%; the seasons come from the axial tilt.
Precession: The slow wobble of Earth's axis, one turn in about 25,800 years. It moves the equinox westward against the stars, which is why the tropical and sidereal zodiacs drift apart.

Refraction: The atmosphere bends light, lifting objects near the horizon by up to about 34′ (a little more than the Sun's width). Altitudes here include it.
Retrograde: A planet's apparent westward drift against the stars, seen from a moving Earth when it overtakes an outer planet or is overtaken by an inner one. The planet itself never reverses.
Right ascension: Angular distance measured eastward along the celestial equator from the vernal equinox, usually in hours (1 h = 15°). With declination it fixes a direction on the sky.

Sidereal longitude: Measured relative to a stellar reference frame. It is the tropical longitude minus the ayanamsa, so that 0° stays tied to the stars rather than to the equinox.
Sidereal zodiac: The zodiac anchored to the stars: tropical longitude minus an ayanamsa. Its signs stay put against the constellations while the seasons slowly move through them.
Sign: A 30° stretch of the ecliptic, named after a constellation. Signs are labels in a chosen frame (tropical or sidereal); they are not the constellations, which are of unequal size.
Solar declination: The Sun's angle north or south of the celestial equator: +23.4° at the June solstice, 0° at the equinoxes, −23.4° at the December solstice. It sets the length of daylight.
Solstice: The instant the Sun reaches its farthest north (June) or south (December) of the celestial equator: the year's longest and shortest days, depending on the hemisphere.
Speed: Daily motion in star-fixed ecliptic longitude. Negative means apparent retrograde motion: the planet appears to drift westward against the stars as Earth overtakes it or is overtaken.
Star-fixed (J2000): Coordinates referred to the mean ecliptic and equinox of 1 January 2000, 12:00 TT. They do not drift with precession, so they stay fixed relative to the distant stars.
Station: The moment a planet's apparent motion turns — from direct to retrograde (station retrograde) or back (station direct). It seems to stand still against the stars for a few days around it.
Sub-solar point: The place on Earth where the Sun is directly overhead at that moment. The day side of the world is the hemisphere centred on it; the sub-lunar point is the same for the Moon.

Terminator: The line between day and night on Earth. Civil, nautical and astronomical twilight are the bands beyond it where the Sun is less than 6°, 12° and 18° below the horizon.
Transit: Today's sky measured against a birth sky: the angle between where a body is now and where a body or point was at birth. Here transits are measured star-fixed (J2000), so precession since birth is accounted for.
Tropical longitude: Measured from the vernal equinox. Ecliptic longitude along the true ecliptic of date, counted from the point where the Sun crosses the celestial equator in March — the zero of the tropical zodiac.
Tropical zodiac: The zodiac that begins at the March equinox. It keeps its signs aligned with the seasons, so it drifts against the stars as the equinox precesses.
Twilight: The light before sunrise and after sunset. Civil twilight ends when the Sun is 6° below the horizon, nautical at 12°, astronomical at 18°; after that the sky is fully dark.

Void of course: A traditional convention: the Moon is 'void' from its last major aspect in a sign until it enters the next sign. It is shown as tradition, with its rules named, not as a measurement.

05Learn

Method: how the sky is measured

Astronomy is measured; astrology is an interpretive tradition. This is exactly how every page keeps the two apart.

Principles

Astronomy first

What’s My Sky? reads astrology’s symbols against the sky as it actually is. Six rules hold on every page, in every reading, and in every answer the Guide gives.

01Measure first
Every position, time and event is computed from a validated ephemeris before anything is interpreted. How accurate it is has been measured, and is published below.
02Name the frame
Every coordinate carries a coloured badge for its frame — tropical, sidereal, star-fixed, equatorial or horizon. Frames are never mixed silently.
03Geometry before labels
Angles between bodies, declinations and altitudes are the same in every zodiac. Signs are labels laid on the ecliptic, so the geometry comes first.
04Conventions, shown
The ayanamsa, the house system and the orbs are choices, not measurements. The one in force is always named, and you can change it.
05Honest about the unknown
Without a birth time there are no houses, angles or rising sign. Approximate times flag what they affect. Nothing unknown is filled in.
06Tradition, attributed
Interpretations are offered as what a tradition says — “traditionally interpreted as…” — never as science, and never as a forecast.

Measuring today’s values…