Fact-checked by Grok 2 weeks ago

Ecliptic

The ecliptic is the apparent path traced by the Sun on the celestial sphere over the course of one year, corresponding to the projection of the plane of Earth's orbit around the Sun onto the imaginary surface of the sky.^[1] This great circle is inclined at an angle of approximately 23.44° to the celestial equator, a tilt known as the obliquity of the ecliptic, which varies slightly over long periods due to gravitational influences and as of November 2025 stands at about 23°26'09".^[2] In astronomy, the ecliptic defines a fundamental reference plane for the ecliptic coordinate system, where celestial objects are located using two angular coordinates: ecliptic longitude, measured eastward from the vernal equinox along the ecliptic to 360°, and ecliptic latitude, measured northward or southward from the ecliptic plane ranging from -90° to +90°.^[3] This system is particularly useful for describing the positions of the Sun, Moon, and planets, as their orbits lie close to the ecliptic plane, causing them to appear clustered along this band in the sky.^[4] The intersections of the ecliptic with the celestial equator mark the vernal and autumnal equinoxes, points that have historically guided calendars and seasonal observations.^[5] Historically, the ecliptic held central importance in ancient astronomy, serving as the basis for predicting solar and lunar eclipses—hence its name, derived from the Greek ekleipsis, meaning "abandonment" or "fail to appear"—since these events occur only when the Moon passes through the plane.^[6] Ancient Greek astronomers, building on earlier Mesopotamian and Egyptian traditions, recognized the ecliptic as the Sun's annual path and divided the zodiacal band around it into twelve constellations, most named for animals, which facilitated star catalogs and timekeeping.^[7] These zodiacal signs, though now misaligned with the actual constellations due to precession, continue to influence astrological practices while underscoring the ecliptic's enduring role in mapping the heavens.^[8]

Fundamentals

Apparent Motion of the Sun

From Earth's perspective, the Sun appears to trace an annual path across the celestial sphere, a vast imaginary dome encompassing the sky, due to our planet's orbit around it. This apparent motion results from the relative positions of Earth and the Sun over the course of a year, causing the Sun to shift eastward relative to the fixed stars by approximately 1° each day, completing a full 360° circuit in about 365.25 days.^[9]^[10] This yearly trajectory defines the ecliptic, the great circle on the celestial sphere that marks the Sun's apparent path and lies in the plane of Earth's orbit. The ecliptic is inclined to the celestial equator—the projection of Earth's equatorial plane onto the sky—by roughly 23.5°, a tilt known as the obliquity that underlies seasonal changes in daylight and weather patterns.^[11]^[12] Ancient astronomers meticulously tracked this solar progression, noting how it wove through a sequence of 12 prominent constellations along the ecliptic. Greek scholar Hipparchus, working in the 2nd century BCE, contributed precise observations of the Sun's positions against these stellar backdrops, enhancing early understandings of celestial cycles.^[13]^[14] The ecliptic thus delineates a narrow band across the sky, traditionally called the zodiac, where not only the Sun but also the Moon and the five visible planets—Mercury, Venus, Mars, Jupiter, and Saturn—predominantly appear to wander due to their near-coplanar orbits with Earth. This concentration of luminous bodies within the zodiac facilitated ancient calendrical and navigational practices.^[15]^[16]

Geometric Definition

The ecliptic plane is defined as the imaginary plane containing Earth's orbit around the Sun, serving as a fundamental reference in celestial geometry. The ecliptic itself is the great circle formed by the intersection of this plane with the celestial sphere, representing the mean path traced by the Sun over one year.^[5] This geometric definition remains consistent across reference frames. In the heliocentric model, the ecliptic plane directly coincides with Earth's orbital plane relative to the Sun at its center. In the geocentric model, the same plane underlies the apparent annual motion of the Sun against the background stars, with the observer's position on Earth merely altering the perspective without changing the plane's intrinsic properties.^[1] The normal vector to the ecliptic plane is aligned with the angular momentum vector of Earth's orbit, perpendicular to the plane and pointing toward the north ecliptic pole. This vector quantifies the plane's orientation in three-dimensional space, with its direction fixed by the conservation of orbital angular momentum in the absence of perturbations.^[17] Although nearly invariant on human timescales, the ecliptic plane's orientation undergoes gradual precession over millennia due to gravitational torques from other planets, termed planetary precession. This effect rotates the plane at a rate of approximately 0.47 arcseconds per year, causing a slow shift in the position of the ecliptic pole relative to distant stars.^[18] The apparent motion of the Sun along the ecliptic arises as the projection of this orbital geometry onto the observer's celestial sphere.

Orientation and Geometry

Obliquity to the Celestial Equator

The obliquity of the ecliptic, denoted ε, is defined as the angle between the ecliptic plane—the apparent path of the Sun projected onto the celestial sphere—and the celestial equatorial plane, which is the projection of Earth's equatorial plane onto the same sphere.^[19] This angle arises from the tilt of Earth's rotational axis relative to its orbital plane around the Sun.^[20] Numerically, ε equals Earth's axial tilt and is approximately 23.436° (or 23°26'10") as of November 2025.^[2]^[21] Ancient measurements of this angle were pioneered by Eratosthenes in the 3rd century BCE, who determined a value of about 23° 51' using observations of the Sun's position at the summer solstice, as reported in later accounts.^[22] Over long timescales, ε exhibits secular variation primarily due to dissipative tidal torques acting through core-mantle coupling, causing a gradual decrease at a rate of approximately 0.47 arcseconds per year.^[23] This linear trend, combined with cyclic fluctuations from planetary gravitational perturbations, projects ε to reach a minimum of about 22.1° in roughly 10,000 years.^[20] In astronomical practice, the obliquity plays a critical role in coordinate transformations between ecliptic and equatorial systems, where the rotation matrix elements incorporate sin ε and cos ε to account for the tilt between the reference planes.^[24] For instance, converting right ascension and declination (equatorial) to ecliptic longitude and latitude requires rotating the coordinate frame by ε around the line of nodes (the vernal equinox).^[25] This transformation is fundamental for analyzing solar system dynamics and historical star catalogs aligned to different epochs.

Relation to Earth's Equator

The Earth's equatorial plane is defined as the plane perpendicular to its axis of rotation, intersecting the planet's surface along the geographic equator, which divides Earth into northern and southern hemispheres. In contrast, the ecliptic plane is the plane of Earth's orbit around the Sun, perpendicular to the vector of its orbital angular momentum. These two planes are misaligned, with the angle between the equatorial plane's normal (Earth's rotation axis) and the ecliptic plane's normal known as the axial tilt or obliquity. This tilt measures 23.436° as of November 2025.^[2]^[26] The origin of this obliquity traces to Earth's formation through accretion of material in the solar nebula approximately 4.6 billion years ago, during which a Mars-sized protoplanet (Theia) collided with the proto-Earth in a giant impact event. This collision ejected debris that coalesced to form the Moon and imparted the initial tilt to Earth's rotation axis. Without the Moon, Earth's obliquity would vary chaotically over geological timescales; however, the Moon's gravitational influence provides a stabilizing torque that maintains the tilt within a narrow range of about 22.1° to 24.5°, preventing extreme fluctuations that could disrupt climate stability.^[27]^[28]^[29] The geographic equator represents the fixed reference on Earth's surface perpendicular to the instantaneous rotation axis, while the celestial equator is the projection of this equatorial plane onto the infinite celestial sphere for astronomical observations. Their alignment is not static; gravitational torques from the Sun and Moon induce axial precession, causing the celestial equator to shift slowly relative to the fixed stars over a cycle of about 25,772 years, with additional minor effects from the regression of lunar nodes influencing long-term variations.^[5]

Solar System Context

Ecliptic Plane

The ecliptic plane represents the fundamental geometric plane in which the planets of the Solar System predominantly orbit the Sun, serving as a close approximation to the least-squares best fit across their orbital paths. This plane is defined by the collective layout of these orbits, with the vast majority of planets exhibiting low inclinations relative to it—typically within 7°—reflecting the system's overall coplanarity. For instance, Mercury has the highest inclination among the classical planets at 7.0°, while Venus, Mars, Jupiter, Saturn, Uranus, and Neptune range from 0.8° to 3.4°; Earth's orbit defines the reference at 0° by convention.^[30] This alignment minimizes deviations and underscores the ecliptic's role as the Solar System's primary orbital reference, distinct from the more idealized geometric definition tied solely to Earth's path. A related but distinct concept is the invariable plane, which arises from the conservation of the Solar System's total angular momentum and provides an even more precise dynamical reference. The invariable plane passes through the system's barycenter and is perpendicular to its net angular momentum vector, remaining fixed over long timescales due to momentum conservation. It differs slightly from the ecliptic, tilted by approximately 1.6° relative to the latter (for the J2000 epoch), primarily because the ecliptic is anchored to Earth's orbit rather than the weighted angular momentum contributions of all bodies, including planets and the Sun itself. This small offset highlights how the ecliptic, while practical, is not perfectly invariant under gravitational perturbations.^[31] The origin of the ecliptic plane traces back to the formation of the Solar System from a collapsing protoplanetary disk, where conservation of angular momentum flattened the rotating cloud of gas and dust into a thin, disk-like structure. During the early stages of solar nebula collapse, material accreted preferentially in this equatorial plane, leading to the aligned orbits observed today and explaining why planetary inclinations to the ecliptic remain small. This primordial alignment, a byproduct of the disk's rotational dynamics, set the stage for planet formation through coagulation and migration within the plane, ensuring the Solar System's largely coplanar architecture. In modern astronomy and space exploration, the ecliptic plane forms the basis for planning interplanetary trajectories, as missions traveling near this plane can efficiently encounter multiple bodies with minimal propulsion adjustments. For example, the Voyager 1 and 2 spacecraft were launched along paths closely aligned with the ecliptic to sequentially visit Jupiter, Saturn, Uranus, and Neptune, crossing planetary orbits with only slight out-of-plane deviations to avoid hazards like the asteroid belt. This strategic use leverages the plane's natural geometry, reducing fuel requirements and enabling the grand tours that have expanded our understanding of the outer Solar System.^[32]

Reference Plane in Astronomy

In astronomy, the ecliptic serves as a fundamental reference plane, defined by the International Astronomical Union (IAU) as the mean plane of the orbit of the Earth-Moon barycenter around the Sun, determined from and designated by a specific planetary ephemeris such as DE405.^[33] This plane is projected onto the celestial sphere to form the great circle known as the ecliptic, providing a natural framework for celestial navigation and positional measurements. The standard IAU ecliptic coordinate system employs either the ecliptic of date (adjusted for the observation epoch) or the fixed mean equinox and ecliptic at the J2000.0 epoch (January 1, 2000, at 12:00 Terrestrial Time). Positions within this system are specified using two angular coordinates: ecliptic longitude λ, measured eastward from the vernal equinox along the ecliptic from 0° to 360°, and ecliptic latitude β, measured northward or southward from the ecliptic plane ranging from -90° to +90°.^[3] Transformations between the ecliptic system and the more commonly used equatorial system (with right ascension α and declination δ) rely on a rotation matrix that accounts for the obliquity ε, the angle between the ecliptic and equatorial planes. The rotation aligns the common line of nodes at the vernal equinox. A key component of this transformation is the formula for ecliptic latitude:

\beta = \arcsin\left( \sin \delta \cos \varepsilon - \cos \delta \sin \alpha \sin \varepsilon \right)

Similar equations derive λ from α and δ, enabling precise conversions for any celestial object.^[24] These formulas form the basis of the full 3x3 rotation matrix used in computational astronomy software. The ecliptic system's primary advantage lies in its alignment with the orbital planes of Solar System bodies, where most planets and minor bodies exhibit low ecliptic latitudes (typically |β| < 10°), facilitating simpler modeling of their trajectories compared to the equatorial system, which is Earth-centric and less intuitive for heliocentric dynamics. This makes it ideal for ephemerides like the Jet Propulsion Laboratory's DE430, a high-precision model spanning 1550 to 2650 CE that computes positions of the Sun, planets, and Moon relative to the ecliptic plane for mission planning and orbital predictions.^[34] For long-term applications, such as historical or future observations spanning centuries, adjustments for precession (the gradual shift of the equinox due to Earth's axial wobble) and nutation (short-term oscillations) are essential to maintain accuracy in the ecliptic's orientation. IAU models, including the 2006 precession theory, incorporate these effects to refine the mean equinox and obliquity, ensuring the reference plane remains dynamically consistent with ephemeris data.

Key Phenomena

Eclipses

Eclipses occur when the Sun, Earth, and Moon align closely within the ecliptic plane, the reference plane defined by Earth's orbit around the Sun. The Moon's orbit is inclined by approximately 5.15° relative to this plane, so alignments are possible only when the Moon passes through one of two intersection points known as the ascending and descending nodes. Solar eclipses take place near new moon when the Moon is at or near a node between Earth and the Sun, casting its shadow on Earth; lunar eclipses occur near full moon when Earth is between the Sun and Moon at a node, with Earth's shadow falling on the Moon.^[35]^[36] Solar eclipses are classified into three main types based on the Moon's apparent size relative to the Sun and the observer's location within the shadow: total, where the Moon completely obscures the Sun along a narrow path (the umbra), revealing the solar corona; annular, where the Moon appears smaller and a ring of sunlight remains visible around it; and partial, where only part of the Sun is covered, visible over a broader region in the penumbra. Lunar eclipses include total, where the Moon enters Earth's umbra and often takes on a reddish hue from atmospheric scattering; partial, where only a portion of the Moon passes through the umbra; and penumbral, where the Moon enters only the faint outer penumbra, causing a subtle dimming.^[38] The recurrence of similar eclipses follows the Saros cycle, a period of about 18 years, 11 days, and 8 hours (6585.3 days), equivalent to 223 synodic months, after which the Sun, Earth, and Moon return to nearly the same relative positions for eclipse geometry. This cycle produces a series of up to 70–80 related eclipses, with paths shifting gradually northward or southward due to the regression of the lunar nodes caused by nodal precession over an 18.6-year period.^[39]^[40] Predictions of eclipse paths and timings rely on Besselian elements, a set of geometric parameters derived from orbital mechanics that allow calculation of the shadow's position, duration, and visibility for specific locations on Earth. Modern computations extend these using numerical integration of the equations of motion for the Earth-Moon-Sun system, enabling accurate forecasts centuries in advance.^[41]^[42] Historically, eclipses held profound significance, as exemplified by the solar eclipse of May 28, 585 BCE, reportedly predicted by the Greek philosopher Thales of Miletus, which halted a battle between the Lydians and Medes, leading to a truce brokered by eclipse awe. This event, one of the earliest attributed predictions in Western records, underscored early recognition of periodic patterns in celestial alignments.^[43]

Equinoxes and Solstices

The equinoxes mark the instants when the Sun's path along the ecliptic crosses the celestial equator, occurring at ecliptic longitudes of 0° for the vernal (spring) equinox and 180° for the autumnal (fall) equinox.^[44] These crossings result in nearly equal lengths of day and night worldwide, as the Sun's declination passes through 0°.^[5] In contrast, the solstices occur when the Sun reaches its extreme declinations of approximately +23.44° (summer solstice) and -23.44° (winter solstice) in the Northern Hemisphere, corresponding to ecliptic longitudes of 90° and 270°, respectively.^[44] These positions represent the points of maximum northward and southward extent of the Sun's apparent motion, driven by the obliquity of Earth's axis relative to the ecliptic plane.^[20] In the Northern Hemisphere, the vernal equinox typically occurs around March 20, the summer solstice around June 21, the autumnal equinox around September 22, and the winter solstice around December 21.^[45] These dates vary by one or two days annually due to the irregularities of the Gregorian calendar and leap year insertions, which prevent excessive drift from the tropical year.^[45] For example, in 2025, the vernal equinox is on March 20 at 09:01 UTC, the summer solstice on June 21 at 02:42 UTC, the autumnal equinox on September 22 at 18:19 UTC, and the winter solstice on December 21 at 15:03 UTC.^[46] The solstices and equinoxes define the seasonal transitions, with the summer solstice marking the longest day and the winter solstice the shortest in the Northern Hemisphere. The equation of time quantifies the discrepancy between apparent solar time—based on the Sun's actual position—and mean solar time, which assumes a uniform day.^[47] This variation, reaching up to about 16 minutes, stems primarily from two factors: the obliquity of Earth's axis, which causes the Sun's speed along the ecliptic to vary seasonally, and the eccentricity of Earth's elliptical orbit, which affects orbital speed according to Kepler's second law.^[47] Near the solstices, the equation of time shifts the dates of earliest sunset and latest sunrise away from the solstice itself.^[47] Equinoxes and solstices form the astronomical foundation for many calendars, particularly the Gregorian calendar, which reformed the earlier Julian system to correct for a gradual drift in equinox dates.^[48] Introduced in 1582, the Gregorian adjustments—skipping leap years in certain centuries—ensure the vernal equinox aligns closely with March 21 over centuries, maintaining seasonal consistency for agricultural and religious purposes.^[49] This reform addressed an accumulated error of about 10 days by the 16th century, where the equinox had shifted earlier.^[48]

Cultural and Historical Uses

Position in Constellations

The ecliptic traces an apparent path through the sky that historically has been divided into twelve equal segments of 30° each, known as the zodiac signs from Aries to Pisces, a convention originating in Babylonian astronomy around the 5th century BCE. However, the actual constellations intersected by the ecliptic possess unequal boundaries, as formally delimited by the International Astronomical Union (IAU) in 1930 to standardize celestial cartography; for instance, the constellation Scorpio spans only about 7° along the ecliptic, while Virgo extends over roughly 44°. These IAU boundaries, defined in equatorial coordinates, ensure every point in the sky belongs to exactly one of the 88 constellations, but they result in varying durations for the Sun's passage through each zodiacal group, ranging from about 6 days in Scorpius to 45 days in Virgo.^[50]^[51] Due to the precession of the equinoxes—a slow wobble of Earth's rotational axis caused by gravitational torques from the Sun and Moon, completing a full cycle in approximately 25,772 years—the position of the vernal equinox along the ecliptic has shifted westward relative to the fixed stars. Around 2000 years ago, this point marked the beginning of Aries, but it entered Pisces around the start of the Common Era and has since progressed through that constellation; as of 2025, it lies in Pisces near the boundary with Aquarius, having moved about 30° from its ancient position in Aries. This gradual drift, first quantified by Hipparchus in the 2nd century BCE at a rate of about 1° every 72 years, continues to alter the stellar backdrop against which the equinox occurs.^[13]^[52] The distinction between the sidereal zodiac, which is aligned with the fixed positions of the constellations, and the tropical zodiac, which is fixed relative to the vernal equinox and Earth's seasons, arises directly from this precession. The angular offset between the two systems, termed the ayanamsa, currently stands at approximately 24.2° for the widely used Lahiri formulation, meaning sidereal signs lag behind their tropical counterparts by this amount and will continue to diverge over time. This discrepancy ensures that while the tropical zodiac remains seasonally anchored, the sidereal version better reflects the actual stellar configurations but requires periodic adjustments to maintain alignment with observed constellations. In practice, the Sun's annual transit along the ecliptic passes through these constellations at varying times due to their unequal extents; for example, it moves through Taurus from mid-May to mid-June, appearing against that constellation's stars during late spring in the Northern Hemisphere. Modern astronomy further notes that the ecliptic actually intersects thirteen constellations, including Ophiuchus between Scorpio and Sagittarius, through which the Sun passes from late November to mid-December—a segment spanning about 18° that was excluded from the traditional twelve due to historical Babylonian conventions favoring equal divisions.^[53]^[54]

Role in Astrology

In astrology, the ecliptic serves as the foundational pathway for the zodiac, a belt divided into twelve equal signs of 30 degrees each, originating from Babylonian astronomers around the 5th century BCE who formalized this segmentation to track planetary movements.^[55] This division, initially sidereal and aligned with constellations, evolved into the tropical zodiac system, which fixes the signs relative to the vernal equinox rather than stellar positions, thereby disregarding the precession of the equinoxes.^[56] The Greek astronomer Claudius Ptolemy adopted and systematized this tropical framework in his influential 2nd-century CE text, the Tetrabiblos, establishing the ecliptic's role in generating horoscopes by assigning planetary positions within these seasonal signs to interpret personal and mundane events. Central to astrological practice is the concept of planetary aspects, which measure angular separations between celestial bodies along the ecliptic's longitude, such as conjunctions at 0 degrees (planets appearing to occupy the same point) or oppositions at 180 degrees (planets directly across from each other).^[56] These configurations, detailed in Ptolemy's Tetrabiblos, inform interpretive narratives; for instance, Mercury's retrograde motion—when it appears to reverse direction against the zodiac's progression—is viewed as a period of introspection, miscommunication, or reevaluation rather than an optical illusion caused by relative orbital speeds. Horoscopes thus map the ecliptic into twelve houses corresponding to life areas, with the Sun's position at birth determining one's zodiac sign in this tropical system. Despite its enduring cultural influence, the astrological use of the ecliptic faces scientific dismissal as a pseudoscience lacking empirical validation, with no demonstrated causal link between celestial positions and terrestrial events.^[57] Controlled studies have consistently failed to support astrological predictions, attributing any perceived accuracies to confirmation bias or the Barnum effect.^[58] Nevertheless, the tropical zodiac persists in Western astrology for personality profiling and forecasting, while Vedic (Jyotisha) traditions adapt a sidereal variant along the ecliptic for karmic and predictive purposes, maintaining global relevance in spiritual and cultural contexts.^[56]

References

[1]
What Is the Plane of the Ecliptic? - NASA
Mar 23, 2008 · The ecliptic is the imaginary plane containing the Earth's orbit around the Sun. In the course of a year, the Sun's apparent path through the sky lies in this ...
[2]
Obliquity - JPL Solar System Dynamics
The obliquity of the ecliptic for the Earth is the angle between the equatorial and ecliptic planes.
[3]
[PDF] Reference Frames Coordinate Systems
Ecliptic Plane. Vsun relative to earth. X. Y = component of Vsun perpendicular to X. Y. Z. – The GSE frame also can be defined using the mean ecliptic of date.<|control11|><|separator|>
[4]
Planetary Alignments and Planet Parades - NASA Science
Feb 4, 2025 · This line, referred to as the ecliptic, represents the plane in which the planets orbit, seen from our position within the plane itself. NASA/ ...
[5]
Chapter 2: Reference Systems - NASA Science
Jan 16, 2025 · Another important feature intersecting the celestial sphere is the ecliptic plane. This is the plane in which the Earth orbits the Sun, 23.4° ...
[6]
What Is the Ecliptic? - Sky & Telescope
Jul 28, 2022 · The word comes from the Greek for “fail to appear,” and ancient astronomers named it such because it's the place where eclipses happen. A ...
[7]
1a The Celestial Sphere - PWG Home - NASA
Mar 28, 2014 · The ancients distinguished 12 constellations along this path, and since most are named for animals, they are known as the zodiac, the "circle of ...
[8]
The Path of the Sun, the Ecliptic - PWG Home - NASA
Mar 28, 2014 · The apparent path of the Sun across the sky. In summer, the Sun's path is longest, and so are the days. In winter, the Sun's path is ...Missing: astronomy definition
[9]
Motions
This daily eastward drift is about 1° per day (there are 365 days in a year, but 360° in a circle). This apparent motion is a reflection of the Earth's annual ...
[10]
Lecture 6: Daily & Annual Motions
Sep 17, 2007 · This apparent motion is a reflection of the Earth's annual orbit around the Sun. The Ecliptic. The Ecliptic is the apparent path of the Sun ...
[11]
Celestial Sphere
... Sun, The apparent motion of the Sun through the sky during the year is a circle that is inclined 23 1/2 degrees from the celestial equator. This circle is ...
[12]
Celestial Cooridnates - University of Louisville Physics and Astronomy
Aug 24, 2020 · Ecliptic is the great circle arc on the celestial sphere that is the intersection of Earth's orbital plane with the sky. It is also the annual ...
[13]
Precession - PWG Home - NASA
Oct 10, 2016 · They studied the heavens, mapped their constellations, identified the path of the Sun and estimated the periods of the Moon and Sun as they ...
[14]
The Historical Development of Celestial Co-ordinate Systems
... ecliptic, respectively. “Right Ascension” in ancient Greek astronomy, like “Declination,” was a term originally used only for a special purpose, and with a ...
[15]
Seasons and the Zodiac - Motions of the Sun - NAAP - UNL Astronomy
The Zodiac was extremely important to historical astronomy. At times many believed that the stars either directly influenced or were portents of one's fate. ...Missing: path | Show results with:path
[16]
AstroPages | Zodiac | Western Washington University
The ecliptic is a line where the plane described by the Earth's orbit around the Sun crosses the celestial sphere. The plane is close to those described by many ...<|control11|><|separator|>
[17]
[PDF] Fundamental Concepts
Ecliptic plane. Plane defined by movement of the earth around the sun. Equatorial plane. Plane normal to the earth's spin axis, Z. Intersection of equatorial ...
[18]
Comparison between high precision precession models for the ...
Adopting these expressions for the planetary precession, the solution for the precession of the equator was obtained by means of a fit to VLBI data of ...
[19]
Milankovitch (Orbital) Cycles and Their Role in Earth's Climate
Feb 27, 2020 · Obliquity – The angle Earth's axis of rotation is tilted as it travels around the Sun is known as obliquity. Obliquity is why Earth has seasons.
[20]
Astrodynamic Parameters - JPL Solar System Dynamics
JPL asteroid and comet ecliptic orbital elements are based on the adopted IAU 1976 constant for the obliquity of the ecliptic.
[21]
Obliquity - an overview | ScienceDirect Topics
Obliquity is defined as the angle between the Earth's rotational axis and a perpendicular to its orbital plane, with an actual value of approximately 23.45°.
[22]
The Sources of Eratosthenes Measurement of the Earth - NASA ADS
According to Ptolemy (circa 142, Chapter I. 12), Eratosthenes took the obliquity to be 230 5', 20". Therefore Eratosthenes took this value to be also the ...
[23]
Secular Decrease of Obliquity due to Dissipative Core—Mantle ...
01 ± · 0″. 05 cy0−1 between the observed secular rate of change of the obliquity and that due to calculated planetary perturbations of the ecliptic plane.
[24]
3. Coordinate transformations
For the horizontal system, only the equations for the transformation to the equatorial system are given. 3.1. Ecliptic and equatorial coordinates. The obliquity ...
[25]
Background information module celestial — Kapteyn Package (home)
In converting equatorial coordinates to ecliptic coordinates, only one angle is involved. This angle is known as the obliquity of the ecliptic. The value ...
[26]
None
Nothing is retrieved...<|separator|>
[27]
The Moon's Influence on Us
Stable Seasons – The giant impact that formed the Moon may have tipped the Earth ... Giant Impact hypothesis as the predominant explanation of its beginnings.
[28]
Moon Formation - NASA Science
Debris left over from the formation of the Sun coalesced into a disk around the star, creating clumps that ranged in size from dust flecks to minor planets.Missing: obliquity accretion stabilized
[29]
Stabilization of the Earth's obliquity by the Moon - Nature
Feb 18, 1993 · Here we investigate the stability of the Earth's orientation for all possible values of the initial obliquity, by integrating the equations of precession of ...
[30]
None
Nothing is retrieved...<|control11|><|separator|>
[31]
The solar system's invariable plane - Astronomy & Astrophysics (A&A)
Thus, the invariable plane1 is defined as the plane perpendicular to the total angular momentum vector of the solar system that passes through its barycentre.<|separator|>
[32]
https://svs.gsfc.nasa.gov/4139
[33]
11 Definitions
Ecliptic: mean plane of the Earth's orbit around the Sun as determined from and designated by an ephemeris of the Earth, (e.g. ecliptic of DE 405). Ecliptic ...
[34]
https://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/planets/de430_and_de431.pdf
[35]
[PDF] The Planetary and Lunar Ephemerides DE430 and DE431 - NASA
Feb 15, 2014 · The coordinate system and units are similar to those used for DE421 and DE405, but include changes to the definition of coordinate time and the ...
[36]
NASA - Eclipses and the Moon's Orbit
Jan 12, 2012 · The largest inclination of 5.30° occurs when the difference in longitude is either 0° or 180°. In other words, the inclination is always near ...
[37]
Lunar Eclipse - HyperPhysics
This does not occur because the plane of the Moon's orbit is tilted 5.2° with respect to the plane of the Earth's orbit around the Sun (the ecliptic plane).
[38]
Types of Solar Eclipses - NASA Science
Contents · Total Solar Eclipse · Annular Solar Eclipse · Partial Solar Eclipse · Hybrid Solar Eclipse · Lunar Eclipses · Discover More Topics From NASA.
[39]
Solar Eclipse Basics - EclipseWise
Sep 10, 2024 · An annular eclipse is visible within the antumbra, while a partial eclipse is seen within the penumbra. Types of Solar Eclipses. There are four ...
[40]
NASA - Eclipses and the Saros
Jan 12, 2012 · The periodicity and recurrence of eclipses is governed by the Saros cycle, a period of approximately 6,585.3 days (18 years 11 days 8 hours).Missing: precession | Show results with:precession
[41]
Determining the Saros - Astronomical League
Saros cycles usually start and end at the poles, usually with poor partial eclipses seen only by polar bears.
[42]
NASA - Besselian Elements of Solar Eclipses
Aug 25, 2009 · To define the Besselian elements of an eclipse, a plane is passed through the center of Earth which is fixed perpendicular to axis of the lunar shadow.
[43]
Eclipses Frequently Asked Questions - NASA Science
Apr 1, 2024 · How do modern-day scientists predict eclipses? Astronomers first have to work out the geometry and mechanics of how Earth and the Moon orbit the ...
[44]
The Eclipse That Ended a War and Shook the Gods Forever
Apr 7, 2024 · Thales, a Greek philosopher 2600 years ago, is celebrated for predicting a famous solar eclipse and founding what came to be known as ...
[45]
[PDF] Glossary of Terms and Acronyms
solstice: either of the two points on the ecliptic at which the apparent longitude. (see longitude, celestial) of the Sun is 90° or 270°; also the time at which ...<|control11|><|separator|>
[46]
Earth's Seasons - Equinoxes, Solstices, Perihelion, and Aphelion
The times of the equinoxes mark the beginning of spring and fall. The times of the solstices mark the beginning of summer and winter. The seasons are hemisphere ...
[47]
Earth's Seasons - Equinoxes, Solstices, Perihelion, and Aphelion
8.0 hours West of Greenwich (UTC). Phenomenon, Date, Time. Perihelion, 2025 January 4, 05:28 ST. Equinox, 2025 March 20, 02:01 DT. Solstice, 2025 June 20 ...
[48]
The Equation of Time - Astronomical Applications Department
What Causes the Equation of Time? · Seasonal variations due to the 23.4° tilt, or obliquity , of the Earth's axis. · The non-circularity, or eccentricity of the ...
[49]
Calendars and their History - NASA Eclipse
Oct 14, 2012 · 2.3 History of the Gregorian Calendar By the thirteenth century it was realized that the true equinox had regressed from March 21 (its supposed ...
[50]
Introduction to Calendars - Astronomical Applications Department
It eventually standardized 21 March as the date of the vernal equinox and introduced a simple leap year rule: insert an extra day every four years.
[51]
iMIS
**Summary:**
[52]
What are the RAs of the boundaries between traditional zodiacal ...
Aug 27, 2018 · The resulting RA coordinates are: Aries 0h 0m 0s; Taurus 1h 51m 39s; Gemini 3h 51m 16s; Cancer 6h 0m 0s; Leo 8h 8m 44s; Virgo
[53]
Precession of the Equinox - Brad's Astronomy Pages
The position of the Sun on the day of the vernal equinox is presently in the constellation of Pisces near the border of Aquarius.
[54]
Sky Tellers - Constellations - Lunar and Planetary Institute
If you include all the constellations encompassed by this broadened definition of the ecliptic plane, you have 21 to 24 constellations of the zodiac!<|control11|><|separator|>
[55]
On other planets, does the sun appear to pass through the same ...
Nov 22, 2021 · But the ecliptic plane passes through 13 constellations, with Ophiuchus being the ecliptic constellation not included in the astrological zodiac ...
[56]
Origins of the ancient constellations: I. The Mesopotamian traditions
In Paper II, we will review how the Babylonian zodiac and para-zodiacal constellations were combined with nonMesopotamian constellations - probably from an ...
[57]
Hellenistic Astrology | Internet Encyclopedia of Philosophy
Ptolemy is the first astrologer to employ Hipparchus' zodiac modified ... (This “tropical” zodiac would become the standard in the Western practice of ...
[58]
#8. NASA Accused of Changing Astrological Signs | RealClearScience
Dec 12, 2016 · NASA does a lot of things, but altering astrological signs is not one of them. The space agency deals with genuine science, and astrology falls ...<|separator|>
[59]
A Misleading Theory: The Pseudoscience Behind Astrology
Dec 14, 2021 · However, the conclusions made are not scientific, rather mere predictions or observations. An interactive checklist by The University of ...Missing: ecliptic | Show results with:ecliptic