04Time Machine02

The 26,000-year axis

Earth’s axis is not fixed among the stars. It sweeps a slow cone, so the celestial pole traces a circle around the pole of the ecliptic and the equinoxes slide westward along the ecliptic, one circuit in about 26,000 years.

Pole of the ecliptic · looking upAround the pole of the ecliptic · seen looking up

Precession changes the relationship between Earth's equatorial coordinate system and the distant stellar background. It does not physically move the planets into different locations.

The celestial pole in 2026 CE

Right ascension (J2000 frame): 23h 59m
Declination (J2000 frame): +89°51′
Nearest bright star to the pole: Polaris0°38′ away

The axis

Obliquity (mean): 23°26′09″
Rate of precession: 50.29″a year
General precession since J2000 (the equinox's westward drift): +0°22′

The equinox and the two zodiacs

Ayanamsa (Lahiri): tropical − sidereal: +24°14′
Vernal equinox in (IAU, 1930 boundaries): Pisces

Open in What would Ptolemy have seen?

Pole stars

Closest approach of each star to the pole, from the stars' own motions and the long-term model.

From outside the sky

The axis in three dimensions

The same long-term model seen from outside: Earth's axis sweeping its cone around the pole of the ecliptic. The view follows the year set above, now 2026 CE; its own dock runs time inside the view without moving the page.

Axis & Precession · 3D

Twenty-six thousand years

The tilt and the drift

Both computed with the long-term precession model. The shaded span is 500 BCE to today; tap a chart to move the instrument to that year.

Obliquity of the ecliptic (mean)

Ayanamsa, Lahiri (tropical − sidereal)

What the instrument shows

Precession in the record

Statements from the historical research behind these pages; values in mono are computed by the engine.

GlossaryPrecession of the equinoxes: the slow westward motion of the equinoxes along the ecliptic, caused by the precession of Earth’s axis. It amounts to about 50.3″ per year, or a cycle of about 25,772 years [27][28]. The name was introduced by Copernicus [38].
HIP-6Hipparchus found that stars near the ecliptic had shifted about 2° relative to the equinoxes over about 150 years [23][25].
HIP-9The true rate is about 1° per 72 years [25]. The modern general precession is 5028.796195″ per Julian century at J2000, or about 50.29″ per year [28].
REN-4Copernicus lived 1473–1543. De revolutionibus appeared in 1543, and in it slow changes in the direction of Earth’s axis account for precession [48].
Misconception“Precession is a motion of the stars.” That was Hipparchus’s interpretation, and it was the standard one until Copernicus. It is a motion of Earth’s axis [23][48].
WWP-13The vernal point crossed from IAU Aries to Pisces in 68 BCE and will cross to Aquarius in 2597 (Meeus) [66][65]. Engine check: 68 BCE and 2597 CE.
WWP-14IAU boundaries: Delporte, along right ascension and declination for 1875, approved at Leiden in 1928 and published in 1930 [68].

Sources

Where these statements come from

Researched and fact-checked for this app on 22 September 2026. Numbers in brackets refer to this list; the letter after each entry is how directly the source was read. Every value marked as computed comes from the app's astronomy engine, never from this list.

[23]Jones, A. R. “Hipparchus.” Encyclopaedia Britannica online. www.britannica.com/biography/Hipparchus-Greek-astronomer.Level R: reference work, read
[25]Linton, C. M. (2004). From Eudoxus to Einstein: A History of Mathematical Astronomy (Cambridge UP), ch. 3 “The Ptolemaic universe”, section “The motion of the Sun and precession”, with notes 9, 10 and 20.Level S: scholarly source, read
[27]Britannica editors. “Precession of the equinoxes.” Encyclopaedia Britannica online. www.britannica.com/science/precession-of-the-equinoxes.Level R: reference work, read
[28]Kaplan, G. H. (2005). The IAU Resolutions on Astronomical Reference Systems, Time Scales, and Earth Rotation Models. USNO Circular 179, Table 5.1. arXiv:astro-ph/0602086. (the IAU 2006 value 5028.796195″ per century comes from Capitaine et al. 2003).Level R: reference work, read
[29]Vondrák, J., Capitaine, N. & Wallace, P. (2011). “New precession expressions, valid for long time intervals.” Astronomy & Astrophysics 534, A22, as implemented in ERFA eraLtpequ, eraLtpecl and eraLtp (BSD-3). Used for the computed checks.Level S/C: scholarly source, read / computed check
[38]Nothaft, C. P. E. (2017). “Criticism of trepidation models and advocacy of uniform precession in medieval Latin astronomy.” Archive for History of Exact Sciences 71: 211–244. doi.org/10.1007/s00407-016-0184-1. Author’s copy on ORA (Oxford). (the page numbers of the published version were not seen).Level S: scholarly source, read
[48]Westman, R. S. “Nicolaus Copernicus.” Encyclopaedia Britannica online. www.britannica.com/biography/Nicolaus-Copernicus.Level R: reference work, read
[65]Strous, L. “Constellations”, Astronomy Answers (Utrecht), Table 2 and §7 “The Age of Aquarius”. www.aa.quae.nl/en/antwoorden/sterrenbeelden.html. (by an astronomer).Level W: general web source
[66]EarthSky, “When will the Age of Aquarius begin?” (reporting J. Meeus’s computations and N. Campion’s survey). earthsky.org/human-world/when-will-the-age-of-aquarius-begin/. (Meeus and Campion: not read directly; cited through another source).Level W: general web source
[68]Ridpath, I. “Constellation boundaries” and “Délimitation Scientifique des Constellations” (with a translation of Delporte’s 1930 introduction). www.ianridpath.com/boundaries.html and www.ianridpath.com/delporte.html. (Delporte 1930: primary text or a scholarly translation, read in translation).Level W: general web source

Computed with astronomy-engine 2.1.19 (MIT, Don Cross) and the long-term precession model of Vondrák, Capitaine & Wallace (2011), ported from ERFA (BSD-3-Clause). Stars: the Yale Bright Star Catalogue, 5th revised edition (Hoffleit & Warren 1991, via CDS) and SIMBAD (CDS, Strasbourg). Constellation figures: d3-celestial (Olaf Frohn, BSD-3-Clause). Constellation boundaries: IAU (Delporte 1930).

04Time Machine02

The 26,000-year axis

Tracing the pole across 26,000 years…