☄ Faye 4P/Faye

How to follow comet Faye live

The panel above recomputes the position of Faye every second in your browser: its distance from the Sun and from Earth, its position in the sky (right ascension and declination), and a live countdown to the next perihelion. It runs on the same kind of engine observatories use, a Kepler solver applied to the JPL osculating orbital elements, so the numbers are not a static snapshot, they keep ticking.

Just below, the top-down map of the Solar System shows exactly where Faye is right now among the planets. You can fast-forward time with the day slider, zoom and pan, compare its distance to another body with a click, and press "Next event" to jump straight to perihelion. It is the most direct way to grasp the orbit of Faye with no math at all.

Comet fact sheet

About Faye

Hervé Faye was an astronomer at the Paris Observatory when, on November 22, 1843, he logged a fuzzy object that matched no catalogued star. What he had found was a short-period Jupiter-family comet with a nearly circular orbit compared to the great parabolic comets that occasionally sweep through the inner Solar System. Over 180 years of unbroken observations, 4P/Faye has been recovered at each of its perihelia without a single miss, a rare achievement among short-period comets.

4P never dazzles. It rarely brightens past magnitude 9, and its coma is compact with no prominent tail. Its value lies in the combination of orbital regularity and observational longevity: each return adds data to a record now spanning more than 25 documented apparitions, enabling refined models of cometary nucleus evolution and precise measurement of the non-gravitational forces driven by gas sublimation.

History and discovery

Faye logged the comet on November 22, 1843, but bad weather delayed confirmation until the 25th. Calculations later showed the object had already passed perihelion about a month before discovery; only a close Earth approach had brightened it enough for Faye's instrument. Friedrich Wilhelm Argelander and Thomas James Henderson independently established in 1844 that it was a short-period comet, and by May of that year the period had been estimated at roughly 7 years.

The designation 4P reflects that it was the fourth periodic comet confirmed by astronomy, after Halley (1P), Encke (2P), and Biela (3P, now disintegrated). Biela split visibly in 1846 and vanished; 4P/Faye, by contrast, has survived every documented return. In 1843, the year of discovery, observers were also tracking the Great Comet of 1843 (C/1843 D1), one of the brightest of the nineteenth century, which turned 4P/Faye into a secondary curiosity during a period of intense cometary excitement.

Orbit and returns

4P/Faye belongs to the Jupiter family: its aphelion lies at about 6.03 AU, near the Jovian orbit, while perihelion occurs at roughly 1.61 AU, between the orbits of Mars and Earth. The mean orbital period is 7.48 years. Because it does not approach the Sun closely, the nucleus suffers less thermal stress per pass than comets with perihelia near 1 AU, which helps explain its observational longevity.

Jupiter has gradually shortened the comet's orbital period over the centuries: before a close planetary encounter in 1840 the period was about 7.7 years; today it stands at 7.48 years. This ongoing perturbation is characteristic of all Jovian family members and prevents accurate long-range predictions without periodic orbital recalculation. The next perihelion is forecast for March 9, 2029.

Nucleus and family

The nucleus of 4P/Faye is estimated at about 3.54 km in diameter based on Hubble Space Telescope observations made between 1999 and 2000. More recent NEOWISE data point to a geometric albedo of roughly 0.04, typical for dark cometary nuclei. This means the nucleus reflects only 4 percent of the sunlight it receives, making it nearly black even in high-resolution imaging.

As a Jupiter-family member, 4P shares general characteristics with other comets gravitationally captured by the giant planet: periods of 3 to 20 years, low to moderate orbital inclinations, and a history of perturbations from Jupiter encounters. Unlike many Jovian comets, 4P/Faye has no known associated meteor shower, probably because its orbit crosses Earth's at an angle and distance too unfavorable to deposit detectable debris.

• Nucleus diameter: ~3.54 km (Hubble, 1999-2000)
• Geometric albedo: ~0.04 (NEOWISE)
• Orbital inclination: 9.1 degrees
• Eccentricity: 0.578
• Group: Jupiter family (JFC)
• IAU status: periodic comet confirmed at every apparition since 1843

How to observe

4P/Faye rarely exceeds magnitude 9, so binoculars or a telescope are needed. At good oppositions it appears as a small, diffuse coma with no prominent tail. The 2021 perihelion brought the comet to around magnitude 10.5 at its best, reachable with a 6-inch telescope under dark skies.

For 2029, preliminary orbital calculations suggest a favorable geometry for northern-hemisphere observers in the first quarter of the year. Geocentric distance will remain relatively high, but adequate solar elongation should allow pre-dawn observations at mid-northern latitudes from February 2029 onward. Southern observers may catch it before perihelion, albeit fainter. Updated ephemerides are available on JPL Horizons and In-The-Sky.org.

• Minimum recommended instrument: 10x50 binoculars or a 4-inch telescope
• Best window in 2029: January through April, pre-dawn northern sky
• Ideal conditions: moonless night, target at least 30 degrees above the horizon
• Ephemeris source: JPL Horizons (horizons.jpl.nasa.gov)

Science and historical observations

The scientific value of 4P/Faye lies in its extended observational record. With more than 25 documented apparitions since 1843, it enables study of how cometary activity varies from cycle to cycle and how non-gravitational forces accumulate their effect over decades. Systematic photometric measurements show that 4P's activity level has been relatively stable across recent apparitions, suggesting the surface still retains enough active patches to sustain sublimation.

Non-gravitational forces, produced by the rocket-like effect of gas emission from the nucleus, cause measurable deviations from purely gravitational orbits. For 4P/Faye these deviations are small but detectable, and studying them contributes to models of how sublimation alters small-body trajectories over geological timescales. The 7.48-year orbital period means that over a century the comet completes roughly 13 orbits, accumulating offsets that, without correction, would make ephemerides progressively less accurate.

Facts

• 4P/Faye is the fourth numbered periodic comet in history, after Halley, Encke, and the now-disintegrated Biela.
• It has been observed at every return since 1843 without a single miss, a rare distinction among short-period comets, many of which are lost due to unfavorable geometry or nucleus weakening.
• In 1843, the year 4P was found, the Great Comet of 1843 (C/1843 D1) blazed across the sky as one of the brightest objects of the century, making Faye a secondary curiosity in an exceptional cometary year.
• Unlike comets such as Halley or Encke, 4P/Faye has no known meteor shower: its orbit crosses Earth's at an angle and distance that produce no detectable debris flux.
• The nucleus diameter (3.54 km from Hubble) is modest for the Jovian family; 10P/Tempel 2, for comparison, carries a nucleus estimated at 10.6 km.
• The name follows the nineteenth-century convention of naming comets after the surname of whoever first logged them: Hervé Faye, astronomer at the Paris Observatory.

Other comets

See the full comet catalogue.