☄ Finlay 15P/Finlay

How to follow comet Finlay live

The panel above recomputes the position of Finlay 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 Finlay 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 Finlay with no math at all.

Comet fact sheet

About Finlay

15P/Finlay was a quiet comet, catalogued since 1886, considered low-activity, with no associated meteor shower and no prospect of exceptional brightness. That changed in December 2014, when the comet produced two outbursts of material weeks apart, expelling dense clouds of gas and dust that were not expected from a nucleus considered dormant. The consequence was the detection in October 2021 of meteors directly from that ejected material, confirming the birth of a new shower: the Arids (IAU code ARD, #1130).

The Arids are a unique case in meteor astronomy history: this was the first time a direct line was drawn between telescopically detected cometary outbursts and a meteor shower confirmed by subsequent observations. The radiant lies in the constellation Ara (the Altar), visible primarily from the southern hemisphere and tropical latitudes, which limits observability but does not diminish scientific interest.

History and discovery

William Henry Finlay was an astronomer at the Cape of Good Hope Observatory in South Africa when he discovered the comet on September 26, 1886. The observatory's geographic position gave Finlay privileged access to the southern sky, and the new comet was quickly confirmed by other observers. The orbital period was calculated at roughly 6.5 years, placing it in the Jupiter family.

For decades 15P was a routine target: tracked at every return but revealing nothing remarkable. Its nucleus was estimated to be small and its cometary activity modest. The 2014-2015 return completely changed that picture, when two distinct outbursts in December 2014 and January 2015 revealed that the apparently quiet nucleus harbored volatile reserves capable of releasing energy abruptly and intensely. The event was published in detail in a 2015 Astrophysical Journal paper titled "Bangs and Meteors from the Quiet Comet 15P/Finlay."

Orbit and returns

15P/Finlay has an orbital period of 6.58 years and belongs to the Jupiter family. Its perihelion sits at 0.99 AU from the Sun, a very narrow margin relative to Earth's orbit, while aphelion reaches about 5.8 AU. With a Minimum Orbital Intersection Distance (MOID) with Earth of just 0.009 AU (roughly 1.3 million km), 15P is one of the short-period comets that approaches our planet most closely within the known Jovian population.

This orbital proximity is directly responsible for the possibility of a meteor shower: when Earth crosses the debris trail left by the comet, particles enter the atmosphere at speeds of 15 to 20 km/s and produce meteors. The 2014 outbursts deposited fresh, dense material in a region of the trail that Earth crossed in October 2021, generating detectable meteor activity for the first time in the comet's recorded history.

Nucleus and family

The nucleus of 15P/Finlay is small, with a diameter estimated at roughly 1 to 3 km based on inactive-nucleus photometry. The albedo is low, typical of the Jovian family. Despite its modest size, the nucleus demonstrated an ability to release energy explosively during the 2014 outbursts, suggesting that specific surface regions held highly volatile ices (possibly CO2 or CO) that were exposed by some mechanism, perhaps the collapse of a surface depression or the uncovering of subsurface material by a micrometeorite impact.

15P's outbursts are not unique in cometary astronomy: comets such as 17P/Holmes (2007 outburst that made it naked-eye for weeks) and 29P/Schwassmann-Wachmann 1 (frequent outbursts) have also shown explosive activity without warning. The difference is that in the case of 15P/Finlay it was possible to trace the direct connection between the material expelled in the outbursts and the resulting meteor shower.

• Estimated nucleus diameter: ~1 to 3 km
• MOID with Earth: 0.009 AU (~1.3 million km)
• Group: Jupiter family (JFC)
• Notable trait: explosive outbursts in 2014 without clear precursor signals
• Analogy: similar behavior to 17P/Holmes (2007 outburst) and 29P/SW1

How to observe

15P/Finlay rarely exceeds magnitude 10 to 11, making it a target for a 6-inch amateur telescope or larger. Under favorable conditions it appears as a diffuse patch with a moderate coma. The next perihelion is expected in 2028, when the geometry should be checked to determine whether the Arid meteor shower will have sufficient material for detectable production.

To observe the Arids, the ideal window is the first week of October, peaking around October 6 to 7. The radiant lies in the constellation Ara (the Altar), a southern constellation little known in the northern hemisphere (declination roughly -60 degrees), which limits visibility to southern-hemisphere and tropical observers (below roughly 30 degrees north latitude). The 2021 ZHR reached ~80 at peak, but future activity depends on the positioning of the 2014 ejecta trails relative to Earth's path.

• Arid radiant: constellation Ara, declination ~-60 degrees
• Activity window: late September to early October
• Peak: around October 6 to 7
• 2021 ZHR: ~80 (peak Oct 6-7, 2021)
• Visibility: southern hemisphere and tropics (latitudes below ~30 N)
• Next 15P perihelion: ~2028

Arids: the 2021 meteor shower

On December 15-16, 2014, observers recorded the first outburst: 15P's brightness rose abruptly from magnitude 11 to 9 in hours. A second outburst followed on January 15-16, 2015, raising brightness to magnitude 8 just 12 days before perihelion on January 27. Both events were documented in detail by professional and amateur astronomers and published in a 2015 Astrophysical Journal paper.

Numerical analysis of the ejecta trails by Jeremie Vaubaillon (IMCCE, Paris) and collaborators predicted that material deposited by the 2014 outbursts would cross Earth's orbit in October 2021. The event happened: on the night of October 6-7, 2021, observers in Chile and other southern-hemisphere locations recorded meteors with ZHR up to 80 at peak, originating from a radiant in Ara. Detection was also confirmed by meteor radar. The IMCCE announced the shower as the "2021 Arids," and the IAU registered it as #1130 with code ARD. A 2026 study using data from Mauna Kea Observatory in Hawaii confirmed detection from the northern hemisphere, showing that activity reached higher latitudes than initially expected.

Facts

• The Arids are one of the newest meteor showers on the calendar: activity was confirmed in 2021, 135 years after the discovery of the parent comet.
• The MOID of 0.009 AU (~1.3 million km) places 15P/Finlay among the short-period comets that approach Earth most closely within the known Jovian population.
• Predicting Arid activity from the 2014 cometary outbursts was the first time in history that a direct line was drawn between telescopically detected outbursts and a confirmed meteor shower, a milestone in meteor astronomy.
• The Arid radiant lies in Ara (the Altar), a southern constellation little known in the northern hemisphere, which limits observability but does not diminish scientific interest.
• William Finlay worked at the Cape Observatory for years and made important contributions to southern-hemisphere astrometry, but is remembered today primarily through the comet that bears his name.
• A 2026 study confirmed that the Arids were detected at Mauna Kea Observatory in Hawaii, showing the shower is observable from moderate northern latitudes in years of elevated activity.

Other comets

See the full comet catalogue.