☄ Tuttle-Giacobini-Kresak 41P/Tuttle-Giacobini-Kresak

How to follow comet Tuttle-Giacobini-Kresak live

The panel above recomputes the position of Tuttle-Giacobini-Kresak 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 Tuttle-Giacobini-Kresak 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 Tuttle-Giacobini-Kresak with no math at all.

Comet fact sheet

About Tuttle-Giacobini-Kresak

41P/Tuttle-Giacobini-Kresak accumulates three names because it took three astronomers and 65 years to confirm its periodic nature. Discovered by Horace Tuttle on 3 May 1858, rediscovered by Michel Giacobini in 1907 and again by Lubos Kresak in 1951, only then was it possible to link all three apparitions to a single object with a 5.4-year period.

The comet gained notoriety through its brightness outbursts: in 1973 the magnitude increase was about 10 units over a few weeks, briefly making it naked-eye visible. In 2017, during an exceptionally close Earth approach, data from the Hubble Space Telescope and the Swift satellite revealed that the nucleus was decelerating and reversing its spin direction, a phenomenon never before observed in any comet, confirmed in a 2026 publication.

History and discovery

Horace Tuttle of the United States Naval Observatory spotted the comet in May 1858 but could not gather enough orbital data to compute the period. On 2 June 1907 French astronomer Michel Giacobini, at Nice, independently rediscovered the object; the computed orbit resembled the 1858 one, but the connection was not immediately made.

In 1951, Slovak astronomer Lubos Kresak at Skalnate Pleso Observatory in Czechoslovakia made a third independent discovery. It was the detailed calculation of the 1858, 1907 and 1951 orbits that confirmed the common identity of the three comets and established a period of 5.4 years. The IAU convention named the object 41P/Tuttle-Giacobini-Kresak, preserving all three discoverers.

Orbit and returns

41P's perihelion lies at 1.05 AU from the Sun, nearly at Earth's orbital distance, while aphelion reaches about 5.1 AU. The current orbital period is approximately 5.42 years. The Tisserand parameter T_J is 2.96, firmly placing it in the Jupiter family.

In 2017 the comet had an exceptionally favourable return: it passed just 0.14 AU from Earth on 1 April 2017, reaching magnitude 6 to 7 and becoming naked-eye visible for about a week. During that same return it was the primary target of NASA's Swift space telescope and the Discovery Channel Telescope at Lowell Observatory for rotation and ultraviolet emission studies.

Nucleus and dynamic family

The nucleus of 41P/Tuttle-Giacobini-Kresak has an effective radius between 440 and 560 metres, measured by the Hubble Space Telescope in 2017. It is one of the smallest nuclei of periodic comets with a well-documented orbit. The nucleus light-curve amplitude is about 0.4 magnitudes, implying an elongated body with an axis ratio of at least 1.4:1.

As a Jupiter-family member, 41P has a Tisserand parameter T_J of 2.96, close to the upper boundary of the group (T_J = 3). That means the comet sits on the dynamical frontier: future encounters with Jupiter could substantially alter its orbit. The low nucleus mass (estimated at under 10^12 kg) makes it particularly susceptible to radiation pressure and asymmetric outgassing forces, which is precisely what caused the observed spin reversal in 2017.

How to observe and the historic outbursts

On typical returns 41P/Tuttle-Giacobini-Kresak reaches magnitude 8 to 11, requiring binoculars or a small telescope. The coma is normally diffuse with low central condensation. On major returns such as 2017 it can be seen naked-eye from moderately dark sites.

The outbursts are the comet's most striking feature. In May and June 1973, brightness rose from magnitude 14 (invisible without a powerful telescope) to 4 (naked-eye even from urban skies), a 10-magnitude jump equivalent to a factor of 10,000 in light flux. Kresak, one of the discoverers, published the hypothesis that outbursts are caused by sudden exposure of fresh ice through crustal collapse, a mechanism that more recent literature associates with sublimation of CO or CO2.

• 1973 outburst: +10 magnitudes, from mag 14 to mag 4 (naked eye)
• 2017 return: mag 6 to 7, minimum Earth distance 0.14 AU
• Rotation: reversed in 2017 (Hubble result published 2026)
• Next return: ~2027

Science: spin reversal detected by Hubble

The 2017 return produced the most important discovery ever made about 41P: the first documented case of a complete reversal of a comet's spin direction. Between March and May 2017, the nucleus rotation period increased from about 20 hours to more than 46 to 60 hours, a deceleration recorded by the Discovery Channel Telescope at Lowell Observatory and confirmed by NASA's Swift satellite.

Hubble Space Telescope data obtained in December 2017 showed the nucleus spinning much faster again, now with a period of approximately 14 hours, more than three times the speed measured in October. The simplest explanation, published by David Jewitt of UCLA and collaborators in 2026 in the Astronomical Journal, is that gas jets on the surface acted as asymmetric thrusters: they slowed the rotation until it nearly stopped, then drove the nucleus to spin in the opposite direction. It was the first time this had been observed in any comet.

Facts worth knowing

• Hubble detected the first complete spin reversal of a comet in 41P/TGK; results were published in 2026 by David Jewitt and collaborators.
• The 1973 outburst was studied by Lubos Kresak, one of the comet's own discoverers, who published the most influential explanation of the phenomenon.
• The nucleus has an effective radius between 440 and 560 metres, measured by Hubble, one of the smallest known periodic cometary nuclei.
• The comet carries three names because it was independently rediscovered three times, but the full name is so long that astronomers usually write only "41P" or "TGK" in scientific papers.
• The spin reversal was driven by asymmetric gas jets acting as thrusters: they slowed the nucleus almost to a stop and then spun it in the opposite direction.
• With a radius between 440 and 560 metres, the nucleus could fit comfortably inside a mid-sized city, yet its outgassing torques reversed its spin within months.

Other comets

See the full comet catalogue.