Comet Giacobini–Zinner (official designation: 21P/Giacobini–Zinner) is a periodic comet in the Solar System.

It was discovered by Michel Giacobini (from Nice, France), who observed the comet in the constellation of Aquarius on December 20, 1900. It was recovered two passages later by Ernst Zinner (from Bamberg, Germany) while observing variable stars near Beta Scuti on October 23, 1913.

During its apparitions, Giacobini–Zinner can reach about the 7-8th magnitude,[4] but in 1946 it underwent a series of outbursts that made it as bright as 5th magnitude. It is the parent body of the Giacobinids meteor shower (also known as the Draconids). The comet currently has an Earth-MOID of 0.035 AU (5,200,000 km; 3,300,000 mi).[1]

Giacobini–Zinner was the target of the International Cometary Explorer spacecraft, which passed through its plasma tail on September 11, 1985. In addition, Japanese space officials considered redirecting the Sakigake interplanetary probe toward a 1998 encounter with Giacobini–Zinner, but that probe lacked the propellant for the necessary maneuvers and the project was abandoned.

The comet nucleus is estimated to be 2.0 kilometers in diameter.[1]

Comet 21P Giacobini-Zinner September 2018
Near 2018 perihelion
Comet 21P Giacobini-Zinner
Discovered byMichel Giacobini, Ernst Zinner
Discovery dateDecember 20, 1900
1900 III; P/1900 Y1; 1913 V;
P/1913 U1; 1926 VI; 1933 III;
1940 I; 1946 V; 1959 VIII;
1966 I; 1972 VI; 1979 III;
1985 XIII; 1992 IX
Orbital characteristics A
EpochMarch 6, 2006
Aphelion6.014 AU
Perihelion1.038 AU
Semi-major axis3.526 AU
Orbital period6.621 a
Earth MOID0.035 AU (5,200,000 km)[1]
Dimensions2 km[1]
Last perihelion2018-Sep-10[1][2]
February 11, 2012[3]
July 2, 2005[3]
Next perihelion2025-Mar-25[3]


  1. ^ a b c d e "JPL Small-Body Database Browser: 21P/Giacobini–Zinner" (last observation:2013-04-01). Jet Propulsion Laboratory. Retrieved 2016-01-10.
  2. ^ Syuichi Nakano (2012-02-05). "21P/Giacobini-Zinner (NK 2191)". OAA Computing and Minor Planet Sections. Retrieved 2012-02-18.
  3. ^ a b c MPC
  4. ^ King, Bob (29 August 2018). "Comet 21P/Giacobini-Zinner Shines in September - Sky & Telescope". Sky & Telescope. Retrieved 15 September 2018.

External links

Numbered comets
21P/Giacobini–Zinner Next
1978 in spaceflight

1978 saw the launch of the Pioneer Venus missions launched by the United States, on 20 May and 8 August. The Pioneer Venus Multiprobe landed four spacecraft on the planet, one of which transmitted data for 67 minutes before being destroyed by atmospheric pressure. ISEE-C, which was launched on 8 December, flew past comet 21P/Giacobini–Zinner in 1985, and Halley's Comet in 1986.

1985 in spaceflight

The following is an outline of 1985 in spaceflight.


20D/Westphal was a periodic comet with an orbital period of 61 years. It fits the classical definition of a Halley-type comet with (20 years < period < 200 years). It was originally discovered by the German astronomer J. G. Westphal (Göttingen, Germany) on July 24, 1852.

It was independently discovered by the American astronomer Christian Heinrich Friedrich Peters (Constantinople) on August 9.

The comet was last seen between September 27 and November 26, 1913, first by Pablo T. Delavan (La Plata Astronomical Observatory) and then others. It was predicted to return in 1976 but was never observed, and is now considered a lost comet.


Comet Kopff or 22P/Kopff is a periodic comet in the Solar System. Discovered on August 23, 1906, it was named after August Kopff who discovered the comet. The comet was missed on its November 1912 return, but was recovered on its June 1919 return. The comet has not been missed since its 1919 return and its last perihelion passage was on May 25, 2009. Close approaches to Jupiter in 1938 and 1943 decreased the perihelion distance and orbital period. 22P/Kopff’s next perihelion passage is 18 March 2022.


276P/Vorobjov (previously P/2012 T7 (VOROBJOV)) is a Jupiter-family comet discovered on 15 October 2012 by Tomáš Vorobjov on three 120-s images taken remotely using the 0.81-m f/7 Ritchey-Chretien Schulman Telescope located at the Mt. Lemmon SkyCenter via the Sierra Stars Observatory Network in the course of a minor-planet search survey undertaken as part of the International Astronomical Search Collaboration (IASC) school campaigns. After posting on the Minor Planet Center's NEOCP webpage, other observers have commented on the object's cometary appearance. The discovery was announced by the Minor Planet Center on 18 October, three days after the discovery.

Bow shocks in astrophysics

Bow shocks form the boundary between a magnetosphere and an ambient (or at least surrounding) magnetized medium. This occurs when the magnetic field of an astrophysical object interacts with the nearby flowing ambient plasma. For example, when the solar wind, flowing with a relative speed of order 400 km/s, encounters the magnetic field of Earth, a bow shape boundary forms. For Earth and other magnetized planets, it is the boundary at which the speed of the stellar wind abruptly drops as a result of its approach to the magnetopause. For stars, this boundary is typically the edge of the astrosphere, where the stellar wind meets the interstellar medium.

C/2012 E2 (SWAN)

Comet C/2012 E2 (SWAN) was a Kreutz group sungrazing comet discovered by Vladimir Bezugly in publicly available images taken by the SWAN instrument (Solar Wind ANisotropies) on board the SOHO spacecraft. It is recognized for being the first Kreutz sungrazer observed in SWAN imagery.

C/2015 F3

Comet C/2015 F3 (SWAN) was discovered in March 2015 by Rob Matson, Vladimir Bezugly and Michael Matiazzo in near real time images taken by the SWAN instrument aboard the SOHO spacecraft. At discovery the comet was already shining at around 10th magnitude as it was already near perihelion

. Orbital studies revealed C/2015 F3 to be a related fragment to long periodic comets C/1988 A1 (Liller) and C/1996 Q1 (Tabur), which were already thought to have broken off each other at a previous perihelion passage. As of May 2015, Comet SWAN was fading rapidly, as both C/1988 A1 and C/1996 Q1 ultimately did. .

C/2015 F5 (SWAN-XingMing)

Comet C/2015 F5 (SWAN-XingMing) was discovered on March 29, 2015 in near real time SWAN images of the SOHO spacecraft, by Szymon Liwo and Worachate Boonplod. It was also independently discovered on April 4, 2015 by Guoyou Sun and Gao Xing at the XingMing observatory near Ürümqi, China. At discovery, the comet had just passed perihelion and was only 0,35 AU from the Sun, shining at about +10 mag. As of May 2015 the comet had faded below mag +13. The comet is periodic with an orbital period of about 61 years .


The October Draconids, in the past also unofficially known as the Giacobinids, are a meteor shower whose parent body is the periodic comet 21P/Giacobini-Zinner. They are named after the constellation Draco, where they seemingly come from. Almost all meteors which fall towards Earth ablate long before reaching its surface. The Draconids are best viewed after sunset in an area with a clear dark sky.

The 1933 and 1946 Draconids had Zenithal Hourly Rates of thousands of meteors visible per hour, among the most impressive meteor storms of the 20th century. Rare outbursts in activity can occur when the Earth travels through a denser part of the cometary debris stream; for example, in 1998, rates suddenly spiked and spiked again (less spectacularly) in 2005. A Draconid meteor outburst occurred as expected on 2011 October 8, though a waxing gibbous Moon reduced the number of meteors observed visually. During the 2012 shower radar observations detected up to 1000 meteors per hour. The 2012 outburst may have been caused by the narrow trail of dust and debris left behind by the parent comet in 1959.

List of Solar System probes

This is a list of space probes that have left Earth orbit (or were launched with that intention but failed), organized by their planned destination. It includes planetary probes, solar probes, and probes to asteroids and comets, but excludes lunar missions, which are listed separately at List of lunar probes and List of Apollo missions. Flybys (such as gravity assists) that were incidental to the main purpose of the mission are also included. Flybys of Earth are listed separately at List of Earth flybys. Confirmed future probes are included, but missions that are still at the concept stage, or which never progressed beyond the concept stage, are not.

List of meteor showers

Named meteor showers recur at approximately the same dates each year. They appear to "radiate" from a certain point in the sky (the radiant) and vary in the speed, frequency and brightness of the meteors. As of November 2018, there are 112 established meteor showers.

List of missions to comets

As of 2013, the United States, Soviet Union, Japan and the European Space Agency have conducted missions to comets.

Meteor shower

A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller than a grain of sand, so almost all of them disintegrate and never hit the Earth's surface. Very intense or unusual meteor showers are known as meteor outbursts and meteor storms, which produce at least 1,000 meteors an hour, most notably from the Leonids. The Meteor Data Centre lists over 900 suspected meteor showers of which about 100 are well established. Several organizations point to viewing opportunities on the Internet.

Michel Giacobini

Michel Giacobini (1873–1938) was a French astronomer.

He discovered a number of comets, including 21P/Giacobini-Zinner (parent body of the Giacobinids meteor shower), 41P/Tuttle-Giacobini-Kresak, and 205P/Giacobini. The latter he had discovered at Nice on 4 September 1896, but it was not seen on its return, a little less than 7 years later, and was considered a lost comet and consequently designated D/1896 R2. On 10 September 2008, amateur supernova hunters Koichi Itagaki and Hiroshi Kaneda rediscovered it, on its seventeenth return.

He won the Lalande Prize in 1900 and worked at the Nice Observatory until 1910, when he requested a transfer to the Paris Observatory. He was awarded the Valz Prize by the French Academy of Sciences in both 1905 and 1908.In 1903, Giacobinin received the Prix Jules Janssen, the highest award of the Société astronomique de France, the French astronomical society.

He volunteered for military service in World War I and suffered the effects of poison gas. He recovered and resumed his astronomical activities after the war.

Potentially hazardous object

A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make exceptionally close approaches to the Earth and large enough to cause significant regional damage in the event of impact.Most of these objects are potentially hazardous asteroids (PHAs), defined as having a minimum orbital intersection distance with Earth of less than 0.05 astronomical units (19.5 lunar distances) and an absolute magnitude of 22 or brighter. As of January 2018 there are 1,885 known PHAs (about 11% of the total near-Earth population), of which 157 are estimated to be larger than one kilometer in diameter (see list of largest PHAs below). Most of the discovered PHAs are Apollo asteroids (1,601) and fewer belong to the group of Aten asteroids (169).A potentially hazardous object can be known not to be a threat to Earth for the next 100 years or more, if its orbit is reasonably well determined. Potentially hazardous asteroids with some threat of impacting Earth in the next 100 years are listed on the Sentry Risk Table. Potentially hazardous asteroids are normally only a hazard on a time scale of hundreds of years as the known orbit becomes more divergent. After several astronomical surveys, the number of known PHAs has increased tenfold since the end of the 1990s (see bar charts below). The Minor Planet Center's website List of the Potentially Hazardous Asteroids also publishes detailed information for these objects.


Sakigake (さきがけ, lit. "pioneer" or "pathfinder"), known before launch as MS-T5, was Japan's first interplanetary spacecraft, and the first deep space probe to be launched by any country other than the USA or the Soviet Union. It aimed to demonstrate the performance of the new launch vehicle, test the schemes of the first escape from the Earth gravitation for Japan on engineering basis, and observe space plasma and magnetic field in interplanetary space. Sakigake was also supposed to get references for scientists. Early measurements would be used to improve the mission of the Suisei probe several months later.

Sakigake was developed by the Institute of Space and Astronautical Science for the National Space Development Agency (both of which are now part of the Japanese Aerospace Exploration Agency, or JAXA). It became a part of the Halley Armada together with Suisei, the Soviet/French Vega probes, the ESA Giotto and the NASA International Cometary Explorer, to explore Halley's Comet during its 1986 sojourn through the inner Solar System.

Suisei (spacecraft)

Suisei (すいせい, lit. "Comet"), originally known as Planet-A, was an unmanned space probe developed by the Institute of Space and Astronautical Science (now part of the Japanese Aerospace Exploration Agency, or JAXA).

It constituted a part of the Halley Armada together with Sakigake, the Soviet/French Vega probes, the ESA Giotto and the NASA International Cometary Explorer, to explore Halley's Comet during its 1986 sojourn through the inner solar system.

Uncrewed spacecraft

Uncrewed or unmanned spacecraft are spacecraft without people on board, used for robotic spaceflight. Uncrewed spacecraft may have varying levels of autonomy from human input; they may be remote controlled, remote guided or even autonomous, meaning they have a pre-programmed list of operations, which they will execute unless otherwise instructed. Many habitable spacecraft also have varying levels of robotic features. For example, the space stations Salyut 7 and Mir, and the ISS module Zarya were capable of remote guided station-keeping, and docking maneuvers with both resupply craft and new modules. The most common uncrewed spacecraft categories are robotic spacecraft, uncrewed resupply spacecraft, space probes and space observatories. Not every uncrewed spacecraft is a robotic spacecraft; for example, a reflector ball is a non-robotic uncrewed spacecraft.

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