Ejection-trajectory comets

These are comets with an eccentricity so large that they only made one pass through the Solar System. These comets are further divided into near-Parabolic and Hyperbolic comets. A hypothetical true parabolic comet would have an eccentricity of exactly 1, and hyperbolic comets are any comet with an eccentricity of over 1. Most of the comets marked with an X are from the material cited here^[1] and the other comets are sourced from JPL Small-Body Database.^[2] Due to their hyperbolic orbits, it is impossible to determine where they come from, but it is expected that they are from the Oort Cloud, a cloud of icy bodies several thousand Astronomical units away from the Sun. However a few of these may be Interstellar comets

Comets observed in early times, which were later found to be observations of numbered periodic comets, are marked with [periodic comet number]/[comet name]. For instance, X/-239 K1 was an appearance of Halley's comet in 239 BC, and as such is written as 1P/-239 K1. A significant portion of the comets passing closer than 0.01 AU to the Sun are fragments of the comet of 371 BC, which fractured into several pieces on the 326 AD perihelion, which further fractured into thousands of pieces on the 1106 AD perihelion, creating the cometary group now known as the Kreutz sungrazers. Due to the sheer size (2000+ known members), and the fact that none of the group members have been given a numbered designation, the members are not stated on this list, and instead are listed in a separate list further below.

Near-parabolic comets

Comets with a very high eccentricity (generally 0.99 or higher) and a period of over 1,000 years that don't quite have a high enough velocity to escape the Solar System. Often, these comets, due to their extreme semimajor axes and eccentricity, will have small orbital interactions with planets and minor planets, most often ending up with the comets fluctuating significantly in their orbital path. These comets probably come from the Oort cloud, a cloud of comets orbiting the Sun from ~10,000 to roughly 50,000 AU.

Halley-type comets

Comets with a period between 20 and 200 years, named after the first identified member, Halley's Comet. These comets orbit between the orbit of Jupiter and Pluto, and are thought to be long-period comets that slowly migrated inwards, or Jupiter family comets that had been slingshotted outwards by Jupiter's gravity.

Unnumbered Jupiter-family comets

While Jupiter-family comets are officially defined by (2< T_Jupiter <3), they can also be loosely defined by any comet with a period of less than 20 years, a relatively low inclination, and an orbit coinciding loosely with that of Jupiter's. These comets are often patchily observed, as orbital interactions with the planet often cause comets' orbits to become perturbed, causing them to not be found at the expected position in the sky and subsequently lost.

Kreutz sungrazers

The largest group of them all, the Kreutz sungrazers are a group of comets descended from the breakup of a comet in 326 AD. They live up to their name, typically traveling less than 2 solar radii from the Sun. Because they travel so close, they often burn up, and it is the cause of their breakup. Many bright comets are members of the group, including Comet Ikeya–Seki, which broke in 3 pieces.

Meyer group

This is the second largest sungrazing group, and the only one with no discerned period. Further observations of this group may eventually find one, however.

Kracht group

This and the Marsden group, both are periodic, both with periods of approximately 3 years. They contain fewer members than the Meyer and Kreutz groups, probably as a result of their periodic nature, leading them to burn up more frequently. They are believed to be the parent bodies of the Southern Delta Aquariids meteor shower, occurring between July and August and usually having 15–20 meteors an hour.

Marsden group

Ungrouped sungrazers