Comet Bennett (C/1969 Y1)

Discovered by:        John Caister Bennett
Discovery date:       December 28, 1969
Peak magnitude:     0.0
Aphelion:                282 AU (42.0 billion kilometres or 26.1 billion miles)
Perihelion:              0.538 AU (80.48 million kilometers or 50.01 million miles)
Semi-major axis:     141 AU (21.0 billion kilometres or 13.0 billion miles)
Eccentricity:            0.9962
Orbital period:         1678 years
Inclination:              90.0 degrees

Last perihelion:       March 20, 1970
Next perihelion:       3600 (estimate)

Comet Bennett in 1970 (Pretoria Centre of the ASSA)

Discovered on December 28, 1969 from Pretoria by renowned South African amateur astronomer and comet hunter John Caister Bennett.

Was at magnitude +8.5 when discovered, appearing small and diffuse and with no sign of tail. At the time Bennett was situated 1.70 AU from Earth and 1.68 AU from the Sun, just outside the orbit of Mars.

Perihelion was reached on March 20, 1970 with Bennett peaking at magnitude 0.0 and displaying a tail of 15 degrees in length.

Closest approach to Earth occurred 6 days later on March 26 (0.69 AU distant).

Bennett was widely observed in April in the morning sky as its position improved. Although now moving away from the Earth and the Sun and therefore fading the comet remained a superb sight especially during the first part of April.

By the beginning of May it was down to the limit of naked eye visibility.

With an orbital period of 1678 years, Bennett is expected to next return sometime around 3600.

Comet Arend-Roland (C/1956 R1)

Discovered by:        Sylvain Arend and Georges Roland
Discovery date:       November 8, 1956            
Peak magnitude:     -0.5
Aphelion:                N/A
Perihelion:               0.316 AU (47.27 million kilometres or 29.37 million miles)
Semi-major axis:     45,000 AU (6730 billion kilometres or 4180 billion miles)
Eccentricity:           1.00024
Orbital period:         N/A
Inclination:              119.9 degrees

Last perihelion:        April 8, 1957
Next perihelion:       N/A (ejection from Solar System)

Comet Arend-Roland photographed on April 26, 1957 with the 48-inch Palomar Schmidt telescope (Palomar Observatory).

Discovered on November 8, 1956 by Belgian astronomers Sylvain Arend and Georges Roland from photographic plates taken at the Uccle Observatory (Royal Observatory of Belgium) in Brussels.

The comet was magnitude +10 when discovered exhibiting a prominent central condensation and a short tail.

Perihelion occurred on April 8, 1957. It was well seen from the Northern Hemisphere during April, peaking at magnitude -0.5.

The tail of Arend–Roland reached a length of 15 degrees and for a few days in April a prominent anomalous tail (or antitail) about 5 degrees in length was visible. This remarkable event resulted in a rarely spectacle of a "spiked" comet.

For the first time attempts were made to detect the comet at radio frequencies. However, these efforts were unsuccessful.

This was the one and only appearance of this comet from Earth. With a hyperbolic orbit, Arend–Roland is traveling fast enough to completely escape from the Solar System and therefore will never return to our vicinity.

Comet Arend–Roland was the subject of the very first edition of the BBC's long running astronomy program The Sky at Night on April 24, 1957.

Comet Halley (1P/Halley)

Discovered by:          Prehistoric, Edmond Halley first recognised the periodicity
Discovery date:         Prehistoric       
Peak magnitude:      +2.4 (1986 return)
Aphelion:                  35.08 AU (5.248 billion kilometres or 3.261 billion miles)
Perihelion:                0.5860 AU (87.66 million kilometres or 54.83 million miles)
Semi-major axis:       17.83 AU (2.667 billion kilometres or 1.657 billion miles)
Eccentricity:              0.9671
Orbital period:            75.32 years
Inclination:                162.3 degrees

Last perihelion:          February 9th, 1986
Next perihelion:         July 28th, 2061

Halley's Comet (ESA)

Comet Halley or Halley's Comet is the best known and most famous comet of all.

It's a short period comet that's visible from Earth every 75–76 years and has been observed by astronomers since at least 240 BC.

In 1066, Halley's appearance was recorded on the Bayeux Tapestry.

Usually comets are named after the person or persons who discovered them. Halley (along with a few other comets) is different in that it was named after the person who first computed its orbit; English astronomer Edmond Halley in 1705.

Before this, the comet was recorded many times by Chinese, Babylonian, and medieval Europeans, but never recognised as being the same object.

Holds the distinction of being the only naked-eye comet that can be seen twice in a human lifetime.

Was first photographed and spectroscopic data obtained during the 1910 approach. On this occasion the comet passed close to Earth and was a spectacular sight; the Earth even passing through part of the comet tail.

Last appearance was in 1986 when Halley was best seen from the Southern Hemisphere. Sadly, the apparition was a poor one; Halley was on the opposite side of the Sun to the Earth and although visible to the naked-eye it reached at best only 2nd magnitude.

An armada of spacecraft visited Halley in 1986, including the Giotto and Vega missions that gave planetary scientists their first view of its surface and structure.

Nucleus of Halley's Comet (Halley Multicolor Camera Team, Giotto Project, ESA)

The comet nucleus is irregular, measuring about 15 x 8 x 8 kilometers (9.4 x 5 x 5 miles).

About 25% of the nucleus has been imaged by spacecraft flybys, revealing an extremely varied surface with hills, mountains, ridges, depressions and at least one crater.

Will next return in 2061.

Of all periodic comets, this one is the most active.

Halley's Comet is the parent body of two annual meteor showers, the Eta Aquariids (in May) and the richer Orionids (in October).