Comets are the great interplanetairy travelers. Some have very short orbits of a few years, some take several thousands of years. Comet Holmes was the first comet I photographed. It unexpectedly brightened from a magnitude of about 17 to about 2.8 in a period of only 42 hours, making it visible to the naked eye. This represents a change of brightness by a factor of about half a million and is the largest known outburst by a comet. The outburst took place from October 23 to 24, 2007. The first person reportedly to notice a change was J. A. Henríquez Santana on Tenerife in the Canary Islands; minutes later, Ramón Naves in Barcelona noticed the comet at magnitude 7.3. It became easily visible to the naked eye as a bright yellow “star” in Perseus, and by October 25 17P/Holmes appeared as the third brightest “star” in that constellation. Although large telescopes had already shown fine-scale cometary details, naked-eye observers saw Holmes as merely star-like until October 26.
After that date, 17P/Holmes began to appear more comet-like to naked-eye observers. This is because during the comet’s outburst, its orbit took it to near opposition with respect to Earth, and because comet tails point away from the Sun, Earth observers were looking nearly straight down along the tail of 17/P Holmes, making the comet appear as a bright sphere.
Based on orbital computations and luminosity before the 2007 outburst, the comet’s nucleus was estimated at 3.4 km.
Comet Holmes not only became brighter, but it also swelled in size as its coma expanded. In late October 2007 the coma’s apparent diameter increased from 3.3 arcminutes to over 13 arcminutes, about half the diameter of the Moon in the sky. At a distance of around 2 AU, this means that the true diameter of the coma had swelled to over 1 million km, or about 70% of the diameter of the Sun. By comparison, the Moon is 380,000 km from Earth. Therefore, during the 2007 outburst of Comet Holmes the coma was a sphere wider than the diameter of the Moon’s orbit around Earth. On 2007 November, the coma had dispersed to a volume larger than the Sun, briefly giving it the largest extended atmosphere in the Solar System.
The Second comet was Comet Hartley 2. The comet passed within 0.12 AU (18,000,000 km; 11,000,000 mi) of Earth on 20 October 2010, only eight days before coming to perihelion (closest approach to the Sun) on 28 October 2010. From northern latitudes, during early November 2010, the comet was visible around midnight without interference from the Moon.
Despite its current close passage by Earth’s orbit, the comet is not yet a known source of meteor showers. However, that could change. Dust trails from the recent returns of 103P/Hartley 2 move in and out of Earth’s orbit, and the 1979-dust trail is expected to hit in 2062 and 2068.
After the 2010 perihelion passage, not accounting for nongravitational forces, Hartley 2 is estimated to come back to perihelion around 20 April 2017.
The Third comet was Comet Jaques. In late March 2014, C/2014 E2 (Jacques) appeared to contain a dense, bright coma (11.5-12 magnitude), visible with an 8-inch telescope. It crossed the celestial equator on 8 May 2014 becoming a northern hemisphere object. From 3 June 2014 until 17 July 2014 it had an elongation less than 30 degrees from the Sun. The comet was visible in LASCO C3 on 21 June 2014. C/2014 E2 peaked around apparent magnitude 6 in mid-July and was visible in binoculars above the glow of morning twilight.
C/2014 E2 passed 0.085 AU from Venus on 13 July 2014. On 20 July 2014 the comet was near the naked eye star Beta Tauri.On 22 August 2014 it passed Epsilon Cassiopeiae. It reached perigee (closest approach to Earth) on 28 August 2014, at 0.56 AU. The comet passed about 3 degrees from Deneb from 4-5 September 2014. On 14 September the comet was near Albireo. By October 2014 the comet had fainted to magnitude 10.