Article Written by Gavin Ramsay
Comets have been known for millennia with Halley’s Comet famously being shown in the Bayeux Tapestry illustrating events which took place in 1066. They were also thought to foretell catastrophic events. Today we know them as having a small nucleus made up of ice and dust and when they near the Sun some of this material is vaporised forming a ‘Coma’ around the nucleus and a tail facing away from the Sun. More than 4000 comets have been discovered. Some, such as Comet West, which was seen in 1976, are unlikely to be seen again. In contrast, Comet Halley famously returns approximately every 76 years with its next visit expected in 2061.
The European Space Agency (ESA) sent the Giotto spacecraft to Comet Halley approaching within 600 km before encountering Comet Grigg-Skjellerup six years later. In 2003 the Japanese Space Agency launched the satellite Hayabusa to closely study the near-Earth asteroid Itokawa. These missions helped determine the physical characteristics of these small solar system bodies. However, the most famous recent mission was ESA’s Rosetta mission to Comet Churyumov– Gerasimenko in which they deployed the probe Philae on to the surface of the Comet. Because of the orientation of the probe its solar cells couldn’t see the Sun and its battery eventually failed. A mission highlight was showing that much of the water on the Earth was unlikely to have originated from Comets.
Despite these missions which were able to examine Comets up and close, there are still great opportunities for astronomers to study Comets with binoculars and small telescopes. Using the GOTO group of telescopes on the island of La Palma in the Canaries, four work experience students have been studying images of three comets made on three consecutive nights at Armagh Observatory and Planetarium. Comet 2017o1 was discovered using the ‘ASASSN’ survey based in Hawaii and Chile in 2017, while Comet Schaumasse was discovered in 1911 and orbits the Sun every 8.2 years and Comet Tsuchinshan was discovered in 1965 and takes 6.6 years to orbit the Sun.
The students, Glen Chambers (Enniskillen Royal Grammar School), Caoimhe Hillen (St Paul’s High School, Bessbrook), Jake Walsh (Banbridge Academy) and Shane Ferris (Wellington College, Belfast) were able to measure the position of the Comets on the three nights and measure their brightness by comparing with the brightness of nearby stars which had known magnitudes. They were also able to make false colour images of the Comets since we had images taken in blue, green and red light. However, since the Comet moves across the sky at a slow but detectable rate, the Comet is not at the same position in the sky in each of the three frames, so a ‘rainbow’ type effect is seen. The position and brightness of the Comets have been reported to the Minor Planet Center in the USA.
Three images of comets 2017o1, Comet 24/P Schaumasse and Comet 62/P Tsuchinshan made using Blue, Green and Red images taken using the GOTO UT2 0.4 m telescope on La Palma. The ‘rainbow’ effect on two images is due to the Comet moving relative to the stars over the time it took to make the each image.
The Gravitational-wave Optical Transient Observer (GOTO) project is supported by the Warwick-Monash Alliance (Warwick University, Monash University) and Sheffield University, Leicester University, Armagh Observatory & Planetarium and the National Astronomical Research Institute of Thailand. See GOTO Observatory for more details.