Scroll & select a comet from the previews below to display the respective image(s).
C2022/E3 (ZTF)
C2022/E3 (ZTF)
C2020/F3 (Neowise)
C2019/Y4 (Atlas)
Comet 17P (Holmes)
C/2006 M4 (Swan)
C/2006 A1 (Pojanski)
Comet 9P/Tempel 1
C/2004 Q2 (Machholz)
C/2004 Q1 (Tucker)
Comet 78P (Gehrels)
C/2003 K4 (Linear)
C/2003 T4 (Linear)
C/2002 T7 (Linear)
C/2001 Q4 (Neat)
Asteroids
(7482) 1994 PC1
C2019/Y4 (Atlas)
(Ivor Trueman)
C2019/Y4 (Atlas)
This comet was discovered in Dec. 2019 by the ATLAS (Asteroid Terrestial-impact Last Alert System), a robotic astronomical survey project in Hawaii.
It was hoped that this would be another of the great comets, but as it approached the Sun it split into four pieces and subsequently broke up further into 25-30 fragments.
The above image is a composite of 45 × 60 second exposures taken in Cookridge on the 22nd March 2020, with a DLSR and Skywatcher 130dps newtonian. Because comets appear to move in relation to the background stars, the processing of the data requires stacking the images with respect to the comet position, as well as the usual method of aligning & stacking the images using the star positions. In the 'Comet' image the stars appear to trail & have to be removed, and in the 'Stars' image the comet appears blurred & has to be removed. The 'Comet' and 'Star' image then have to be recombined. The results are always that great!
Below is a short video that compresses the 45 minutes plus, of the unprocessed data, into 8 seconds. The Comet can be seen moving in the bottom left of the picture.
For more info. on C2019/Y4 (Atlas) see the Wikipedia.
Comets
Comets are small, but nonetheless significant visitors to the Solar system.
Typically they have a mass of about one-billionth × that of the Earth and their nucleus is just a few kilometres across. The nucleus is the core of the Comet and consists of a 'dirty snowball' of dust, water ice, carbon dioxide, ammonia and methane.
Comets are classified as either 'long-period' or 'short-period' depending on how often they approach Earth. Long-period comets appear at intervals of over 200 years and originate in the Oort Cloud, a spherical halo of icy bodies that lies about 40 AU's from the Sun. Short-period (or periodic) comets are thought to originate in the Kuiper Belt, a region of icy material that lies between the orbits of Neptune and Pluto. These are also sub-divided into two further categories, with Halley Type having periods of 20-200 years, and Jupiter Type with a period of less than 20 years.
As Comets approach the Sun, at about a ditance of about 3 AU's, they develop an extended region of gas and dust called the coma. When the Comet temperature reaches 215 K (-58° C) sublimation of water ice to vapour occurs. This material flows outward at approx 0.5 km/s and can extend 105 to 106 km in size. The coma then becomes visible from reflected sunlight, and may also emit radiation as the sunlight excites the gas.
If the Comet moves closer to the Sun, it may develop a large visible tail of up to 1 AU long. The tail actually consists of two tails. There is a gas tail or an ion tail which appears to point away from the Sun, and a dust tail which lies behind the Comet in the wake of it's path.
The gas tail (or ion tail) is due to the solar wind hitting the comet and contains a variery of molecular ions. Emission from CO+ is responsible for the blue colour of the tail which can extend 108 km.
The dust tail which trails behind the Comet is from material that is ejected by radiation pressure. These continue to follow a Kepelerian orbit and the dust tail can also be 107 km long.
Comets are brightest when they reach perihelion (their closest distance to the Sun), and they mostly traverse elliptical orbits, although their eccentricity and periodicity vary greatly.
Long-period comets are also of particular interest to scientists, as the Oort cloud is sufficiently far enough away to remain unaffected by heat from the Sun. They are therefore thought to be composed of original material from the formation of the solar nebula, whilst Short-period comets from the Kuiper belt provide information on the the formation of the outer Solar system.
The Astronomical Unit, or AU was originally defined as the average distance from the Earth to the Sun when at the closest and farthest points apart (called the aphelion and perihelion respectively). i.e. 1 × AU is about 150 million km (93 million miles) or about 8 light-minutes.
In 2012 the AU was defined to be exactly 149,597,870.7 km.
Measuring distances in Astronomical Units, provides a reasonable 'yardstick' for measuring distances on the scale of the Solar system, which would otherwise become unwieldy if they had to be represented in km or miles.
For the even larger distances outside of the Solar System, the Astronical Unit forms the basis of another distance measurement the parsec.
A parsec is defined as the distance which one AU subtends an angle of one arcsecond (1/3600th of a degree), and is equivalent to approx. 206,264.8 AU's or 3.262 light-years.
i.e. if when the Earth moves through a distance of 1 AU, a star appears to move by 1/3600th of a degree when compared to background stars, then the disance to the star is 1 parsec.
For example our closest major galaxy, Andromeda is 778,000 parsecs away, or approx. 160 billion AU (or 2.537 million light-years).