Appendix A: Atmospheric Extinction Tables

The following tables were initially published by Dan Green in the July 1992 issue of the International Comet Quarterly. The original paper may be found at http://www.icq.eps.har- vard.edu./ICQExtinct.html.

Table A.1 “Average” atmospheric extinction in magnitudes for various elevations above sea level (h, in km) z h = 0 h = 0.5 h = 1 h = 2 h = 3 1 0.28 0.24 0.21 0.16 0.13 10 0.29 0.24 0.21 0.16 0.13 20 0.30 0.25 0.22 0.17 0.14 30 0.32 0.28 0.24 0.19 0.15 40 0.37 0.31 0.27 0.21 0.17 45 0.40 0.34 0.29 0.23 0.19 50 0.44 0.37 0.32 0.25 0.21 55 0.49 0.42 0.36 0.28 0.23 60 0.56 0.48 0.41 0.32 0.26 62 0.60 0.51 0.44 0.34 0.28 64 0.64 0.54 0.47 0.37 0.30 66 0.69 0.59 0.51 0.39 0.32 68 0.75 0.64 0.55 0.43 0.35

© Springer International Publishing Switzerland 2017 241 D.A.J. Seargent, Visually Observing Comets, Astronomer’s Pocket Field Guide, DOI 10.1007/978-3-319-45435-1 242 Appendix A: Atmospheric Extinction Tables z h = 0 h = 0.5 h = 1 h = 2 h = 3 70 0.82 0.70 0.60 0.47 0.39 71 0.86 0.73 0.63 0.49 0.40 72 0.91 0.77 0.66 0.52 0.43 73 0.96 0.81 0.70 0.55 0.45 74 1.02 0.86 0.74 0.58 0.48 75 1.08 0.92 0.79 0.62 0.51 76 1.15 0.98 0.84 0.66 0.54 77 1.24 1.05 0.91 0.71 0.58 78 1.34 1.13 0.98 0.76 0.63 79 1.45 1.23 1.06 0.83 0.68 80 1.59 1.34 1.16 0.91 0.74 81 1.75 1.48 1.28 1.00 0.82 82 1.94 1.65 1.42 1.11 0.91 83 2.19 1.86 1.60 1.25 1.03 84 2.50 2.12 1.83 1.43 1.17 85 2.91 2.46 2.13 1.66 1.36 86 3.45 2.93 2.53 1.97 1.62 87 4.23 3.59 3.10 2.42 1.99 88 5.41 4.59 3.96 3.09 2.54 89 7.38 6.26 5.40 4.22 3.46 90 11.24 9.53 8.23 6.42 5.28

Table A.2 “Winter” atmospheric extinction in magnitudes for various elevations above sea level (h, in km) z h = 0 h = 0.5 h = 1 h = 2 h = 3 1 0.25 0.21 0.19 0.15 0.13 10 0.25 0.22 0.19 0.15 0.13 20 0.26 0.23 0.20 0.16 0.14 Appendix A: Atmospheric Extinction Tables 243 z h = 0 h = 0.5 h = 1 h = 2 h = 3 30 0.28 0.25 0.22 0.17 0.15 40 0.32 0.28 0.24 0.20 0.17 45 0.35 0.30 0.26 0.21 0.18 50 0.38 0.33 0.29 0.24 0.20 55 0.43 0.37 0.33 0.26 0.22 60 0.49 0.42 0.37 0.30 0.25 62 0.52 0.45 0.40 0.32 0.27 64 0.56 0.48 0.43 0.34 0.29 66 0.60 0.52 0.46 0.37 0.31 68 0.65 0.57 0.50 0.40 0.34 70 0.72 0.62 0.55 0.44 0.37 71 0.75 0.65 0.57 0.46 0.39 72 0.79 0.69 0.60 0.49 0.41 73 0.84 0.72 0.64 0.52 0.43 74 0.89 0.77 0.68 0.55 0.46 75 0.94 0.82 0.72 0.58 0.49 76 1.01 0.87 0.77 0.62 0.52 77 1.08 0.94 0.82 0.67 0.56 78 1.16 1.01 0.89 0.72 0.60 79 1.26 1.10 0.97 0.78 0.66 80 1.38 1.20 1.06 0.85 0.72 81 1.52 1.32 1.16 0.94 0.79 82 1.70 1.47 1.29 1.05 0.88 83 1.91 1.65 1.46 1.18 0.99 84 2.18 1.89 1.66 1.34 1.13 85 2.53 2.20 1.93 1.56 1.31 244 Appendix A: Atmospheric Extinction Tables z h = 0 h = 0.5 h = 1 h = 2 h = 3 86 3.01 2.61 2.30 1.86 1.56 87 3.69 3.20 2.82 2.28 1.91 88 4.72 4.09 3.60 2.91 2.45 89 6.44 5.58 4.91 3.97 3.34 90 9.80 8.50 7.49 6.05 5.08

Table A.3 “Summer” atmospheric extinction in magnitudes for various elevations above sea level (h, in km) z h = 0 h = 0.5 h = 1 h = 2 h = 3 1 0.32 0.26 0.22 0.17 0.14 10 0.32 0.27 0.23 0.17 0.14 20 0.34 0.28 0.24 0.18 0.15 30 0.37 0.30 0.26 0.20 0.16 40 0.41 0.34 0.29 0.22 0.18 45 0.45 0.37 0.32 0.24 0.19 50 0.49 0.41 0.35 0.26 0.21 55 0.55 0.46 0.39 0.30 0.24 60 0.63 0.53 0.45 0.34 0.27 62 0.68 0.56 0.48 0.36 0.29 64 0.72 0.60 0.51 0.39 0.31 66 0.78 0.65 0.55 0.42 0.34 68 0.85 0.70 0.60 0.45 0.36 70 0.93 0.77 0.65 0.50 0.40 71 0.97 0.81 0.69 0.52 0.42 72 1.02 0.85 0.72 0.55 0.44 73 1.08 0.90 0.76 0.58 0.47 Appendix A: Atmospheric Extinction Tables 245 z h = 0 h = 0.5 h = 1 h = 2 h = 3 74 1.15 0.95 0.81 0.61 0.49 75 1.22 1.01 0.86 0.65 0.53 76 1.30 1.08 0.92 0.70 0.56 77 1.40 1.16 0.99 0.75 0.60 78 1.51 1.25 1.07 0.81 0.65 79 1.64 1.36 1.16 0.88 0.71 80 1.79 1.49 1.26 0.96 0.77 81 1.97 1.64 1.39 1.06 0.85 82 2.19 1.83 1.55 1.18 0.95 83 2.47 2.06 1.75 1.32 1.07 84 2.82 2.35 1.99 1.51 1.22 85 3.28 2.73 2.32 1.76 1.41 86 3.90 3.25 2.75 2.09 1.68 87 4.78 3.98 3.38 2.56 2.06 88 6.11 5.09 4.32 3.28 2.63 89 8.33 6.93 5.89 4.47 3.59 90 12.68 10.56 8.97 6.80 5.47 Appendix B: The Phase Angle of a Comet

Dusty comets display a significant phase effect at large phase angles due to the forward scattering of sunlight from small particles within their comas. A smaller effect, due to back- scattering, is also evident at very small phase angles, that is to say, when the comet is almost opposite the Sun in the sky. Phase angles may be calculated as follows:

C α ∆ r E R S

In the above diagram: S = Sun E = Earth C = Comet R = Radius vector of Earth (i.e., the distance from Earth to Sun) r = Radius vector of comet (i.e., distance of comet from Sun) Δ = Geocentric distance of comet α = Phase angle. The phase angle is defined by

© Springer International Publishing Switzerland 2017 247 D.A.J. Seargent, Visually Observing Comets, Astronomer’s Pocket Field Guide, DOI 10.1007/978-3-319-45435-1 248 Appendix B: The Phase Angle of a Comet

CosraD=+22- Rr2 / 2 D ()

Alternatively, the phase angle may be calculated by

sin/()12aD= ()12//Ö-()()Rr+ ()Rr+-DDr

Appendix C: “Lost” Short-Period Comets

Short-period comets can become “lost” for several reasons. The reason may simply be that the orbit of a particular comet was not sufficiently well determined at its discovery apparition and the calculated period was therefore inaccurate. For a comet with a relatively long period (say, a few decades rather than a few years), this type of error can be quite large. Other comets have become lost due to drastic alterations in their orbits resulting from close approaches to one of the large planets, most frequently Jupiter, whereas others appear to have been abnormally lustrous at their discovery apparition and returned to their normal meager brightness subsequently. Many short-period comets that were lost through these factors (sometimes a combination of more than one of them) have been recovered in recent years thanks to the improve- ment in both orbital computation and observational tech- niques. However, a number of objects continue to elude observers even though they should, theoretically, have made favorable returns and been readily recoverable. These comets are thought to have either disintegrated or, if they remain intact, have ceased either permanently or temporarily to pro- duce gas and dust. The following list consists of the short-period objects that appear most likely to have become “extinct”, either through total disintegration or through permanent or temporary dor- mancy. The comets 3D and 5D are the ones most widely

© Springer International Publishing Switzerland 2017 249 D.A.J. Seargent, Visually Observing Comets, Astronomer’s Pocket Field Guide, DOI 10.1007/978-3-319-45435-1 250 Appendix C: “Lost” Short-Period Comets thought to have disintegrated. Some of the others are more problematic. For instance, the comets Denning-Fujikawa and Perrine-Mrkos were both lost for several returns after what were apparently abnormally bright apparitions, only to be rediscovered decades later at brightness levels more or less equal to their original sighting. The second of these has again become lost and maybe this time truly has disintegrated. However, in view of its history, who can say that it will not outburst again at some future time? Another interesting object is Haneda-Campos. This comet was discovered independently by two visual comet hunters during its rather close approach to Earth in 1978. That apparition was just about as good as it gets, with closest approach, perihelion and opposition all happening at about the same time. The intrinsic brightness and appearance of the comet were also somewhat variable and it is almost certain that it was in outburst during its discovery return. It has not been seen since, however there were no obvious signs of disintegration in 1978. Even though the outer coma became very diffuse, the final observations revealed a condensed core having little resemblance to the elongated debris cloud displayed by disintegrating comets. Future outbursts should definitely not be ruled out. The possibility that one or more of these comets (some of which were initially rather bright objects) may again outburst is something of which visual comet hunters should always be aware. There are precedents for “lost” comets flaring back into view and although visual searches specifically for these objects is probably not justified, it might be worth checking whether any are theoretically well placed before starting the night’s comet sweep. Past, present and future orbits of periodic comets (including the “lost” ones) are available at Kazuo Kinoshita’s website at http://jcometobs.web.fc2.com/ index.html. A quick check to see if any are (hypothetically!) in the sky takes little time and, just possibly, might prove to be rewarding! Appendix C: “Lost” Short-Period Comets 251

COMET PERIOD (Years) 3D/Biela 6.65 5D/Brorsen 5.46 18D/Perrine-Mrkos 6.72 20D/Westphal 61.7 25D/Neujmin 5.43 34D/Gale 11.00 75D/Kohoutek 6.67 83D/Russell 6.10 85D/Boethin 11.81 D/1766 G1 (Helfenzrieder) 4.35 D/1884 O1 (Barnard) 5.38 D/1886 K1 (Brooks) 5.60 D/1894 F1 (Denning) 7.42 D/1895 Q1 (Swift) 7.22 D/1918 W1 (Schorr) 6.71 D/1952 B1 (Harrington-Wilson) 6.38 D/1978 R1 (Haneda-Campos) 5.97 Appendix D: Lunar Phases 2017–2027

New First quarter Full Last 2017 Lunar phases Jan. 5 Jan. 12 Jan. 19 Jan. 27 Feb. 3 Feb. 10 Feb. 18 Feb. 26 Mar. 5 Mar. 12. Mar. 20 Mar. 27 Apr. 3 Apr. 11 Apr. 19 Apr. 26 May 2 May 10 Map 18 May 25 Jun. 1 Jun. 9 Jun. 17 Jun. 23 Jun. 30 Jul. 9 Jul. 16 Jul. 23 Jul. 30 Aug. 7 Aug. 14 Aug. 21 Aug. 29 Sep. 6 Sep. 13 Sep. 20 Sep. 27 Oct. 5 Oct. 12 Oct. 19 Oct.27 Nov. 4 Nov. 10 Nov. 18 Nov. 26 Dec. 3 Dec. 10 Dec. 18 Dec. 26 2018 Lunar phases Jan. 1 Jan. 8 Jan. 16 Jan. 24 Jan. 31 Feb. 7

© Springer International Publishing Switzerland 2017 253 D.A.J. Seargent, Visually Observing Comets, Astronomer’s Pocket Field Guide, DOI 10.1007/978-3-319-45435-1 254 Appendix D: Lunar Phases 2017–2027

New First quarter Full Last Feb. 15 Feb. 23 Mar. 1 Mar. 9 Mar. 17 Mar.24 Mar. 31 Apr. 8 Apr. 15 Apr. 22 Apr. 29 May 7 May 15 May 21 May 29 Jun. 6 Jun. 13 Jun. 20 Jun. 28 Jul. 6 Jul. 12 Jul. 19 Jul. 27 Aug. 4 Aug. 11 Aug. 18 Aug. 26 Sep. 2 Sep. 9 Sep. 16 Sep. 24 Oct. 2 Oct. 8 Oct. 16 Oct. 24 Oct. 31 Nov. 7 Nov. 15 Nov. 23 Nov. 29 Dec. 7 Dec. 15 Dec. 22 Dec. 29 2019 Lunar phases Jan. 5 Jan. 14 Jan. 21 Jan 27 Feb. 4 Feb. 12 Feb. 19 Feb. 26 Mar. 6 Mar. 14 Mar. 20 Mar. 28 Apr. 5 Apr. 12 Apr. 19 Apr. 26 May 4 May 11 May 18 May 26 Jun. 3 Jun. 10 Jun. 17 Jun. 25 Jul. 2 Jul. 9 Jul. 16 Jul. 24 Jul. 31 Aug. 7 Aug. 15 Aug. 23 Aug. 30 Sep. 5 Sep. 14 Sep. 21 Sep. 28 Oct. 5 Oct. 13 Oct. 21 Oct. 27 Nov. 4 Nov. 12 Nov. 19 Nov. 26 Dec. 4 Dec. 12 Dec. 18 Dec. 26 Appendix D: Lunar Phases 2017–2027 255

New First quarter Full Last 2020 Lunar phases Jan. 2 Jan. 10 Jan. 17 Jan. 24 Feb. 1 Feb. 9 Feb. 15 Feb. 23 Mar. 2 Mar. 9 Mar. 16 Mar. 24 Apr. 1 Apr. 7 Apr. 14 Apr. 22 Apr. 30 May 7 May 14 Jun. 21 Jun. 28 Jul. 5 Jul. 12 Jul. 20 Jul. 27 Aug. 3 Aug. 11 Aug. 18 Aug. 25 Sep. 2 Sep. 10 Sep. 17 Sep. 23 Oct. 1 Oct. 9 Oct. 16 Oct. 23 Oct. 31 Nov. 8 Nov. 15 Nov. 21 Nov. 30 Dec. 7 Dec. 14 Dec. 21 Dec. 29 2021 Lunar phases Jan. 6 Jan. 13 Jan. 20 Jan. 28 Feb. 4 Feb. 11 Feb. 19 Feb. 27 Mar. 5 Mar. 13 Mar. 21 Mar. 28 Apr. 4 Apr. 11 Apr. 20 Apr. 26 May 3 May 11 May 19 May 26 Jun. 2 Jun. 10 Jun. 17 Jun. 24 Jul. 1 Jul. 9 Jul. 17 Jul. 23 Jul. 31 Aug. 8 Aug. 15 Aug. 22 Aug. 30 Sep. 6 Sep. 13 Sep. 20 Sep. 28 Oct. 6 Oct. 12 Oct. 20 Oct. 28 Nov. 4 Nov. 11 Nov. 19 Nov. 27 256 Appendix D: Lunar Phases 2017–2027

New First quarter Full Last Dec. 4 Dec. 10 Dec. 18 Dec. 26 2022 Lunar phases Jan. 2 Jan. 9 Jan. 17 Jan. 25 Feb. 1 Feb. 8 Feb. 16 Feb. 23 Mar. 2 Mar. 10 Mar. 18 Mar. 25 Apr. 1 Apr. 9 Apr. 16 Apr. 23 Apr. 30 May 8 May 16 May 22 May 30 Jun. 7 Jun. 14 Jun. 20 Jun. 28 Jul. 6 Jul. 13 Jul. 20 Jul. 28 Aug. 5 Aug. 11 Aug. 19 Aug. 27 Sep. 3 Sep. 10 Sep. 17 Sep. 25 Oct. 2 Oct. 9 Oct. 17 Oct. 25 Nov. 1 Nov. 8 Nov. 16 Nov. 23 Nov. 30 Dec. 7 Dec. 16 Dec. 23 Dec. 29 2023 Lunar phases Jan. 6 Jan. 14 Jan. 21 Jan. 28 Feb. 5 Feb. 13 Feb. 20 Feb. 27 Mar. 7 Mar. 14 Mar. 21 Mar. 28 Apr. 6 Apr. 13 Apr. 20 Apr. 27 May 5 May 12 May 19 May 27 Jun. 3 Jun. 10 Jun. 18 Jun. 26 Jul. 3 Jul. 9 Jul. 17 Jul. 25 Aug. 1 Aug. 8 Aug. 16 Aug. 24 Aug. 30 Sep. 6 Sep. 14 Sep. 22 Sep. 29 Oct. 6 Appendix D: Lunar Phases 2017–2027 257

New First quarter Full Last Oct. 14 Oct. 21 Oct. 28 Nov. 5 Nov. 13 Nov. 20 Nov. 27 Dec. 5 Dec. 12 Dec. 19 Dec. 26 2024 Lunar phases Jan. 3 Jan. 11 Jan. 17 Jan. 25 Feb. 2 Feb. 9 Feb. 16 Feb. 24 Mar. 3 Mar. 10 Mar. 17 Mar. 25 Apr. 1 Apr. 8 Apr. 15 Apr. 23 May 1 May 7 May 15 May 23 May 30 Jun. 6 Jun. 14 Jun. 21 Jun. 28 Jul. 5 Jul. 13 Jul. 21 Jul. 27 Aug. 4 Aug. 12 Aug. 19 Aug. 26 Sep. 2 Sep. 11 Sep. 17 Sep. 24 Oct. 2 Oct. 10 Oct. 17 Oct. 24 Nov. 1 Nov. 9 Nov. 15 Nov. 22 Dec. 1 Dec. 8 Dec. 15 Dec. 22 Dec. 30 2025 Lunar phases Jan. 6 Jan. 13 Jan. 21 Jan. 29 Feb. 5 Feb. 12 Feb. 20 Feb. 27 Mar. 6 Mar. 14 Mar. 22 Mar. 29 Apr. 4 Apr. 12 Apr. 20 Apr. 27 May 4 May 12 May 20 May 26 Jun. 2 Jun. 11 Jun. 18 Jun. 25 Jul. 2 Jul. 10 Jul. 17 258 Appendix D: Lunar Phases 2017–2027

New First quarter Full Last Jul. 24 Aug. 1 Aug. 9 Aug. 16 Aug. 23 Aug. 31 Sep. 7 Sep. 14 Sep. 21 Sep. 29 Oct. 6 Oct. 13 Oct. 21 Oct. 29 Nov. 5 Nov. 12 Nov. 20 Nov. 28 Dec. 4 Dec. 11 Dec. 19 Dec. 27 2026 Lunar phases Jan. 3 Jan. 10 Jan. 18 Jan. 25 Feb. 1 Feb. 9 Feb. 17 Feb. 24 Mar. 3 Mar. 11 Mar. 18 Mar. 25 Apr. 1 Apr. 10 Apr. 17 Apr. 23 May 1 May 9 May 16 May 23 May 31 Jun. 8 Jun. 14 Jun. 21 Jun. 29 Jul. 7 Jul. 14 Jul. 21 Jul. 29 Aug. 5 Aug. 12 Aug. 19 Aug. 28 Sep. 4 Sep. 10 Sep. 18 Sep. 26 Oct. 3 Oct. 10 Oct. 18 Oct. 26 Nov. 1 Nov. 9 Nov. 17 Nov. 24 Dec. 1 Dec. 8 Dec. 17 Dec. 23 Dec. 30 2027 Lunar phases Jan. 7 Jan. 15 Jan. 22 Jan. 29 Feb. 6 Feb. 14 Feb. 20 Feb. 28 Mar. 8 Mar. 15 Mar. 22 Mar. 29 Apr. 6 Apr. 13 Apr. 20 Apr. 28 May 6 May 13 May 20 May 28 Appendix D: Lunar Phases 2017–2027 259

New First quarter Full Last Jun. 4 Jun. 11 Jun. 18 Jun. 27 Jul. 3 Jul. 10 Jul. 18 Jul. 26 Aug. 2 Aug. 9 Aug. 17 Aug. 24 Aug. 31 Sep. 7 Sep. 15 Sep. 23 Sep. 29 Oct. 7 Oct. 15 Oct. 22 Oct. 29 Nov. 6 Nov. 13 Nov. 20 Nov. 27 Dec. 6 Dec. 13 Dec. 20 Dec. 27 Glossary of Terms

Active asteroid An asteroid displaying comet-like, or super- ficially comet-like, activity, not necessarily caused by the sublimation of ices. For example, a dust coma and/or tail may result from a collision between an asteroid and meteorite or from the disruption of an asteroid through rotational instabil- ity. Active asteroids orbiting within the main Asteroid Belt, between the orbits of Mars and Jupiter, that display sublimation-driven cometary activity are also known as “main-belt comets.” Altazimuth telescope mount A telescope mount enabling motion in a horizontal (in azimuth) and vertical direction (in altitude). This type of mounting has traditionally been favored by comet hunters. Aphelion For an object following an elliptical orbit around the Sun, the point in distance and time where and when that object is furthest from the Sun in its orbit. Arc minutes There are 60 min of arc (denoted as 60’) in 1°. The disc of the Sun and full Moon are about 30 arc minutes or one half of a degree in diameter and there are 90° from the horizon to the zenith. There are 60 s of arc (denoted as 60”) in 1 min of arc. Astrometry The careful, precise measurement of the position of astronomical objects, usually made with respect to standard catalogs of star positions. Astronomical Unit (AU) A measure of distance, normally used for giving the distances of objects within the Solar System. One Astronomical Unit (denoted as AU) is approxi- mately equal to the mean Earth-Sun distance, i.e., about 93,000,000 miles, or 150,000,000 km. Formally, the AU is actually slightly less than Earth’s mean distance from the Sun (semi-major axis) because it is the radius of a circular orbit of negligible mass (and unperturbed by other planets) that revolves around the Sun in a specific period of time. Its precise value was defined by the International Astronomical Union in 2012 as equal to 149,597,870.700 km, or 149,597,870,700 m. 262 Glossary of Terms

Azimuth Angular distance measured clockwise around the observer’s horizon in units of degrees; astronomers usually take north to be 0°, east to be 90°, south to be 180°, and west to be 270°. Barycenter The center of mass of a system of bodies as, for example, the Solar System. When a comet is well beyond the orbit of the planets, it behaves dynamically as if the Sun and major planets are a single object of summed mass, and the center of this mass (called the barycenter of the solar system) is offset somewhat from the Sun. “Original” and “future” orbits of long-period comets are computed for this barycenter, while perturbed, osculating orbits of currently observed objects in the inner Solar System are computed for heliocentric orbits. Bolide The name given to a bright exploding meteor. CCD This denotes a “charge-coupled device,” that is to say, a very sensitive electronic device that has been revolutioniz- ing astronomy in recent decades. CCD cameras are composed of silicon chips that are sensitive to light, changing detected photons of light into electronic signals that can then be used to make images of astronomical objects or to analyze how much light is being received from such objects. CCDs require computers for reduction of data and can detect much fainter objects than conventional photographs. Coma A comet’s “atmosphere” composed of dust and/or various gases surrounding its nucleus. The coma is not a true atmosphere in so far as the material comprising it is not retained by the nucleus. Because the gravitational attraction of the latter is weak, the coma material escapes into surrounding space as it is released from the nucleus. Comet A celestial body orbiting the Sun that displays (at least during a portion of its orbit) some diffuseness and/or a “tail” of debris that points generally in the anti-solar direction. Declination One element of the astronomical coordinate system on the sky that is used by astronomers. Declination, which can be thought of as latitude on Earth projected onto the sky, is usually denoted by the lower-case Greek letter delta and is measured north (+) and south (−) of the celestial Glossary of Terms 263 equator in degrees, minutes, and seconds of arc. The celestial equator is defined as being at declination zero (0) degrees; the north and south celestial poles are defined as being at +90 and −90°, respectively. Degree A unit used in the measurement of angles, heavily used particularly in astronomy. Following ancient Babylonian mathematics, a circle is divided into 360 even units of arc, each of which constitutes 1°. The entire sky, therefore, spans 360°. One degree is composed of 60 min of arc or 3600 s of arc. Ecliptic The apparent path of the Sun against the sky back- ground (celestial sphere); formally, the mean plane of Earth’s orbit around the Sun. Elongation Angular distance of a celestial object from the Sun in the sky. Enthalpy A thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of a system plus the product of pressure and volume. Enthalpy of solution The enthalpy of solution is the enthalpy change associated with the dissolution of a substance in a solvent at constant pressure, resulting in infinite dilution. Heat released through enthalpy of solution as super-volatile gases dissolve in liquid methane beneath the surface of 29P/ Schwassmann-Wachmann has been proposed as the trigger for the large brightness outbursts frequently experienced by this comet. Ephemeris (plural: ephemerides) Pronounced ee-FEM-er- is (ef-fi-MARE-uh-deez). A table listing specific data of a moving object, as a function of time. Ephemerides usually contain right ascension and declination, apparent angle of elongation from the Sun (in degrees) and magnitude of the object; other quantities frequently included in ephemerides are an object’s distances from the Sun and Earth (given in AU), usually given as Roman letter “r,” and Greek letter “Δ,” respectively. The object’s phase angle and the Moon phase may also be included. Equatorial mount An equatorial mount is a mount for instruments that follows the rotation of the sky by having one rotational axis parallel to that of Earth’s axis of rotation. 264 Glossary of Terms

Equinox Either of the two points (vernal, autumnal) on the celestial sphere where the ecliptic (which is the apparent path of the Sun on the sky) intersects the celestial equator. Due to precession, this point moves over time, so positions of stars in catalogs and on atlases are usually referred to a “mean equator and equinox” of a specified standard epoch. Prior to 1992, most astronomers used “equinox 1950.0,” but since then equinox 2000 has been the standard. The differences in an object’s position when given in equinoxes 1950.0 and 2000.0 amounts to several arc minutes. Extinction, atmospheric The diminishing of light from astronomical objects due to Earth’s atmosphere, in which molecules (air, dust, etc.) of the atmosphere absorb, reflect and refract light before it reaches the ground. Extinction becomes a severe problem for astronomers when objects are viewed close to (especially within 20° of) the local horizon. Gegenschein Literally meaning “counterglow,” this phenomenon of the zodiacal light arises from sunlight back- scattered from interplanetary dust located outside of Earth’s orbit and opposite to the Sun in the sky. Head The nucleus and coma of a comet are collectively referred to as the head. Heliocentric orbit A heliocentric orbit is one based on the Sun as one of the two foci of the (elliptical) orbit (or as the center of a circular one). Heliocentric magnitude This refers to the brightness of an object as would be seen from a heliocentric distance of 1 AU (i.e., from a distance of 1 AU from the Sun). m1 (total magnitude) Total, integrated magnitude of a comet’s head (meaning coma + nuclear condensation). This can be estimated visually, as the comet’s “total visual magnitude.” The variable m1 is usually found in ephemerides pre- dicting a comet’s future motion, position on the sky and brightness. m2 (nuclear magnitude) The magnitude value measured (or predicted) for a comet’s nuclear condensation. Because the true or physical nucleus of a comet is rarely observed from

Earth, the m2 values are fraught with problems as to their Glossary of Terms 265 true meaning. They are also extremely dependent upon instrumentation (aperture, focal-ratio, magnification) and wavelength, and their relation to m1 values are not at all straightforward. Nuclear magnitudes are chiefly used for astrometric purposes, in which predictions are made for the brightness of the comet’s nuclear condensation so that astrometrists can gauge how faint the condensation is likely to be and thus how long an exposure is needed to get a good, measurable image. Such predictions have little relevance to visual observations. Magnitude The unit used to describe the brightness of astronomical objects. The smaller the numerical value, the brighter the object. The human eye can detect stars to 6th or 7th magnitude on a dark, clear night far from city lights; in suburbs or cities, stars may only be visible to mag. 2, 3 or 4, due to light pollution. The brightest star, Sirius, shines at visual magnitude −1.5. Jupiter can get about as bright as visual magnitude −3 and Venus as bright as −4. The full Moon is near magnitude −13, and the Sun near mag. −26. Main-belt comet A term given to a class of objects moving in stable orbits typical of asteroids in the main Asteroid Belt, between the orbits of Mars and Jupiter, but which neverthe- less display periods of comet-like activity, apparently driven by sublimating ices. Meteors Small rocky and/or icy particles that are swept up by Earth in its orbit around the Sun. Also called “shooting stars” or “fireballs” if at least as bright as Venus, they travel across the sky in a very short time, from less than a second to several seconds, and they do so because they are only a mat- ter of tens of miles above the surface of Earth. Meteor showers are generally thought to be produced by the debris left by comets as the latter orbit the Sun. Meteorite A natural particle reaching the surface of Earth from space after traveling through Earth’s atmosphere. Meteoroid A natural particle in space before it enters Earth’s atmosphere, or a similar particle in space that does not encounter Earth. 266 Glossary of Terms

Non-gravitational forces Forces changing a cometary orbit that are not due to gravitational effects. They are attributed to forces arising from the sublimation of gases from the nucleus, the so-called “rocket effect.” Orbit The path of one object about another (used here for an object orbiting the Sun). Orbital elements Parameters (numbers) that determine an object’s location and motion in its orbit around another object. In the case of Solar System objects such as comets and planets, one must ultimately account for perturbing gravitational effects of numerous other planets in the Solar System (not merely the Sun), and when such account is made, one has what are called “osculating elements” (which are always changing with time and which therefore must have a stated epoch of validity). Six elements are usually used to determine uniquely the orbit of an object in orbit around the Sun, with a seventh element (the epoch, or time, for which the elements are valid) added when planetary perturbations are taken into consideration. The six orbital elements used for comets are usually the following: time of perihelion passage (T) perihelion distance (q), usually given in AU eccentricity (e) of the orbit argument of perihelion (ω) longitude of the ascending node (Ω) inclination of the orbit with respect to the ecliptic (i). The mean equinox must be specified for these three angles. Perihelion The point where (and when) an object orbiting the Sun is closest to it. Perturbations Gravitational influences (“tugging” and “pulling”) of one astronomical body on another. Comets are strongly perturbed by the gravitational forces of the major planets, particularly by the largest planet in the Solar System, Jupiter. These perturbations must be allowed for in orbit computations, and they lead to what are known as “osculating elements” (which means that the orbital element numbers change from day to day and month to month due to Glossary of Terms 267 continued perturbations by the major planets, so that an epoch is necessarily stated to denote the particular date that the elements are valid). Precession A slow but relatively uniform motion of Earth’s rotational axis that causes changes in the coordinate systems used for mapping the sky. Earth’s axis of rotation does not always point in the same direction, due to gravitational tugs by the Sun and Moon (known as lunisolar precession) and by the major planets (known as planetary precession). Radiation pressure Electromagnetic radiation (for example, visible light, infrared radiation, X-rays, etc.) has the property of being able to transfer momentum to materials and thereby push them away from the source of radiation. Though negligible for large bodies, this force is very significant for particles having the dimensions of the finest cometary dust, and it is this phenomenon that propels solid particles into the dust tails of comets. Reflector A telescope that uses as its primary optical element a mirror. Most large telescopes in use today by both amateur and professional astronomers are reflecting telescopes. Refractor A telescope that uses as its primary optical element a lens. Binoculars are a type of refractor. Right ascension One element of the astronomical coordinate system on the sky, which can be thought of as longitude on Earth projected onto the sky. Right ascension is usually denoted by the lower-case Greek letter alpha and is measured eastward in hours, minutes and seconds of time from the vernal equinox. There are 24 h of right ascension, though the 24-h line is always taken as 0 h. More rarely, right ascension is given in degrees, in which case there are 360° of right ascension to make a complete circuit of the sky. Rock comet An asteroidal object displaying a form of comet-like activity apparently driven by thermal disruption of hydrated minerals rather than sublimating ices. The asteroid 3200 Phaethon, parent object of the Geminid meteor shower, is an object of this type. 268 Glossary of Terms

The term is also applied to certain extrasolar planets that orbit so close to their parent stars that surface rocks vaporize into comet-like comas and tails. Scattering Small particles of the order of 1 μm (one tenth of a mm) in size have the property of not simply reflecting light and making shadows but also of scattering the light that falls on them in all directions. In certain situations, forward-scattered light, appearing where one might expect to see a shadow, is actually brighter than back-scattered, or “reflected” light. Dusty comets observed close to the Sun in the sky and located between Earth and the Sun (and therefore at large phase angles) have their apparent brightness significantly enhanced due to forward-scattering of sunlight by the particles of dust in their comas. Solar wind Ionized gases carrying magnetic fields are blown off the Sun at velocities in the range of 450 km/s. It is this “wind” that propels the ion tails of comets. Striae Narrow, rectilinear structures sometimes observed within the dust tails of comets. They arise from relatively large particles that were released from the nucleus at the same time and later disintegrate into fragments. The parent particles of striae, released in a stream over time, form the concave edge of curving dust tails, and as those released together at various times disrupt, patterns of striae are produced more or less across the breadth of the tail. Sublimation The change of a solid (such as ice) directly into a gaseous state (bypassing the liquid state). This happens in the vacuum of space with comets, as the heating effects of solar radiation cause ices in comets to “steam off” as gases into space. The ice molecules present in the nucleus actually break up (or dissociate) into smaller atoms and molecules after leaving the nucleus in gas form. Synchrones The loci of particles released from the nucleus simultaneously. They are sometimes evident as straight or moderately curved structures within the dust tail that are not, however, to be confused with striae. Syndynes (syndynames) The loci of particles within dust tails that are subjected to equal force. Particles of equal size Glossary of Terms 269 are subjected to the same degree of force, resulting from the opposing push away from the Sun caused by solar radiation pressure countered by the gravitational attraction toward it. The resulting path of the particle depends upon the degree to which it is affected by either, which, in turn, depends upon its size, large particles being affected more by solar gravity and less by the radiation pressure than small ones. Universal Time (UT, or UTC) A measure of time used by astronomers. UT conforms (within a close approximation) to the mean daily (apparent) motion of the Sun. UT is determined from observations of the diurnal (daily) motions of the stars for an observer on Earth. UT is usually used for astronomical observations. Zero hours UT corresponds to local midnight at Greenwich (zero terrestrial longitude). Vernal equinox The point on the celestial sphere where the Sun crosses the celestial equator moving northward, which corresponds to the beginning of spring in the Northern Hemisphere and the beginning of autumn in the Southern Hemisphere (in the third week of March). This point corresponds to zero (0) hours of right ascension. Zenith The point directly overhead in the sky. Zodiacal light A general glow throughout the sky resulting from the scattering of sunlight by interplanetary dust. It is brightest near the Sun and along the ecliptic. The zodiacal light pyramids seen before dawn and following evening twilight are often referred to as the zodiacal light. Zodiacal light pyramid A triangular glow seen on the west- ern horizon after evening twilight and on the eastern horizon before morning twilight. It is the brightest component of the zodiacal light. Author Index 271

AUTHOR INDEX

A Ephorus, 4, 6 Alcisthenes, 5 Epigenes, 5 Alcock, G.E.D., 87, 88, 128, 217, 218 Apian, P., 12, 13 Aristotle, 3, 5, 43, 48 F Armstrong, N., 80, 81 Fabry, L., 43 Fayet, C., 180 Finlay, W., 159 B Forbes, G., 213 Barnard, E.E., 215, 216 Fujikawa, S., 218 Becvar, A., 218 Bessel, F., 177 Beyer, M., 85–86 G Biela, W., 15–17 Galileo, G., 6, 43 Bobrovnikoff, N., 45, 86, 87, 132 Giacobini, M., 144, 147, 215 Borrelly, A., 164 Giclas, H., 180 Bradfield, W.A., 164, 216, 217 Brooks, W., 174, 177, 215 Bullock, J.B., 96 H Halley, E., 9, 10, 12, 14, 47 C Hartley, M., 167 Caesar, J., 12 Herschel, C., 141, 211–213, 215 Chodas, P., 222 Herschel, W., 211 Coggia, J., 150, 213 Hevelius, J., 7, 127 Crommelin, A.C.D., 48, 214 Honda, M., 138, 216 Cysat, J., 127 Howell, E., 157 Hynek, J.A., 80

D Daniel, Z., 217 I d’Arrest, H., 162 Ikeya, K., 12, 218 Da Vinci, L., 7

K E Kepler, J., 6, 7, 119 Edgeworth, K., 54 Kinoshita, K., 137 Encke, J.F., 141, 174 Kracht, R., 222, 223

Kresak, L., 144, 218 Rigollet, R., 213 Kreutz, H., 221 Roemer, E., 25, 28, 34, Kuiper, G., 54 174, 181 Kushida, Y., 172 Rumker, C., 141

L S Laplace, P., 43, 44 Schaumasse, M., 180 Levy, D., 218 Schiaparelli, J., 44 Lexell, A.J., 209 Schwassmann, A., 191 Lovejoy, T., 66, 128 Schwittek, W., 76 Lyttleton, R.A., 20–26, 28, 46, 193 Sekanina, Z., 106, 123, 124, 126, 222, 223 M Seki, T., 218 Machholz, D., 66, 67, 218 Seneca, L., 4–6 Mechain, P., 141, 209–211 Somerville, M., 211 Messier, C., 207–211 Stephan, E., 150 Miles, R., 193, 194 Swift, L., 16, 215 Mori, H., 218 Morris, C.S., 74, 84, 132 Mrkos, A., 138, 177, 218 T Tempel, W., 16, 183 Thatcher, A.E., 16 N Trouvelot, E., 127 Nakano, S., 137 Tuttle, H., 16 Newton, I., 9, 12, 47 Nolke, F., 45 V Van Flandern, T., 49 O Von Humboldt, A., 14 Olbers, W., 13, 177 Von Seeliger, H., 43 Oort, J., 49, 51–53 Vozarova, M., 218 Opik, E., 52 Vsekhsvyatskij, S., 46–48, 60, 90 Oterma, L., 150

P W Pajdusakova, L., 138, 218 Wachmann, A., 191 Peltier, L., 216, 217 Weissman, P., 54 Perrine, C.D., 215 Whipple, F., 26, 27, 29, 32, 35, 46, Pingre, A., 127 51, 114 Pons, J., 141, 174, 213–215 Winnecke, F., 127, 213, 215 Ptolemy, C., 6 Wirtanen, C.A., 152

R Z Reinmuth, K., 192 Zhang, D., 12 Richter, N.B., 193 Zinner, E., 147 Subject Index 273

SUBJECT INDEX

A Comets, 11, 22, 29, 30, 35, 47, 73, 92, Active asteroids, 63 94, 99, 102, 104, 127, American Association of Variable 137–139, 141, 142, 144, Star Observers (AAVSO), 79 145, 147, 148, 150, 152, Anti-tails, 37, 39, 129, 130 153, 155, 157, 159, 162, Atmospheric extinction, 80–82 164, 167, 170, 172, 174, Averted vision, 110 177, 178, 180, 181, 183, 184, 186, 188, 191–215, 226–230, 233 B 372 BC, 4, 5 Babylonians, 4 214 BC, 222 Back-scattering of sunlight, 94 44 BC, 12 Brightness 1106 AD, 12, 222, 223 estimates (methods of making 1618, 127 same), 79, 80, 82, 83, 86, 1652, 127 87, 131, 132, 172 1680 V1, 9, 10, 12 outbursts, 22, 30, 89–97, 102, 1702 D1, 221, 222 104, 105, 147, 191, 1769 P1 (Messier), 127, 208 192, 195 1793 A1 (Gregory), 210 surges, 64, 91, 93, 94, 102, 104, 1801 N1 (Pons), 210, 214 159, 183 1811 F1, 13, 18, 26, 214 1843 D1, 19, 219, 221, 222 1858 L1 (Donati), 36, 100, 119, C 127, 144 Centaurs 1861 J1 (Tebbutt), 96 Echeclus, 195 1861 (Thatcher), 16, 17 Central condensation, 26, 31, 32, 84, 1874 H1(Coggia), 31, 100, 125, 96, 99–102, 104, 105, 132, 127, 150 175, 195 1880 C1, 13, 219, 222 Chinese astronomers (ancient), 3, 13 1882 K1(eclipse comet of May), Coma 216 dust, 18, 21, 35, 68, 94–97, 101, 1882 R1, 19, 20, 23, 29, 219, 222 104 1887 B1, 177, 221, 222 gases, 18, 21, 22, 27, 28, 30, 35, 1927X1 (Skjellerup-Maristany), 37, 45, 68, 93, 101, 106, 95, 191 120, 131 1945 X1 (du Toit), 221, 223 neutral hydrogen, 27, 28 1957 R1 (Arend-Roland), 121, 130

Comets (cont.) 19P/Borrelly, 164, 226 1962 C1 (Seki-Lines), 121, 125, 21P/Giacobini-Zinner, 147, 130, 218 148, 226 1963 A1 (Ikeya), 218, 223 24P/Schaumaasse, 180, 181, 1963 R1 (Pereyra), 221 226 1964 L1 (Tomita-Gerber-Honda), 26P/Grigg-Skjellerup, 214, 226 117, 218 29P/Schwassmann- 1965 S1 (Ikeya-Seki), 35, 121, 125, Wachmann (1), 22, 94, 104, 128, 218, 222, 223 191–206, 226 1969 T1 (Tago-Sato-Kosaka), 27 38P/Stephan-Oterma, 150, 226 1969 Y1 (Bennett) 39P/Oterma, 226 1970 K1 (White-Ortiz-Bolelli), 221 41P/Tuttle-Giacobini-Kresak, 1973 E1 (Kohoutek), 27 144, 145, 226 1975 V1 (West), 218 42P/Neujmin, 30, 226 1980 O1 (Cernis-Petrauskas), 130 45P/Honda-Mrkos- 1980 E1 (Bowell), 44 Pajdusakova, 138, 139, 1983 H1 (IRAS-Araki-Alcock), 87, 188, 226 88, 217 46P/Wirtanen, 152, 153, 226 1983 J1 (Sugano-Saigusa- 53P/Van Biesbroeck, 30, 227 Fujikawa), 74 55P/Tempel-Tuttle, 227 1989 Y1 (Austin), 118 67P/Churyumov- 1995 O1 (Hale-Bopp), 89, 119 Gerasimenko, 29, 227 1996 B2 (Hyakutake), 35, 88 73P/Schwassmann-Wachmann 2006 P1 (McNaught), 121 (3), 104, 227 2011 W3 (Lovejoy), 128, 223 88P/Howell, 157, 227 2013 X1 (PANSTARRS), 93 103P/Hartley, 167, 228 listed discoveries by 109P/Swift-Tuttle, 228 Herschel (C.), 141, 211–213, 122P/de Vico, 228 215 144P/Kushida, 172, 229 Mechain, 141, 209, 210 153P/Ikeya-Zhang, 229 Messier, 127, 207–209, 211 209P/LINEAR, 73, 99, 230 Pons, 141, 174, 213–215 332P/Ikeya-Murakami, 233 “lost” (list thereof), 142 D/1993 F2 (Shoemaker-Levy), numbered (list thereof), 225 47 Periodic P/2016 BA 14 (PANSTARRS), 73 1P/Halley, 11, 102, 226 Unnumbered (list thereof), 2P/Encke, 137, 141, 142, 155, 235–239 170, 186, 210, Comparison stars, 77, 79–82, 84–88, 213, 226 100 3D/Biela, 15-17, 115, 249, 251 “Coruscations” in tail, 127, 128 6P/d’Arrest, 162 Cryovolcanism, 94, 194, 195 8P/Tuttle, 29, 210, 226 10P/Tempel, 102, 183, 184 12P/Pons-Brooks, 35, 102, D 174, 177 Deep impact, 167 13P/Olbers, 177, 178, 226 Deep Space 1, 164 15P/Finlay, 159, 226 Degree of condensation (of coma), 17P/Holmes, 92, 226 98–100, 131, 132 Subject Index 275

Diameter of coma, 17–19, 25, 27–29, K 74, 84, 85, 88, 89, 97, 98, Kreutz comet family. See Sungrazers 131, 167, 180, 191 Kuiper Belt, 54 “Dirty snowball” comet model. See Icy-conglomerate comet model M Disconnection events (DEs), Mars, 7, 49, 194 114–117, 132 Meteors, 5, 14–17, 32, 53, 100, 147 Drawings of comets, 132 Meteor showers, 17, 32 Dynamically new comets, 53–56 Draconids, 147 Leonids, 15–17 Lyrids, 15–17 E Perseids, 15–17, 100 Edgeworth-Kuiper Belt. See Kuiper belt Elliptical orbits, 15, 21, 44, 51, 141, N 150, 180, 213 Non-gravitational effects, 34, 45, 180 Nova, 76, 192, 217 F Nucleus (of comet), 11 Forward scattering of sunlight, 95, 96 O Oort Cloud, 52–54, 65, 91 G Opik-Oort cloud. See Oort cloud Gegenschein, 215 “Gravel bank” comet model, 17, 19, 32 Gravity (theory of), 9, 13, 29, 43, 44, P 121, 194 Phaethon, 53 Greeks (ancient), 4 Phase angle, 94–97 Pluto, 54 Position angle (PA) H of secondary nuclei, 113 Hyperbolic orbits, 44–46 tails, 103, 113 Purkinje effect, 83

I Icy-conglomerate comet R model, 26 Rays (in comet tails), 11, 36, 37, 40, Interstellar theory of comet origins, 54, 114, 119, 120, 127, 132 43–46, 51, 52 Rock comet, 53

J S Jupiter, 6, 22, 29, 44, 46–49, 52, 54, “Sandbank” comet model, 20, 95, 152, 164, 191, 209, 215, 24–30, 193 219 Saturn, 22, 44, 47, 48, 191 276 Subject Index

Secondary comets, 15, 103–106, 159, Sungrazers (sungrazing comets), 19, 160 23, 24, 28, 29, 48, 64, 125, Secondary nuclei, 103, 113, 160 128, 218, 221–224 “Shadow of nucleus”, 31, 125–126 Swan-band filters, 68, 97 Skalnate Pleso Observatory, 218 Synchrones, 120, 122–125 Sky crossbow, 111 Syndynes, 124 Solar and Heliospheric Observatory (SOHO), 64, 121, 222, 223, 233, 235–237, 239 T Solar Maximum Mission (SOLAR Tail flare, 117 MAX), 222 Tails (of comets) Solar System (as place of estimating the length thereof, comet origin), 24, 44, 5–7, 13, 18, 21, 23, 35, 37, 46–49 42, 78, 109–111, 113, 114, Solar Terrestrial Relation 117–121, 123–125, 127, Observatory (STEREO), 129 117, 222, 240 Triton, 194 Solar wind, 18, 37, 114, 117 SOLWIND, 222 Star charts, 77, 103, 109–111, 113 U Striae, 121–125, 132 Universal Time (UT), 69, 76