Comets

Copyright

Copyright © 2020, Anura Gurugé.

All Rights Reserved.

No part of this book may be reproduced, stored in a retrieval system, or transmitted by any means without the written permission of the author.

First published in May 2020.

WOWNH LLC

New Hampshire

USA

www.wownh.com

Photographic Credits:

All of the images used in the body of this book are from the public domain (e.g., Wikipedia, NASA, JPL, etc.). The cover picture, from Wikipedia, is of C/1995 O1 (Hale-Bopp) – the last truly naked-eye comet seen in the Northern Hemisphere, and that was in 1997. The comet with the extraordinarily long tail shown on the title page is C/1843 D1. The image is a painting by Mary Morton Allport (1806 – 1895) of what it is said to have looked over Tasmania (off Australia).

Dedication

To

Danielle,

my first-born,

in lieu of the book I still have to write

for her.

Figure 1: C/2012 S1 (ISON), the hoped for ‘Great Comet of 2013’, imaged by the Hubble Space Telescope, in early October 2013, as it was heading for its sungrazing rendezvous with the Sun on November 28, 2013 (U.S. Thanksgiving Day). It got too close, as with Icarus of myth, and disintegrated. Only some debris rounded the Sun.

Figure 2: C/2011 W3 (Lovejoy), the ‘Great Christmas Comet of 211’ (albeit only seen in the Southern Hemisphere), imaged on Christmas day 2011, in Queensland, Australia, by ‘Naskies’ (& posted on Wikipedia).

Figure 3: Closeup of numbered periodic 67P/Churyumov–Gerasimenko obtained by combining 4 images taken by the ESA’s robotic spacecraft Rosetta’s navigation camera, in September 2014, when it was just 18-miles away from the comet – 8-weeks ahead of ESA’s Philae lander making a more-or-less soft landing on the comet. This is one of the closest & most detailed pictures we have, to-date, of a comet. More on Rosetta/Philae in Chapter 8. The resemblance to a Chinese pottery horse overall, or the roaring lion’s head on the right, has to be considered a coincidence.

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Table of Contents

Preface

Notes for Reading This Book

1. What, When, Where & Why

2. The Anatomy of a Comet

3. The Origins Of Comets

4. The Orbits Of Comets

5. The Discovery Of Comets

6. The Naming Of Comets

7. The Brightness Of Comets

8. The Exploration Of Comets

9. Great Comets

10. Meteor Showers

Essential Vocabulary

Useful Web Resources

Metric Conversions

Preface

I am lucky in that I, despite being a habitual Northern Hemisphere dweller, am old enough to have seen at least one mesmerizing comet. That was ‘Hale-Bopp’ (i.e., C/1995 O1) in 1997. I have seen two others, one (viz., C/2011 L4 (PANSTARRS)) through binoculars in 2013, & the other (viz. C/1973 E1 (Kohoutek)) faintly, in the 1970s. Seeing ‘Hale-Bopp’, in its glory, night-after-night, was magical. I so want to experience another like it, & alas, circumstances do not permit me to move to the Southern Hemisphere, where, based on what has transpired of late, my chances might be better. But, when it comes to comets, I am not selfish. I want others, including my kids, to have the privilege of seeing a naked-eye comet – even if it is not truly a ‘great’. It is an absolute shame that we currently have a generation (or more) of folks in North America & Europe that have yet to see a naked-eye comet emblazoning the sky.

In 2013, I expended much time & effort hoping that ‘ISON’ (i.e., C/2012 S1) might prove to be an unforgettable ‘great’. A comet that might even have been daylight visible! It, sadly, was not to be. It, as it got real close to the Sun, travelling at over 225,000 mph (i.e., 62.5 miles per second), started to catastrophically disintegrate. I was having Thanksgiving dinner with a family of recent refugees! I always knew that ISON going ‘poof’ was a possibility – but it was a terrible letdown. I had written three books on ISON, set up a blog & done numerous public presentations. And in the end, there was nothing to show for it. No naked-eye comet. Truth be told, I have been waiting for another ISON ever since.

Comets are unpredictable. Comets beguile. That is a part of their charm. I know all of that.

There have been a few promising candidates, but they never delivered – at least not for us in the Northern Hemisphere. And just in case you are wondering, I am not obsessed re. ‘Hemispheres’. It just that those ‘Down Below’ have been regaled by a number of ‘good’ comets in the 21st century – including two outlandishly spectacular ‘greats’ in 2007 & 2011. But, for those, up North. NADA. Zilch.

In 2020, we had the promise of both ‘Comet ATLAS’ (i.e., C/2019 Y4) & ‘Comet SWAN’ (i.e., C/2020 F8). ATLAS, alas, started to disintegrate even before it got past Mars. That was unexpected & a shame. Comets usually are still solidly frozen & nonfragile that far from the Sun. Not so, ATLAS.

SWAN made it around the Sun, intact, but remained hard-to-see, naked-eye. It would have been so great if either or both of these comets ‘put on a show’ during April, May or June of 2020. This was the year of the COVID-19 pandemic. A bright comet in the sky in May would have been an unmistakable beacon of hope & resurgence. The worst was over. We are cresting the hump. That, again, alack, was not to be.

I started writing this book initially in the hope of ATLAS & then SWAN. I started writing it in early 2020 & hoped to get it published by May. Well, it looks like I will still meet my self-imposed May deadline – though ATLAS is now but history & SWAN remains elusive. C’est la vie.

I wanted to write this book. It was on my ‘Bucket List’.

I like comets. I like writing about comets, asteroids & dwarf planets. I, to my amazement, discovered that there was no real, definitive ‘Guide to Comets’ book readily available. So, I am glad I wrote this book. The goal of this book is very simple & straightforward. I want you to get to know comets. I want to make comets ‘accessible’. Demystify them. Show you what they can do – in terms of transforming the night sky. I want you to dream about comets. I want you to look forward – like I do – for the next ‘great’. I want you also to like comets.

There should be nothing complicated about this book. Just a simple, non-formal narrative. Me ‘talking’ to you, one-on-one. Below I provide a few notes as to how the book is structured. But, it should really be self-explanatory.

I hope you like this book. Even if you don’t, I am sure you will learn from it. That is good. That will make me happy.

I am a denizen of the Web. I am easy to find on the Web. You can contact me by e-mail at: [email protected].

Anura Gurugé

Lakes Region, New Hampshire

May 2020

Notes for Reading This Book

‘Essential Vocabulary’ (i.e., a glossary) can be found towards the end of the book; after Chapter 10 ‘Meteor Showers’. If you are new to comets you may want to have a quick skim of it before you start.

Comet names are ‘shaded’, for emphasis, when they first appear in a given section of narrative; e.g., C/1965 S1 (Ikeya-Seki).

Formal & correct designations for comets are in the forms: C/year nn (Names), 1P/(Names), P/year nn (names) etc. Examples: C/2020 F8 (SWAN), 1P/Halley, 1P/, 1P, P/2012 T1(PANSTARRS).

Use of highlighting: Various types of text highlighting has been used extensively and sometimes arbitrarily: (1) for emphasis & (2) to denote ‘value-added’ background details.

One irrefutable advantage of eBooks is that they support color at no extra cost. So, color has been (hopefully) judiciously for emphasis & to break & delineate sections.

Figures & references within the book are shown in purple.

You should be able to skip around the book – if you so desire.

The orbital diagrams used in the book are based on those provided by ‘JPL’. Refer to ‘Useful Web Resources’ section towards the end of this book.

‘Words’ (‘phrases’) in quotation marks: Used to indicate when words/phrases that are either: used outside of their conventional context, proper names, or being afforded emphasis.

Figure 4: Long-term comet C/1965 S1 (Ikeya-Seki), ‘the great of 1965’, the brightest comet since reliable records started to be kept in 1935. It was not just naked-eye visible; it was daylight visible when it was close to the Sun (though you had to block the Sun with your hand or another object to eliminate its glare). This comet gets mentioned quite a few times within this book. This picture was taken, in 1965, by James W. Young (TMO/JPL/NASA) & can be found on Wikipedia.

Figure 5: Close up of periodic, short-term comet 9P/Tempel, taken by NASA’s robotic spacecraft Deep Impact, on July 4, 2005, from 311-miles away, 1.67-seconds after a 820-pound Impactor capsule fired by the spacecraft crashed into the comet to create a dust cloud that could be analyzed to determine the makeup of the comet. More on this exploratory-mission (and all the others) in Chapter 8.

1. What, When, Where & Why

What?

A comet is an icy, frozen cosmic snowball covered in dirt and dust. Comets originate in the far reaches of the solar system. A comet (like a planet) is bound to the Sun (as in, it is loosely tied or ‘coupled’ to the Sun). As such it orbits the Sun. The orbital path of a comet