Storm Dunlop - 2021 Guide to the Night Sky Southern Hemisphere

Contents

Time Zones

The times of events in this book are given in Coordinated Universal Time (UTC), here abbreviated to Universal Time (UT). This time is equivalent to the time on the Greenwich meridian (GMT), and is used by astronomers around the world so that observations may be compared easily, without having to convert from local (zone) times. Universal Time is always given on a 24-hour clock (sometimes known as military time or Zulu, Z). In many countries times are generally given as a.m. or p.m. and such times are shown on the charts showing the appearance of the sky for each month. Giving the times of individual events as a.m. or p.m. would be complex and confusing, so those times may need to be converted from UT.

Australia

Australian time zones are shown on this map. There are three: Australian Western Standard Time (AWST); Australian Central Standard Time (ACST); and Australian Eastern Standard Time (AEST). Some individual states (Western Australia, Northern Territory and Queensland) do not use daylight saving time (DST) during the summer months. To obtain local (zone) time from Universal Time (UT), add the hours shown in this table. If the result is greater than 24, subtract 24 hours. If the initial or subsequent result is less than 12:00, the zone time is a.m.; if greater, subtract 12 hours to get the time p.m. The dates when Daylight Saving Time begins and ends are shown on the individual calendars inside the book. At the time of writing, it is introduced on the first Sunday of October and ends on the first Sunday in April.

New Zealand

New Zealand uses a single time zone for the North and South Islands: New Zealand Standard Time (NZST) which is 12 hours ahead of UT. Daylight saving time (NZDT) is used in the summer, and begins on the last Sunday in September and ends on the first Sunday of April. (Note that it begins one week before the Australian start of Daylight Saving Time.) As for Australia, the hours shown above should be added to Universal Time (UT). If the result is greater than 24, subtract 24 hours. If the initial or subsequent result is less than 12:00, the zone time is a.m.; if greater, subtract 12 hours to get the time p.m. The dates when Daylight Saving Time begins and ends are shown on the individual calendars inside the book.

South Africa

South Africa uses a single time zone: South Africa Standard Time (SAST). This is two hours in advance of UT. Daylight Saving Time / Summer Time is not used. To obtain local (zone) time, add two hours to UT. If the result is greater than 24, subtract 24 hours. If the initial or subsequent result is less than 12:00, the zone time is a.m.; if greater, subtract 12 hours to get the time p.m.

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Text and illustrations Storm Dunlop and Wil Tirion

Photographs see acknowledgements .

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A catalogue record for this book is available from the British Library

eBook Edition Sep 2020

ISBN 9780008399801

Version: 20200624

Contents

The aim of this Guide is to help people find their way around the night sky, by showing how the stars that are visible change from month to month and by including details of various events that occur throughout the year. The objects and events described may be observed with the naked eye, or nothing more complicated than a pair of binoculars.

The conditions for observing naturally vary over the course of the year. During the summer, twilight may persist throughout the night and make it difficult to see the faintest stars. There are three recognized stages of twilight: civil twilight, when the Sun is less than 6 below the horizon; nautical twilight, when the Sun is between 6 and 12 below the horizon; and astronomical twilight, when the Sun is between 12 and 18 below the horizon. Full darkness occurs only when the Sun is more than 18 below the horizon. During nautical twilight, only the very brightest (navigation) stars are visible. During astronomical twilight, the faintest stars visible to the naked eye may be seen directly overhead, but are lost at lower altitudes. At Sydney, full darkness persists for about six hours at mid-summer. Even at Christchurch, NZ (not shown), full darkness lasts about four hours. By contrast, as far south as Cape Horn, at mid-summer nautical twilight persists, so only the very brightest stars are visible.

Another factor that affects the visibility of objects is the amount of moonlight in the sky. At Full Moon, it may be very difficult to see some of the fainter stars and objects, and even when the Moon is at a smaller phase it may seriously interfere with visibility if it is near the stars or planets in which you are interested. A full lunar calendar is given for each month and may be used to see when nights are likely to be darkest and best for observation.

The celestial sphere

All the objects in the sky (including the Sun, Moon and stars) appear to lie at some indeterminate distance on a large sphere, centred on the Earth. This