Sky-High 2013 Transit of Venus 2012 This is the 21st annual guide to astronomical phenomena visible from Ireland during the year ahead (naked-eye, binocular and beyond) by John O’Neill and Liam Smyth Published by the Irish Astronomical Society 75 years in Astronomy in 2012-13 € 5 (Phone: 087-6398143) [email protected] www.irishastrosoc.org Page 1 Foreword Contents We send greetings to all fellow astronomers and welcome you to this, the twenty-first edition of 3 Your Night Sky Primer our annual almanac for Irish Observers, Sky-High. 5 Sky Diary 2013 We are always glad to hear what you liked or what Phases of Moon; Sunrise and Sunset for you would like to have included in Sky-High. And if 8 you like to clarify your understanding of anything 2013 feel free to contact us at the Society e-mail ad- 9 The Planets in 2013 dress [email protected]. Any updates or errata for Sky-High will be posted at the 12 Eclipses in 2013 Sky-High 2013 web page (see page 27). 13 Comets in 2013 Please acknowledge use of Sky-High if it has helped you. 15 Meteors Showers in 2013 We thank the following contributors for their arti- 16 Asteroids in 2013 cles: John Flannery and James O’Connor. The re- maining material was written by the editors John 17 Variable Stars in 2013 O’Neill and Liam Smyth. The times of sunrise, vari- able star minima, etc. are from software by 20 Space in 2013 J. O’Neill. The charts were generated using Guide 9. LPV Maxima are from Elizabeth Waagen (AAVSO). 22 Tales of the Unexpected This year the electronic version is made available 25 A Touch of Nostalga to download free (i.e. without cost), for personal use only. 27 Useful web sites Wishing you clear skies for 2013, 28 Gallery John O’Neill and Liam Smyth Sky-High 2013 © IAS, 2012 The Irish Astronomical Society The Irish Astronomical Society was founded in The Society also has a well stocked library of 1937. It caters for those of all ages and interests in books, journals and videos that members can bor- astronomy and space. row as well as access to a number of telescopes that can be loaned for a period. You don’t have to be an expert to be part of our society. Many of our members are taking their A number of IAS members have made their own first steps in the hobby and you are sure to receive telescopes, while others possess telescopes ranging friendly advice from some of the more experienced in size to well above 50 cm aperture. Many are now amateur astronomers among us. experimenting with the latest technologies to hit the amateur community such as robotic tele- Activities include monthly meetings, receiving scopes. our bi-monthly newsletter Orbit, observing groups, e-mail alert notices of transient astronomical phe- If you are considering purchasing a telescope nomena such as aurora, and outings to places of then we’ll point you in the right direction before astronomical interest. you part with your hard-earned cash. Members have joined expeditions to observe The Dublin Sidewalk Astronomers hold public several total solar eclipses world wide. Also note, star parties at regular intervals, usually by the the printed Sky-High is a free benefit of IAS seafront in Sandymount, Dublin (see IAS website membership. for details). Page 2 Your Night Sky Primer As with any hobby, astronomy seems to have For more detailed studies, especially with bin- its own set of terminology designed to confuse. oculars or a small telescope you will need a more However, with a little patience you'll soon pick up detailed map showing all stars to at least sixth the jargon and be well on the way to knowing your magnitude. A handy atlas is the Pocket Star Atlas way around the sky. published by Sky Publishing (for about €15). This shows stars to magnitude 7.6 and the positions of The revolving heavens many deep sky objects. We all know the Heavens don't revolve, it is the other way round, the Earth rotates on its axis. But An idea of size or scale it looks otherwise and it is easier to describe things If you have seen a picture of a total eclipse of as we see them for our immediate purpose. The the Sun you will have noticed that the black disk of fact that the Earth turns on its axis about every 24 the Moon just about covers the bright disk of The hours causes the Sun to rise in the east and set in Sun. If you were to suspend a one Euro coin about the west, and it is due south at noon. A similar two and a half metres in front of your eye, it situation applies to all the other heavenly bodies would just about cover the Moon's disk. except that since they appear to move relative to the Sun they are not south every day at noon. The Sun is nearly 1.4 million km in diameter, the Moon is 3476 km and the one Euro coin is just The stars appear to drift west in such a way over two centimetres in size. Yet they appear that any particular star is due south four minutes nearly equal. This is because they all seem to take earlier each day or night. If you multiply four min- up the same amount of the space in front of our utes by 365 you get something close to 24 hours. eyes. We may say they have the same angular di- So if a star is south at eight o'clock tonight, it will ameter. In this case it is about half a degree (½°). be south four minutes earlier tomorrow, and two hours earlier in a month. In six months it will be Degrees are further divided into 60 arcminutes south at about eight in the morning. In a year it (60') with each arcminute made up of 60 arc- will again be south at eight in the evening. It fol- seconds (60"). The scale allows us to measure an- lows that we see different constellations in differ- gles in the sky or apparent size of a celestial ob- ent seasons, but over a year, we see all that por- ject. For example, the Full Moon measures an aver- tion of the heavens that can be seen from Ireland. age of half a degree, or 30 arcminutes, in diame- ter. Star maps You will need at least one star map. This could Your closed fist held at arms length is about ten be a set of monthly charts such as are included in degrees (10°). Your stretched out hand, i.e. from many books on astronomy. A Planisphere is very the tip of your thumb to the tip of your little fin- useful. They come in various sizes at equivalent ger, is about twenty degrees. Between four and cost. It allows you to show the constellations visi- five outstretched hands or twice as many closed ble at any time of the night, any time in the year. fists will take you from the horizon to zenith. If you know the Plough you will find that its overall You could get away with using the monthly length is rather more than one outstretched hand - charts published in newspapers but there are a it is almost 25 degrees. couple of drawbacks. Each chart is correct for only one time on a given night, say 10 p.m. If you are Some familiarity with angular measure is neces- observing two hours later you would need the fol- sary to find your way easily about the sky. lowing month's chart. These charts also show the planets visible for a particular month, so they can Positioning in the sky be confusing unless you tippex them out. When Starting at any landmark and going right around learning the constellations check first from the the horizon is three hundred and sixty degrees. The monthly notes if there is a bright planet in the azimuth of an object is a measure of its position area. relative to the horizon as measured from true north which starts at 0° with due east being 90° Once you can find the constellations you will and so on. Going from a point on the horizon enjoy learning more about them. straight up to the point overhead - the zenith - is ninety degrees and a measure of altitude. A useful guide is the Collins Stars & Planets Astronomers use a kind of celestial longitude (now in its 4th edition) which has constellation and latitude called right ascension and declina- charts as well as all-sky charts, along with sections tion to accurately plot the position of an object in on the stars and planets. the sky. Page 3 halt, move back to the right, halt, and then re- The basis for this system is the equator and the sume direct motion once again. poles. Right ascension is expressed in hours (h), min- A note on time utes (m) and seconds (s) running eastward from 0 Times throughout Sky-High are given, unless to 24 hours around the equator. The zero point of noted otherwise, in Universal Time (UT). This is right ascension is taken as the vernal equinox - the the 24-hour system starting at mean midnight as point where the Sun crosses the celestial equator, measured at Greenwich. It is the same as Green- moving from south to north, in its course around wich Mean Time GMT.