MAY 2016 The May 2016 Newsletter of the Dunedin Astronomical Society We had a good couple of nights with the recent “Wild Dunedin” open evenings. The cloud and rain marred one night but we were well received and gained a potential member or two along the way. Thanks to those who turned out to show the public some wonders of our skies. The highlight of the month is the eta Aquarii meteor shower on the 6th, expect 40 to 60 meteors, well worth an early morning rise to see these, as the moon is new and just cloudless sky required. I thought that with the large and very welcome influx of new I2A members, an article about the “basics” may be useful, and a good grounding into finding your way around. Located towards the end, if this leads you to a question or need a further explanation, please don’t hesitate to contact me on the email address. Welcome to your Dunedin Astronomical Society!

Presidential Piece At a recent committee meeting, a comment was made along the lines of “who was Beverly Begg”? The immediate response was that there is information posted around the walls of the annex. But with that, it’s a fair question and, bearing in mind that the Society has existed for over a century, and one of the committee members has been involved for over 40% of that period, it would be unfair to assume that more recent members would be aware of the rich variety of membership and history. I will take it on myself to share some of the Societies background over the following months. There is a booklet available covering the first 50 years, just ask; it is a worthwhile read. A considerable amount of meeting minutes and records are stored in the Hocken Library. Cottage: Next Saturday night could be a perfect opportunity to look at the three planets now perfectly placed, there is also a bright comet in our sky (see the comet section). Let me know if you are interested. Our “Introduction to Astronomy” course is scheduled to commence in the middle of May. Having just 34 seats in the annex, that is the limit of our attendance so it looks like we have to consider a second course such is the interest in the Astronomy! If anyone is available to help on the nights we hold the sessions please speak to any of the committee members, just having a few extra hosts would be of great help. First night is Tuesday 17th May, 7 pm start. On a more tempered note on returning home from the long weekend I checked my answer phone to learn that an old friend of many members and of the Society, Clive Rowe, now living in Nelson is seriously ill. Clive has been

an active innovative promoter of Astronomy for most of his long life, no one quite like Clive. We wish him all the best. Clear skies, Ash Pennell

Notebook for May Mercury will transit the Sun on the 9th but sadly, this rare event isn’t visible from NZ shores. Mercury is too close to the sun to observe at the start of May but becomes a morning object after the inferior conjunction, visible some 60 minutes before the sunrise by May’s end. Venus is close to the sun all month and I won’t recommend your seeking it out for obvious reasons. Mars reaches opposition on the 22nd and is now bright at -2 magnitude or so. Look to the Scorpius region, Mars is very obviously red, displaying dark markings through a good scope.

Jupiter still sits in Leo and will do so all month. At the society cottage night, the seeing was superb and we could visually see 5-6 bands and the famous “great red spot”. This picture was taken by S. Todd with a Philips SPC900NC webcam and the Meade 10” SCT. The picture is a stack of 780/3400 frames using the freeware Registax6 program. Jupiter and the moon will form a lovely close pair on the 15 th.

Saturn is becoming better placed now as it rises in Ophiuchus but is a bit low in the evening. A good view is afforded in the wee small hours in May when Ophiuchus is higher and therefore behind less atmosphere. Uranus remains in Pisces and just at naked eye visibility at magnitude 5.9. Easily found with binoculars using the finder chart, limiting magnitude is 12.

Neptune is visible with binoculars or small telescope at 8 th magnitude. Languishing in Aquarius, a good finder star is lambda Aquarii (above the water jar asterism), the two very close mid-month. Finder chart limit is 7th magnitude.

Pluto is faint and still in the 14s, sitting in Sagittarius.

May Comet Watch (mv<=13) 252P/ LINEAR reachable in binoculars and sits in the northern part of Ophiuchus. Now at around 7th magnitude, this comet is a good target for your binoculars, small telescopes and DSLRs. We will have a go at locating this one from the Cottage night vantage point in Sutton.

Comet 116P/Wild is in Scorpius still, but on our limit of inclusion here. This comet will reach a magnitude of 11.6 or so before fading once more.

C/2013 X1 (PANSTARRS) has brightened to a reported 9th mag and will travel from Pisces to Aquarius in the morning sky.

81P/Wild is becoming difficult to see as it stays low down along the north western horizon as it brightens towards a predicted maxima of 8.6 in July.

9P/Tempel or Tempel1 is in Leo, making a curl around Denebola at the eastern end of the lion. Brightening from 11.8 to 11.2 during May, use the chart to point your telescope in the correct place.

May Meteor Showers Big things for May as the famed eta Aquariids peak at dawn on the 6th. The radiant is the famous “water jar” asterism. The good news is that there will be no moon to interfere so the display should be fantastic and expect a maximum ZHR of 40+ meteors! The meteors in the eta Aquariids are the first of two showers that occur each year as a result of Earth passing through dust released by (1P/Halley) Halley's Comet, with the second being the Orionids. Halley's Comet does not currently have an orbit that brings it near enough Earth orbit to produce a meteor shower, but this was not the case centuries ago. Several minor showers present themselves in May also. The Librids run between the 1st and 9th with peak of 6 meteors an hour on the 6th. The weak Northern May Ophiuchids discovered in 1896 run from early April to 16 th June with a peak ZHR of 3 or so on the 18 th. Again, with a ZHR of 1-4, the long running (21st April to 4th June) Southern May Ophiuchids will be difficult to pick from the mean sporadic rate. Being slow runners however, it should be easy to trace the trails towards Ophiuchus if indeed, your meteor is one of these. In the May mornings, the Sagittariids should give a rate of 5-7 per hour, this shower peaking on the morning of the 20 th. More out of interest, the epsilon Aquilids (May 4th to 27th) are apparently only visible with some optical aid, as no visual or photographic detection has ever been made. The discovery of the epsilon Aquilids should be credited to B. L. Kashcheyev and V. N. Lebedinets (Kharkov Polytechnical Institute, USSR), who detected 17 radio meteors from this stream during May 1960. No visual observations of this stream appear in any records of the last 150 years.

Constellation of the Month With many new members on board (and hopefully you got this far!), I want to introduce Crux, the Southern Cross. Just take time to browse the area with binoculars. Full of glittering stellar clusters and clouds of dust. It is also a great starting point in learning your skies. With astronomy apps, planetarium software aplenty and GoTo mounts the norm, learning the constellations is a bit of a dying art. Crux contains double stars, a cluster, variable stars and a dark type of nebula too! Smallest of the 88 constellations, it was visible to the Europeans in 4000BC and the classical Greeks considered it a part of Centaurus, which now surrounds it on 3 sides. The effect of “precession” saw Crux disappear from European eyes by 400AD. Historians generally credit João Faras, who accompanied Pedro Álvares Cabral in the discovery of Brazil in 1500, for being the first European to depict it correctly. Faras sketched and described the constellation in a letter written on the beaches of Brazil on May 1, 1500, to the Portuguese monarch Manuel I.

Alpha Crucis or “Acrux” at the point end of the cross is the brightest star in the cross. It is a multiple system with hot spectral class O9-B0 stars the two brightest components visible to us. At 320 Light Years (Ly) away, the star is the southernmost 1st magnitude star. Beta Crucis “Mimosa” is a very hot, fast burning giant star with a companion star too close to separate visually. The system is therefore a variable and a third star in the Mimosa system was discovered by X ray observation n 2007. It is also a variable of the Beta Cepheid type, as are Lambda and Theta2. Gamma Crucis or Gacrux, is an optical double star. The primary is a red-hued giant star of magnitude 1.6. The secondary is mag 6.5 and lies some 264 light-years from Earth. A nice object in small scopes. The dimmest of the “cross” is unsurprisingly Delta Crucis. A white star at 265 Ly from us. Have a go at Mu Crucis with your scope or large bins. It is a visual double star at 370 light-years from Earth. The primary is a blue/white star of mag 4, the secondary is at mag 5.1. Two famous objects of note in this constellation. Most obvious when looking with the naked eye is the Coal Sack Nebula. The dark patch of dust is the most prominent example in the skies, and certainly known to prehistoric southern hemisphere dwellers. The cloud of dust and “unexcited” gas lies at 600 Ly from our planet. Discovered by Nicolas Louis de Lacaille in 1751, The Jewel Box (or officially NGC 4755) is one of the most

beautiful open cluster in the southern night sky. Sitting at 6450 Ly distant, this famous cluster was named “the Jewel Box” by Sir John Herschel when he described its telescopic appearance as "a casket of variously coloured precious stones". It is easily visible to the naked eye as a hazy “star” some 1° southeast of the first-magnitude star Beta Crucis. Binoculars should resolve at least nine of its stars as a tight cluster, located between Beta and

the Coal Sack. Multi-coloured with more than 50 stars, Kappa Crucis is the orange supergiant near its centre. Always a popular sight on DAS public evenings! Variable stars are an interesting part of astronomy. Crux boasts four Cepheid variables that we can see. BG Crucis ranges from magnitude 5.3 to 5.6 over 3.3 days whilst T Crucis ranges from 6 to 6.9 over 6.7 days. S Crucis ranges from 6.2 to 6.9 over 4.7 days and R Crucis ranges from 6.4 to 7.2 over 5.8 days. BH Crucis, also known as “Welch's Red Variable”, is a Mira variable that ranges from magnitude 6.6 to 9.8 over 530 days. Crux is a great starting point to your “star hopping” adventures, learning the constellations without relying on modern tech. Crux points to the celestial pole and Hydrus near the Magellanic clouds, lies next to the “Pointers” in Centaurus, above Musca the fly, have a look with a star chart and work your way outwards.

Learning your way around the night sky – A beginners guide. Hints and tips by Stu Todd

Learning the night sky always seemed a daunting prospect when I first became interested in astronomy. So many stars, nebulae and planets which constantly moved around, not to mention the moon which seemed to come and go at will. Galaxies, planetary nebula, comets, meteors and the theory behind it all. Don’t be dismayed by the seemingly infinite. Keep it simple and take your time with the basics, you will be rewarded with a lifetime’s enjoyment of the beautiful and wondrous universe in which we live. The trick is to realise that no-one knows everything. One is always learning, the beauty of astronomy is that you can enjoy the universe in a multitude of different ways, be it just looking with your naked eyes, through binoculars or telescopes. Some people like taking pictures and imaging nebula, planets or the moon. Others may delve into photometry (recording stellar brightness changes) or spectroscopy (analysing stellar light). The society has an occultation section (no black chickens involved…) which looks for drops in star brightness as asteroids pass in front of them. Ash Pennell is our main force behind that aspect. Studying the light fluctuations of “variable stars” is also very valuable work, and, along with photometry, spectroscopy and occultations, amateur help is actively encouraged, nay positively required by the professionals to aid them in their studies. But we must begin somewhere and you have taken the best step by joining the Dunedin Astronomica l Society. Asking questions and helping out are great ways of learning and there are no stupid questions. The internet is a fantastic resource too but can be overwhelming. However, I began by learning a few pointers, I share these with you now.

 Imaginary Lines As every Earth based location has an “address” in longitude and latitude, so too do celestial objects. Instead of longitude and latitude though, we use “right ascension” (equivalent of longitude) in hours, minutes and seconds, and “declination”, (the equivalent of latitude), written in °, minutes (‘) and seconds (“). These are sometimes written as “R.A” or “α” and “dec” or “δ”. To make sense of how things move, imagine you are in the centre of a ball and the sky is the inside surface. Look directly up above your head. The point directly above is called the zenith (its opposite point below your feet is the nadir but not much use to us). We are at latitude -45° here in Dunedin, the point on which the Earth spins is 45° up from the horizon in the south, a point called the south celestial pole or SCP. This point is near a faint star in the constellation of Octans.

A great way to find the area of the SCP is to imagine a line through Crux (the Southern Cross constellation) intersecting another line which runs from between “the pointers” in Centaurus, as the above diagram shows. In relation to Dunedin, and distorted by perspective so bear with me, the SCP will look something like below. The circles represent 30° of declination, to the celestial equator marked +00 at the edges ...

We can see that if a star is within say 45° of the SCP, then as the Earth rotates, those stars will never set. These are said to be circumpolar and are visible all year round. As we move further north, stars will rise and set until we come to stars we can never see from New Zealand, those around the north celestial pole. INFO: If we were at the South Pole, the SCP would be at the zenith and no stars would set as the Earth rotates. On the equator, we would see the SCP and north celestial pole or NCP on opposite horizons and every star would rise and set as the Earth rotates.

Draw an imaginary line through the SCP and the zenith northwards so you have a line running due north and south. This is the meridian line, an important line for us to remember later. In order to get declination we need the celestial equator. This is a line running from west to east at 90° from the SCP (and NCP) and is the Earths equator (as imagined) projected onto the celestial sphere. Declination is written as +0 to +90° for objects north of the celestial equator, and as -0 to -90° for objects south of the celestial equator.

Half our co-ordinate system sorted already. Now for right ascension, the starry equivalent of longitude. This is written in hours, minutes and seconds, like the time. But where to begin? Where is 0 hours? The yellow ecliptic line in the above diagram gives us a clue. If the Earth wasn’t tipped over the Sun, planets and moon would pretty much follow the celestial equator as we head on our 365.24 day passage round the Sun. However, the Earth is tipped over by 23.5° as it spins. As the sun appears to move against the background stars throughout the year as we travel round it, the path it (and the moon, planets) takes is a 16° wide band through the sky called the ecliptic. You will be familiar with “star signs”, constellations through which, the ecliptic passes. Virgo, Libra, Scorpius, Sagittarius, Capricorn, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo and…Ophiuchus. When the sun crosses the celestial equator in the autumn we get the Vernal equinox (20th March or so). This point is where our 0 hour of right ascension is located. The hours of right ascension then run eastwards from that point. INFO: The “equinox” translates to “equal night” and occurs at the point when the sun crosses from one hemisphere to the other in the yearly cycle. It is the only time when the north and south hemispheres are equally illuminated by the sun, hence the name. The Vernal equinox is also called the “first point of Aries”, so named by Greek mathematician and astronomer Hipparchus in 130 BC. Due to the effect of precession, this point now falls in neighbouring Pisces. Our spring equinox is called “first point of Libra” but now lies in Virgo!

Ok, I hope you haven’t fallen asleep or got lost yet. We need a few more terms before we are done. 

Sidereal time and Precession

At the start I said every object has a R.A and dec assigned to it, a map reference. I now give you an example from a planetarium program I use called C2A. We are going to deal with a real object; its co-ordinates are

R.A: 14h 39m 36s

Dec: -60° 50’ 07”

Ok. Our target is about 2/3 between 14 and 15 hours. Follow with a finger. Now look for the declination. The curved lines are in 5° increments so find the -60° line. Declination is presented in degrees (°), minutes (‘) and seconds (“). Minute is 1/60th of a degree and a second is 1/60th of a minute or 1/3600 of a degree. So 60° 50’ is just shy of 61°… What have you found? Answer at the end!

The Earth spins once every solar day, our familiar 24 hours. However, during that day we have gone just over 1/365th of the way around the Sun. This gives rise to the sidereal day, some 23 hours 56 minutes long. Remember our meridian line? A star crossing the meridian at 20.00pm today will be crossing the meridian some 4 minutes earlier, 19.56pm tomorrow due to our 1/365th passage round the sun. So over a month, the difference is around 2 hours! This gives rise to the seasonal changes of stars and constellations, and the reason the sun appears to travel along the ecliptic through the zodiac! As an object crosses the meridian, it reaches its highest point in the sky, it is said to reach culmination. The best time to view the object is at that time, at its highest and with least atmosphere to look through. So the right ascension of an object is the culmination time of the object in sidereal time. Online calculators are freely available to do the math for you, or indeed, your favourite planetarium software. One last point before you grab the paracetamol, the whole co-ordinate system is shifting! The Earth is slowly wobbling like a spinning top (albeit very slowly) taking 26,000 years to complete a circuit. That is precession, the reason the points of equinox have changed and why the south and north celestial poles are moving too, and therefore the whole R.A and dec grid. INFO: Out of interest and due to precession, the famous ancient Greek constellation of Centaurus the Centaur can’t be seen from Greece anymore! Not to stress though. Astronomers use star charts which are updated every 50 years (for the hard copy ones available in the observatory), the latest are epoch 2000 or J2000.0. Although 16 years out of date and precession has moved the co-ordinate system, it is only by a small amount, good enough for us mere mortals. Most planetarium software can display the sky in Jnow, bang up to date for the day! I hope that has helped you grasp why things move the way they do and how to read charts and find objects. Once you know where the SCP is, the meridian and had a look at the society’s Orrery, it will all fall into plac e with breath-taking logic. I would urge you to learn the constellations by NOT looking at an iPad screen or iPhone app. Where is the fun in that? It is more impressive to name a star or constellation before a tech equipped competitor has had chance to warm up their device. Just my thought…

Zenith – the point directly above an observers head. Celestial pole – the point on which the Earth seems to rotate, located at 45° above the horizon from Dunedin. It is seen at the zenith in the South Pole, on the horizon at the equator. Celestial Equator – runs through the sky at 90° to the celestial poles. Meridian – an imaginary line running through the celestial poles and passing through the zenith. Culmination – an object reaches culmination when it crosses the meridian line and is therefore at its highest point in the sky. Ecliptic – the apparent path of the Sun, Moon and planets in relation to the background stars as we orbit. Tilted 23½° to the equator. Right Ascension – R.A or α – hours, minutes and seconds. Celestial longitude, the sidereal time of an object crossing the meridian. 0 and 24 hours are at the points where the ecliptic crosses the celestial equator and the Sun passes from one hemisphere to another. Sidereal time – “star time”. An object at the meridian will cross the meridian again in 23 hours 56 minutes, not 24 hours (the solar day) due to the Earth having travelled 1/365 th of the way round the Sun. The right ascension of an object i s the sidereal time of its crossing the meridian. Declination – dec or δ – degrees, arc minutes and arc seconds. Starting from the celestial equator. 0° to -90° for south of the celestial equator, 0° to +90° for north of the celestial equator.

Any Other Business 

It is good news to see the cottage at Middlemarch being used on a more regular basis as all members are welcome and encouraged to use the facilities. However, with running such a facility there are costs involved and when we made the buildings available in 2001, the arrangement was that self-sustainment was the key. Simply put - if you use the premises there is a gold coin charge. Please leave in the tin on the mantelpiece. You carry in what you require and leave the premises tidy, filling in the log book before departing.

Sometimes there may be a situation that requires attention i.e. gas bottle, wood repair or whatever - please do not leave unwelcome surprises for those next visiting. THEMS THE RULES! Enjoy the facilities. 

Alpha Centauri news http://www.msn.com/en-nz/news/techandscience/what-do-we-know-aboutalpha-centauri/ar-BBrN8KU

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FOR SALE: Atik 414Ex mono CCD camera in mint condition.

My new 414 has been used once for 15 minutes but is surplus to requirements due to fringing issues affecting high resolution spectroscopy. This doesn’t affect normal usage whatsoever. Asking around $1950. “The Atik 414EX is the most sensitive camera in our range, and perfect as a first cooled CCD camera. It follows in the footsteps of the world renowned Atik 314L+, and with 60% more sensitivity at 650nm, it’s proudly living up to the exceptional standard set by its predecessor. The generous 6.45 µm pixel size not only adds to its exceptional sensitivity, but also makes it suitable across a broad range of telescopes, from short focal lengths with a reducer right up to longer focal lengths not catered for in a small pixel camera. The incredible Sony ICX825 EXview sensor combined with our high performance 4-Series design really does set the standard for cooled CCD cameras”. For more details contact [email protected] or 027 663 1711

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Please feel free to forward questions and thoughts to me via the [email protected] address, or on the Facebook page at https://www.facebook.com/Dunedin-Astronomical-Society276103432412175/

Clear Skies!

Alpha Centauri