Wadhurst Astronomical Society Newsletter November 2014

Transcription

1 Wadhurst Astronomical Society Newsletter November 2014 MEETINGS OCTOBER MEETING The October meeting was opened by Phil Berry who, after outlining the evening s programme, talked about the Dark Skies event to be held in February next year. As mentioned in the last Newsletter, the High Weald AONB (Areas of Outstanding Natural Beauty) is joining together with the Campaign for Dark Skies and ourselves to hold a public awareness event regarding the dark skies in the Wadhurst area to be held on the 25 th of February There will be a large indoor planetarium holding about 80 people at a time at 2 a head. There will be two children s showings, one at 1830 and another at 1915, then one for adults at At the same time we will have some of our telescopes for people to see and with luck we may be able to have some viewing if the sky is clear enough together with some constellation recognition. Our Chairman, John Vale-Taylor was then introduced who gave a short talk about the Society s telescopes. Last Chance Saloon John Vale-Taylor The Society owns a number of telescopes and the Committee wish to reduce the number and think one of them should be offered to members. John showed a picture of this telescope, which is a Bresser refracting 60 mm telescope with two eye-pieces, 22 mm and 30 mm both with the 24 mm diameter fitting. The telescope has its own finder scope all on a manually adjusted equatorial mount fitted onto a sturdy tripod. Anyone interested in this telescope should contact John. Bresser 60 mm telescope on offer to members. Then Phil introduced tonight s speaker. My First Steps in Planetary Imaging Jan Drozd Jan is a well-known member of the Society and has given many interesting talks about various aspects of science and astronomy, but as he explained this is the first time he has spoken about his own practical experiences. For some time he has been interested in the techniques of astro-imaging and now talks about his early achievements.

2 He began with the very first surviving photograph taken in France in 1827 of a roof scene taken on bitumen which hardens on exposure to light but taking 8 hours to expose. This was followed by a brief description of the development of photography over the years that used various chemical methods. Then in the early 1990s the first digital cameras began to appear on the market which had what Jan called colour-blind sensors converting optical images into electrical signals and needing red, green and blue filters to produce a colour image. There are two basic types: the CCD where the pixel charge is moved to one end of the sensor and then converted into a voltage output. the other is the CMOS chip where the image is converted to a voltage in each pixel. Then Jan explained how a mosaic coloured filter layer now placed in front of the sensor is used to provide the colour information employing an amazing algorithm that works out the actual colour of each pixel by comparing the charge on the surrounding pixels. This is called the Bayer Colour System. Without the mask, the sensitivity of the monochrome sensor is much greater and making separate exposures with red, green and blue filters, then combining the results can produce images with much higher resolution. When astro-imaging, sometimes the required detail may only be in a small part of the image but by cropping and then increasing the image size overcomes this but results in pixilation where the individual pixels become obvious. A new development is to use free software called GIMP, which smoothes the picture by increasing the number of blocks in each pixel. Now Jan looked at the very first successful photograph ever taken of the moon and in fact the start of astrophotography. This was in 1840 and with a 20 minutes exposure, using a process called Daguerreotype. This was followed by photographs of Jupiter and Saturn taken in 1885 at the Paris Observatory by two French astronomers. We moved on to the 1930s, 40s and 50s with film and digital pre-space age images. Jan referred to a NASA web site that he said was a very good source of material on the history of astrophotography. Sometimes poor images gave rise to wild theories for example Percival Lowell s Martian canals. Part of the problem is due to turbulence in the Earth s atmosphere and here Jan talked about some of the solutions to poor seeing. Observatories need to be on high mountains and even better still, we can now use space telescopes such as Hubble. Another solution is to use Adaptive Optics, which is a new development in professional telescope technology where the mirror is made to distort and compensate for turbulent seeing. Jan now turned to amateur imaging by first mentioning Lucky Imaging where the atmosphere becomes steady just for a moment. Amateurs who use web-cams can take advantage of this by taking a series of images and then using free software called Registax to select the best images and then stack them together to produce stable and sharper images. To begin his own adventure into amateur astro-imaging, Jan bought himself a CMOS Orion StarShoot Solar Colour Imager IV costing just 85, intended for imaging lunar and planetary objects and using the Bayer Colour System. It had 1.3 megapixels. His second camera was a ZWO ASI120MM monochrome 1/3-inch CMOS USB2.0 camera costing 260 and was capable of exposures up to 1,000 seconds. ZWO ASI120MM CCD camera Jan s set up with his Dobsonian We were introduced to Jan s first telescopes, which included a Skywatcher 80 Refractor, a Meade ETX 105 mm Maksutov and a 203 mm Orion SkyQuest XT8i 8-inch Dobsonian. At present he uses a Celestron Advanced VX8 203mm telescope. We then looked at some of the challenges he encountered. Because the chip is so very small, it is extremely difficult to get the target onto the sensor and for this, an illuminated reticule eyepiece helped to line up the object before the eyepiece was replaced with the camera. Just 30 seconds of video can generate files as large as 6 GB but there is software to help such as Castrator or VirtualDub which is free to edit files and can be found by going to:

3 We were shown an image of Saturn Jan had taken using his Dobsonian, where the image was way off from the centre of the frame and wavering about because of the difficulty of stabilising the telescope with such a small chip. He used free software on the images called PIPP (Planetary Image Pre-processing) found through that magically centred Saturn in the frame and also offered the option to select the best images, reducing the file size. We were shown images of Saturn subsequently taken on the ETX 105 using polar alignment with the monochrome camera taken through red green and blue filters. A 3x Barlow lens was tried but the light loss proved a problem. Jan had included a number of images using different techniques and filters for comparison purposes. We were shown some images of Mars he had taken but we were told that at present the planet appears only about 5 arc-seconds across, never the less it was possible to make out the ice caps and other features.. Jan s image of Mars The Moon through Jan s 80 mm Skywatcher The Moon through the VX8

4 The first image Jan took of the Moon taken through the 80 mm Skywatcher was compared with images taken more recently through his ETX in monochrome and using an infrared filter to reduce glare and the detail was now very creditable. Finally we saw images taken on his Celestron VX8 for comparison. Jan concluded by saying that despite frustrations and confusions he had found imaging great fun but pointed out the importance of keeping detailed notes of what you have done. There are so many options such as telescopes and lenses, cameras and settings and software choices. He now intends to learn more about the construction of colour images using separate filters. Jan modestly compared his image of Jupiter with that taken by Damien Peach saying this was something to aim for Again, what Jan is aiming to achieve, this time with amateur Damien Peach s Saturn Red, Green and Blue Filters John Jutkin To begin, John told us how he had become infected by astronomy some time ago and became fascinated in various aspects, one of them being optical filters and their use in observation and astro-photography. The basic filters are red, green and blue with luminance in what is called the additive technique although as we were told there is also another system using Cyan, Magenta and Yellow called the subtractive technique. We mainly use the first system. For imaging purposes the filters are especially chosen to compensate for the response of the CCD chip, which is different from that of the human eye. We looked at the colour temperature scale where deep blue is the colour of a clear sky, equivalent to a temperature of 10,000 Kelvin, down to the red of a candle flame with a temperature of 1,800 Kelvin. John told us this is why hot stars are blue and cool stars are towards the red end of the scale such as red giants as they near the end of their life. The first filter we were introduced to was the neutral density filter (reducing all colours equally), used to reduce contrast and help control the amount of light so preventing the CCD from overloading. Then John talked about red, green and blue filters, the parts of the spectrum each one covered and how they come in different colour strengths. Particular filters being chosen for the CCD chip response. We were then introduced to the Wratten Filter Scale, a recognised way of specifying filters and originally intended for film cameras, each indicated by a number for example a dark blue filter is W47B.

5 John then gave a very useful guide to the various filters recommended for observing different objects in the Solar System and the reason why they were chosen. Mercury: Difficult to observe because of its visual size and closeness to the Sun. Use red (W25, W29), orange (W21, W23A), yellow (W15) and green (W57) Venus: Filters are used to increase the contrast because of the lack of surface markings. Use deep blue (W46, W47). When observing Venus in daylight, a red filter darkens the background blue of the sky. Baader make a specific filter for observing Venus. The Moon: A green filter (W57) is often used together with a neutral density filter. Mars: Yellow (W12, W15) brightens the desert regions and darkens the bluish and brownish features. Orange (W21, W23A) further increases contrast between the light and dark features, and helps penetrate dust clouds. Red (W25, W29) gives maximum contrast of surface features and enhances fine surface details, dust clouds and polar boundaries. Green (W57) darkens red and blue features and enhances frost patches. Blue-green (W64) helps detect ice fogs and polar hazes. Blue (W80A, W38, W38A) and deep blue (W64, W47) shows atmospheric clouds, discrete white clouds and limb hazes, equatorial cloud bands, polar cloud hoods and darkens reddish features. Magenta (W30, W32) will enhance red and blue features and darkens green ones. Improves polar region features and some Martian clouds. Jupiter: Blue (W28A, W80A) enhances the contrast within the bright zones and sharpens boundaries of faint cloud currents. Jupiter s belts are brown, both green (W57) and blue (W47) filters darken them. Yellow (W12, W15) will darken the blue festoons that appear near the North Equatorial Belt s southern edge and equatorial zone. Magenta (W30) great to brighten and enhance those white ovals seen in the South Temperate Belts and Zone. Saturn: Brighter patches sometimes appear and are best seen on green or blue-green light. The rings are highlighted using a light green (W57) filter and at times a magenta filter (W30). Uranus and Neptune: Yellow-green (W12), green (W57) and magenta (W30) filters are recommended on these bluish and greenish planets. Their blue-greenish colour begins to change to a bright blue using a moderately to large aperture telescope (12 to 24 inches).

6 NOVEMBER MEETING Wednesday 19 th November Members of the Society will be giving short talks about astronomically related subjects. One will be about Stellarium software and another about SOFIA, the NASA Stratospheric Observatory for Infrared Astronomy. FUTURE MEETINGS Wednesday 11 th December 2014 Our Director of Observations will be giving another of his popular talks. He calls the December talk The Story of Longitude. Wednesday 21 st January 2015 The AGM followed by John Wayte who is giving a talk he calls The Big Bang VIDEO CLIP OF THE PROGRESS OF THE ROSETTA MISSION Once again Phil Berry has gathered together a number of video clips from the internet to edit together information about how the Rosetta Mission is progressing after its launch by the European Space Agency in It showed how the mission has used Mars and the Earth to gain speed through sling-shot passes during its journey to gain the necessary speed and now, after a journey of over 6.4 billion km it has matched its speed to that of comet P67. The space craft has made a number of manoeuvres to get in close to the comet having made many observations of the surface partly to survey a place to set down the lander named Philae, which is expected to take place in December. Planets SKY NOTES FOR NOVEMBER 2014 Mercury reaches greatest western elongation on 1 st November when, in angular terms, it will be 19 from the Sun. With a maximum altitude of 11, this will be the best morning apparition of the smallest planet for Fig.1 shows Mercury s position on the day of elongation with the Sun 6 below the horizon as nautical twilight is ending and civil twilight is beginning, whilst Fig.2 shows how the planet s position changes in altitude and azimuth.

7 As you can see Mercury will be visible for the first half of the month after which it becomes too close to the Sun for observation. It reaches superior conjunction on 8 th December. Venus, having passed through a superior conjunction at the end of October, is too close to the Sun for observation this month. However, by the end of December or beginning of January, we should be able to glimpse it low down in the south west after sunset. Mars is visible quite low down in the south-south-west after sunset although its position will improve gradually over the coming months. Sadly both its apparent diameter and brightness are on the wane as the Earth, on the inside and faster orbit, pulls away from the red planet. The map in Fig. 3 gives its position in the middle of the month amongst the stars of Sagittarius around 13 above the horizon. Jupiter is now technically an evening object rising at GMT at the start of the month, and by at the end. The planet spends all of November moving direct (east to west) in Leo and continues to do so until it reaches its first stationary point early in December. Jupiter s magnitude rises slightly to -2.2 during November, whilst its diameter reaches 40 (forty arc seconds) by the end of the month. The motions of Jupiter s four largest natural satellites, known as the Galilean moons after the man who discovered them, can be followed with nothing more complex than a pair of binoculars. However, unless you can mount them on a tripod or secure them in

8 some other way it will be almost impossible to hold them still enough to be able to see Io, Europa. Ganymede and Callisto. Their ease of observation is due partly to their size. If they were bodies orbiting the Sun independently they are massive enough to be classed as dwarf planets in their own right. Ganymede for example, which is the largest natural satellite in the solar system, is larger than the planet Mercury. The Galilean moons are not, in fact, the closest bodies to the parent planet. There is another family of satellites orbiting even closer, although Metis, Adrastea, Amalthea and Thebe that make up the so called Inner Group are generally smaller. The position of Jupiter mid-month is shown in the maps below with Fig.4a providing a late evening view of the planet 8 above the eastern horizon whilst 4b shows it just past the meridian (nearly due south) at a height of 53 in the early morning. It is by far the brightest object in that part of the sky, so should be easy to identify given its proximity to the sickle of Leo. Saturn is in conjunction with the Sun on 18 th November and is therefore not visible this month. Following this the planet becomes a morning object and should be visible during the second half of December. It will be late March 2015 before it is an evening object again, although the change to BST will have an effect on this.

9 As far as planets outside of the Earth s orbit are concerned, conjunction refers to the time when the planet (either Mars, Jupiter, Saturn, Uranus or Neptune) is directly behind the Sun with reference to the Earth. At that time all three bodies are in a line with the Sun in the middle. If conjunction is the worst time to observe a particular planet, then opposition is the best. This is when the three bodies are again in a line, but now it is the Earth that is in the middle. Because the planet in question is opposite the Sun it will rise at sunset and set at sunrise being visible throughout the hours of darkness. Incidentally, Saturn next comes to opposition on May 23 rd Lunar Occultations In the table below I ve listed events for stars down to magnitude 7.0 that occur before midnight although there are many others that are either of fainter stars or occur at more unsociable hours. DD = disappearance at the dark limb. The column headed mm (millimetres) shows the minimum aperture telescope required for each event. Please remember that the Society has telescopes that members can borrow, all of which are suitable for the such events. Times are in GMT. Nov Time Star Mag Ph Alt % illum. mm 1 st Aquarii 7.0 DD th omicron Piscium 4.3 DD th ZC DD th Aquarii 6.6 DD Phases of the Moon for November Full Last ¼ New First ¼ 6 th 14 th 22 nd 29 th ISS Unfortunately there are no passes of the International Space Station (ISS) that occur before midnight during November. There are a large number that occur in the early hours of the morning and these can by found by going to Iridium Flares The flares that I ve listed are magnitude -2.0 or brighter although there are a lot more that are fainter or occur after midnight. If you wish to see a complete list, or obtain timings for somewhere other than Wadhurst, go to Remember that when one of these events is due it is sometimes possible to see the satellite before and after the flare although, of course, it will be much fainter at those times. Times are in GMT. Nov Time Mag. Alt Az. Nov Time Mag. Alt Az. 1 st (NNE) 15 th (NNE) 2 nd (NNE) 24 th (NNE) 3 rd (NE) 25 th (NE) 6 th (NE) 26 th (NE) 7 th (NE) 27 th (ENE) 13 th (NNE) 28 th (ENE) 14 th (NNE) 29 th (ENE) The Night Sky in November (Written for 22.00hrs GMT mid month) In the north the fact that Ursa Major is once again climbing away from the horizon means that we have lost both the bright star Arcturus and the constellation of Corona Borealis from view, though by way of compensation the winter groups are now appearing. The great bear contains a myriad of galaxies, the most popular photographically being M81 and M82 that lie a little over half a degree apart. M81 is also known as NGC 3031 or Bode s Nebula and named after its discoverer, Johann Elert Bode who first observed it in It is a spiral galaxy lying at a distance of 12 million light years, that is an easy binocular object having a visual magnitude of 6.9. M82 is fainter, at magnitude 8.4, and is often referred to as a starburst galaxy where an encounter with M81 triggered a period of extremely vigorous star formation. It was originally thought to be irregular but the discovery of spiral arms in 2005 proved that this was not the case. The familiar W of Cassiopeia lies on the meridian and close to the zenith, with Shedir (α Cassiopeiae) only 5.5 from the overhead point. To the east of Cassiopeia lies Camelopardalis, and to the west Cepheus which contains the emission nebula IC1396. At magnitude 3.6 it should be visible to the naked eye under dark and clear conditions. As we turn towards the east Capella is already at an altitude of 55 and some of Orion s retinue, in the form of Taurus and Gemini, have cleared the horizon. Auriga, lying as it does on the galactic plane, boasts a number of open clusters, the brightest of which is M37 at magnitude 5.6. It s Messier neighbours, M36 and M38 are magnitudes 6.0 and 6.4 respectively. Gemini contains M35, a bright open cluster of magnitude 5.1 that can be found at the feet of the heavenly twins. It should be visible to the naked eye under good conditions, but a small telescope is all that is needed to start resolving its constituent stars. Of course Taurus is home not only to the photogenic Pleiades cluster but also the first item on Messier s list, M1, the Crab Nebula which is the remnant of a supernova outburst that occurred in Some of the nebulous material can be seen with large binoculars when conditions are good. High up in the south we find the lines of stars that make up Andromeda, with the well known M31 just past the meridian and lying just 15 from the zenith. It is an easy naked eye object when seeing is good although I have always found that averted vision helps considerably. Location is easy because it is only necessary to count two stars from the top left corner of the Square of Pegasus (which is actually α (alpha) Andromedae) and then two stars north to ν (nu), and M31 is a little west and north of that. Below

10 Andromeda lie the two small but obvious groups of Triangulum and Aries, the former of which contains M33, the Pinwheel galaxy. South of these two constellations we find Cetus which is home to one of the best known variable stars - Mira. Its variations take it from magnitude 3.5 at maximum down to 9.5 at minimum. Just skimming the horizon is the small constellation of Sculptor wherein lies the South Galactic pole. In the west the Milky Way rises almost vertically towards the zenith passing through Aquila and Cygnus, where dark rifts can be seen, on its way to Cassiopeia near the zenith. The third member of the Summer Triangle, Vega in Lyra, is still 20 high and not far from the head of Draco. A pair of binoculars will give some beautiful views of the star fields in and around the Milky Way. What Objects Can I Look For This Month? 1. Fomalhaut Fomalhaut is the brightest star in Piscis Austrinus (the southern fish) and is the 18 th brightest in the night sky. The constellation is one of the original 48 that were devised by the astronomer and mathematician Ptolemy during the second century AD. At one time Fomalhaut was considered to be the first star to have an exoplanet in orbit around it although there is now considerable and varied debate as to whether this is the case or if it may be that there is simply a disk of material awaiting planetary formation. To find Fomalhaut use Fig.6 and draw a line through the two western (right most) stars in the Square of Pegasus and continue them towards the horizon. There are no other bright stars in that area before you reach Fomalhaut. 2. Uranus Uranus currently resides In the other fish constellation, Pisces, and will continue to do so until The planet s position is shown in Fig. 6, just below the line of stars that make up the lower of the two fish. It s magnitude is currently 6.1, so is just below naked eye visibility although it is an easy binocular object. Fig. 7 is a larger scale map of the area around Uranus and the nearby stars in Pisces. Delta Piscium (δ) especially should be used as a guide, and once this is located it is an easy matter to star hop southwards towards the planet.

11 Meteors The Taurids are active from the end of October all the way through to late November with double maxima on the 5 th and 12 th of November. The zenithal hourly rate (ZHR) is expected to be in the region of 10 at maximum although the Moon will interfere particularly badly on the 5 th. On the 12 th it rises at 21.30, so early evening watches are likely to be the most fruitful. The radiant is shown as an R in a red circle in fig. 8. The Leonids begin on 15 th November and end on the 20 th with a sharp maximum occurring on 18 th November at GMT. The ZHR at maximum is expected to be around 20 with no outstanding displays predicted for this year. A very slim crescent Moon rises at but is unlikely to affect observations. The radiant position is shown in fig. 9. Advance warning for December 8 th to 17 th - Geminid meteor shower. 17 th to 25 th - Ursid meteor shower. Brian Mills

12 CONTACTS General address to contact the Committee Chairman John Vale-Taylor Secretary & Events Phil Berry Treasurer Mike Wyles Editor Geoff Rathbone Director of Observations Brian Mills Committee Members Paul Treadaway Jim Cooper John Lutkin Eric Gibson John Wayte Wadhurst Astronomical Society website: SAGAS web-sitewww.sagasonline.org.uk Any material for inclusion in the December 2014 Newsletter should be with the Editor by November 28 th 2014