Wednesday, 19 August 2015

Stars in the city: an introduction to urban astrophotography

As a twelve year old astronomy nut, I was lucky enough to receive a small refracting telescope. Almost immediately, I utilised scrap timber to build an observatory in my back garden, just about large enough for two children (plus star charts, a moon map and at least as important in my opinion, a flask of hot chocolate). I recall it even had a sliding roof, thanks to a pair of dismantled wardrobe doors.

Although the imaging wasn't too bad - I lived in a small town, so light pollution was relatively low - I soon discovered that good optics are only part of the story: without a proper mount, a telescope can be next to useless. In this particular case, I obviously hadn't read the brief introduction to mounts in my trusty The Observer's Book of Astronomy by Patrick Moore. At any rate, I clearly didn't understand the difference between proper equatorial or alt-azimuth mounts and the piece of junk that allowed my refractor to sit on a table top. Therefore, except for getting to know the lunar landscape, I saw little that I couldn't more easily view with my 20x50 binoculars.

Jump forward thirty or so years and courtesy of a large tax refund I found myself in possession of a small reflector, complete with equatorial mount and right ascension motor. After some months getting to know it I started buying accessories, aiming to learn the ins and outs of astrophotography. Thanks to numerous websites I picked up some useful techniques and excellent free software - and as importantly, how to use the assemblage - and now feel it's about time I offered a one-stop-shop guide to getting the best images on a low budget in your own backyard. Of course there are plenty of books available, but most are at least one to two hundred pages long and often specify expensive kit, so this post is an attempt to cover the gap for those wanting an astrophotography 101 with the absolute minimum of basic equipment. Of course, it's entirely my approach, so there are no doubt plenty of other tutorials out there. But at least mine's short!

1. Equipment

I have to admit that I order all my kit from overseas, since New Zealand has few astronomy retailers and those there are appear to have a fairly limited range, often at uncompetitive prices. However, it is possible to accumulate a decent beginner's assortment for around a NZ$1000 / £500. I would always recommend a reflector as a first telescope, being far cheaper than a refractor with similar capability. The Newtonian is the most common, least expensive and easiest to maintain type of reflector, mine being a Sky-Watcher 130. As per the name, the primary mirror is 130mm (about five and a half inches in old money), which is really the minimum useful size for a reflector.

The telescope came with a red dot finder scope, several okay-ish eyepieces, a right ascension motor drive, a poor 2x Barlows and a reasonably stable equatorial mount. Since then I've bought a planetary camera, a good quality 2.5x Barlows, a compact camera adaptor, an adjustable polarising filter and a collimating eyepiece*. I've also made my own Bahtinov mask, courtesy of a website that supplies patterns for various diameter/focal length combinations. Although 'go-to' mounts are available, I agree with the general consensus that the best way to learn the night sky is by manually pointing the telescope, not just programming a target and letting the telescope slew into position for you.

*For complete newbies, a Barlows is a cheap method for increasing magnification with only a limited number of eyepieces, fitting into the eyepiece holder below the eyepiece. A collimator is used to check and correct misalignment between the primary and secondary mirrors, whilst a Bahtinov mask is a simple focussing aid.

I'm lucky to live in the 'winterless north' of New Zealand, but for those in colder climates it's probably wise to make or purchase a dew cap, or rather one for the main tube and another for the finder scope. A rubber eyecup for the eyepiece might also be a good idea; there's not much point in trying to observe anything if water is condensing on the mirrors or lenses.

I would recommend a CCD or CMOS telescope camera or modified webcam, since they are a lot cheaper than a digital SLR and far lighter. The EQ2 mount supplied with the Sky-Watcher needs adjusting on both axis depending on the combination of items in the eyepiece holder, otherwise at high angles it has a tendency to droop. The EQ2 counterweight can just about handle the long tube: experiments with a compact digital camera in a purpose-built mount have confirmed that additional off-centre mass requires regular fine-tuning to retain balance. Incidentally, I use a colour planetary camera since I tend to have short sessions - around two hours - and so only want to film each pass once rather than repeating in triplicate for colour filters, even if mono cameras achieve better resolution.

2. Where to observe?

Of course this is the least flexible part of astrophotography, since you are restricted by the buildings and trees in your garden - or any other convenient location. Not only is your view of the night sky limited by physical obstructions but pollution can severely impact viewing. As I have discussed previously, light pollution is the most obvious form, with street lighting often worse than that of buildings. I've found that even as low as ten percent cloud cover can degrade astrophotography, due to the artificial light reflecting off the clouds.

Heat pollution may be less obvious but can also severely reduce image quality. Therefore, try to avoid pointing the telescope directly above nearby rooftops or you will be looking through a rising column of hot air, either the radiating heat from earlier that day or leaking from poorly-insulated buildings that are heated at night. Also, never set the telescope up indoors and point it through an open window: the thermal variations will generate shimmering galore. Wind above the lightest of breezes cannot be recommended either, not just for 'scope instability but also because dust and particulates can deteriorate the viewing. High water vapour content is bad for the same reason; here in humid Auckland I'm frustrated by the hours before and after rain, meaning the best seeing I've ever had has been in high summer after a rain-free week.

Before using a reflecting telescope, it needs to be set up outdoors well in advance of the viewing session in order to allow the mirror to cool down to the ambient temperature. The cooling time is directly proportional to the primary mirror diameter, which for my 130mm is usually about one hour.

3. What to photograph?

For urban astrophotography I've found the moon and planets to be by far the best targets. By planets I mean just Mars, Jupiter and Saturn. Venus may be both large and bright but due to its cloud cover will never present anything other than a featureless crescent or globe.

The moon is endlessly fascinating, best observed between new moon and first or last quarter (i.e. half full). During these periods, the low-angle sunlight generates shadows that model the features without being overly bright. When observing closer to full moon I always use a polarising filter to reduce the incredibly intense light, but since sunlight is then perpendicular there is little modelling to give relief to the geology.

Jupiter is by far the best planetary target for small telescopes; in addition to the cloud patterns you can see some or all of its four largest moons (Ganymede, Callisto, Europa and Io), their number and position changing on a nightly basis. Saturn is an excellent target too, the angle of the rings varying widely. I've also found Mars to be surprisingly worthwhile even when not at its closest to Earth, with the major features clearly visible in reasonable seeing conditions.

The problem with deep sky objects in urban astronomy is that they are both difficult to locate and their light is easily degraded by light pollution and particulates. I've attempted to get images of more familiar DSOs such as the Orion Nebula with several cameras, but the results are hopeless.

Once you have some experience under your belt, you may want to attempt photographing the International Space Station. Various websites list details for near-future visible passes over any location, when it is easy to spot due to being obviously brighter than any other man-made orbiting object. However, since the ISS will only be visible for around four minutes each pass you have to quickly manoeuver the telescope whilst keeping it in an area that is only about thirty arc seconds in diameter. If I manage to get any image at all, it is usually a few dozen frames resembling an out of focus capital 'H', so it's definitely a target for those with a lot of patience - and good hand-eye co-ordination.

4. Locating targets

Although I'm against beginners using go-to mounts, there are various planetarium programs and mobile apps that are extremely convenient for locating target objects. I use Stellarium, excellent freeware that can be set to any location on Earth and has a night time (i.e. red on black) mode to help keep your eyes sensitive to the dark.

Northern Hemisphere observers are at an advantage compared to their counterparts south of the equator due to the ease with which the North Celestial Pole can be found. Not only is Sigma Octantis slightly further from the SCP than Polaris is from the NCP, it is considerably dimmer. Therefore I've always had great difficulty in lining up the telescope to the South Celestial Pole for setting circles with the polar axis motor drive. There are telescope-camera combinations that allow use of auto guiding software but I prefer the manual approach to finding your way around the night sky. Besides which, spotting the closer planets is pretty easy, the most common potential mix-up being Mars with the red star Antares (whose name after all means 'equal to Mars')! All in all, manually slewing the telescope using a printed or online star chart as a guide is the best way to learn.

5. Harvesting ancient light

I tend to take 20-60 seconds of video or still sequences when imaging the moon and planets, depending on various factors such as target brightness and seeing conditions. Planetary cameras allow some manual adjustments such as exposure length and gain, with shorter exposure lengths usually better so as to minimise degradation within a single image. When the seeing is reasonable I stack the planetary camera on top of the 2.5x Barlows, which gives a decent angular size for the planets. I've also used a compact CCD camera with an eyepiece and Barlows combination, but the camera adaptor is fiddly to align on three axis with the eyepiece and the extra weight can mean regular adjustments to the mount, depending on telescope angle.

6. Image processing

Once you have the raw video or sequence of stills there is a lot that can be done to improve the image quality, initially by aligning and stacking the best individual frames and discarding the rest. Again, there is a lot of freeware available to help with this. I use RegiStax, often creating 3 or 4 permutations from each sequence and then loading the best one in Photoshop for final tweaks. (If you cannot afford the latter, then GIMP - GNU Image Manipulation Program - is a great freeware alternative.) It can take a while to understand how to use the likes of RegiStax, but there are YouTube tutorials covering various processes and I always consider a trial and error approach to be a good way to learn!

So what sort of results can you expect from all this effort? The biggest factor in quality is undoubtedly the seeing conditions, which are outside of your control. However, just occasionally you get a perfect night. I find that it can take a few sessions to generate a half-decent image, so it definitely takes perseverance.  Since a picture is worth a thousand words, you can judge the results for yourself here.

Thursday, 23 July 2015

Dung roaming: a controversial approach to cleaning up New Zealand's cattle waste

Although I've already discussed the dangers of using biological control in various countries, a couple of recent events suggested I should write an update that concentrates on one particular example in New Zealand. I've mentioned elsewhere that my local reserve in Auckland is home to a large number of non-native species, from Australian eucalyptus trees and the associated (but accidentally imported) Emperor Gum moth, to California quail and Mexican gambusia fish. But having seen rainbow skink in my local environs, including a neighbour's garden, I was surprised to learn last week they are not native but yet another unplanned Australian import. Sure enough, the 1947 classic Powell's Native Animals of New Zealand makes no mention of the species in the page on the indigenous common skink and copper skink.

Earlier this year I read Quinn Berentson's superb Moa: the life and death of New Zealand's legendary bird, which lists fifty-eight avian species as having become extinct since humans first arrived in the country less than a thousand years ago. And of course this decimation of native fauna and flora may not yet have ended, with NIWA for example fighting a rear guard action against unwanted marine incomers such as polychaete worms arriving on ship's hulls and in discharged ballast water. Various sources suggest that well over one hundred introduced species of land animals, birds and fish are now widespread in New Zealand: what chance does the native ecosystem stand against this onslaught?

To add insult to injury, I recently read an OECD chart delineating business spend on research and development as a percentage of GDP, and was shocked to find that New Zealand was fourth from bottom of twenty-six nations, coming below western Europe, South Korea, Japan, Australia, Canada and the USA. Are our captains of industry really so short-sighted? As a country that depends extremely heavily on its dairy industry - an industry that is currently in dire straits - it seems sensible to invest a large amount of R&D in this sector. But alongside the eco-friendly solutions such as minimising methane emissions, there has been a new programme of biological control aimed at one particular side effect of dairy farming, namely the enormous amounts of cattle dung produced.

Across the Tasman, Australia has already been working on a similar scheme for the past half century, deliberately introducing numerous species of non-native dung beetles. New Zealand, home to over ten million cattle in a 3:2 dairy-to-meat ratio, obviously has issues with bovine manure management. Due to the lack of native ruminants the country's fifteen indigenous dung beetle species have evolved to mostly inhabit forests rather than grazing land.

There are various reasons why speeding up the rate of dung decomposition would improve farm land and the landscape in general, from preventing mineral imbalance in the soil and contamination of waterways to reduction in animal-infesting parasites such as nematode worms. But is it worth the risk to the greater environment, considering the dismal track record of biological control schemes around the world?

The new project is not the first time such insects have arrived in the country: in addition to three species accidentally imported from Australia and South Africa from the late Nineteenth Century onwards, the Mexican dung beetle (Copris incertus) was deliberately introduced into three areas in the 1950s but only thrived in the warm Northland climate. It is the scale of the new research that has set it apart: following caged field trials, the past two years has seen the widespread introduction of eleven non-native species across seven regions on both North and South Islands.

Bodies such as the Institute of Environmental Science and Research (ESR) have investigated the potential dangers to human health and the local ecology, even testing if possums, carriers of bovine tuberculosis, might see the exotic insects as a new food source. Even so, some professional scientists have deemed it a biosecurity disaster and one can see their point: using data from other countries' programmes is hardly a fool-proof comparison, considering the profoundly different indigenous ecosystems of Australia and New Zealand.

As a child I heard about the food chain or pyramid, but this is something of a misnomer. Just as natural selection works with bushes rather than linear progression, so there are food webs consisting of a complex series of trophic interactions. Although exotic dung beetles are unlikely to displace their native counterparts due to lack of shared environments, it is possible that other native species of grassland-living insects could suffer, such as humble earthworms. The problem is that without testing in various regions over long periods of time, it isn't viable to rule out such side consequences. Yet it isn't possible to undertake such tests without release into the wild: do we have something of a catch-22?

Having said that, there are no obvious signs that Australia's long-established dung beetle programme has had anything like the deleterious effects of its other biological control schemes, such as the cane toad fiasco. But then fifty years is a very short time in ecological timeframes and what to the casual glance of a farmer appears to be equilibrium could be apocalyptic at dung beetle scale. I wish the project good luck, but cannot help feeling that having received far more than its fair share of obnoxious aliens, New Zealand is the last place that needs yet more exotic species introduced onto its green and pleasant land.