Archive for category review

The Argo Navis, as reviewed by a non-technical user

When we were debating which telescope to buy initially, one of the considerations was whether to get something with a guidance system or not. I voted nay, at least partly for money reasons, but also because I felt like a guidance system was basically cheating. I wanted to learn my way around the sky, and find things all by myself thank you very much.

About a year later, we went to the 2010 Ice in Space camp. It was the first time I’d ever been around lots of fellow amateur astronomers, and it turns out that actually a lot of them have guidance systems of one sort or another. And most of them still know something about the sky and finding their way around it. By this stage I had started getting interested in searching out double stars, and was finding it increasingly frustrating: I was often having trouble just finding the point-of-reference star, let alone the faintish double that was meant to be close by.

You can tell where this is leading. I soon sucked it up and agreed to getting a guidance computer. It helped that James had had his Dobsonian blinged out with a ServoCat and a computer and that I was just a wee bit jealous.

UnknownWe both got an Argo Navis. The first thing I asked on seeing the product was “Why is their symbol an Egyptian hieroglyph when their name is Greek?”, but that’s neither here nor there.* The Argo is of Australian design and manufacture, which is very cool, and it works an absolute treat. (I also had to get a new mount to go with the Argo, and we went with the Losmandy GM8. But that’s another post.)

The Argo is very simple to use. It has two buttons and a scroll wheel, and a screen that can show two lines of text. The Losmandy is a GEM (German Equatorial Mount), so setting it up is easy: having aligned the mount with celestial south (so that it tracks properly… and let’s be honest, it’s close to south but probably usually “southish”), wait for two bright stars to be obvious, line the telescope up with your finder/telrad, let the Argo know which stars they are, and you’re away.

There are several ways you can use the Argo, and you can of course change your method over the night. If you don’t have specific plans for your night’s viewing, you can use the Argo’s Tour mode, and choose what you’d like to have a look at: Popular Deep Sky objects? Planets? Messier objects? Planetary nebula? Choose your category, state whether you want to look within a small area (if, say, Sagittarius is high and you want to know what’s within it) or over the entire sky, and what magnitude limit you want, and then… go where the Argo tells you. What sort of mount you have will determine how you actually find things, of course, but for me it’s just a matter of pushing the scope around, following the arrows, and watching the numbers for RA and Dec count down to zero (and then the arrow reverse, and the numbers rise, when I overshoot…). The Dob has a ServoCat, so it automatically goes to your object when you hit ‘enter’. The whine of the motors is amusing in the middle of the night…

Alignment is an important part of how the Argo works. The Argo gets a sense of where it is, what the sky looks like, and hence where other stars and objects should be according to Right Ascension (RA) and Declination (Dec). When you dial up M42, for example (who doesn’t love the Orion Nebula?), the display will indicate in which directions (up/down, left/right) the telescope needs to be moved in order to centre on it. The numbers reduce as you get closer, and become more precise as the object gets closer. I found it quite intuitive, and easy to use. And I’m pretty hopeless spatially.

As I said, there are other ways of using the Argo while observing. There are some clever flow-on effects of the Argo knowing where it is pointing; for example, you can identify an object you’re looking at, by going to the appropriate mode setting (Identify). Because it also tells you the coordinates of the area in the sky you’re pointing at, you can also use the Argo to find something – say from an atlas – that isn’t otherwise listed in the Argo’s menus. This is particularly useful when looking, for example, for double stars.

The Argo comes with a cradle, and with the Dob it was simply a matter of constructing a little tray for it and the Servo controls. The ingenious solution for using it on my tripod was velcro. I have velcro on all three legs of the tripod and on the back of the Argo (and the hand control, and the dew heater…). So I can move the Argo around to whatever side I’m on, and I can just slap it onto the tripod when I want to have my hands free. Velcro: best invention ever.

In all, the Argo is very easy to use, even for someone like me who is neither particularly tech-savvy nor very good with directions.

*Turns out Argo Navis is the name of the constellation that today is Carina, Puppis and Vela. There you go.


, , ,

1 Comment

UHC, Oxygen III and Hydrogen Beta Filters by Astronomiks

OIII Transmission

If you own a scope 8 inches or larger then filters can make a big difference to the fine details you see in a range of non-stellar objects. They work by blocking out some wavelengths of light, while allowing full transmission of others. Depending on their type and composition, different nebulae emit light at different wavelengths and by using a filter matched to these the overall background and star brightness is reduced significantly more than the nebulae itself. While all filters cause some overall reduction in light transmission, the differential reduction of the background (especially under light polluted skys) and the transmission of the nebulae’s specific emission lines increases the relative contrast allowing the eye to see more detail than is possible without the filter.

Filters are not magic; their effect is minimal or negative for many objects because of the reduction in total light transmission. However, for some objects – especially marginal ones – the contrast increase can make it significantly easier to make out the details of an object. The Tarantula Nebula in the LMC is one of my favourites to view through a UHC or OIII filter: it reveals different and fascinating details through both. The OIII filter is also ideal for making planetary nebulae stand out from the background stars. NGC2438 in M46 is a excellent example for this.

UHC Transmission

David Knisely has done an extensive and detailed comparison of the UHC, OIII and Hb filters on almost 100 objects using a 10 inch scope. I’m not going to try and replicate this excellent analysis; instead I recommend you read the descriptions for objects you’re familiar with to get an idea of the improvement you can expect with the different filters.

Many companies make filters. Personally I have the UHC, OIII and Hb 2″ Astronomik filters mounted on a moonlight filter slide with a heater strip and temperature sensor set up to keep them dew free. The filters don’t appear to introduce a colour cast, or any other undesirable artefacts when viewing. They do however require a slight refocusing when changing between a filtered and non-filtered view.

Like many astronomy accessories filters are not cheap, so here’s my buying advice. If you’re only going to buy one filter, get a UHC. Next buy an OIII, especially if you enjoy planetary nebulae. An Hb filter is honestly an excessive luxury, but if you have a big Dob (15+ inches) and you want to be able to enjoy some very faint nebulae objects like the Horsehead it makes a noticeable improvement.

, , , , ,

Leave a comment

Pocket Sky Atlas

Just buy it.

Seriously. Just buy it. Are you just getting into astronomy? Can’t actually buy a telescope yet but interested in learning about constellations and the various objects you’ll be able to see when you do get one? Just buy this. Been observing for a while but don’t have a nice handy little reference to take with you for short sessions at the telescope? Buy this.

We own two, because we each need one when observing. (And we’re bad at sharing.)

Halfway between A5 and A4 in size, and spiral-bound, this is immediately an appealing book. The blurb describes it as fitting into the glove box, which is a good way of selling it. It’s not quite a genuine pocket-book, but compared to most atlases it’s a treat. It has slightly waxy pages which means they don’t mind a bit of dew, too, which is marvellous when observing in damp conditions.

The book opens with a very brief introduction, explaining the origins of the atlas – in the search for convenience – and what it actually shows – stars down to about mag 7.6; doubles, variables, galaxies brighter than 11.5, globular clusters brighter than 10.5, planetary nebulae brighter than 12. It also explains the labels used, how the charts are arranged, and includes a select bibliography which can be used for those wanting something than goes further (or just a good collection…).

The charts are arranged in order of Right Ascension, in sets of ten. It begins with RA 0-3, and the introductory page (a similar one appears at the head of each ten) explains in which months this part of the sky is high in the evening, at midnight, and in the morning (in this case, Nov and Dec; Oct; Aug and Sept). It also has a map, repeated in many places, of the entire sky, with major constellations and the maps on which they appear; the section under specific consideration is shown in bold. Turn the page and, before getting to the maps themselves, there is a key to understanding the maps: how to identify galaxies, nebulae, clusters, and stellar magnitudes.

The maps themselves are quite detailed, with lines connecting the stars of a constellation in green, galaxies in red and other non-stellar objects mostly in yellow. Each map has arrows and labels showing which other maps it connects to (there is good overlap), and RA and Dec are easy to follow. There are four detailed maps: of the Pleiades, of Orion’s Sword, the Virgo Galaxy Cluster, and the Large Magellanic Cloud.

One of the most useful aspects of this map is that the front cover is not part of the spiral binding, meaning that when the book is laid open the front cover juts out beyond the page. On this jutting-out section there are three things: a ruler indicating angular distance on the charts (up to 15 degrees); the scale for determining star magnitude from -1 to 7 (because as usual this is indicated by relative size on the map); and a red Telrad finder with circles at 2 and 4 degrees. For quick referencing while observing, this inclusion is invaluable.

The book closes with several indices. It has a list of bright stars, by name; a list of galaxies by NGC and IC reference, as well as name; open clusters; globular clusters; bright and dark nebulae; and planetary nebulae. All of these, listed separately, also have a reminder of the legend used to indicate them on the maps. Lastly, the book includes objects in the Caldwell Catalogue and the Messier Catalogue. Excellent for those of us who like lists and/or challenges, or who are feeling lazy when it comes to planning an observing run.

Would I buy it again? I already mentioned that we own two, so: absolutely. It’s invaluable.


Leave a comment

Double Star Atlas

When I announced that I might be interested in checking out double stars, James bought The Cambridge Double Star Atlas, by James Mullaney and Wil Tirion, for me. It’s a big book – larger than A4 – although only 148 pages long. It’s spiral bound, meaning that despite its size it’s quite useable: you’re not forced to to deal with an A3 map on your lap while at the eye piece. The paper seems to be good quality and slightly waxy; I’ve had mine sitting on dewy grass and although some of the pages have slight ripples in them now, the book itself hasn’t suffered at all. And it’s got wonderful content, with an excellent introduction and superb maps.

In the introduction, Mullaney takes the reader – anyone from a novice to expert – through the process of making the book itself, then tabulates the codes that are used to signal the discoverer and/or catalogue used when discussing individuals pairs/systems. There is an excellent section on the practicalities of observing – useful not just for doubles hunting – explaining how to train the eye to observe, as well as the impact of sky conditions and the resolution and magnification of telescopes. He also discusses the idea of record-keeping, and it was from reading this that I decided to keep a journal of my observations.

Before getting to the maps, Mullaney has a list of 133 ‘showpiece’ double and multiple stars. As well as giving the name of the object, its coordinates and magnitude, he includes a short and usually evocative description of each object. For those of us who like lists, this is something akin to having a Messier list for double/multiples. It’s a fabulous challenge (although disappointingly for me a fair number are beyond my viewing range, here at 37 degrees south).

The heart of the book is the 30 double-page maps that cover the entire sky (p1 is the North Celestial Pole, p30 the South). The maps show about 900 non-stellar objects as well as the doubles, so it can make an excellent all-round atlas too. The stars making up constellations are connected by faint blue lines, and the ‘spheres of influence’ of the constellations is also shown, which is useful when trying to locate specific objects. The doubles that are specifically listed objects (all 25,000 of them) are labelled in green, making them easier to read under red light. I’ve never been especially good with maps, but these are easy to read and easy to use, both while planning an observation session and while at the telescope.

Finally, there are the Appendices. App A lists the constellations and which pages they appear on; B has the ever-useful table of Greek letters. But C is where the money really is: a list, in order of RA, of the doubles Mullaney specified be in the Atlas. The table has the object’s designation, RA and Dec, magnitude, and the pair’s separation, as well as occasional helpful remarks (this is Antares, this is in the middle of the Pleiades). This appendix can be used to give the astronomer a better idea of exactly what she is looking at on the map; when used in conjunction with an Argo, if a random double is spotted it can be looked up via the RA/Dec to see whether it is listed and if so its name.

Would I buy this Atlas again (or get James to buy it)? In a heartbeat. Of immense value to anyone who is interested in looking at double stars. It’s easy to use, lovely to flick through when planning, and sturdy into the bargain.

, ,

Leave a comment

Observing the Sun with Coronado Telescopes

While it does discuss other brands, this book – as the name suggests – is designed to inform the reader about solar telescopes as made by Coronado (acquired by Meade in the last few years). Overall, it is a nicely presented book, with some detailed information about the telescopes and solar observing in general. The pictures in particular are a wonderful part of the package: there are numerous pictures of the sun itself, taken via Coronado instruments, which demonstrate what it is possible to see, as well as numerous pictures of the instruments themselves. However, this book is not without its flaws.

The thing which frustrated me the most about this book was the poor editing. It’s not so poorly written that it becomes unintelligible, but it is filled with enough silly mistakes to become quite irritating: mistakes which the author ought to have picked up on re-reading, and which an editor certainly ought to have corrected. That aside, the non-technical sections are clearly written and easy to follow. The audience is definitely imagined to be beyond novice at astronomy; unless you are an astronomy novice but an experienced photographer or otherwise have a good working knowledge of lenses, there will be sections of this book that will be difficult to follow. It’s also written in quite an idiosyncratic style. Philip Pugh, the main author, acknowledges this early on; it’s based largely on what he, and the other contributors, have personal experience with. They do mention some accessories and telescopes they haven’t personally used, which is good, but does leave room for the possibility that they’ve missed something. It also has numerous personal anecdotes throughout, which in general I found quite nice, although the mentions of business trips to Brazil got a little wearing.

Fortunately, the flow of the book itself is easy to follow. It opens with an exceptionally detailed contents page, and there are clear headings throughout all of the chapters. The Introduction begins with a little bit of the history of solar observing – but so little that he might as well just have skipped on it. It also includes a smattering of scientific information about the sun, which again was so limited that it felt like it didn’t really fit. Both of these really needed to be quite separate sections to feel warranted. The best part about the Introduction is Pugh’s discussion of the differences between white light and hydrogen alpha (Ha) observing in terms of what the eye can actually see, as well as his recommendations on how to keep records of observations. Reading the introduction is probably a good way to decide if solar observation is really for you: it’s certainly cheaper than buying a telescope and discovering that you hate it.

Chapter 2 focusses on the PST: the Personal Solar Telescope, one of which I own and is the reason why I bought this book. This chapter is excellent if you are considering buying one. It has great detail on what the PST looks like; how to attach it to various types of mounts; accessories (he doesn’t always come down in favour of the official ones); and how to find the sun using its inbuilt finder. There is a great deal of information about eyepieces, and includes an interesting appraisal of the PST overall.

Chapter 3 looks at the PST’s bigger sibling, the MaxScope. The chapter is largely the same as Chapter 2, although it has more information on photography. I am unlikely ever to even consider the MaxScope, so I will admit I did not pay a great deal of attention to the chapter details; it does seem as thorough as that on the PST, however.

Other Coronado products are the focus of Chapter 4. It seems to be a good rundown of the various options, with useful comparisons to other Coronado products throughout. It includes a brief section on accessories and options for mounting.

Imaging the sun is discussed in Chapter 5. This seems to be something a lot of solar observers get into, and while I was unconvinced when I first started using the PST, the appeal is slowly growing on me. The chapter includes very detailed discussion of how to attach and use a webcam (the best option for solar photography it seems), as well as post-processing and the advantage of stacking images. There are some lovely photos, of course, to serve as inspiration. The problem, of course, is that although this book is quite current – written in 2006 – the rate of change in digital imaging and associated software has been so rapid that this chapter is almost certainly hopelessly out of date in terms of its recommendations regarding the best or cheapest options for cameras, and what software to use (additionally he only suggests software for Windows machines). This chapter might give an interested imager somewhere to start, it could by no means be used as a sole guide.

In Chapter 6, the book moves away from Coronado products to give brief reviews and evaluations of solar telescopes and accessories from other brands which the authors have tried, while Chapter 7 discusses products they have not personally experienced. Having no experience with these things I of course cannot evaluate whether they are being completely fair or not, but the book as a whole gives no reason to suspect anything other than honesty.

Finally, Chapter 8 provides a fairly comprehensive summary of the book as a whole, and it concludes with a glossary which, while not being very detailed, is still useful.

Would I buy this book again? Probably not. It’s not the book I was expecting; I had hoped for more on solar observation itself, not what is essentially a buyer’s guide. Since I am unlikely to buy another solar telescope (my PST suits me down to the ground) it isn’t particularly useful. This is the sort of book which ought to be in libraries – particularly astronomical society libraries – where potential buyers can borrow it to read the relevant chapter.

, , ,

Leave a comment