Archive for the ‘Observing tips’ Category


Marking up sky atlases

February 4, 2017

I’m a book lover. Any space I’m in for long will have books on every available surface and piles of extras on the floor. Because of this love of books, for a long time I wouldn’t mark them up. This hands-off reverence extended to my sky atlases. But eventually I realized that sky atlases are tools, not heirloom pieces, and anything that makes them more useful when I’m observing is justified.


Here’s a representative page from my working copy of the Pocket Sky Atlas (I also have a second copy, autographed by John Dobson, that actually is an heirloom piece now). The circles and polygons flag objects from various Astronomical League observing projects. Triangles are double and multiple stars, rectangles are Herschel 400 objects, big circles are for the Binocular Deep Sky objects, and an open letter C designates Caldwell objects. I also drew in the position of Almach, which is just off the edge of this chart, wrote in the number for the multiple star 57 Persei, and wrote down the magnitudes of Algol and some of the useful reference stars, including Almach. Arrows in the margins are left over from my Caldwell tour.

I’ve finished all of those projects except the Herschel 400. You’ll see that some of the little rectangles have a diagonal slash across one corner – that’s how I flag which ones I’ve already observed. I’ve actually seen all of the H400s on this chart, I just got lazy about marking them off in the atlas. But I did write ‘CLEAR’ in the corner of the page so I know not to waste my time looking for unobserved H400s here. Other pages have the numbers of the H400s I still need written in the margins, for quick sorting and bookkeeping at the eyepiece.

These marks are very helpful while I am working on a project, because I have an instant visual reminder of what’s available to see in any given stretch of sky. And once I’m done with a particular project, the marks still point me to a lot of ‘best in class’ objects that I might otherwise overlook or forget.

Oh, I also sketch in the positions of comets from time to time, with the dates of observation.

This method has worked so well for me that I have thought about picking up extra copies of the PSA (for $13!) just so I could mark them up with objects from other observing projects. I’ve done that with a couple of my other atlases. My copy of the Cambridge Double Star Atlas has all of the AL Binocular Double Star targets marked, and I use my Jumbo PSA (which is ridiculously useful) to keep track of targets from the last several years of Sky & Telescope’s Binocular Highlight column, to help me avoid repeats. Of course I have other lists for all of these things, both physical and digital, but it’s nice to have an easy reminder when I am out observing or doing desk research.

Do you mark up your atlases? If so, what system do you use? Let me know in the comments.


Observing tip: make a comparison chart for your eyepieces

October 16, 2013

MJW eyepiece comparison chartSherlock Holmes once exclaimed, “Data, data, data! I cannot make bricks without clay!”

I often feel the same way at the eyepiece. The more I know about what I’m looking through, and what I’m looking at, the more I understand what’s going on and can make meaningful evaluations and comparisons. At a minimum, I like to know what magnification I’m working at, and it is often helpful to know the true field of view (TFOV) and exit pupil (the width of the beam of light entering my eye). So I made a table with all of that information, for every combination of eyepiece and telescope in my inventory, and I keep it on a clipboard with a few other odds and ends.* So if I’m using a 21mm Stratus in my Apex 127, I don’t have to stop observing and do long division to work out the magnification.

* Single-sheet all-sky maps of the Messier and Caldwell objects (from here and here), often a tear-out map of the moon or the Milky Way from S&T, and the logbook for whatever project I’m working on.

As you can see, my table is a pretty bare-bones affair. I didn’t even give it a title,  just left it as “Sheet 1”. And when I got the C102 last week, I just wrote in the additional column by hand. But it’s a crazy useful thing to have along, and if you haven’t made one for yourself, I recommend it.

How do you calculate all this stuff?

Magnification is telescope focal length divided by eyepiece focal length. So in the XT10 (f/l = 1200mm), the 14mm ES82 gives a magnification of 1200/14 = 86x.

True field of view is apparent field of view divided by magnification. It’s important for star-hopping and celestial navigation; if you know that a certain object is two degrees west of a given star, that’s two eyepiece-fields if the EP gives a one-degree field. The ES82s have an 82-degree apparent field, the ES68 and Stratuses have 68-degree fields, the Expanse has a 66-degree field, and the Plossls all have 52-degree fields. In the same example listed above, the 14mm ES82 in the XT10 gives a TFOV of 82/86 = about 1 degree (0.95 to be exact).

Exit pupil equals the diameter of the scope’s objective lens or primary mirror divided by magnification. That’s pretty much what magnification is: taking a wide beam of light with a small image scale and turning it into a narrow beam of light with large image scale. To keep using the same example, in the XT10 (250mm diameter) the 14mm ES82 give an exit pupil of 250/86 = 2.9mm.

A lot of people, myself included, find that eyepieces become a lot less comfortable to use when the exit pupil gets under 1mm. In contrast, large exit pupils are very comfortable because you can move your eye around a bit without losing the light beam. Most veteran deep-sky observers recommend an exit pupil of about 2mm as the optimum for picking out faint details. This is explicitly a trade-off between brightness and image scale: lower magnifications offer a brighter image but smaller image scale; higher magnifications give a larger image scale but spread out the light so the image is dimmer. The only way to beat that trade-off is to move up to a bigger scope, which will let you have a brighter image at a larger image scale. That’s why aperture matters.


Observing Report: binoculars vs. cloudy skies

January 20, 2010

70mm of EPIC WIN -- times two!

Contrary to popular belief, it does rain in southern California. We’re in the middle of what is projected to be a solid week of rainy weather. Today we had thunderstorms and a small tornado even came ashore in Orange County. So I hadn’t planned to get any observing done until after this coming weekend.

Rather, I should say that I hadn’t counted on getting any observing in. But I had hoped that there might be some breaks in the clouds, and I had planned accordingly. The point of generating all of the AL observing club logbooks was to have all my ducks in a row when the sky cleared up this rainy season (I can’t bring myself to call it “winter”, and we really only have two seasons anyway, rainy and dry).

By the way, it may look like I’ve gone completely mad for AL observing clubs, with six active projects. But there’s a lot of overlap; some observations for the Messier and Deep Sky Binocular clubs also count for the Urban club, and Deep Sky Binocular work is basically observing the brighter NGCs that never made it into the Messier list, so except for the Galileo and Lunar II clubs, all of my observing projects involve hunting down faint fuzzies. And they all can be done with binoculars, at least to a point, although ‘nokks are only required for the two clubs with ‘binocular’ in the title.

ANYWAY, this evening the clouds cleared out for a bit so I grabbed my observing kit and headed out into the driveway to hunt for goodies. What’s in my binocular observing kit? Glad you asked!

  1. My ‘nokks of choice, Celestron SkyMaster 15x70s. These are big, and they really gobble up the photons. The views are sharper when they’re mounted, but I prefer the freedom of handheld scanning, and that’s how I use them most of the time. If I’m going to use smaller binoculars on a given evening, I have to do so before I look through these; going back to 50mm of aperture is like having someone shut off the lights. Huge bang for the buck, but if you’re going to freehand them, get a wide padded neck strap instead of the shoelace guillotine that comes included.
  2. Sky & Telescope’s Pocket Sky Atlas. I love, love, love this atlas. It’s small enough to hold in one hand, spiral bound to lay flat or fold over in the field, easy to read with a red flashlight, conveniently organized…with this atlas, my 15x70s, and reasonably dark skies, I can ‘nokk off DSOs about as fast as I can look them up on the charts. In the city I can’t always see the faint fuzzies, but I can always get myself to the place in the sky where they would appear if I wasn’t under the LA light dome.
  3. Notebook. I use a hardbound 8×5 off the bargain rack at Borders, but anything would do, even a blank piece of paper. At the top of the page for each observing session I note the date, location, and sky conditions. Entries include time, instrument used, target,  and a brief description. I transcribe everything into my AL logbooks after I come back inside, because its easier to do that than juggle four floppy 8×11 notebooks in the field.
  4. Red flashlight. Mine is a Mini Maglite with the window painted over with a double coat of red nail polish. I wear it around my neck on a lanyard so it’s always to hand. Bright enough to let me use the atlas and record my observations without trouble, small enough to fit in my teeth when I’m laying on my back and two-handing the atlas overhead.
  5. Writin’ iron. I use the cheapest stick pens that money can buy, so I don’t have to worry about breaking or losing them, but whatever you like will do.
  6. Hooded  sweatshirt. Surprisingly useful. Not only keeps me warm, I can stash the binocular lens caps in one pocket and my pen in the other. The biggest benefit is being able to pull the hood around my face like a cowl to block out stray light and improve my eyes’ dark adaptation. This makes a BIG difference in seeing faint stuff I would otherwise miss. Patience, and knowing I’m looking in exactly the right place (thanks to the atlas) are the other two legs of this triad.
  7. Towel or folding chair. Depending on how my targets are. If low in the sky, I may choose to sit in a folding chair. If high in the sky–where I prefer to work, both for ergonomic reasons and because things look the best when you’re looking straight up, through as little atmosphere as possible–I lay a beach towel on the car and lay back against the windshield. The towel keeps me warmer than I would be otherwise and keeps me from scratching up the car.

That’s it. For  walking out the door, I’ve got the sweatshirt on, binoculars and red flashlight both hanging from their neck straps, pen in my pocket, atlas and notebook in one hand, towel or folding chair in the other. I’m outside in one trip, and observing about 5 minutes after the  mood strikes.

That comes in handy on nights like tonight; between 5:30 and midnight I was out four times, because the sky was clear four times and cloudy three times in between. It would not have paid to set up a telescope, and I would not have felt comfortable doing so considering the amount of moisture  still falling down out of the trees–when the slightest breeze hits the tall palm in my front yard, it shakes itself like 60 feet of wet dog. So it was ‘nokks or nothing, which suited me just fine because I’ve been on a serious binocular observing bent lately.

I spent the first session ‘nokking off some easy Messiers. Nothing new, all things I’d already seen and logged from the Salton Sea and just needed to dupe for the Urban Club. Still nice to check those off the list.

The rest of the sessions I was hunting clusters. I’ll give the full run-down on how I do this in another post. Suffice to say that by the end of the night I had logged 24 DSOs, including 15 objects that I’d never seen before. Some of them were just gorgeous–there is a nice run of little clusters off the feet of Gemini that must been seen to be believed. Plus I got in some sweet views of the moon and had a quick peek at Mars and Saturn, too.

Now it’s late and I’m bushed, so I and my victory energy are going to bed. Catch you on the flip side.


Observing and photographing the moon with binoculars

January 5, 2010

I’m always saying that you can see craters on the moon with binoculars, but I suspect that many people don’t believe me. So here’s the proof.

Here’s a raw, completely unretouched image I took on the evening of January 2nd.

The same image, cropped and lightly sharpened using “unsharp mask” in GIMP.

Then converted to grayscale, which gets rid of the annoying coloration on the limb. That’s chromatic aberration or CA, which is present in any optical system that uses lenses to collect light. The problem is that different wavelengths of light have different refractive properties, so a lens can never bring all of the wavelengths to focus at the same point. In telescopes and binoculars, the out-of-focus wavelengths at either end of the spectrum make yellowish and purplish halos around bright objects, even in daytime. You can knock down the CA to unnoticeable levels by using combinations of very expensive glass in the lenses, as in apochromatic refractors or APOs, or with anti-fringing filters, but it can never be completely eliminated.

Here’s the final version of the image, in which I tweaked the brightness and contrast using the “Curves” function in GIMP. This lets you selectively brighten and darken pixels of different values, and I use it on almost everything.

So what have we got? Well, first of all, there are dozens of craters in view. Now here I have to confess that looking at these photographs is cheating, a bit. The digital images are magnified by the camera and blown up to a convenient size on your screen, so you can pick out a LOT more detail from these pictures than you would out in the dark with the binoculars alone, even if they were mounted.

Nevertheless, the camera couldn’t capture detail that wasn’t there, so all of this was at the eyepiece, and how much you might get would depend on your visual acuity and level of experience. Experience counts, and the more experience you have, the more you realize that it counts. A big part of one’s growth as an observer is learning to see, which largely means cultivating the patience that it takes for your eyes to suss out the subtle details present in whatever you’re observing.

I decided to take this picture because I was really blown away by the sharpness of the features along the terminator, especially Mare Crisium and the nearby craters. Like all of the maria or lunar seas, Mare Crisium is an impact basin that was flooded with basalt; unlike most of the other maria, Crisium actually looks like a giant, flooded crater. Just north of Mare Crisium is the ancient crater Cleomedes, which you might easily pass over when it is less dramatically lit. Farther north along the terminator, the flat-floored crater Endymion is a black pool of shadow.

A final confession. Despite the title of this post, I didn’t take this photo through binoculars. I took it through the 9×50 finderscope on my big telescope. A pair of commonly available 10×50 binoculars would offer the same angular resolution and slightly more magnification, and would therefore show you even more–especially if they were solidly mounted. Here is a much better picture from a couple of years ago that I really did take through 10×50 binoculars.

Okay, so you can get serviceable pictures of the moon using a point-and-shoot digital camera and cheap binoculars. But how?

First, mount the binoculars on a tripod to keep them steady. Ideally, once you get them aimed and focused you won’t have to touch them at all while you’re taking pictures, except to periodically re-aim them as the moon crawls across the sky.

Second, use a digital camera that offers optical zoom instead of electronic zoom, and use as much optical zoom as the camera will give. I get the camera lined up behind the eyepiece first, get the moon on the little screen at back, and then start zooming. Once the camera is zoomed, its field of view is so small that if you lose your target, you may have to start all over again.

Third, I turn off the flash and set the camera to macro (“flower”) mode. I know that other people have gotten good results focusing the camera at infinity, and more power to ’em, but I get my best results in macro mode.

Fourth, it is really super-handy if you have a camera that allows you to manually set the exposure time. My old Nikon Coolpix 4500 does this  easily. If the feature is available on my much newer Coolpix L19, I haven’t found it yet. One of these days I need to rant about how most newer point-and-shoot digital cameras suck compared to the 4500, but not today.

Fifth, take tons of pictures. Seriously. For every photo of mine you see posted here, there are on average 99 others that I took and discarded. I’m not kidding, and I’m not exaggerating. If I come off as a half-decent photographer, it’s because digital cameras allow me to take zillions of pictures and present the handful that worked out. Storage space is effectively free these days, so take as many pictures as you can at the eyepiece and sort ’em out later. It’s worth fiddling with the focus of the binoculars or scope a bit between blocks of photos, just in case the camera’s sweet spot is slightly different from your eyes’ (for example, because you’re farsighted or astigmatic or whatever).

Sixth, download GIMP, which is free, fairly easy to use, and will allow you do just about everything that Photoshop does. Then make a new folder with copies of your best images and start experimenting with Unsharp Mask, Curves, and the rest (do not experiment on your original files).

Seventh, read up on how other people get their shots. What astronomers call ‘afocal projection photography’ is more widely known as ‘digiscoping‘, especially amongst birders, and there are tons of sites out there with advice and examples.

Good luck!


On faffing about

October 30, 2009
DwarfStar 02 small

My little Mak sporting a big eyepiece and, more importantly, a 6x30 finder.

My good friend, fellow paleontologist and sometime astronomer Mike Taylor sent this a few weeks ago:

By the way, we had a very clear sky a few nights ago, so I got the telescope out and — after an AMAZING amount of faffing about — I saw Jupiter and four moons.  Pretty neat!

To which I replied:

Awesome! No worries on the faffing about. One of the things I need to blog about on 10MA is how long it can take to find something for the first time, and how much you feel like a tool while you’re bumbling around in the dark, but also how much easier things get over time. Part of it is learning to point–it takes me much less time to get the telescope aimed where I want it these days–and part of it is learning to see. There are things that I’ve looked for in the past two years with no success that I found pretty easily this summer, just because I’ve been out looking and gotten my expectations in line with reality.

So, if you’re new or relatively new to this and you are frustrated because it’s hard to find stuff and most stuff is too dim and occasionally you spend half an hour or more just trying to find one stinking thing and still fail, take heart. I’ve been there. A lot. I still end up there occasionally–just last night, in fact. I think every astronomer has been there. It will get better.

What helps?

  • Aperture, for one. As much as I like my small scopes, there’s just no arguing with physics: bigger glass gathers more photon, makes things brighter and therefore easier to recognize.
  • Field of view is good, too. I’ve found some things this fall with my 15×70 binoculars that I never found in my 6″ reflector just because I had a nice big field in which to recognize them. A good low-power eyepiece for a telescope is indispensable.
  • For a telescope, a good finder is very helpful. I upgraded my 6″ scope with a 9×50 RACI (right angle correct image) finder and put its 6×30 RACI finder on my little Mak, and both scopes have benefited tremendously.
  • For anything, a steady mount to put it on so you’re not contending with the shakes. This is not a trivial consideration. For the first year that I owned the little Mak I had it on a cheap camera tripod, and I hated it. Never used it. Seriously. Then I got a nice tripod and a solid, smoothly-moving head and almost overnight that scope went from being my most hated to my most favorite. There is a saying in amateur astronomy that the mount is half the telescope. I think it might even be a little more than half. I’d rather use a merely average scope on a solid mount than a world-class instrument on a shaky mount.

All these things are good. They’re fixable, and you can fix them without breaking the bank. But they’re not really what this post is about. There are people with thousands invested in their equipment who still can’t find anything in the sky, and other folks with homemade scopes cobbled together from odds and ends that can line ’em up and shoot ’em down on the deep sky. The difference is experience, and that comes with time, and only with time.

So how do I find things, in terms of actual step-by-step instructions that you can use?

  1. I start with a map. It might be one of the monthly sky maps in Sky & Telescope or Astronomy, or a planisphere, or a star atlas.
  2. Using the naked eye, I orient the map to the bright stars in the sky and get an idea of roughly where I need to point the telescope.
  3. Usually I don’t try to point the telescope at the object of interest immediately. Instead I start on a nearby bright star so I can get my bearings, and then star hop to my target.
  4. If I’m having a hard time finding the star I want, I pull out some regular binoculars and do a quick scan around the sky. Binoculars are the perfect intermediate between the naked eye and the telescope, even if the telescope has a good finder. My friend with the 16″ telescope uses tripod-mounted binoculars as a kind of superfinder, which goes to show that the longer you do this, the more useful you’re likely to find your binoculars.
  5. Once I know where I want to point the telescope, I crouch behind it or lean over and sight down the tube. Even on the little Mak this is a helpful step.
  6. Hopefully that will put my starting star in the field of the finderscope. Sometimes I end up faffing about even at this stage! Once I’ve got my quarry, I move the scope so that the object is centered in the finderscope.
  7. Hopefully that will put my starting star near the center of the field of the telescope, using whichever eyepiece yields the lowest magnification and the widest field. If it doesn’t, the alignment of the finder needs to be adjusted. A good target for this is Polaris, because unlike the other stars in the sky, it doesn’t move noticeably as the Earth turns.
  8. Using the finderscope and the low-power eyepiece, I star hop to the object of interest. This step is not necessary for bright objects like the moon, bright planets, some double stars, and the brighter deep sky objects, but for everything else–most nebulae, star clusters, and galaxies–it’s crucial. Star hopping involves recognizing simple patterns of stars, like lines, basic shapes, and so on, that will guide you from your starting point to the object of interest. The first time you do any given hop, it’s imperative to have the map in your lap or sitting on a chair or table right next to the scope. More on star-hopping in a future post, but at its heart it’s really just doing this repeatedly.
  9. Once I’ve found the object of interest with the low-power eyepiece, I center it in the field of view and swap out that eyepiece for something yielding more magnification. The optimum magnification for any given object will vary depending on the condition of the sky–how much skyglow from the setting or rising sun, the moon, light pollution; the quality of the seeing (atmospheric turbulence). Frequently I push the magnification until the image starts looking ugly and then back down a step or two. Many objects, especially open clusters, look better at relatively low magnifications. But now we’re off of finding and on to observing, about which much more later.

So if you’re having trouble getting your targets in the eyepiece, don’t give up hope, and don’t give up observing. There’s no shame in taking a break after a failed search and treating yourself to something pretty and easy, like Jupiter or one of your favorite DSOs. I did so just last night.

Don’t forget to step away from the instrument from time to time, lean back, and try to absorb it all with the ole Mark 1 eyeball. Your nose may be bloody but you’re in the game. You’re out under the stars, and you’re finding your way around the universe. There’s a lot of it to learn. Give it time.