EDIT – as this is one of my most frequently referred to blog posts, scroll down to the horizontal break to get to the sections where I dispense my advice. It starts about one-fifth of the way down; you’ll see the headers. Enjoy!
Astronomy definitely has its seasons. As the months come and go, so do the different objects in the sky. I tend to observe things as they rise high in the east for the first time, and I also like to try to do that as late in the night as possible, after 10pm, or even 11pm, so as to minimize light pollution as people go to bed and turn out their lights. Summer has the great Milky Way arcing across the sky, with first Scorpio and then, later in the season, Sagittarius and all of its nebulae in all of their glory, as well as the Summer Triangle, including some planetary nebula (M57 and M27). Fall has Andromeda, the return of the open clusters of Cassiopeia and Perseus, while the Summer Triangle still rides high in the sky towards the west. Winter has Taurus and the Pleiades, plus the greatest constellation of them all, Orion, as well as the numerous open clusters from Auriga and Gemini through Canis Major.
But spring? Meh. The nights start late: sundown isn’t even until after 8pm, and around 8:30pm closer to the summer solstice, and then it’s at least another hour until astronomical twilight ends and it gets really dark. The days are sticky enough with humidity; as the night comes and the temperature goes down a bit, the air becomes saturated with the stuff, making it even stickier. (And yes, I do realize that we’ve already crossed over into summer as of last week, but I was referring to April, May, and June generally.)
And what’s to see? Yeah, sure right now we’ve got three great planets: Jupiter, Mars, and Saturn; I’m not going to deny that. I love looking at them. There are some globulars, sure, and some galaxies, but my little 5-inch Mak can’t do too much in terms of showing much detail in either of these kinds of DSOs, especially from Manhattan. These are all big reasons why I need to either move up in aperture or move out of Manhattan, both of which may be happening in the not-too-distant future, as my plan is to move to Denver in about a month, and once I figure out my life there, maybe getting an 8-inch scope. But the spring sky just has never really done that much for me. Which is why there has been a significant drop-off in my blog posts here.
I just flew back home from Denver (and boy are my arms tired!) where I did get a chance to take a good look at the sky from Cherry Creek State Park, a huge park (4 times the size of Central Park, which is pretty big) in the far southeastern part of the city. I was primarily trying to determine how much deeper I could go in terms of visual magnitude, which hopefully corresponds directly to going deeper in telescope magnitude as well.
Denver is a relatively large city, approaching 700,000 in the city limits itself, and 2.8 million in its metropolitan area. It is also spread out over a large area – suburban sprawl, to be sure. However, Denver has significantly less population than the New York metro area – about 15% of NYC’s metro population of 20 million (!!!) in about 60% of the land area – so that the light pollution should be appreciably less, especially as I was roughly a dozen miles removed from Denver’s much smaller downtown area.
And it was less. Observing naked eye from the park, I was able to see the entire parallelogram of Lyra, including 4.3 magnitude Zeta Lyrae, which would be impossible anywhere in New York City. Notably, I could still see it even with a 10-day old, 75% phase moon high in the sky. I was also able to see the entire constellation of Leo for the first time in ages, including the complete backwards question mark that makes up the head. However, that isn’t nearly as impressive, because none of the stars in Leo even approach 4th magnitude; but Leo was relatively close to the light-polluting moon, and I could still see it all.
So, Denver seems to be a promising place to move astronomy-wise, as it wouldn’t be all that difficult to get down to this park and have skies that are more than a full magnitude darker than I’m used to in New York, and probably more like a magnitude and a half darker without the moon. And of course, the ideal part of being in Denver would be being able to easily travel about an hour out-of-town to get to some truly black, black skies, completely unaffected by light pollution. You can’t really do that in New York at all; one hour of traveling only gets you about 30 miles or so out of town, still well within the enormous metropolitan light dome.
To remedy my relative lack of spring blog posts, allow me to present to you my accumulated astronomy wisdom of the ages. Well, accumulated over the past 2 years of the ages, anyway, since I got back into the hobby in a big way. A lot of this sage advice is directed at beginners just entering the hobby, but at least some of it is a bit more advanced than that as you go further and further along. Although I’ve already written much of this in various places scattered throughout the various blog posts, I am concentrating all of this information in one place both for ease of reference, and so that the sheer weight of the information will have more impact so you can see how truly brilliant I am. Well, at least astronomically. (And yes, ah say, ah say, that’s a joke, son.) As a result, this will be by far my longest blog post, but hopefully the headers for each topic will help you get through this.
When newbs ask “What telescope should I get?”, the answer invariably, in four-part harmony, is, “Get a dob” (sha-na-na-na, sha-na-na, na-na), and usually it’s an 8-inch one. I fervently disagree with this recommendation. Not that there’s anything wrong with an 8-inch dob; it’s a terrific scope, as it can show you literally hundreds of objects. There are three main reasons why I don’t recommend a big dob as a first scope to newbs:
1) It’s kinda big and kinda heavy. Oh, I know it’s not “that” big or “that” heavy, but when I think of a first-timer, I think mainly of a kid, 9-14 years old, or someone who’s recently retired and in their late 60s, and looking to get back into the hobby after a long layoff. For either of these groups, lugging around an 8″ dob would be a chore. Plus, there’s plenty of other segments of the population for whom having an 8″ dob would be tough – people living in apartments without space for a water-heater sized scope, people with finicky spouses who don’t want to see a water-heater sized scope in their living room or bedroom, and people (other than kids and retirees) for whom moving the two 20-pound pieces of the scope out to their observing site would be a struggle, like apartment dwellers who have to negotiate stairs.
2) Collimation. I know that it’s not “that” difficult for the vast majority of people. But it is difficult for some, like myself (see the Collimation header, below), and I feel like something new and exciting shouldn’t involve an additional chore before going out and viewing the sky.
3) The best telescope is the one you use. Let’s say you’ve been socked in with clouds for the past week or two – which can easily happen on the east coast. You’d love to get out there and do some observing. The weather forecast finally declares it’s going to be clear tonight. But you get home from a long hard day at work or school, you look over at that huge, heavy, water heater-sized dob sitting in the corner, and just sigh. Instead of going out observing, you just ease back in your recliner in front of the TV, beer in hand. Ah, well; another observing night lost.
That’s why I recommend to newcomers to buy their second scope first: the grab-and-go scope, which will result in a lot less sighing and a lot more observing. “Huh?” you say. What I mean by that is this: many people in this hobby have more than one scope. They have their main huge, humongous scope that they take with them to very dark sites and use to go deep and see a lot: an 8-inch, 10-inch or even a 12-inch dob. Or a nice big SCT on a sturdy mount. Something like that, a big heavy scope with a lot of aperture.
But many of us also have what’s called a “grab-and-go” scope. Something small, lightweight, easy to take out to the backyard, ready to use quickly. That’s your second scope. It’s not as large as your “main” scope, and that’s entirely the point.
Just like shoes, different scopes are used differently. You wear sneakers for some occasions; dress shoes for others. (This is also a handy analogy for explaining to the spouse why you “need” (ahem) a second scope!) Some scopes are great at wide-field, low-powered views of big patches of the sky; some are great at close-in, high magnification views of the moon and planets. Some are great at gathering enough light from far-away galaxies and nebulae to allow you to see detail in them.
The best scope is the one you use. Not the biggest, not the fanciest, not the most expensive, but the one that gets you out under the night sky, observing. So, for someone’s “second” scope, I recommend a nice, widefield refractor. Refractors don’t have to be collimated, because they come collimated from the factory and just stay that way. Refractors don’t require much cool-down time to get to the ambient outside temperature after being inside, so they are ready to use within a couple of minutes after you get them out the door and set them up.
(When there’s a temp difference between inside and outside, the telescope has to acclimate to the outside temp before giving you its best views. Until the mirror temp equalizes, there will be a layer of unstable air rising off of the primary mirror. This will cause the images in the scope to shimmer, like you’re looking at a mirage, or like you’re looking at the air shimmering as it rises above a black tar road on a hot day. Refractors need about 10-15 minutes to cooldown, versus reflectors which will typically require 30-45 minutes, or even more, depending on different factors.)
My primary “second” scope recommendation is invariably the Meade Infinity 102mm refractor, available new at Amazon for just over $200 (they fiddle with the price from week-to-week).
This is a nice first scope for a beginner on a sturdy mount, definitely a huge step up from the rickety, wobbly, shaky mounts that come with cheapo 60mm department store refractors. Four inches of aperture is enough to let you see some of the brighter deep space objects (DSOs). The alt-az mount is easy to use; you just move it to exactly where you want to point it, no muss, no fuss. It comes with 3 decent eyepieces (Kellners) and also a 2x Barlow lens. The spread of EPs and Barlow allows this scope to provide nice widefield views, and to get up to some high-powered views on the moon and planets as well.
My fallback “second” scope recommendation is the Astronomers Without Borders One Sky scope. Well, actually, whenever I’m responding to someone’s first-scope request, I usually talk about the Infinity, and someone brings up the AWB. This is a terrific little 130mm tabletop collapsible truss dob for just $200. Obviously, it has more than a full inch additional aperture over the Infinity, and that’s certainly nice, especially to show you a bit more on DSOs.
But, it has two major drawbacks in my view: 1) it really is a little scope; just 14 inches long. Even though it is on a small dob mount, you can’t just put it on the ground, unless you like to observe while lying in the grass. You have to put on top of something, like a sturdy table or high bar stool; and 2) of course, like any Newtonian reflector, it needs to be collimated.
Notably, however, my “field sources” tell me that even though it is a collapsible truss dob – that you have to uncollpase each time you use it – it holds its collimation very well. Unlike the Infinity, the AWB comes with just 2 EPs (also Kellners), but no Barlow. Because the AWB (like the Infinity) is a short focal length scope, you WILL need to buy a Barlow for the AWB to let the scope get up to high magnifications, so that will be another added expense.
The AWB One Sky is a very popular model, both because it’s a good scope and because it’s a good cause. And because of that, it is frequently listed as being out of stock. If you don’t care to wait for the AWB to come back in stock, the SkyWatcher Heritage 130P is exactly the same scope at the same price. However, it appears that the Heritage is only for sale outside of the US.
Alternatively, the Meade Lightbridge Mini 130mm dob is also just about the same scope, although it is not a collpasible truss-tube dob, but a regular solid tube dob. It is actually about $25 cheaper than the AWB to boot. But I would ask that you please try to support AWB in their worthy outreach programs, if you can.
My Collimation Shpiel
Before I let any newb that I’m advising go and buy a reflector, I make sure they understand what collimation is. I tell newbs the following, so that they are fully informed about collimation BEFORE they buy a reflector:
Collimation is the act of getting all of the optical components of a telescope in perfect alignment with each other – the primary aligned with the secondary, and the secondary aligned with the focuser. If all three components aren’t aligned very well to each other, the quality of the image you see degrades.
Do yourself a favor, take 15 minutes, go to Youtube now, and take a look at a couple of videos on collimation. As you watch, ask yourself two questions: 1) “can I do this?” and 2) “do I want to do this?” Because if the answer to either of those questions is “no”, you should get a refractor instead. The Meade Infinity 102 (discussed above in the First Telescope section) is a good one, it’s about $200 at Amazon.
Collimation isn’t supposed to be too hard, unless you’re slightly dyslexic like I am when it comes to spatial relations; and I also tend to get frustrated very easily. People liken collimation to being about as difficult as stringing and tuning your own guitar. But unlike, for example, piano tuners, there is no job called “collimator” where they come to your house and collimate your scope for you. You’ll have to do it yourself, every few months, or even every few weeks, depending on how you use the scope. Because I had no inclination or ability or patience to do this kind of maintenance on my scope, I bought a Maksutov-Cassegrain for myself instead. Your mileage may vary.
I’m not trying to scare you off of reflectors; I just want you to have full information before you buy one.
If you watch a collimation video or two and say to yourself, “Eh, no big deal,” then that’s great! A dob could be the right scope for you, as they will give you the most bang for your buck aperture-wise. Along those lines, take a look at the Apertura AD8, an 8-inch dob that comes very well-equipped. It has a two-inch dual speed 10:1 focuser and a primary mirror cooling fan. It’s sells for about $450, and I think it’s head and shoulders above the similar Orion dobs. Not that the Orion dobs are bad; they’re perfectly good scopes. It’s just that the Apertura is better. The 8-inch dob can be a lifetime scope, meaning that it has enough aperture that it can show you literally hundreds of objects and keep you astronomically satisfied forever.
I frequently have to warn beginners off of buying the dreaded Bird-Jones telescope. These reflectors are often advertised as being capable of 300x, 400x, even 500x and 600x. Some people look at certain 114mm, 127mm, and 130mm short-tube reflectors and see “#1 scope!” or “Scope of the Year!” recommendations attached to them and think, “Well, these have gotta be pretty decent scopes if they’re getting all those accolades.”
Unfortunately, that’s just plain wrong. Those “accolades” are just marketing hype by the vendors who slap them onto the webpages. There is no J.D. Power and Associates for scopes, handing out awards. These scopes are a special short-tube design called Bird-Jones. The reason these Bird-Jones scopes are in such short tubes is because they have a lens element at the bottom of the focusing tube that works to extend the focal length – while keeping the entire tube, and scope, nice and compact, so that department stores can keep more of them on the shelves in less space.
Theoretically, a Bird-Jones scope could be just as high-quality as a Mak. Like the Mak, the Bird-Jones scope has a spherical primary mirror, and the lens element at the bottom of the focuser should have the same effect as the Mak’s meniscus, even though it’s placed in a different position. Again, wrong!
The manufacturers of these Bird-Jones scopes have cut every corner to save a buck here and a quarter there. That lens element at the bottom of the focuser is nowhere near being the quality of a Mak’s meniscus. These Bird-Jones scopes are literally called “department store” telescopes, and that’s not a compliment. You will find these Bird-Jones scopes on the shelves of your local big box store, and that’s the last place you want to be shopping for telescopes. They are the cheapest of cheap scopes so that the big box stores can stock them and say, “Look, we even sell telescopes!”
Other than their inherent lack of quality, the other major problem with these Bird-Jones scopes is that they are practically uncollimatable. (See my Collimation Shpiel, above.) Oh, it is possible, but it is at least 4 times harder to collimate a Bird-Jones reflector than a regular Newtonian reflector, as it involves partially disassembling and reassembling the telescope each and every time you have to collimate it.
At its best, even if it is properly collimated, a Bird-Jones scope is only going to be capable of giving you about 100x magnification. And as it falls out of collimation, that view is only going to get worse. That means that you are guaranteed to have subpar views from a Bird-Jones. Unfortunately, I know this first-hand because I made the mistake of buying one about 10 years ago, and it is sitting 10 feet away from me as I type this. I wouldn’t even give this scope away; these scopes are exactly that bad. They will frustrate you and drive you right out of the hobby. I wish they would simply stop making them, and collect all the ones that are currently out there and melt them down for scrap.
Instead of buying a Bird-Jones scope, buy a regular Newtonian reflector. It is hard to tell the difference between the two just by looking at the photos on the vendor websites, as all the tubes for these 4 1/2 and 5-inch scopes are short and stubby. Every Bird-Jones scope that I know of has a focal length of 1000mm = 1 meter = 40 inches, but it’s in a 20 inch long tube.
EDIT – It has been pointed out to me by a few of my loyal readers that there is another category of these abominations: the 1400mm = 55 inches Bird-Jones. These are all 150mm telescopes, but again, they all come in that same “tube that’s half as long as 55 inches”. If you find any scope that’s 150mm/1400mm, stay away!
Here is a list of the various short-tube reflectors out there:
For all the many negative things I say about Orion (their tendency to overcharge for the same equipment that can be bought more inexpensively elsewhere; their lack of support to third-party purchasers, i.e., if you buy any Orion product used, they don’t know you), I can easily and graciously compliment them in this department – Orion does not sell any Bird-Jones scopes. Just about every beginner reflector you buy from them is going to have a parabolic mirror – which obviates the necessity for any Bird-Jones corrector lens.
Starblast 4.5 = Regular Newt
Starblast 114mm = Regular Newt
Spaceprobe 130ST = Regular Newt
Spaceprobe 3 EQ = Regular Newt – but with a spherical mirror. The negative effects of the spherical mirror are mostly counteracted by the very long f/9.2 focal ratio.
Astromaster 114 = Bird Jones
Astromaster 130 = Regular Newt
Powerseeker 114 = Regular Newt
Powerseeker 127 = Bird Jones
Omni XLT AZ 114 = Regular Newt
Omni XLT AZ 130 = Regular Newt
Computerized 114LCM = Bird Jones
NexStar 114SLT = Bird Jones
NexStar 130SLT = Regular Newt
114EQ-AST = Bird Jones
StarNavigator 130 = Bird Jones
Polaris 114 = Regular Newt
Polaris 127 = Bird Jones
Polaris 130 = Regular Newt
Astronomers Without Borders One Sky = Regular Newt
Skywatcher Explorer 130M = Regular Newt
iOptron N114 = Bird-Jones
Vixen R130SF = Regular Newt
Bresser Spica 130 = Regular Newt
Bresser Messier NT130 = Regular Newt
Konusmotor 130 = Bird Jones
Bushnell Northstar 114 = Regular Newt
Seben Big Boss 150-1400mm = Bird-Jones
ProTelescope.com’s “6” GPS Computer Controlled Reflector Telescope Astrophotography Package” = Bird-Jones
Visionking 5.9 inches 150 – 1400mm = Bird-Jones
Baytronix 150/1400 = Bird-Jones (this seems to have morphed into the VisionKing)
TS-Optics Megastar1550 – 150/1400 mm = Bird-Jones
AstroVenture 6″ Short Tube Reflector Telescope = Bird-Jones
Most newbs are excited about buying these kits, because they want additional eyepieces beyond what came with their scopes. They price out all the individual items in them and see that the kits will “save” them money. I am generally against the standard Celestron and Meade 1.25″ Plossl kits. There’s absolutely nothing wrong with the EPs themselves – they’re all perfectly good for what they are, which is that they are standard Plossls. And the metal case they come in is AWESOME! But the problem with these kits is that they’re duplicative, plus they’re giving you all sorts of other stuff you don’t need or want, so you end up spending more than you otherwise would have to get the good stuff that would actually help you.
Let’s take the Celestron 1.25″ kit. It has a good Barlow, and it has 32, 17, 13, 8, and 6mm EPs. But if you take the 32 and use the 2x Barlow, you get a 16. That’s really no different from the 17. Most scopes come stock with a 25 when you buy them. Double that and you get a 12.5, which is the same as the 13. Double the 17 to get 8.5, which is the same as the 8 in the kit. Double the 13 to get 6.5, same as the 6.
Plus, a 6mm Plossl is tough to use. Not impossible at all; I have a 4mm Plossl that I use. But it’s tough, because it has limited eye relief – you have to hold your head very still to use it to get into the very short and narrow shaft of light coming out of the EP. (See the section on Eye Relief, below.) So you’ve got at least 3 out of the 5 EPs in the kit that are duplicative of each other, or what you already have, or are tough to use. That leaves only 2 EPs worth getting, the 32mm and the 8mm.
The kit comes with all sorts of colored filters. Only about two of these are of any use – the 80A blue filter (which works well on planets to show more detail) and the moon filter, to reduce its overwhelming brightness and show more contrast details. What will happen is that you will check out the other colored filters, decide that they don’t help you see any additional detail, and then you’ll put them in a sock drawer after you’ve used them one time, never to be seen or heard from again. (This isn’t a knock against filters in general; only against the colored ones that come with these kits. Other, more expensive filters really do help you see more.)
All this being said, these eyepiece kits come up for sale on Cloudy Nights at least a couple of times a month. The Celestron kit normally sells new for $130 (the Meade is $180!), but used they generally sell for around $80-90 or so on Cloudy Nights. If you can get the kit for that price, then YES, that’s worth it, because you can pick through it, figure out what you like, sell off the EPs that you don’t and KEEP THAT CASE. But if you’re paying over $100 for one of these kits, you’re wasting some money in my opinion.
The one exception to my advice not to get these kits is the Zhumell eyepiece kit. The Zhumell comes with only 4 Plossls, instead of the usual 5 in the other kits. It’s got the 32, 12.5, 6, and 4. Plossls are pretty much Plossls; as long as you’re spending about $30-40 each on one, they’re relatively generic. (Below that amount, and you might run into some significant quality differences.) No one type of Plossl is really better than another, with perhaps the exception of TeleVue. Perhaps.
Most new scopes don’t come with a 32mm, so that’s useful to get you the lowest magnification and widest field of view your scope is capable of. This is important on most beginner scopes, as you want to have the widest field of view possible so that it’s easier to find what you’re looking for. The 4 and 6 are still difficult to use because of the limited eye relief, but not impossible. And the 12.5 will be duplicative of Barlowing the 25 that likely came with your scope. So, not a lot going on with the Zhumell Plossls that’s different from the other kits.
The Zhumell kit also comes with a nice Barlow (as do the Celestron and Meade kits), as well as the similar array of relatively useless colored planetary filters. Unfortunately, the Zhumell kit doesn’t include the useful #80A blue filter. However, it does come with a moon filter and, what I think is even better, a polarizing filter. The polarizing filter reduces glare from bright objects to let you see more detail – very useful.
The significant difference between the Zhumell kit and the others is the price. The Zhumell kit is only $90, and of course, you’re still getting that awesome – although smaller – case. The Zhumell kit is just about worth that $90.
EDIT – For information on what you should be looking for in eyepieces, see my full-blown article on the different attributes of eyepieces here.
Some of the more inexpensive scopes – especially department store scopes, but also a good number of scopes that are above the “piece of junk” line that is at about $200 – have perfectly good optics, but not the best mounts. Inadequate mounts can be particularly frustrating because they wobble and shake, both at the slightest touch, especially while focusing, and at the slightest breeze as well. This will make whatever you’re looking at bounce all over the field of view. A lot of this bounciness can be controlled and eliminated by a few simple modifications.
First, put a weight on the accessory tray. About 5 – 7 pounds or so. If you can’t put a weight on the tray (or if your mount doesn’t have one), a gallon of water weighs just over eight pounds; you can tie a rope or bungee cord through the handle of a mostly filled jug and hang if off of the bottom of the mount. Second, go around the entire mount/tripod, and tighten up every screw one-quarter of a turn to make the mount even tighter, so that there’s less play in between the connections holding the scope together. Don’t tighten more than that, because you don’t want to crack the plastic that’s usually in between the screw and the metal legs. Third, don’t extend the legs all the way out. The weight on the accessory tray, and keeping the telescope low both help to keep the center of gravity lower so that the mount vibrates less.
And also, if you keep the scope low by not extending the legs very much, you can observe while sitting down. Observing while sitting isn’t for your legs, although that’s a nice side benefit. It’s for your eyes. It’s so that you can observe instead of just looking. This is because the atmosphere is unstable, and the telescope magnifies that instability. This is a concept known as seeing (discussed, where else, under the header Seeing, below). For a few seconds out of every few minutes you observe, the seeing steadies down, and you have great clarity – details just pop into view where they weren’t visible just a few moments before. You can’t just look at an object for just 30 to 60 seconds; you’ve gotta observe it for 5 -10 minutes or more for the seeing to get steady like this.
A fourth thing to do is to make yourself some anti-vibration pads. Don’t spend 40 bucks on the ones Celestron sells you. Instead make your own for $1.55 with these furniture cups from Home Depot or something similar from your local home improvement store. Take these cups and tape some dense foam, like packing foam, into the round tops. Doing just these four things will really make the mount much more stable and less prone to vibration.
Eye relief is the maximum distance between the top lens of the eyepiece and the bottom of the lens in your eyeball where you can still see the entire field of view that that eyepiece offers. If you move your eyeball further away, you will start to see less and less of the sky through the eyepiece. On the other hand, moving your eye in closer than that will not allow you to see anything more.
This measurement is important to consider when buying eyepieces; eye relief is listed under the specifications tab wherever you shop online for eyepieces. This is because it becomes increasingly harder to hold your head and neck stock still as the eye relief diminishes. For example, a standard Plossl will generally have eye relief that is roughly about two-thirds of the eyepiece’s focal length. So, for example, a standard 9mm Plossl will have an eye relief of about 6mm. That’s okay. It isn’t too hard to hold your head within a 6mm range variation for 5-10 minutes or so while you observe.
But consider a 4mm Plossl with less than 3mm of eye relief. That means you have to hold your neck and head even steadier to observe through that eyepiece and see everything for any length of time. This could lead to neck or back strain. A 4mm Plossl becomes difficult – but not impossible – to use for that reason. If you already suffer from any kind of back or neck problems, a 4mm Plossl is not the eyepiece for you.
Orthoscopic eyepieces, which are considered the gold standard for high-powered lunar/planetary observing, have an eye relief that is roughly 3/4 of the focal length of the eyepiece. So an 8mm ortho has roughly the same 6mm eye relief that a 9mm Plossl has. Notably, Barlows do not affect the native eye relief of an EP – in fact, they lengthen it slightly by a millimeter or so – so that you can Barlow a higher focal length EP to get to higher magnifications while preserving eye relief. I specifically had this particular fact in mind when I bought a 12.5mm ortho. It has a comfortable 10mm of eye relief, and I Barlow it go from 123x to 246x while maintaining that comfortable eye relief.
Eye relief is an especially important consideration for those people who suffer from astigmatism and must wear eyeglasses at the scope. (If you are near- or far-sighted, the scope takes the place of your glasses, so you should take them off while observing.) My understanding is that eyeglass wearers need about 16mm of eye relief to be comfortable, and a little more is even better. As you might imagine, those eyepieces cost more.
Vendors offer many kinds of “long-eye-relief” EPs, usually labelled as being “planetary” EPs. This “planetary” label is nothing more than marketing hype, as any EP can be used to observe the planets. Other than the comfortable eye relief, there is nothing special about these so-called “planetary” EPs in terms of additional sharpness over other EPs that aren’t labelled that way.
You know how, on a hot sunny day, you can see the heat rising off of a black tar road – the air shimmers? The air is actually doing that all the time, except it’s almost always invisible to the eye. A telescope has two jobs: one, to collect as much light as possible, and two, to magnify what’s invisible to our eyes. When you use a telescope to look through the atmosphere, it is magnifying this instability, this turbulence, that’s always present everywhere in the atmosphere to a greater or lesser degree. In astronomical terms, that turbulence is what’s called seeing.
Poor seeing can occur for a lot of reasons. It could be because your scope’s optics – your primary mirror – hasn’t gotten to the same temperature as the outside air. If that happens, then a thin layer of unstable air forms above the mirror, and that will ruin your high-magnification views. Depending on the size of the mirror and the temperature difference, most mirrors will reach ambient temperature in about 15-45 minutes or so. This could take even longer if you’re observing in the frigid cold, or if you’re using a closed-tube scope like an SCT or Mak, which take longer to cooldown.
Another reason is because of local conditions. For example, because Saturn is relatively low in the sky for most Northern Hemisphere observers – and will remain that way for a number of years to come – you’re looking through a longer and thicker column of air than you do when it’s higher in the sky. Looking at something that’s just 30 degrees above the horizon means that you’re looking through twice the column of air as you would if that object were directly overhead. Twice as much air doubles your chances for poor seeing. This is why, to minimize this, you want to observe when the moon or planet has reached its culmination, its highest point in the sky for the evening. A program like Stellarium (downloadable for free!) can tell you when this will be each night.
Also, because the planet is lower in the sky, you might be looking at it right over the roofs of neighbors’ houses. Those roofs have been absorbing heat all day, and they let it out slowly all night. That causes the same layer of unstable air that comes off of your mirror.
Or, you could be observing from a tar/asphalt/concrete driveway that does the same thing as a tar or terracotta roof. The best observing surface is grass for that reason, because the earth, the soil, doesn’t radiate heat all night.
Finally, another cause of bad seeing is something completely out of our control – the jet stream, miles above our heads. Because the jet stream isn’t a smooth flow of air, it too can raise turbulence and wash out fine detail. For the same reason, being downwind from mountains wreaks havoc on seeing. While observatories are generally located on the tops of mountains that have a smooth flow of wind, the mountain peaks break up otherwise smooth airflow to create eddies and wakes that ruin seeing beyond them.
For this reason, believe it or not, while a hazy humid summer night won’t be so great for observing DSOs, the seeing will be excellent for observing the moon and planets. That high haze is an indication that the atmosphere is very steady. Another good time to observe is after a high-pressure zone has moved in overhead, to being clear stable skies.
On your typical night, the local seeing conditions will generally limit the magnification to around 200x – regardless of the aperture of your telescope. If the seeing is better than average, you can get up to 250x, or maybe a little more.
On the other hand, sometimes, on rare nights, maybe just a handful of nights all year-long, all of these things will coincide in your favor, and you can get up past magnifications of 300x or 400x or more. This is called “stupid-high powers.” It’s not really worth it to buy an EP just for these rare nights. Instead, that’s the time when you use a good Barlow and double your magnification.
The most important aspect of seeing is to just keep observing. Because of the effects of seeing, you can’t just look at an object for 30 or 60 seconds and expect it to give up all of its details to you. Even on average seeing nights, every few minutes, the atmosphere quiets down, gets still, and the seeing becomes much better for just a few seconds. You have to observe an object for 5-10 minutes, or more, to catch those few seconds of good seeing in between all of the bad. That’s when those details will just pop right out at you.
Some people think that your eye adapts to the darkness within a few seconds of being in the dark, as your pupil quickly expands to let more light in. That much is true; but that is only a relatively minor part of dark adaptation. What’s more important is what’s going on in the back of your eye at your retina, not up front at your pupil. Your retina has two structures for detecting light: cones and rods. The cones detect color, and require significantly more light to activate, which is why it is very difficult to detect color in most astronomical objects – with some important exceptions, like the planets and bright stars, such as the glorious double star Albireo.
The rods are what come into play in the dark adaptation game. The longer you are in the dark, the more a special chemical called rhodopsin floods your retina, enabling your rods to be more and more sensitive to light. As you look through the eyepiece for a couple of minutes, your eyes (or at least the one eye at the eyepiece) gets more and more dark-adapted. More and more low-light level detail comes out the longer you look at something.
The biggest killer of dark adaptation is, of course, light. This could be because of just general light pollution lighting up your skies, which in turn lights up your observing site. More usually, it’s because there is some ambient light somewhere around where you’re viewing from, like streetlights, or a neighbor’s porch lights. This ambient light keeps your eyes from ever becoming fully dark-adapted.
Full dark adaptation can take up to 30 minutes, believe it or not. How do I know? Last summer I went out to look at the Perseid meteor shower. When I started out observing, I could not see Albireo, the eye star in Cygnus. It’s magnitude 3.05. (I observe off of my roof in Manhattan, so the light pollution here is about the worst it could possibly be.) After 10 minutes or so of doing nothing but staring at the sky, I could just see Albireo with averted vision. After another 10 minutes, I could just see it directly. After another 10 minutes, it was practically staring me in the face.
Of course, even a half hour’s dark adaptation can get wiped out in an instant if you look at something bright – like the moon, especially through the scope, or if you go back inside. Then the clock resets back to zero, and you have to start all over from scratch. This is why a red light flashlight is handy, as red light has the least effect on dark adaption.
To speed up dark adaptation, you can wear an eye patch. Yes, really, an eye patch, like you’d get in a pirate costume for Halloween, or available at your local pharmacy for a couple of bucks. Wear it over your observing eye for a half hour before you go out (yes, you’ll look silly) to save time on having it dark adapt while at the scope.
The myth is that this is why pirates wore eye patches when going into battle – they would have it on one eye when fighting on deck in the sunlight; then when they went below decks where it was dark, and the enemy was hiding out, they would take off the eye patch and already be dark-adapted so that the enemy wouldn’t have an advantage – if you believe that sort of thing. 🙂
Another way to dark adapt is to observe with a “hood” over your head to block out any ambient light sources. It’s just like those old-timey photographers from the 19th century, when they would go back behind the camera and underneath the hood. You can just use any dark-colored t-shirt to do this. All you have to do is cover your entire head and the eyepiece so that all you can see is what you’re looking at in the eyepiece.
The best combo is to wear the eyepatch inside before you go out, and then to remove it ONLY when you’re all set up to view underneath the hood, so that the ambient light can’t ruin your dark-adaptation. When you’re done with that object, put the patch back over your observing eye, and only then come out from underneath the hood.
There are a couple of important things to know about using binos for astronomy. First of all, don’t bother with any binos that have that “ruby-red” coating on the objective lenses. Those are cheap pieces of junk. Once you get beyond this, note that you can’t go above 12×60 binoculars and use them handheld. There are two reasons for this. One is the magnification – you can’t hold your hands steady enough to keep whatever you’re looking at from bouncing around. The second is that unless your first name is Ah-nold, you can’t hold big binoculars like these up to your eyes steady for a very long time, because they get very heavy very quickly, your arms get tired, and you’re right back at the first reason.
This doesn’t mean you can’t or shouldn’t get 12x60s, or 15x70s, or even 25x100s to use for astronomy. But just know that you will need to buy a separate tripod to use them, so factor in that expense.
In my reading about astro binos, many people like the Celestron 15×70 Starmasters. They’re good and cheap. However, if you buy these, make sure you buy from a vendor who accepts returns without question. (Amazon would be your friend here.) This is because, at 70 bucks or so, it is likely that these binos will arrive to you out of collimation such that you can’t merge the images you’re receiving from each eye into one. If that’s the case, you’ll have to return them until you get a pair that are properly collimated. According to what I’ve read, this may even take more than one return.
Another thing to know about in terms of buying binos are the exit pupils of the eyepieces on the binos. The exit pupil of the binos could put out more light than the entrance pupil in your eyeball can take in. The pupil in your eye can only open up to be so wide, and that maximum width decreases with age. For kids under 20, your pupils open to about 7mm wide; in your 30s and 40s, it’s 6mm; and in your 50s it’s down to 5mm. (This does depend on the individual, and is more of a guideline than a hard and fast rule.)
Just like eyepieces, binos have exit pupils, too – that is the diameter of the shaft of light that comes out of the binos’ eyepieces. The formula to know the size of the exit pupil in binos is easy – it’s the aperture divided by the magnification. What’s important to note here is that if that shaft of light is larger than the pupil of your eye, that light will not enter your eye. Instead, that light will hit your iris, the colored part of your eye, and splash off, wasted, so that the overall view will be dimmer than it otherwise would be with that aperture.
So, if you’re 50 and you have 7×50 binos, you will be losing a lot of light. The binos are sending out a shaft of light just over 7mm wide, but your eyes are letting in a shaft of light that’s only 5mm wide. All that other light is wasted. The solution? Buy binos that match your eye pupil. In this case, 10x50s would be appropriate. In fact, 10x50s are pretty much the best bino solution for most people. They’re still reasonably light to hold in your hand, they give you significant magnification, and they won’t waste light as I just described.
EDIT – see my full-blown article on astro binos here.