Archive for September, 2009

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Traveling in space and time

September 18, 2009

I’m going out of the country for a week, and I doubt if I’ll get anything posted while I’m gone. In the meantime, the Small Telescopes blog has some great targets for binoculars and, uh, small telescopes, that you might want to check out. Cloudy Nights also has a monthly highlights list and a constellation profile.

And speaking of Cloudy Nights, my first article was just published there today. I wrote that little piece ages ago and most of it will be familiar to readers of my blogs; this blog is sort of an extension of that into an ongoing project.

Have fun while I’m gone!

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Reverse aperture fever: the allure of small telescopes

September 17, 2009
The 30-inch Obsession--never be insecure again!

The 30-inch Obsession--never be insecure again!

One of the mantras of amateur astronomy is that “Aperture rules”. There is a lot of truth to this. Set up a telescope on the sidewalk and the first two things passersby will ask are “How much does something like this cost?” (answer: less than you probably think) and “How much can it magnify?” (ditto). Telescopes are unavoidably bound up with magnification in the popular imagination.

Astronomers, amateur and professional alike, are usually much more concerned about a telescope’s light gathering ability and its ability to resolve fine details, both of which depend on aperture. Resolution scales directly with aperture, so a 6-inch scope has twice the resolution of a 3-inch scope–important for teasing out details like the cloud bands of Jupiter, the Cassini division in Saturn’s rings, and for resolving globular clusters from patches of fuzz into clouds of stars. Light gathering ability is a function of area, and thus scales with the square of aperture. A 6-inch scope has four times the light gathering ability of a 3-inch scope, so it will pick out many more faint galaxies and nebulae than the smaller instrument.

There are a couple of caveats, or rather one caveat that cuts a couple of ways. How much you can see with a telescope depends heavily on the sky. If the light pollution is bad enough to swamp out the signal from those faint galaxies and nebulas, the advantage of a 6-inch scope over a 3-inch scope is somewhat reduced. To a certain extent you can fight light pollution with more aperture, but as many or more people choose to fight it by buying more portable scopes than can be easily transported to dark sky sites. I really have seen more with my 3.5-inch scope under dark Oklahoma skies than I have with my 6-inch scope here in the light-polluted swamp of LA county.

The other limitation imposed by the sky is seeing, or atmospheric turbulence, which manifests at the eyepiece as a roiling blur over whatever you’re trying to see. The less atmosphere you have to look through, the better, which is why observatory telescopes are on mountaintops, and why seasoned stargazers try to catch their targets as far from the horizon as possible.

Seeing is the main reason why astronomers are rarely worried about the magnification potential of a particular telescope. The general rule of thumb is that a decent quality telescope can magnify 50x per inch of aperture before the image starts to break down. The limits, then, for my 3.5-inch and 6-inch scopes are 175x and 300x, respectively. But most nights in most places seeing will ruin the image before the inherent limitations of the optics. In other words, the sky gives out before the scope.

So on the telescope ledger we have light-gathering and resolution on the “bigger is better” side, balanced against cost and transportability. Any scope that hits the sweet spot in the middle is bound to sell like hotcakes–6- to 8-inch Dobsonian reflectors and Schmidt-Cassegrains are probably the most popular “serious” telescopes in the world, because they gather quite a bit of light but are not too much, cost- or weight-wise, for average folks.

My 3.5-inch scope set up for birding.

My 3.5-inch scope set up for birding.

And yet…and yet. There is something about small telescopes that many people find hard to define and equally hard to resist. My fellow astro-blogger Treehopper recently wrote a great post about small telescopes, and an e-quaintance in Singapore has dedicated his whole blog to the subject. I suspect that part of the appeal is the ability to really take a small scope to the edge of the envelope. I often sit down behind a little scope with the attitude, “C’mon, little guy, show me what you can do!” I find that with small scopes I am often pleasantly surprised at how good the views are, and with big scopes I am often disappointed that the sky isn’t better. Not the fault of the big scopes, but a factor nonetheless.

My reverse aperture fever is also grounded in the perhaps irrational conviction that stargazing should be inexpensive, accessible, portable, and fun. Yeah, a 12-inch truss tube Dob would show me roughly a zillion times more than my 3.5-inch scope, but I get tired just thinking about wrassling one of those things around. Being able to grab my little scope on its tripod in one hand, a folding chair in the other, and to start soaking up the light of long ago and far away about 30 seconds after I get the urge–I like the idea of doing that, and I like actually doing it even better. Nothing unique here–lots of amateur astronomers have “grab-n-go” setups–it’s just that for me, grab-n-go is where it’s at. Since I got a decent mount for my little scope, my Dob has only gotten used once or twice. And who cares? As Uncle Rod says, “There’s no wrong way to do amateur astronomy.” (My personal emendation: “except to not do it at all”.)

Another factor–and a particularly appropriate one this year–is the knowledge of how much our forebears achieved with modest instruments. Haven’t you ever wanted to be Galileo, who pointed his ‘military instrument’ to the moon out of nothing more than simple curiosity, and ended up discovering how the heavens go? From Turn Left at Orion (p. 202), one of the best books for beginning telescope users:

Galileo discovered the four major moons of Jupiter (forever after called the “Galilean satellites” in his honor); he was the first to see the phases of Venus and the rings of Saturn; he saw nebulae and clusters through a telescope for the first time. In fact, a careful checking of his observations indicates that he even observed, and recorded, the position of Neptune almost 200 years before anyone realized it was a planet. He did all this with a 1″ aperture telescope.

Charles Messier, who found the hundred deep sky objects in the catalog that bears his name, started out with a 7″ reflector with metal mirrors so poor that, according to one account, it was not much better than a modern 3″ telescope. His later instruments were, in fact, 3″ refractors.

The point is this: there are no bad telescopes. No matter how inexpensive or unimpressive your instrument is, it is almost certainly better than what Galileo had to work with. It should be treated well. Don’t belittle it; don’t apologize for it; don’t think it doesn’t deserve a decent amount of care.

Telescope vs beverages

My little scope with beverage containers for scale.

The counterpoint to “Aperture rules” is “The best telescope for you is the one that shows you the most”. I spent my first year and a half in amateur astronomy on a quest (to be detailed in future posts) to find that perfect scope. That it turned out to be a little thing the size of a 2-liter soda bottle is both a happy accident and welcome confirmation of my conviction: stargazing should be inexpensive, accessible, portable, and fun. As Tony Darnell concluded in one of the best pieces ever written about telescopes, “If you’re outside looking at the stars without a big smile on your face or a feeling of awe in your heart, you’re not doing it right.”

The moon through my "humble" 3.5-inch scope.

The moon through my humble 3.5-inch scope, photographed with a humble point-and-shoot digital camera humbly handheld up to the humble eyepiece. Tremble before my awesome humility!

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More mind-blowing pictures from our robotic servants

September 12, 2009

butterfly_hst_big

There is a certain segment of the population that, when encouriaged to get outside to do a little stargazing, says, “Nah, I’ll stay inside and surf for pictures on the internet.” I don’t advocate doing this instead of going outside and seeing things for yourself, but I’m certainly not opposed to surfing for pictures in addition to stargazing. And this is a good time to do it!

Hubble is back, baby, and the Hubble team showed off the rejuvenated telescope’s mojo with a ream of mind-bendingly awesome pictures, many taken by the newly installed Wide Field Camera 3 (WFC3).  These have turned up all over the astro-blogosphere. My favorite is the Butterfly Nebula, NGC 6302, a planetary nebula blown off by a dying star (at top). Would that we could all go out with such grace.

Mars craters from HiRISE

For my money, the coolest non-Hubble camera in existence is the HiRISE camera on the Mars Reconnaissance Orbiter. Image above shows craters and ridges in Hesperia Planum (full version here). The archive of publicly available images from HiRISE continues to grow; go here and spend some time exploring another planet.

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Mission 7: Star clouds of Sagittarius

September 9, 2009

Mission Objectives: Globular Cluster, Open Cluster, Nebula

Equipment: Binoculars

Required Time: 5 minutes

Related Missions: Not Everyone’s Pot of Tea

Instructions: See how many deep space  objects you can see in Sagittarius with binoculars (or, if you must, a telescope). Here’s a guide:

Sagittarius again

Your job will be a lot easier if you’ve got dark skies. Here at the edge of LA County, M7, the Butterfly Cluster (M6), the Lagoon Nebula (M8), M21, M22, M24, and M25 are all fairly easy to spot with binoculars, and everything else is difficult to impossible. If don’t have dark skies and can’t get to any, at least get as much local darkness as possible. We have a little swath of lawn about 10 feet wide between the house and garage, and if I go back in there the buildings block out about half the sky, but the half they don’t obscure looks a lot darker because I can get all the local light sources (like the neighbors’ annoying security light) out of my eyes. Also, remember that pupil dilation just takes a few minutes, but full physiological dark adaptation takes an hour or so.

For my money the best thing in Sagittarius is the M24 star cloud. Go up from the lid of the ‘teapot’ to the first bright star (as indicated by one of the constellation lines in the image above). That star has a little curlique of followers trailing up and to the left. Follow to the curlique to the explosion of stars; that’s M24. It’s not really a cluster in the traditional sense. Rather, it’s a hole in the giant clouds of gas and dust that usually obscure the inner parts of the Milky Way from our view here in the galactic ‘burbs. According to Wikipedia, under optimum sky conditions (which I ain’t got) up to 1000 stars are visible through binoculars in M24. I can only see a few dozen, but it’s still pretty awesome.

Cheap bino mount

Finally, as always, the view through the binoculars will be a heck of a lot better if you can hold them steady. The best solution here is not to hold them at all, but rather to let a device hold the binos perfectly still while you just look through them. Most binoculars have a 1/4-20 socket at the front in between the objective lenses (this is usually covered by a small plastic cap and a lot of casual bino users don’t even know it’s there). You can use this socket to attach the binoculars to a monopod or tripod. Dedicated binocular tripod adapters are available online for a little as ten bucks, or you can build your own for about two. Get a small angle bracket or corner brace, a 1/4-20 wingnut to attach the bracket to the 1/4-20 bolt of the tripod (this is what you would normally screw the camera onto), and a 1/4-20 thumbscrew to attach the binos to the bracket, with maybe an extra wingnut to tighten things down.  BAM! Now you can aim and focus the binoculars, take your hands off and let the shaking settle down, and observe in shake-free comfort. It’s a qualitatively different experience from handheld binocular observing, and you will  see more.

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The moon and Jupiter last night

September 5, 2009

Full moon Sept 4 2009

Last night I attended my first meeting of the Pomona Valley Amateur Astronomers, who, you’ll recall, were kind enough to invite me along on their Mt Wilson trip a few weeks ago. The evening’s feature presentation was  on the Juno mission to Jupiter, which is under construction right now. Juno is slated to launch in two years and arrive at Jupiter in 2016 for a year-long observing run. Unlike the Mars rovers, which can be run until they quit, probes to the Jupiter system are deliberately crashed into Jupiter while they’re still functional. This is to avoid having a probe break down, crash land on Europa, and contaminate it with terrestrial microbes.

It was a great talk and I was feeling jovial–and Jovian–when I got home, so I hauled out my 6-inch reflector to have a look at Jupiter. The atmosphere was fairly clear and steady so I got out my camera. My method–holding the camera by hand up to the eyepiece–is called afocal projection photography by photographers and opticians, digiscoping by birders, and white trash astrophotography by me. My camera is an older model, a 4MP Nikon Coolpix 4500, but it has good optical zoom and it is a favorite for this sort of thing among birders.

If you want all the nitty-gritty, I put the camera in macro (flower) mode, manually set the exposure, zoom to the desired level, let the camera autofocus on the target, and snap away. I usually take between 50 and 100 pictures. This gives me a good sample from which to pick the one or two best shots afterward. Sometimes my hand moves, sometimes the autofocus gets squirrelly. The biggest thing, though, is that atmospheric turbulence varies moment by moment. Even on a night when the sky is roiling there may be short windows of stillness, and vice versa, so it pays to take a lot of pictures in hopes of hitting the jackpot. Many people now are using webcams, which shoot continuously, and then choosing only the sharpest images to stack and process. I haven’t ascended to that level yet.

Last night turned out to be exceptional, at least during the brief interval around midnight when I was out shooting. I got the sharpest pictures of the full moon and of Jupiter that I’ve ever taken, and the first I’ve ever gotten of Jupiter with all four Galilean moons. Click the picture below for the full size, unlabelled version (moon IDs from Stellarium). Clear skies!

Jupiter and moons Sept 4 2009 480

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Mission 6: Not Everyone’s Pot of Tea

September 2, 2009

Mission Objectives: Constellation, Globular Cluster, Open Cluster, Nebula

Equipment: Naked eye, Binoculars, Telescope

Required Time: 5 minutes

Related Missions: Eye of the Scorpion

Instructions: Go outside shortly after dark, face south, find Antares, and to the left/east of Scorpio, look for a teapot.

Sagittarius with lines

Yes, really. The heart of Sagittarius, allegedly the Archer, looks strikingly like a teapot. Which, I think we can all agree, is a considerably less aggressive incarnation. Once you’ve spotted it, it will be hard to avoid seeing it any time you look toward that part of the sky. It’s especially easy if you can trace Scorpio–it looks like the teapot is about to pour on the scorpion’s tail. Here’s the plain version so you can practice:

Sagittarius sans lines

Sagittarius is the thick of the summer Milky Way and contains the core of the galaxy. As a result, it is just loaded with deep sky objects (DSOs)–it hosts 15 of the 110 Messier objects, more than any other constellation. It has star clusters in its hair and hanging out of its pockets. Some are open clusters, the result of relatively recent bouts of star formation (“relatively recent” here means “within the last half-billion years or so”), but many are globular clusters or “globs”, spherical micro-galaxies of up to a million stars apiece that orbit the core of the Milky Way in an extended halo.

Sagittarius also has a stunning emission nebula, M8 or the Lagoon Nebula, which is second only to the awesome Orion Nebula (M42) for Northern Hemisphere observers. Like the Orion Nebula, the Lagoon is a site of active star formation; it is lit by the young stars it contains, and more are forming even as you read this (the Lagoon Nebula is only 4100 light years away, and it is highly unlikely that the multi-million-year process of star formation has suddenly stopped since the pyramids went up).

Sagittarius DSOs

With a clear southern sky and a pair of binoculars–which have hopefully by now been warmed ever so slightly by the brilliant light of Jupiter–you can see three beautiful DSOs that illustrate three stages in the life cycle of stars and of the galaxy itself.

Globular cluster M22 is a fuzzy ball above and to the left of the teapot–I imagine it forming a right angle with the northeastern stars of the teapot lid, as shown above. Through a telescope of less than about 6 inches aperture it will likely remain a fairly fuzzy ball, but pouring on more aperture and magnification will resolve it into something approaching this (image from Wikipedia):

M22HunterWilsonM22 is full of very old main sequence stars, and astronomers estimate its age at about 12 billion years, meaning that it has been around for more than 90% of the history of the universe. Its stars are Population II, which means that they formed shortly after the universe itself, when there had been little time for successive waves of novae and supernovae to seed the universe with heavy elements. No one knows if the Population II stars have planets; if they do, they are probably gas giants and any solid bodies are probably icy and metal-poor. If life arose in this or any globular cluster, it is hard to imagine how any of it could have become starfaring or even radio-using with few or no metals. Nobody knew this back in 1974, when Arecibo sent a “Hey, how are ya?” radio message to the globular cluster M13. M13 was chosen because it is nearby and has tons of stars; somewhat ironically, those stars are the least likely to have civilizations capable of receiving the message or responding (which may be a good thing, if you take a pessimistic view of the likely intentions of technologically superior species).

Closer to us in time of origin is the open cluster M7. It seems to me to form the right wing of an extended kite shape that is otherwise made up of the three stars that form the teapot spout. This bright ball of about 80 stars is about a thousand light years away and its oldest members are about 220 million years old–about 2% the age of those in M22. It is sobering to realize that these cosmic youngsters formed about the time that the first mammals and the first dinosaurs were getting up and running in the Late Triassic Period.

Youngest of all is M8, the aforementioned Lagoon Nebula, which sits right above the spout of the teapot like a tiny puff of steam. In cosmic terms, we’re catching M8 in the act of giving birth. A few tens of millions of years ago it was just another cloud of cosmic flotsam and probably neither bright nor particular pretty. Now it is lit from within, like a paper lantern, by its stellar offspring. In another 200 million years, M8 may look like M7 does today, with all of its ethereal clouds of gas and dust either consumed or blown away by the brash young stars that are even now forming at its heart.

So grab those binos and go see the universe–a stellar nursery (M8), primary school (M7), and retirement community (M22) await. If Jupiter blew your socks off, have a look at M22 and remember that you are looking at stars that are almost three times as old as our solar system. How often do  you get to see something 12 billion years old? Not often, I’ll wager!

…or rather, see these things if you can. There’s a reason that Sagittarius is not everyone’s pot of tea. Like Scorpio, it’s a fairly southerly constellation, which means it never gets very far above the horizon, especially for folks who live up north. Here’s what it looks like from southern England:

Sagittarius from EnglandSo if you’re farther north than about the 40th parallel, you’re probably hosed. You’ll need a clear southern horizon, sans trees, mountains, and especially the light domes of our myriad cities to get a good look. Still, give it a shot–letting the light of 70,000 12-billion-year old stars–photons that have been in transit since the end of the last ice age–fall on your retinas is worth a little effort.

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Mt Wilson in the clear?

September 2, 2009
Martin Mars tanker flies over the dome of the 100-inch Hooker telescope on Mt Wilson.

Martin Mars tanker flies over the dome of one of the CHARA array telescopes the 100-inch Hooker telescope on Mt Wilson.

Yes and no. No because the Station Fire is still a going concern and one front of it is still on the move in the Mt Wilson area. Yes because there are lots of firefighters up there now and the Mt Wilson pumps have been repaired, so the firefighters have access to 750,000 gallons of water on site. That’s equivalent to 100 Martin Mars drops or 37.5 drops by the 747 supertanker. Also, a series of backfires around the observatory has cleared a lot of the fuel from in front of the advancing Station Fire.

The fire has put Mt Wilson back in the public eye. Astronomy has a great article on the history of the observatory and some of the cool ongoing projects there, and the LA Times has a nice op-ed piece about the observatory’s importance. Internet lines to the mountain are out, so the observatory has a backup website with regular updates here. Also check out some amazing photographs of the current LA area fires here, here, and here; image at top from that last link.