Archive for the ‘Planet’ Category

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Why and how to make a sub-aperture mask for a refractor

February 11, 2017

60mm-aperture-mask-6-comet-edition-close-up

Here’s the Bresser Messier AR102S Comet Edition with a homemade aperture mask. I just converted the scope from a 102mm f/4.5 to a 60mm f/7.7.

“WAT!? You took a refractor, the most aperture-challenged of the three basic telescope designs, and made it even smaller?”

Yup. For several reasons.

The first and most obvious is to control chromatic aberration (CA), also known as false color. Despite the name ‘achromat’, which literally means ‘no color’, doublet refractors without extra-low dispersion (ED) glass do show some false color, because their lenses do not bring all of the colors of light to the same focus point (they’re still a LOT better than scopes with a singlet objective lens, like those used by Galileo). For dim objects like galaxies, nebulae, and most field stars, the effect is not noticeable, even in large and optically fast scopes like the AR102S Comet Edition (nickname needed). But bright objects like the moon, planets, and first magnitude stars will be surrounded by purplish halos, and may have yellowish margins. In effect, the purple and yellow-orange parts of the spectrum are forming out-of-focus images that are superimposed on the main in-focus image.

The problem is that CA gets bad fast as refractors get bigger. There are a couple of standards that are commonly used to describe the focal ratio necessary to minimize CA to acceptable levels, the Conrady standard and the Sidgwick standard. By the Conrady standard, the focal ratio must be 5 times the aperture in inches; by the less stringent Sidgwick standard, 3 times the aperture in inches is good enough. Note that the standards describe focal ratios, not focal lengths, so they go up fast with increasing aperture. Here are some apertures, focal ratios, and focal lengths required to meet the Sidgwick standard:

  • 50mm (2″) : f/6 : 300mm
  • 76mm (3″) : f/9 : 684mm
  • 102mm (4″) : f/12 : 1224mm
  • 127mm (5″) : f/15 : 1905mm
  • 152mm (6″) : f/18 : 2736mm

This, along with mounting considerations, explains why reflectors and catadioptric scopes are progressively more common past 4″ in aperture. A 6″, f/8 Newtonian will be free of false color (as are all reflectors) and has such a gently converging light cone that it is easy to collimate and to focus – it’s easy for such scopes to achieve ‘planet-killer’ status if the mirror is good. A 6″, f/8 achromat will be a beast to mount and it will show lurid false color on bright objects.

But people still make, buy, and use such scopes! Why? Horses for courses: big, fast achromats can be superb deep-sky scopes, where chromatic aberration is typically not a problem. With the fixed sizes of standard eyepieces, achieving wide true fields requires short focal lengths (not just short focal ratios), and bright images require aperture, which drives the development of large but optically fast scopes like the AR102S Comet Edition. At f/4.5, it is well into ghastly CA territory on bright targets. The other night I stayed up late to catch Jupiter, and in the AR102S the planet wouldn’t even come to a clean focus. It was just a bright ball of light inside a sea of purple. I switched over to London’s 60mm f/11 Meade refractor and Jupiter snapped into a sharp and essentially color-free focus. There was a moon emerging from behind the limb of planet, already one moon-diameter out into black space, that was completely invisible in the CA-smudged view of the AR102S.

I’m okay with that – as I noted in a previous post, observing bright solar system targets with the AR102S is deliberate misuse of the scope. When I want good planetary views, I have a 5″ Mak and a 10″ Dob that can both be pushed to 500x (assuming the atmosphere is steady enough). But their max fields of view are pathetic compared to the AR102S – about 1.1 degrees for the Mak, and a shade over 2 degrees for the Dob, versus 3.6 degrees for the refractor, which is enough to take in all of Orion’s sword at once, with space left over on either side.

Still, I’m not going to take all of my scopes out with me every time I go observing, and chances are good that at some point I’ll want to look at something bright even if my main goal for the evening was low-power sweeping with the AR102S. Under those circumstances, it’s easier to have an aperture mask shoved in my eyepiece case than to pack a second scope. Hence this project and this post.

But I’m getting ahead of myself. There are other reasons to stop down a scope besides reducing CA:

  • To reduce glare from bright objects. Mostly applies to the moon when it’s full or very gibbous.
  • To give a more aesthetically pleasing image when the seeing is bad. Opinions differ on this point. Some folks prefer to look through a larger aperture despite the increased susceptibility to bad seeing, on the grounds that in the moments when the atmosphere does settle down a bit, you’ll see more detail. I suppose it depends on whether one is in exploration mode or aesthetic observation mode.
  • To make it easier to focus. F/4.5 is a steep light cone, and it’s easy to overshoot the point of best focus. Stopping down the scope makes a shallower light cone, so it’s easier to watch the image transition from out of focus, to near focus, to in focus. I’m going to test this method of finding best focus on some close double stars.

I had done some calculations in advance to figure out what sizes of aperture masks I’d want to try out. Given that the AR102S has a fixed focal length of 459mm, here are the focal ratios at full aperture and at 10mm decrements:

  • 102mm gives 459/102 = f/4.5
  • 90mm gives 459/90 = f/5.1
  • 80mm gives 459/80 = f/5.7
  • 70mm gives 459/70 = f/6.5
  • 60mm gives 459/60 = f/7.7
  • 50mm gives 459/50 = f/9.2
  • 40mm gives 459/40 = f/11.5

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I didn’t want to trade away too much resolving power, so I tested the scope on the moon using cardboard masks of 76mm and 60mm, made from the light cardboard spacers from a box of wet cat food. The 76mm is shown above. Perhaps unsurprisingly, at this aperture and focal ratio (f/6) the view was still unappealingly soft. But 60mm looked good, with minimal CA. This makes sense – the working focal ratio of f/7.7 is a healthy step beyond the f/7.2 that the Sidgwick standard suggests for a 60mm aperture. Going any smaller would be trading away valuable resolution, without significantly improving the image.

60mm-aperture-mask-1-gallon-jar

The light cardboard aperture masks were fast and easy to make, but they weren’t very sturdy. To make a more permanent mask, I needed plastic, heavier cardboard, or foam-core board. So I unscrewed the dewshield from the scope and walked down to the dollar store, where I looked for food packages and storage containers that might fit. Finally on the last aisle I found this 1-gallon plastic jar. The lid slip-fit over the dewshield with just a bit of extra room, which I knew I could shim out with some sticky-back felt.

60mm-aperture-mask-2-marking

I wanted to make sure the lid would fit before I did the hard work of cutting, so I put the felt on first. This was very familiar – it seems like every other scope I get has a loose dust cover that has to be shimmed to fit correctly. I’ve been slowly chipping away at the same package of sticky-back felt since 2010. I didn’t have a compass handy, so I used a small paper ruler to make a ring of marks around concentric 60mm circle inside the lid. Then found a lid to a jar of vitamins that was exactly 60mm in diameter and used that to trace the circle neatly.

60mm-aperture-mask-3-completed-mask

I was going to cut out the aperture using hobby knife, but the plastic was too tough. So I moved up to a box knife, and then a linoleum knife. Then I said heck with it and got the Dremel. The hole I cut wasn’t perfectly circular and had rough edges to boot, so I wrapped some sandpaper around a pill bottle to make a tool for rounding out the aperture.

60mm-aperture-mask-4-comet-edition-before

Here’s the scope before…

60mm-aperture-mask-5-comet-edition-after

…and after.

Even with the aperture mask, the AR102S is not a champion scope on solar system targets. The C80ED blows it away, which makes sense – it has a 33% resolution advantage over the stopped-down AR102S, and frankly just better glass. But at least the view now is clean and not appallingly degraded. A dramatic way to see the difference is to get a good tight focus on the moon with the mask on, then quickly take it off without removing one’s eye from the eyepiece, and watch the view get a lot brighter and a lot softer at the same time.

I have a few more things I want to do. The 60mm aperture mask fits over the end of the scope so securely that it could work as a dust cover, if only I can find or make something to plug the central hole. Also, I think I am going to play with making aperture masks in other sizes, just to see what happens.

And finally, I have another 4″ scope that will be fun to make an aperture mask for. But that will be a subject for another post.
skyscanner-aperture-mask-test-fit-jar-lid

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A little piece of Mars

July 21, 2016

Mini Museum no 3614 DSCN1469

This is my Mini Museum: a collection of tiny samples of rare and interesting specimens from the history and prehistory of Earth and the solar system. There’s a lot of stuff in here that is very satisfying as both a paleontologist and an amateur astronomer. Highlights for me are the preserved woolly mammoth meat, the fiberglass casts of Diplodocus bones used as the Krayt Dragon skeleton in Star Wars: A New Hope, and, above all, the tiny piece of the Martian meteorite Zagami. It’s labeled “Martian atmosphere” because the meteor is known to contain tiny bubbles of Martian atmosphere in pockets of melted glass (Marti et al., 1995).

The specimens are embedded in a single block of acrylic that is 5 inches tall, 4 inches wide, and 1 inch thick. At $299 it’s not cheap, but it’s a pretty astounding collection of objects at any price. There is also a smaller, 10-specimen edition for $99. It doesn’t include Zagami or the Krayt Dragon, but it does have asteroid fragments, Stegosaurus plate, woolly mammoth meat, fulgurite, and the moon tree sample. These will sell out at some point, so if you’re interested in picking one up, don’t tarry.

Reference

Marti, K., Kim, J.S., Thakur, A.N., McCoy, T.J. and Keil, K., 1995. Signatures of the Martian atmopshere in glass of the Zagami meteorite. Science, 267(5206), p.1981.

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Mt Wilson photo tour and a brief observing report

June 5, 2016

Mt Wilson 1 - Geo on the 60-inch

Last night the PVAA had the 60-inch telescope booked at Mt Wilson. It had been ages since I’d been up there – my only other trips up were in 2009 and 2010 (observing reports here and here). So it was very satisfying to be back. It is amazing to look back and realize that in 2010 I was only 3 years into what has now been almost 9 years of stargazing.

The last two times I went up, we didn’t have time for a tour of the grounds, so about all I saw were the parking area, the 60-inch dome, and a few odds and ends in the distance. This time we got a nice long tour from Geo Somoza – most of the rest of this post is a photographic tour of part of the observatory. We didn’t have time to go through the museum up there, or see the solar telescopes – guess I’ll just have to go back again to catch those (which is no bad thing!).

I rode up with Ron Hoekwater, Laura Jaoui, and Gary Thompson, who kindly drove us. We left Claremont early and got up there about 6:00, well in advance of the planned 6:30 start time for the tour. While we were chatting outside the gate, we saw something ominous: a tower of smoke going up from the mountains to the west. This would come back to haunt us.

Mt Wilson 2 - Einstein bridge and the 100-inch

Here’s the dome of the 100-inch Hooker telescope – world’s largest from 1917, when it eclipsed the 60-inch telescope on the same mountain, until 1948, when it was eclipsed in turn by the 200-inch Hale telescope on Palomar Mountain. It is a bit staggering to realize that from 1908 to 1993, when Keck 1 went online on Mauna Kea, the three consecutive world’s largest fully-functional telescopes were all within 92 miles of each other in southern California. (The 240-inch Soviet BTA-6 saw first light in 1976, but it suffered terrible thermal stability and seeing problems and never performed anywhere near its full potential.)

This bridge is nicknamed “Einstein’s bridge” because Einstein paused here for a famous photograph during a visit to Mt Wilson in 1931 – see that historical photograph here.

Mt Wilson 3 - the 100-inch

Here’s the scope itself, the same machine that Edwin Hubble and Milton Humason – a former mule-driver who worked his way up to master observer – used to chart the expansion of the universe. I was scheduled to go up and observe with the 100-inch last year, but I got very sick the day before and couldn’t make it. So that is still on the bucket list.

Mt Wilson 4 - the 100-inch mirror

A view into the back of the mirror cell of the 100-inch telescope. The green champagne-bottle glass of the primary mirror is clearly visible. If you click through to the full-size version you may be able to see bubbles in the glass. The 14-inch-thick mirror had to be made in three separate ‘pours’ of molten glass, and bubbles from the first two pours were trapped by the layer above. The people at Mt Wilson were so concerned about the bubbles interrupting the figure of the mirror that at first they refused to work with it, but St Grobain Glassworks was unable to pour a better one and eventually George Ellery Hale ordered his people to grind and polish this mirror, which turned out to be fine at the optical surface after all.

Mt Wilson 5 - 100-inch eyepiece

In the old days, to observe visually with the 100-inch you had to go down a narrow hallway to a tiny room where light from the scope was bounced to the Coude focus. That was pretty unsatisfying so a few years ago the telescope was modified for more intimate visual observing. Now the primary mirror at the bottom of the scope bounces the light to a secondary up in the upper cage, thence to a tertiary at mid-tube which directs the light out to a quaternary mirror in the diagonal housing at the top of the black tubular assembly on the left of the scope in the above photo, thence down to a quinary mirror at the bottom of the black tube, then into the white refractor that is pointing down and to the right. A diagonal sitting nearby can be placed into the refractor to put the eyepiece into a convenient orientation when the scope is tilted.

Mt Wilson 6 - 100-inch controls

The control board of the 100-inch, with at least three separate control systems lined up right to left in order of age. Most interesting is the old table on the right with the clock and the two periscopes. The periscopes allowed the telescope operator to see the telescope’s setting circles. Nowadays, the scope is controlled by the computers on the left.

Mt Wilson 7 - 100-inch dome

Excited amateur astronomers lingering outside the dome of the 100-inch. We got to walk around on the walkway you can see on the outside of the dome. The entire dome rotates, walkway included. It’s a fearsome engine indeed.

Mt Wilson 8 - CHARA array and 60-inch domes

On the left is one of the six domes of the CHARA array, I believe still the world’s longest-baseline optical interferometer. It has enough resolving power to image the discs of nearby stars. On the right is the 60-inch dome.

Mt Wilson 9 - lightspeed test site

Geo shows us the concrete pier used during the speed-of-light experiments in the 1920s. More on those in a sec.

Mt Wilson 10 - lightspeed test plaque

For decades in the late 1800s and early 1900s, Albert Michelson conducted a series of experiments to measure the speed of light. In a series of famous tests in the 1920s – almost two decades after Michelson earned his Nobel Prize – a beam of light was bounced from this pier on Mt Wilson to a mirror on Lookout Mountain, one of the foothills of Mt San Antonio, better known to locals as Mt Baldy – the mountain at whose base I live. The concrete pier on Lookout Mountain is still there and it is apparently an easy hike. It’s on my to-do list.

Mt Wilson 11 - LA and smoke from wildfire

Sunset over LA. On the left, the marine layer of fog is moving in over the city. On the right, a tower of smoke is going up from a wildfire near Calabasas, about 40 miles to the south and west of Mt Wilson, and spreading out over the LA basin. For a while the smoke was going southeast from the fire, and it looked like it might miss us. But by the time it was getting dark, the wind had shifted and was carrying the smoke directly toward the observatory.

Mt Wilson 12 - going up to the 60-inch

As darkness fell, we trooped into the dome of the 60-inch telescope.

Mt Wilson 13 - Edison bulbs

Here are the controls for the dome’s shutter, which has to be opened for the telescope to see out, and closed again to protect the telescope during the daytime and in inclement conditions. The three light bulbs on the upper left of the console are original Edison bulbs – they have been working without ever being replaced since 1907 or so.

Mt Wilson 14 - control board and mercury tank

Our telescope operator, Christopher Burns, checks something on one of the computers in the control center, while beyond him Geo stands by the mercury tank in which the 60-inch telescope floats. Don’t worry, it’s fully sealed now. In the old days, it was open, and mercury would sometimes splash on the floor as the telescope rotated.

Mt Wilson 16 - Jupiter with blue filter

Our first target was Jupiter. As usual, the photo completely fails to do justice to the naked-eye view. The seeing was imperfect and I think the smoke from the fire might already have been affecting the views. The north and south equatorial and temperate belts were visible, and the Great Red Spot was prominent, but I could see little detail beyond that. I have seen much better on other visits, and indeed in much smaller scopes (see for example the two previous Mt Wilson observing reports linked at the top of this post). But I won’t complain too much – part of the joy of observing with the 60-inch is in the process, not the outcome.

Mt Wilson 15 - 60-inch lit by laser

After Jupiter we moved on to the globular cluster M3, and then the Sombrero Galaxy, M104. M3 was already looking a bit dim – certainly not as bright as it appeared in Ron’s 25-inch scope from RTMC last weekend – and about this time the smell of smoke became pronounced in the dome. We had a hurried look at M104, but it was just a dim smudge of light and I couldn’t even make out the dust lane.

After M104 we had to shut down early to protect the telescope. If ash from the fire was allowed to fall on the mirrors, it would combine with moisture in the air to produce acids which would eat away the coatings. In the photo above, Geo is shining a laser up through the optical train to check for ash on the mirrors.

Mt Wilson 17 - Matt with the telescope

It was a bummer to have to shut down early, but we had an awesome tour and it was fun to observe again with the 60-inch, even if only briefly. Geo and Chris were great hosts and everyone had a good time. We’ll get to reschedule our night on the scope, since we only got about an hour and a half of observing in, so the club’s investment is protected. It’s a shame about Mars, though – we won’t have another opposition this close for some time, and the planet will be noticeably more distant, smaller, and dimmer by next month already. Still, into every observing career a little rain – or ash – must fall, and I’ve been extremely fortunate. Two eclipses (2012, 2014), a Venus transit, and a Mercury transit in the last four years, and not one of them clouded out. Mars will be back, and I’ll be ready.

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Small, medium, large – observing near and far in the last two weeks

June 4, 2016

Matt at Delicate Arch IMG_2984

Preface – Running with the Red Queen

I’ve just finished maybe the busiest spring of my life. January and February were largely sunk into day-job work – time-consuming, but necessary, interesting, and in fact rewarding. Then the last three months have been taken up with travel and public lectures.

  • In March I went to Oklahoma for 10 days of paleontological research in field and lab, and I gave a talk at the Oklahoma Museum of Natural History titled, “Dinosaurs versus whales: what is the largest animal of all time, and how do we know?”
  • In April I did a two-day trip to Mesa, Arizona, for more paleo work. No talk on that trip, but I did participate in the “Beer and Bones” outreach at the Arizona Museum of Natural History.
  • In early May I was in Utah for another 10 days of paleo research, and I gave a talk at the Prehistoric Museum in Price on, “Why elephants are so small”. My colleague Mike Taylor and I took one day off from dashing through museums to tour Arches National Park, which is where Mike took the photo at the top of the post.
  • Last weekend I was up at RTMC, where I gave a Beginner’s Corner talk on, “The scale of the cosmos”.

I’m not complaining – far from it. It’s been exhilarating, and the collaborative work I have rolling in Oklahoma and Utah will hopefully be paying off for years. And planning and executing all of the work has been satisfying. Particularly the RTMC talk, which deserves a whole post of its own. And ultimately this is all stuff that I chose to do, and if I could do it all over again, I would.

BUT there have been consequences. Most frustratingly, I haven’t had enough uninterrupted time to get anything written up for publication – not the sizable backlog of old projects I need to get finished up, and not the immense pile of new things I’ve learned this year. I haven’t gotten out to observe as much as I’d like, and I’ve barely blogged at all.

And it’s not over. In two weeks I leave for a week of paleo fieldwork in Oklahoma, then I’m back for a week, then I’m off to Utah for about 10 more days of digging up dinosaurs. In between I’ll teaching in the summer human anatomy course at WesternU.

But I’ve had a nice little pulse of observing in the last couple of weeks – two weekends ago up at Arroyo Grande, near San Luis Obispo, last weekend at RTMC above Big Bear, and this week at Santa Cruz Island off the coast. No time for separate observing reports, so I’m combining them all into one.

Observing Report 1 (Medium): The Planets and Moon from Arroyo Grande

I was fortunate to be part of a great, tightly-knit cohort of grad students at Berkeley. Of the people I was closest to, some are still in and around the Bay Area and some of us have been sucked into the gravity well of the LA metro area. Occasionally we get together somewhere halfway in between, either up in the Sierras or near the coast. I usually take a telescope, because almost everywhere is darker than where I live, and when I’m traveling by car there’s simply no reason not to.

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This year we met up for a couple of days and nights in Arroyo Grande. We hiked in the hills, went down to Morro Bay to watch ocean wildlife and buy seafood, played poker, and generally got caught up on work, family, hobbies, and life. Our first night was wonderfully clear. I had along the trusty C80ED, which has become my most-used scope. It’s mechanically rugged, optically damn near perfect, and compact enough to not require much time or thought when it comes to transportation and setup. On Saturday, May 21, we spent some time with Jupiter, Mars, and Saturn. Jupiter and Saturn were as they always are: beautiful and surprising in their immanence. I cannot look through the telescope at either of them without being forcefully reminded that they are as real as I am, that as I go about my days full of busyness and drama, they are always out there, hundreds of millions of miles away, go about their own business whether I or anyone else pay them any attention or not. One of my friends had never seen the rings of Saturn with his own eyes, so that was an added bonus.

Mars was the real treat. Using the Meade 5mm 100-degree EP and a Barlow I was able to crank up the magnification to 240x. The dark dagger of Syrtis Major and the white gleam of the north polar cap were both obvious. It is always arresting to see details on this world that has loomed so large in the human imagination, from ancient mythology to science fiction to current and future exploration.

The next night we sat out on the patio, eating oysters and watching the sun set. I didn’t have any of my own binoculars along, but a friend had brought a couple, and after it got dark we watched the still-mostly-full moon rise through the trees on the ridgeline to the east.

It was all shallow sky stuff (solar system, that is), but it was all spectacular, and I’m glad we did it.

Observing Report 2 (Large): Going Deep at RTMC

Last weekend I was up at RTMC, finally. I’ve been wanting to go since I got to SoCal, but in the past it’s fallen on the same week as our university graduation and I’ve been too wiped out. I didn’t make it up for the whole weekend. We went up as a family to stay Saturday and Sunday nights. I went up to RTMC early Sunday morning to look around, give my talk, and hang out. Ron Hoekwater, Laura Jaoui, Jim Bridgewater, Ludd Trozpek, and Alex McConahay of the PVAA were all there and we spent some time catching talks and jawing about skies and scopes. I also chatted with some folks from farther afield, including Arizona and NorCal.

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I took off in the afternoon to spend time with London and Vicki, then went back up after dinner. All I had along were my Celestron 10x50s (yes, those), but Ron had his 25-inch Obsession dob, and he was content to use it as the centerpiece of a group observing session. We looked at the planets, or at least Jim Bridgewater and I did – Ron had checked them out the previous night and didn’t want to blow out his dark adaptation. That was a smart call, as the Obsession gathers a LOT of light and the planets were almost blown out. We could have put in a filter, but ehh, we had other things to be getting on with.

We started with globular clusters. M3, M5, M53, NGC 3053, and one or two other distant NGC globs. The close ones were explosions of stars that filled the eyepiece. The distant ones shimmered out of the black like the lights of distant cities. Then we moved on to galaxies. M81 and M82 were bigger, brighter, and more detailed than I had ever seen them. M51 was just stunning – the spiral arms were so well-defined that it looked like Lord Rosse’s sketch.

M51 sketch by Lord Rosse

As nice as those were, the Virgo galaxy cluster was better. There were so many galaxies that identifying them was a pain – there were so many little NGCs in between the familiar Messier galaxies that my usual identification strategies kept getting derailed. It was kind of embarrassing, actually – I did just write an article about this stuff. But also incredible. NGC 4435 and 4438 – the pair of galaxies known as “The Eyes” – were so big, bright, and widely separated that I didn’t realize I was looking at them until the third or fourth pass.

We finished up on planetary nebulae. The seeing was good but not perfect – the central star in the Ring Nebula was visible about a quarter of the time. The Cat’s Eye, NGC 6543, was a fat green S with a prominent central star – it looked like it had been carved out of jade.

An evening under dark skies with a giant scope is both a blessing and a curse. A blessing because you get to see so many unfamiliar objects, and so many details in familiar objects, that are beyond the reach of smaller scopes. A curse because by the end of the session you may find yourself thinking, “Sheesh, why do I even bother with my little 3-, 5-, and 10-inch scopes?”

Fortunately another observing experience, one that would remind me of the joys of small-aperture observing, was right around the corner.

Observing Report 3 (Small): A Binocular Tour of the Spring Sky

My son, London, is finishing up fifth grade at Oakmont Outdoor School, one of the half-dozen or so different elementary schools in the Claremont Unified School District. We were fortunate when we moved to Claremont to land just a couple of blocks from Oakmont – we would have been happy to land within walking distance of any of the schools, but if we’d had our choice we would have picked Oakmont anyway, since we wanted to raise London with as much exposure to the outdoors as we could.

Oakmont’s slogan is, “Learning in the world’s biomes”. The major activities of each grade are organized around a particular biome, and so is the end-of-year field trip. In third grade, the kids went to Sea World. Last year it was the desert by Palm Springs for a 2-day, 1-night trip. This year it was Santa Cruz Island, in Channel Islands National Park, for a 3-day, 2-night trip. Parent chaperones are needed and I’ve been fortunate to get to go every year.

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The island was amazing. We saw dolphins, sea lions, and petrels on the boat ride out – I took the photo above from the prow of the ship – more sea lions, seals, pelicans, cormorants, gulls, and red pelagic crabs at the shore, and dwarf island foxes, ravens, and the occasional hawk inland. On the final evening, June 2, we hiked up to the top of the cliffs to watch the sun set over the Pacific, which was one of the most beautiful things I have ever seen in my life. I didn’t know it at the time, but I’d see something even more beautiful just a few hours later.

I had binoculars along – Bushnell 10×40 roofs that I got specifically for daytime use, and which I had used a lot on the trip already to watch wildlife. When we got back to camp, a few of the teachers and hung back and started talking about the planets, bright stars, and constellations. I started pointing out a few of the brighter targets and passing around the binoculars, and we ended up having an impromptu binocular star party. (The kids and a fair number of the adults were all exhausted from a full day of hiking, and sensibly went to bed.)

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What followed was one of the best and most memorable observing sessions of my life. The only permanent residents of Santa Cruz Island are a couple of National Park employees, and they turn their lights off after dark. We got a little light pollution on the eastern horizon from Ventura and Oxnard, some 20 miles distant, but for the most part the sky was darkAfton Canyon dark, Hovatter Road dark – what I typically refer to as stupid dark.

We roamed all over the sky, looking at targets large and small, near and far, bright and dim. I didn’t keep track as we were going, but I wrote down a list yesterday morning on the boat ride back to the mainland (we went through a fog bank and only saw a handful of dolphins, so I had plenty of time).

In the northern sky:

  • Polaris and the Engagement Ring asterism
  • Mizar and Alcor
  • M51 – yes, it was visible in the 10×40 bins
  • The 3 Leaps of the Gazelle

In the western sky:

  • M44, the Beehive – easily visible to the naked eye, and just stunning in the binos
  • Leo
  • Coma Berenices star cluster
  • Virgo/Coma galaxies – identifications were tough, but a few were visible

In the eastern sky, Lyra had just cleared the trees when we started observing (at 9:15 or so), and all of Cygnus was above the trees when we finally shut down at 12:45 AM. In addition to tracing out the constellations, along the way we looked at:

  • Epsilon Lyrae, the Double-Double star
  • Albireo
  • Alpha Vulpeculae (the subject of my Binocular Highlight column in the ### issue of Sky & Telescope)
  • Brocchi’s Coathanger (Collinder 399)
  • Sagitta (just traced the constellation)
  • M27, the Dumbbell Nebula
  • Sadr and its surrounding ring of stars in the heart of Cygnus
  • NGC 7000, the North American Nebula – this and the Northern Coalsack were easily visible to the naked eye once Cygnus has risen out of the near-horizon LP

…and we just cruised the Milky Way from Cygnus to Cepheus, not singling out individual objects but just taking in the rich star fields.

But the southern sky was the best. Looking south from Santa Cruz Island, there’s only open ocean, broken here and there by other, distant islands and ultimately by Antarctica. It reminded me of looking south from Punta del Este in Uruguay, only I was in a valley instead of on a beach. The ridgeline to the south did cut off a bit of the sky, but we were still able to see all of Scorpio, including the False Comet, made up of NGC 6231 and Trumpler 24, which was one of the highlights.

It was trippy watching the Milky Way rise. I usually look at the summer Milky Way when it is higher overhead. I usually have to do that, because the objects aren’t visible in the near-horizon haze. But from Santa Cruz Island, things were not only bright but obvious as soon as they cleared the ridgeline to the south. It’s almost pointless to list them – we saw every Messier object in the “steam from the teapot”, from M7 and M6 in the south to M11 in the north, plus a lot of NGCs, plus star clouds and dark nebulae almost beyond counting. They were all great through the binoculars – M7 was a special treat, like a globular cluster on a diet – but honestly the best views of the night were naked-eye.

I realized that I am just never out observing the Milky Way at this time of year. My regular desert observing spots are all too hot in the summer, and when I do go there is often at least some light pollution to the south (El Centro from the Salton Sea, Barstow from Owl Canyon, etc.). I do most of my deep and dark observing in October and November, when the southern Milky Way is setting, not rising.

So I was completely unprepared for how much detail would be visible to the naked eye. When the Milky Way rose, it didn’t look like a band of light, it looked like a galaxy. I searched through a lot of photographs of the rising Milky Way to find one that approximated the naked-eye view, and this is the closest I got:

I am not exaggerating – the bright and dark areas were that defined. The Great Rift was visible from Cygnus to the horizon, and its southern border was notched by distinct deep sky objects from Aquila onward. The Scutum Star Cloud, M16, M17, M24, M23, M8, M6, M7, NGC 6281, and the False Comet were all easily visible to the naked eye as a chain of luminous patches against the dark dust lane of our own galaxy. In fact, I noted NGC 6281 with my naked eyes first, thought, “What the heck is that?”, and had to look it up. We also caught M4, M22, M23, and M25 in the bins, plus a bundle of dark nebulae that I’d never noted before and didn’t bother keeping track of.

Longtime S&T contributor Tony Flanders (now retired but still writing occasionally) is active on Cloudy Nights, and his sig file reads:

First and foremost observing love: naked eye.
Second, binoculars.
Last but not least, telescopes.
And I sometimes dabble with cameras.

Until fairly recently I would have listed my own preferences in reverse order, from telescopes to binos to naked eye. That may sound odd for a “bino guy”, which I guess I am since all of my ‘professional’ astro-writing has been binocular-based. But it’s true – as much as I love binoculars, I would have picked a telescope first. But I am – gradually, belatedly – waking up. In some ways, it would have been great to have a scope, any scope, along on the island trip. I’m sure that even the C80ED would have taken us crazy deep, considering what we could see with a pair of low-end 40mm roof-prism bins. But it would also have come between us and the sky, and I would have spent more time futzing with eyepieces and less time just looking up.

This was a surprising and welcome realization, coming so shortly on the heels of a frankly astonishing session with Ron’s 25-inch dob at RTMC. I was worried that big-telescope observing might spoil me, but that fear turned out to be unfounded. All I need to be happy is a dark sky. If I have some people to share it with, even better. Anything more is just cake at the end of an already long buffet.

Let’s eat.

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Observing report: the transit of Mercury from western Colorado

May 19, 2016

Mercury transit 9 May 2016 - telescope setup

I was in Utah from May 4 to May 15, chasing dinosaurs with Mike Taylor, a colleague of mine from England. I took a telescope along in hopes of getting some dark-sky time, and to hopefully catch the transit of Mercury on May 9.

Things did not look promising at dawn on the 9th. I was in Fruita, Colorado, and when I got out of bed, the sky was completely overcast. Mike and I decided to head out west of town to visit Rabbit Valley, where a nearly complete skeleton of the long-necked dinosaur Camarasaurus is visible in a hard sandstone ledge. (Why is no-one excavating this dinosaur? Because we already have many nice specimens of Camarasaurus, and the sandstone around this one is like concrete. It would be a mountain of work for very little payoff.)

We spent about two hours measuring and photographing the skeleton, and as we did so, the clouds started to break up a bit. By the time we got back to Fruita, a little after 11:00 AM, the sky was clear except for a few scattered wisps of cloud. I set up my telescope in front of the Dinosaur Journey museum and started watching and photographing the transit.

Mercury transit 9 May 2016 - Mercury crossing the sun

I was using the same setup as in the last post: my Celestron C80ED refractor, a Celestron 8-24mm zoom eyepiece, and a GoSky full aperture solar film filter. For photography, I used a Nikon Coolpix 4500 for still photos and my iPhone 5c for video.

I caught about the last hour of the transit, and I got to share the view with about a dozen museum staff and passersby. A few light clouds drifted through the field of view, which looked pretty cool and didn’t obscure the view at all.

At 12:42 Mercury finished exiting the disk of the sun. The next Mercury transit will be in 2019 – I hope I’m as lucky then as I was this time.

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We’ve been through this Pluto thing before

February 17, 2016

Pluto and other former planets

Mike Taylor sent me a link to this post on Quora about why Pluto should still be called a planet. Here’s the response I sent back after reading that piece, only lightly edited and with some links added:

I am unmoved. If we go back to the classical definition of planets as “wanderers” then there are 7: the sun, moon, Mercury, Venus, Mars, Jupiter, and Saturn. Clearly we have the ability to redefine the term from “naked-eye visible objects that move against the background stars as seen from Earth” to “big round things that orbit the sun”.

As for the idea that Pluto was a planet for 70-odd years before being demoted, so what? Ceres and Vesta were planets for half a century, and Juno and Vesta were planets for more than 40 years. Eventually people decided that it was unworkable to classify everything in the rocky belt between Mars and Jupiter as a planet – asteroids are a different class of objects, and referring to them as planets conflates two very different phenomena. Recently many people – an acting majority – have decided that it is equally unworkable to classify everything in the icy belt beyond Neptune as a planet, for the same reason. Kuiper Belt objects are a fundamentally different kind of thing from either the rocky planets or the gas giants. We’ve been through all of this before. We can have 8 planets, or hundreds.

Finally, I am completely opposed to this essentialist idea that terms have to keep their meaning forever and aren’t available for revision as we learn more. I think it’s a harmful doctrine, not least because it’s strongly at odds with the reality of how people actually use language – in science, and in all other areas of life.

That said, thanks for the link. I haven’t seen the pro-Pluto argument couched quite that way before. I disagree with almost all of it, but it’s still useful to know that people think that way.

To which Mike replied:

I’d agree with pretty much all of that, for what it’s worth. I thought it was interesting to see the strongest case made for Pluto’s planetary status by someone with a stake and some expertise, and then to see how far short of being persuasive that was.

What do you think?

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Observing Reports: two perfect imperfect nights at the Salton Sea

November 23, 2015

Apex 127 ready for stars 2015-11-14

The Saturday before last, November 14, I was at the Salton Sea with Terry Nakazono.

Terry Nakazono with Meade Polaris 114 2015-11-14

Terry was rolling with a new scope – a Meade Polaris 114. It’s an f/8.8 reflector – the 1000mm focal length makes it a bit longer than the 900mm, f/7.9 Orion XT4.5 (which London has). UPDATE Nov. 29: Terry writes, “It’s a standard 900mm FL, not 1000mm. A lot of the retailer ads have it wrong and says its 1000mm. I myself was intrigued when I first read about it, but later found out from looking at the PDF manual and those who bought it is that it is an F/7.9 of 900mm focal length.” So it’s not longer than London’s XT4.5, it’s essentially the same OTA.

This Meade is a pretty amazing deal. A lot of small intro reflectors have a short dovetail bar bolted to the side of the tube (like my old scope Shorty Fats), but this one has real tube rings and an EQ-2 mount. The three MA (Modified Achromat) eyepieces it comes with are nothing to write home about, but the focal lengths of 26mm, 9mm, and 6.3mm are at least useful and non-overlapping when doubled with the included Barlow. Terry shared a few views with me and I can confirm that it serves up a sharp, contrasty image, as you’d expect for a scope of this focal ratio. It would be a good deal at the list price of $170, but Amazon has it for $135 as of this writing, and according to Terry it can be found for even less if you look around.

Matt aligning finder on Apex 127

I brought the Apex 127/SV50 combo – I’m sighting on the moon here, to align the finder with the scope – and the C80ED.

Matt digiscoping moon

Here I am digiscoping the moon with the C80ED. I used the Apex 127 for tracking down some planetary nebulae and double stars, and the C80ED for photography and just messing around. It’s a crazy fun little scope. Unfortunately, none of my moon shots worked out this time.

The forecast called for clear skies most of the night, but clouds between 10:00 PM and 2:00 AM. We got set up before the sun set at 4:45, and pushed through until 10:40. Then it got too hazy to observe, so Terry and I sat and jawed about scopes, atlases, and observing projects until the sky cleared a bit at midnight. We got in about half an hour more before the sky clouded over completely about 12:40. We talked a bit more then turned in.

Jupiter and moons 0530 PST 2015-11-15

I got up at 4:00 AM to catch the morning planets – Jupiter, Mars, and Venus. I cannot get the iPhone to take a fast enough picture to capture any detail on Jupiter – it always comes out as a blank circle of light (with some glare from the iPhone, not the scope). But the moons show up nicely. I really need to get a better camera control app.

Clouds at dawn 2015-11-15

I was clouded out again at 5:15, and Terry and I sat up until 5:45 watching the approaching dawn. Then it started sprinkling! Weather Underground, the Clear Sky Chart, and my other weather app all missed that. We packed up quickly and drove out at 6:30. A hearty breakfast at the Coco’s in Indio put a cap on the expedition. Although the skies were less than perfect, we had a good time catching up, and we did see some nice things.

Waxing gibbous moon 2015-11-22

Back Again

As luck would have it, I was back at the sea just eight nights later. London and I hadn’t been to the Salton Sea since last November, and he has all this week off from school, so we went last night. He took his XT4.5, and I took my C80ED. The waxing gibbous moon was only three days short of full, so the skyglow was pretty bad. But the seeing was excellent, easily 8 or 9 out of 10. I could split the four main stars of Orion’s Trapezium wide open at 25x, and fleetingly at 19x with the 32mm Plossl.

I could have held that split more easily with a better low-power eyepiece. I had not noticed it before last night, but my trusty Orion Sirius 32mm Plossl, my go-to widefield and finder eyepiece for many years, has some astigmatism. Not a lot – it was only noticeable immediately after switching from my 24mm ES 68. I tried both eyepieces with and without eyeglasses to confirm that the aberration was in the Plossl and not elsewhere in the optical train, my eyeballs included (I tried both). Another case of getting spoiled by premium eyepieces. It’s fine, though – since the 24mm ES 68 gives the same field of view, I only pull out the 32mm Plossl when I want to drop the magnification even lower, or when I’m doing outreach.

Sigma Orionis sketch 2015-11-22

I spent a lot of time cruising the central part of Orion at 120x with the 5mm Meade MWA, which is now my preferred high-power eyepiece. Just three weeks ago I saw and sketched the multiple star Sigma Orionis for the first time. It’s funny – I’d been observing Orion regularly for eight years before that and I’d never seen it, but now I stop there every night I have a scope out. Even London’s little 60mm Meade refractor split the six main components wide open. But last night I saw a faint, seventh member that I’d previously missed.

I turned in relatively early, around midnight, figuring that I’d get up after the moon set and do a quick morning Messier hunt. And the sky was truly phenomenal after moonset. I was waking up about once an hour and having a quick look around, and it was a spectacularly clear, dark night. But the flesh was weak, and I overslept, only dragging myself out of my sleeping bag at 5:00. By that time the first glimmerings of dawn were lighting the eastern horizon, so I skipped the Messiers and went to Jupiter.

IMG_6362

That planet above the scope is Venus, not Jupiter.

The view was jaw-dropping. The seeing was rock solid and I was able to Barlow the 5mm MWA up to 240x without the image breaking down. At that magnification I could detect at least three delicate brown belts north of the North Equatorial Belt, and the Galilean moons were little spheres, not just points of light. I tried taking some pictures but didn’t get any better results than I had the last time out, so I put the camera away and just stared. I must have spent 45 minutes just watching Jupiter drift across the field of view, mostly at 240x.

Last night I was definitely in aesthetic observing mode. I spent a little over two and a half hours at the eyepiece, entirely on four objects – the moon, Orion nebula and Trapezium, Sigma Orionis, and Jupiter. I had half-formed plans to look at other things, but I kept getting seduced into long sessions of fully immersed stargazing. And I’d do it again in a heartbeat.

IMG_6369

So, neither night had perfect observing conditions. It was hazy the first night, and the moon was out during the convenient observing hours last night. But I had a great time both nights, saw some cool things, learned a little more about my gear, and enjoyed the good company of Terry and London. Couldn’t really ask for more.