author
20Instructables 269,666Views 110Comments Chicago,IL Joined September 18th,2014
I'm a professor of physics and astronomy at Northwestern University.I do a lot of hobbies,including amateur astronomy,woodworking,and Lego modeling among many others.

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Epilog Challenge 9
Contest Winner Runner Up in theEpilog Challenge 9
Big and Small Contest
Contest Winner Runner Up in theBig and Small Contest
Tiny Home Contest
Contest Winner Second Prize in theTiny Home Contest
Audio Contest 2018
Contest Winner Runner Up in theAudio Contest 2018
Explore Science Contest
Contest Winner Second Prize in theExplore Science Contest
Homemade Gifts Contest 2017
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Gaming Contest
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Trash to Treasure
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Optics Contest
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  • gravitino's entryFountain Pen Chestis a finalist in theOrganization Contestcontest 8 hours ago
    Fountain Pen Chest Finalist
  • gravitino's entryThe First Color Photographis a finalist in theRemix Contestcontest 12 hours ago
    The First Color Photograph Finalist
  • gravitino'sinstructableThe First Color Photograph'sweekly stats: 16 hours ago
    • The First Color Photograph
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  • gravitinocommented ongravitino'sinstructableFountain Pen Chest 1 day ago
    Fountain Pen Chest

    It's the same velvet through and through;I just called it flocking because that's what we call velvet we glue on the inside of telescopes! As for the scissors,I agree.I was worried about cutting too close,and then as I laid the velvet down if it got off track the close cut edge would get away from the edge leaving it exposed.Since the wells are round,I didn't think I'd be able to glue the extra edge down without having big wrinkles of cloth.Any ideas there would be appreciated!:-)

    If you ever decide to do it,you can certainly do it on a smaller scale,making even one drawer.The molding idea might make a single drawer really quick and easy to build.:-)

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  • gravitino'sinstructableFountain Pen Chest'sweekly stats: 1 day ago
    • Fountain Pen Chest
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  • gravitinocommented ongravitino'sinstructableFountain Pen Chest 2 days ago
    Fountain Pen Chest

    Thanks -- I'm glad you like it!The collection has been slowing growing since I was in college,but I've never had them all together in a nice display before.:-)

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  • gravitinoenteredThe First Color Photographin theRemix Contestcontest 4 days ago
  • gravitinocommented ongravitino'sinstructableFountain Pen Chest 4 days ago
    Fountain Pen Chest

    Thanks,I'm glad you liked it!

    So I went and measured one of them and you are right,it is 3.1mm.However,in fraction mode my caliper calls this 1/8 in (the smallest fraction it will differentiate in display is 1/64;decimals are finer grades).But the difference between 3.1mm and 1/8" is just under 3/1000 in -- in general I would be surprised if that made a difference working with wood.Do you have experiences that suggest it does?

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  • gravitinocommented ongravitino'sinstructableThe First Color Photograph 6 days ago
    The First Color Photograph

    Thanks!I'm glad you liked it.I'm a physics professor,and I always thought this would be a good project for my students to learn about astronomical imaging.Now I have it written up!:-)

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  • gravitinoenteredFountain Pen Chestin theOrganization Contestcontest 7 days ago
  • gravitinocommented ongravitino'sinstructableFountain Pen Chest 8 days ago
    Fountain Pen Chest

    Thanks -- I'm glad you like it!I was so happy that it turned out well.Though my collection perfectly fills it.I guess I'll have to follow the instructions now and build a second one.:-)

    Ooooo,that's a good idea to use moulding.I didn't even think of that!I'm going to have to make another box (see how this one is full?) for the future,so I may try that -- the routering was the most time consuming bit.Pens: Yes,I have 4 of those Star Wars pens.:-) I also have a few Retro51 roller balls,and those are on that bottom shelf -- I put Space Pen refills in them using the Parker converter end they come with.My favorite is the Smithsonian dino edition one.:-)Glad you liked the build!Let us know if you make one!

    It's so awesome to be able to see all of them and just pull one out when it strikes my fancy.I should have done this a long time ago!:-)

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  • gravitino'sinstructableWinged Guitar Stand'sweekly stats: 4 weeks ago
    • Winged Guitar Stand
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  • gravitinocommented ongravitino'sinstructableWinged Guitar Stand 5 weeks ago
    Winged Guitar Stand

    I'm glad you liked it!We've both been very happy with the way it has turned out.

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  • gravitinocommented ongravitino'sinstructableDymaxion Earth 5 weeks ago
    Dymaxion Earth

    That is awesome!Just another reason why I should think about getting a laser cutter!:-D Also that link you found about projections is great -- I'll have to spend some time reading that.

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  • gravitinoenteredWinged Guitar Standin theEpilog X Contestcontest 5 weeks ago
  • gravitinocommented ongravitino'sinstructableDymaxion Earth 2 months ago
    Dymaxion Earth

    Ah,that's a cool idea,flattening it out into a piece of wall art!I could imagine that looking really nice in my study!:-)

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  • gravitino's entryDymaxion Earthis a winner in theBig and Small Contestcontest 2 months ago
    Dymaxion Earth Winner!
  • Cosmos Mariner: a Large Aperture Dobsonian Telescope

    Telescope building is a great hobby.I hope you give it a try -- I do highly recommend the books I pointed to as a source of information and ideas to get you started.Glad you liked the instructable!

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  • gravitinocommented ongravitino'sinstructableDymaxion Earth 2 months ago
    Dymaxion Earth

    Thanks!I'm glad you enjoyed it!

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  • gravitino's entryDymaxion Earthis a finalist in theBig and Small Contestcontest 2 months ago
    Dymaxion Earth Finalist
  • gravitinocommented ongravitino'sinstructableDymaxion Earth 2 months ago
    Dymaxion Earth

    I thought about doing that with magnets and facing screw heads to help hold it together on your table,but I found in testing that the magnets didn't let go easily and it caused me to mess up other tiles I had laid down;so I opted to not have them "stick" to make playing with the tiles a bit easier.To make it work in 3D,you'd have to bevel the edges,I think.If you did that,then maybe in the 2D layout you'd still be able to slide them around?Hmmm...maybe worth trying a remix...:-).Glad you like the instructable!

    Most articles conflate the map being "accurate" with the fact that projecting onto the icosahedron facets means distortions are localized on each tile AND distortions are spread around and not concentrated in one place (e.g.like they are on a traditional Mercator projection,where the poles are highly distorted).It's good to remember that all maps have deficiencies,even globes,and even the Dymaxion projection!But I'm glad you enjoyed the instructable.:-)

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  • gravitinoenteredDymaxion Earthin theBig and Small Contestcontest 2 months ago
  • gravitinoposted an instructableDymaxion Earth 3 months ago
  • Cosmos Mariner: a Large Aperture Dobsonian Telescope

    Cool!A friend of mine does radio astronomy with one of the old 6 foot diameter TV dishes.He does all sky maps by assembling them from "drift scans".What are you going to use for your receiver?There is a small but dedicated community of amateur radio astronomers out there.

    No,I've pushed my Dobsonians by hand for many years and am used to it at this point.As I noted in the last step,you can build an equatorial tracking table,but I haven't gone down that road yet.:-)

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  • gravitinocommented ongravitino'sinstructableFalling Sand Art Picture Repair 3 months ago
    Falling Sand Art Picture Repair

    Hi Brotchie -- I don't know.I have a round one,and the access hole is a small circle in the middle of the frame (I attach a picture here).Is your frame integral to the piece,or just cosmetic?Maybe it is under the frame somewhere?

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  • gravitinomade the instructableEasy $5 Lightsabers 3 months ago
    Easy $5 Lightsabers

    This was a great instructable!Made a set for my daughter for Christmas.She loved them!Great idea and great put together!

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  • gravitinocommented ongravitino'sinstructableFalling Sand Art Picture Repair 3 months ago
    Falling Sand Art Picture Repair

    I'm glad you found it useful!I was just looking at mine and it is time to fix it again.I'm also glad I wrote it up so I know what to do now!

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  • Wide Angle Reflex Finder for Amateur Astronomers

    Yay!I'm going to try and build one for my next scope project.I've never 3D printed before,so that will be new for me.My library has a print service,so I'm going to talk to them about it.I'll let you know how it turns out,and post here when i've done it.:-)

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  • Cosmos Mariner: a Large Aperture Dobsonian Telescope

    thank you!I'm glad you enjoyed it!

    I'm glad you enjoyed it!I added a new step with a few pictures of the Moon,which are all I have taken through Mariner (using my phone).

    I added a new step with a few pictures of the Moon,which are all I have taken through Mariner (using my phone).Most everything else is too hard to photograph with my phone,though you could upgrade the scope to be used for astrophotography.

    I added a new step with a few pictures of the Moon,which are all I have taken through Mariner (using my phone).I'm glad you liked the project!

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    • Cosmos Mariner: a Large Aperture Dobsonian Telescope
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  • Cosmos Mariner: a Large Aperture Dobsonian Telescope

    Thanks!I'm glad you liked it.

    Thank you!I'm glad you enjoyed the instructable!

    It was definitely a lot more work than building the smaller one.As they get larger,it is harder to engineer them out of wood,though I do know of examples that are in the 36-inch range and made out of wood.A famous example is Tom Clark's "Yard Scope" (the mirror is a yard across!).https://www.cloudynights.com/gallery/image/22005-the-yard-scope-ii/

    Thanks!It was fun to build;hopefully it is all clear!The skies too (though not right now!).:-)

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  • Cosmos Mariner: a Large Aperture Dobsonian Telescope

    Yep,aperture fever is costly.:-( I don't have an instructable for Equinox because I built it so long ago,but the procedure is essentially the same outlined here,just scaled down to the size of the 12-inch mirror.You can do a scope like Equinox for probably less than $1000 -- the main cost is always the primary mirror.It looks like Agena Astro has 12-inch mirrors for $500.https://agenaastro.com/parts-accessories/mirrors-holders/primary-mirrors.html

    Wow!I never got to meet Dobson!I've heard a lot about him;it would have been fun to attend one of his 金宝博娱乐城classes!

    Thank you!It was fun,and it is fun to observe with too!Glad you enjoyed it!

    This was on the order of $10,000 when all was said and done (over half of that for the mirror).Motorizing is done easiest with an equatorial table;there are a couple of other comment threads below about that,but I just discovered last night there are a couple of nice Instructables about making equatorial tables.This one looks promising: //www.sledutah.com/id/Equatorial-Platform-for-the-North/

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  • Cosmos Mariner: a Large Aperture Dobsonian Telescope

    So you can make (or purchase) dual axis drives like you suggest,but operation is a bit more complicated because the two axes have to be driven simultaneously,but the rate and direction each one needs to drive at depends on where the scope is pointing in the sky.For instance,consider a star in the southeast sky.Viewed from above,the azimuth needs to rotate clockwise,and the atltitude bearing needs to lift the scope to track.For a star in the southwest sky,the azimuth again needs to rotate clockwise,but now the altitude bearings need to lower the scope.Systems like this usually need a central brain (computer) to figure out the right thing to do,and need to be alighned at startup.By contrast,an equatorial table preserves the elegance of the Dob bearings you note — the Dob si...

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    So you can make (or purchase) dual axis drives like you suggest,but operation is a bit more complicated because the two axes have to be driven simultaneously,but the rate and direction each one needs to drive at depends on where the scope is pointing in the sky.For instance,consider a star in the southeast sky.Viewed from above,the azimuth needs to rotate clockwise,and the atltitude bearing needs to lift the scope to track.For a star in the southwest sky,the azimuth again needs to rotate clockwise,but now the altitude bearings need to lower the scope.Systems like this usually need a central brain (computer) to figure out the right thing to do,and need to be alighned at startup.By contrast,an equatorial table preserves the elegance of the Dob bearings you note — the Dob sits on the table and still points using its altitude and azimuth bearings,but the table simple turns to track the stars.They are low and quite elegant.Here is a good example of one: http://www.reinervogel.net/index_e.html?/Plattform/Plattform_e.html

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  • gravitinocommented ongravitino'sinstructableBarncaster Electric Guitar 4 months ago
    Barncaster Electric Guitar

    A standard telecaster body is just under 16-inches in the long dimension,and just over 12.75 inches in the short dimension.I cut my boards long (maybe 17-inches?),but only had 13-inch wide across the body after I glued the reclaimed panels together,so that was the tightest constraint.For the thickness,I planed everything before I glued it (step 6) to give me the thickness of 1-5/8 inches.Standard telecaster thickness is 1.75" according to blueprints,but many custom shops make them 1.5" (thickness of dimensional lumber).I had a cardboard template I was using to lay on the wood at each stage to make sure I had the grain I wanted in the right places and to make sure I had the full shape!

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  • Wide Angle Reflex Finder for Amateur Astronomers

    This is really excellent.I always hack my Telrads and put a pulser in them,so it's great to see that built in.The wider rings will also be a great help,especially under moderately light polluted skies.I have a couple of questions:(1) What are the overall dimensions?I was wondering if my dew shield for my Telrad will fit this (I use the one from Astrosystems).(2) What do you do for the base?Does it fit in the standard Telrad base?It looks like you have a custom rail in step 6.Great build!

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  • Cosmos Mariner: a Large Aperture Dobsonian Telescope

    I'm always glad to hear when people fix their telescopes!It means you'll get out under the stars more!:-) I'm glad you enjoyed the instructable.

    No,I'm a completely visual observer.I keep notes about what I see and sometimes make (crummy) sketches,but don't do any astrophotography through the telescope (I will sometimes hold my phone up and snap a pic of the Moon,但我没有任何我相信来自水手)。However,the views are *STUNNING*.I long ago finished my Messier Catalog with my smaller scopes,but the amount of more detail that can be seen with Mariner is amazing (eg.spiral arms on galaxies!),so I'm slowing revisting things I've already seen before just to look at them again.:-) I'm glad you like the instructable!

    Thanks!I'm glad you enjoyed it.Clear skies!

    Good question.I don't have any tracking.I work between 60x and 120x normally,and things stay in the field for a minute or more.To track along you just give it a bit of a bump;after observing with Dobsonians for so long,it's quite natural to track along.The easiest way to add tracking is to build an "equatorial table" -- I've thought about it,but it would require having power in the field to drive the motor.I've been fine so far.:-)

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    • Sonification of Gravitational Waves With Lego Mindstorms EV3
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  • Sonification of Gravitational Waves With Lego Mindstorms EV3

    I'm glad you enjoyed the instructable!Yes,it is calculated directly from a physical model,though I've done some streamlining (mostly factoring out constants and setting them equal to 1,since the true physical numbers are tiny).I'll see if I can boil the basics down to a 1 page PDF and add it to the instructable.You can certainly do it in Matlab/Octave or other environment.Most of us do it in python or Mathematica.The event you speak of was the first LIGO detection (there is a link to the detection page in Step 1).For those interested,you can download all of the data from all of our events at the Gravitational-Wave Open Science Center: http://gw-openscience.orgYou will also find there: tutorials on analysis,explanations of the events,and audio for each of the events we've d...

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    I'm glad you enjoyed the instructable!Yes,it is calculated directly from a physical model,though I've done some streamlining (mostly factoring out constants and setting them equal to 1,since the true physical numbers are tiny).I'll see if I can boil the basics down to a 1 page PDF and add it to the instructable.You can certainly do it in Matlab/Octave or other environment.Most of us do it in python or Mathematica.The event you speak of was the first LIGO detection (there is a link to the detection page in Step 1).For those interested,you can download all of the data from all of our events at the Gravitational-Wave Open Science Center: http://gw-openscience.orgYou will also find there: tutorials on analysis,explanations of the events,and audio for each of the events we've detected that we make with our professional tools (that page is here: https://www.gw-openscience.org/audio/ ).Have fun!

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  • gravitino's entryA Tiny Telescope Observatoryis a winner in theTiny Home Contestcontest 5 months ago
    A Tiny Telescope Observatory Winner!
  • gravitinocommented onmakeorbreakshop'sinstructableHow to Make a Rubber Stamp 5 months ago
    How to Make a Rubber Stamp

    Nice one.I've been thinking about doing this sort of fine scale carving with my xCarve but in some tests (trying to etch on anodized metal) I'm struggling with the right thing to do to get fine details,like around the "and" in your logo.So I have two questions: (1) The way you carved this with the V-big -- you did all the large areas with the V-point?So it just had to make a jillion passes?(2) You said you might do it with an end mill first -- would you have a separate pattern to do the large areas,then one like this for the fine patterns with the V-bit?Thanks!Nice instructable!

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  • gravitinocommented ongravitino'sinstructableA Tiny Telescope Observatory 5 months ago
    A Tiny Telescope Observatory

    Yep,I built both my telescopes (the one in my profile pic,and the one in the observatory).They've been very dependable.:-) Glad you liked the build.

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  • gravitino's entryA Tiny Telescope Observatoryis a finalist in theTiny Home Contestcontest 6 months ago
    A Tiny Telescope Observatory Finalist
  • gravitinocommented onbcrocker1'sinstructableTruck Camper Platform/Bed 6 months ago
    Truck Camper Platform/Bed

    This is great!I've been thinking about this in my Tundra to make camping quick and easy.I've been trying to find a high rise shell like the 122 you used.How much headroom do you have from the top of your rails to the top of the shell?Great build!

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  • gravitinocommented ongravitino'sinstructableA Tiny Telescope Observatory 6 months ago
    A Tiny Telescope Observatory

    Thank you!I'm glad you enjoyed it!

    Lol!Of course,I never get much sleep if I'm out observing.:-) When I built this one,my wife said "There are worse things you could be doing!" I hope you build one -- if you do,make sure to show us the result here on Instructables!

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  • gravitino'sinstructableA Tiny Telescope Observatory'sweekly stats: 6 months ago
    • A Tiny Telescope Observatory
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  • gravitinocommented ongravitino'sinstructableA Tiny Telescope Observatory 6 months ago
    A Tiny Telescope Observatory

    The lock is "to keep the honest people honest." With only single panel wood for construction,I decided there are any number of ways that someone could destructively get into the observatory if they really wanted to.Popping the roof is one,as you note,though it would be at the cost of destroying the overlapping ridge panel.It also would be difficult to get the telescope out that way,as you'd have to lift it over the wall!

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  • gravitinocommented ongravitino'sinstructableA Tiny Telescope Observatory 6 months ago
    A Tiny Telescope Observatory

    Hi Stephen,I'm a completely visual observer,so I don't have the constraints of the photography crowd.IN practice,the floor is a bit over-built,and the observatory is so small there are seldom people walking around inside,so I get very little transfer from the floor to the scope.In the Note to MarkF147 below,I put a picture of another observatory I built where I put the Dob on a wooden pier (because people could walk around),and it worked just fine for visual work.If I was going to do photography,I would have done a pier,but didn't want to pour one.:-)

    That's a neat idea;I've never seen lift-off ends,though I have seen people fold the peak down (typically the south wall).In this case,given the light I have in the north and south,I'm not sure I needed to do that.But I'll put that idea down for the next observatory...:-)

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  • gravitinocommented ongravitino'sinstructableA Tiny Telescope Observatory 6 months ago
    A Tiny Telescope Observatory

    My Dob is a 12.5" f/4.8 that I built when I was in graduate school.It's been a great scope,and is still the one I use most nights.I collapses down in the style of many truss style Dobsonians into just the lower cube of the mirror box,and can easily be transported in a car.Looking at zenith I can look through the eyepiece without a ladder,though I keep a short two-step ladder around because I can't quite get to my finder when it's pointing straight up (though it has a Telrad too,which I use most often).

    The roof cap is a piece of 4" x 4" step flashing.You'll find it with the corrugated metal roofing at your hardware store,and is meant to seal the top of a metal roof,kind of in the fashion that I've used it here;the difference is I've only bolted it down on one side of the roof ridgeline.If you look at the 4th picture in step 7,you see the inverted "wavy wood" piece I put on top of the corrugated roof panel?That's where all the sealing is happening.When the roof is closed,that is the piece the ridge cap rests on,providing a seal.You could probably put a line of weather stripping on it,but I never had anything make it through.The only issue is at the ends,where there is a small hollow,but the rails I hung the counterweights on covered gaps there.I'm a...

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    The roof cap is a piece of 4" x 4" step flashing.You'll find it with the corrugated metal roofing at your hardware store,and is meant to seal the top of a metal roof,kind of in the fashion that I've used it here;the difference is I've only bolted it down on one side of the roof ridgeline.If you look at the 4th picture in step 7,you see the inverted "wavy wood" piece I put on top of the corrugated roof panel?That's where all the sealing is happening.When the roof is closed,that is the piece the ridge cap rests on,providing a seal.You could probably put a line of weather stripping on it,but I never had anything make it through.The only issue is at the ends,where there is a small hollow,but the rails I hung the counterweights on covered gaps there.I'm attaching a quick diagram to this comment -- does it help show how it works?

    My neighbors all know it's a scope and observatory.I think the lights get left on by habit or accident,and at midnight I don't think I should be knocking on doors!My improvised screen works pretty well for the times it happens.But you're absolutely right -- having an impromptu star party for your neighbors does wonders for relations.:-)

    Far and away the best thing to do would be to pour a pier for the Schmidt-Cassegraine -- that is not an uncommon practice in amateur observatories.You need to bury it past the frost line,make sure it is reinforced with mesh/rebar,and pour it to a convenient height for your needs.At the top,as you note,you'll have to put lugs in that will match a wedge or interface plate for your scope.The big deal there is the permanence,as you note.If you want to stick with your tripod,you can isolate it with a little more wood working.If you're doing photography with your scope,I think that is the right way to go.If you're just using your eyeballs though,the tripod is probably easier.I built another observatory where I did that for the Dob by building a platform in the center of the obs...

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    Far and away the best thing to do would be to pour a pier for the Schmidt-Cassegraine -- that is not an uncommon practice in amateur observatories.You need to bury it past the frost line,make sure it is reinforced with mesh/rebar,and pour it to a convenient height for your needs.At the top,as you note,you'll have to put lugs in that will match a wedge or interface plate for your scope.The big deal there is the permanence,as you note.If you want to stick with your tripod,you can isolate it with a little more wood working.If you're doing photography with your scope,I think that is the right way to go.If you're just using your eyeballs though,the tripod is probably easier.I built another observatory where I did that for the Dob by building a platform in the center of the observatory.I framed the floor joists around an open square,then built a mini frame of joists that sat in the square on its own footings that went to the ground.I put weather stripping around where the mini-frame and the main floor joists interfaced to keep critters and bugs out.It worked pretty well;you could probably do something similar with your tripod footing.I clipped together some old photos to show the framing,and the only shot I have that shows the footings.

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  • gravitinocommented ongravitino'sinstructableA Tiny Telescope Observatory 6 months ago
    A Tiny Telescope Observatory

    Mostly that choice was made to keep the walls low.If the center peak of the roof was tall,then either the walls would have been taller for the same size roof panels,or the roof panels would have been larger (steeper angle) and not able to (easily) rotate out of the way.Either way,they would have blocked more of the sky than I was willing to not have access to when the observatory was open.The scope can store either upright or horizontally.I actually have a protective cover I put over it at star parties,and I used it in the observatory as an extra layer of precaution.The natural storage state for that cover is horizontal,as you see in the photos.

    Thanks,I'm glad you liked it!I can't take credit for thinking of this,though.I was sketching out ideas for something that kind of worked like a dumbwaiter system with pulleys and suspended weights when I stumbled on this system on a few other observatories.It was very simple,and very effective.It worked so well,I've thought about doing it on a much larger observatory,though you'd probably have to have a steel frame instead of wood for larger weights.

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  • gravitinocommented ongravitino'sinstructableA Tiny Telescope Observatory 6 months ago
    A Tiny Telescope Observatory

    I'm glad you liked it!If I had been willing to expand the observatory to a full 10x10 size,I would have been within the permitting limits,and could have gone down below the current cut-offs I have.In practice,I haven't found the cut-offs to be that limiting for what I've been observing,so in the end it worked out just fine.One "improvement" I made is I put C-shaped electrical conduit brackets in each interior corner to hold vertical dowels -- my neighbor sometimes leaves his backlight on,so I just drape a black sheet between the dowels to shield me from the direct view of that light when it happens.Something I've been considering is that I use a red LED-light clipboard I made for notes and charts,but I was thinking I could mount a red LED light (kind of like musicians ...

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    I'm glad you liked it!If I had been willing to expand the observatory to a full 10x10 size,I would have been within the permitting limits,and could have gone down below the current cut-offs I have.In practice,I haven't found the cut-offs to be that limiting for what I've been observing,so in the end it worked out just fine.One "improvement" I made is I put C-shaped electrical conduit brackets in each interior corner to hold vertical dowels -- my neighbor sometimes leaves his backlight on,so I just drape a black sheet between the dowels to shield me from the direct view of that light when it happens.Something I've been considering is that I use a red LED-light clipboard I made for notes and charts,but I was thinking I could mount a red LED light (kind of like musicians have on their stands) on my chart table,and always have light when I need it -- it would be easy to wire up and tuck the electronics support under the board the chart table is made of.

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