From e8826d3c441b225648f82a66b488f9a18cdb7412 Mon Sep 17 00:00:00 2001 From: Noah Smith Date: Tue, 2 Apr 2024 09:21:52 +0200 Subject: [PATCH] sync --- _posts/2024-04-01-experiment.md | 4 +-- about.md | 43 ++++++++++++++++++++++++--------- 2 files changed, 33 insertions(+), 14 deletions(-) diff --git a/_posts/2024-04-01-experiment.md b/_posts/2024-04-01-experiment.md index 3415f30..1c8ee9d 100644 --- a/_posts/2024-04-01-experiment.md +++ b/_posts/2024-04-01-experiment.md @@ -1,6 +1,6 @@ -time to try something a bit different. up till now, this project has mostly been about code - at first cpp, then mixed cpp and py, and recently all three side by side in parallel - py, cpp, and mixed. that could evolve and grow now to encompass something wider. part of what is bringing this about is a better understanding that there are two separate tools in hand - +time to try something a bit different. up till now, this project has mostly been about code - at first cpp, then mixed cpp and py, and recently all three side by side in parallel - py, cpp, and mixed. that could evolve and grow now to encompass something wider. part of what's bringing this about is a better understanding that there's two tools in hand now - - sphinx - this is about python. with python, it's standard to do docstrings within the py code files. sphinx is simply a way to convert that into a static html website. - jekyll - this is effectively about github. with github, it's standard to do markdown files within the project. jekyll is simply a way to convert that into a static html website. -project starid has been using sphinx 'docsascode/readthedocs' for years now. what's new is - experimenting with a jekyll 'project website' as well. so two separate websites flowing out of the project - 'docsascode/readthedocs' via sphinx, 'project website' via jekyll. \ No newline at end of file +project starid has been using sphinx 'docsascode/readthedocs' for years. what's new is - experimenting with a jekyll 'project website' as well. so two separate websites flowing out of the project - 'docsascode/readthedocs' via sphinx, 'project website' via jekyll. \ No newline at end of file diff --git a/about.md b/about.md index 265e94d..f13c1a7 100644 --- a/about.md +++ b/about.md @@ -1,8 +1,3 @@ ---- -layout: page -title: "about" ---- - this's been a hobby project for well over three decades now. here's some notes around how that all came about. the 'lost in space' problem - [photos](https://photos.app.goo.gl/ifuTJUNsaRJK21E79){:target="_blank" rel="noopener"} @@ -30,7 +25,7 @@ reflected sunlight from asteroids is dim because of their small size and distanc 1990 - [photos](https://photos.app.goo.gl/vKBxieTbwsbmshCg8){:target="_blank" rel="noopener"} ------------------------------------------------------------- -summer of ninety - university of texas at austin astronomy department - recently the hubble space telescope had finally reached orbit and the berlin wall had fallen - rent was less than two hundred a month, just a short walk north of campus - martha ann zively, the eighty-three year old landlady, lived directly overhead, and mobile phones, notebook computers, and the web were all somewhere over the horizon - home internet was a dialup modem into a university access point. +summer of ninety - university of texas at austin astronomy department - recently the hubble space telescope had finally reached orbit and the berlin wall had fallen - rent was less than two hundred a month, just a short walk north of campus - the eighty-three year old landlady and friend of lbj and john connally, mrs zively, lived directly overhead. mobile phones, notebook computers, and the web were all somewhere over the horizon - home internet was a dialup modem into a university access point. since the previous fall, work meant the hubble space telescope astrometry team - a group with members from the astronomy department, mcdonald observatory, the aerospace engineering department, the center for space research, and the european space agency and its hipparcos project - paul hemenway, an astronomer involved with all those organizations, was mentor and friend. life on the top three floors of rlm, the physics math astronomy tower, was special. high above the green treetops of austin, looking west to the hill country, it was a quiet and mellow time. a hippy vibe permeated the scence. wheatsville food coop, a few blocks away, was still in the seventies, which weren't so long ago after all. @@ -46,17 +41,41 @@ an observing night began a few hours before sunset. down in the telescope contro a stack of white envelopes, each containing a glass photographic plate, waited on a desk - to prepare, a control room terminal with a command line program on the nova generated telescope pointing information for a list of asteroids. using this mini was probably the last serious contact with the large eight-inch floppy disks - they were a vanishing breed by the late 80s. after jotting down notes for the planned observations, the plates were moved up into the dome, where it was pitch black except for clouds of stars in the open slit - the telescope loomed overhead in the darkness. -caution was required climbing up the stairs onto the circular telescope floor - it rose and descended in order to stay near the camera as the telescope moved - one could easily step off in the dark, high above the dome floor. the massive base of the telescope and attached camera hung at eye level - sliding out the plate holder cover opened a rectangular frame of stars, with the silhouette of the telescope secondary mirror housing and its support struts high above. mcdonald maintenance staff had mounted the camera and connected power cables, but fine tuning was always needed, and the telescope itself had to be focused - this meant adjusting the position of the secondary mirror. a rocker switch on the telescope hand controller activated a motor to move the secondary inward or outward - the exact determination of focus was old-school, using a knife-edge. in the telescope’s focal plane, all of the light from a star converges through a single point. when a knife-edge cuts through that point, the light from the star is cut off instantly - if the knife-edge dims the star gradually, then the secondary mirror position needs to be adjusted. the point of instant cut off needed to be where the photographic plates were held by the camera, so a special metal frame mounting a straight knife-edge was fastened into the plate holder, for adjusting the secondary mirror position while watching the knife-edge. if there was a bit of spare time, the metal frame could be replaced with another special frame holding the eyepiece, a glass lens heavy enough to require both hands to lift - peering inside, one saw directly a mysterious world of red or green nebulas or spiraling galaxies... +caution was needed climbing up the stairs onto the circular telescope floor - it rose and descended in order to stay near the camera as the telescope moved - it was easy to take a step onto thin air in the dark, high above the dome floor. the massive base of the telescope and attached camera hung at eye level - sliding out the plate holder cover opened a rectangular frame of stars, with the silhouette of the telescope secondary mirror housing and its support struts high above. + +mcdonald maintenance staff had mounted the camera and connected power cables, but fine tuning was always needed, and the telescope itself had to be focused - this meant adjusting the position of the secondary mirror. a rocker switch on the telescope hand controller activated a motor to move the secondary inward or outward - the exact determination of focus was old-school, using a knife-edge. in the telescope’s focal plane, all of the light from a star converges through a single point. when a knife-edge cuts through that point, the light from the star is cut off instantly - if the knife-edge dims the star gradually, then the secondary mirror position needs to be adjusted. the point of instant cut off needed to be where the photographic plates were held by the camera, so a special metal frame mounting a straight knife-edge was fastened into the plate holder, for adjusting the secondary mirror position while watching the knife-edge. + +if there was a bit of spare time, the knife-edge frame could be replaced with a frame holding 'the eyepiece'. this was a glass lens about the size of a small flower vase and heavy enough to require both hands to lift. peering inside, the eye saw vivid red or green colors in nebulas - much like the popular photos. + +once the telescope was ready, camera configuration came next. with the small field of view of the telescope - effectively a high magnification - asteroids moved significantly, relative to the background stars, over an interval of around ten minutes - each asteroid was a bit different, and various orbital characteristics had to be taken into account - the direction and rate of relative motion had already been computed by the minicomputer - now the camera body was rotated in its mounting, relative to the telescope, and programmed to move at the apparent rate of the target asteroid, so it would appear to be motionless. + +the rear-surface of the image dissector was a round crt screen divided by lines into four quadrants. light from a star, cascading down through the photomultiplier tube, formed a green glow on the screen. a guide-star was found near the asteroid and centered on the screen - with the tracking loop activated, the camera position was updated every few seconds with a mechanical click, keeping the star at the center of the screen. + +an asteroid exposure usually began with guide-star tracking - then the steady clicking of the tracking loop would go silent for a period of asteroid tracking, with asteroid-light builing up a darker spot on the photograph plate - then the guide-star tracking would resume. the result was a dumbbell shape for stars, with two circular peaks connected by a trail - the asteroid was a trail with a circular peak at its midpoint. these peaks and trails became visible the next day when the plates were developed. each plate had many dumbbell shaped stellar trails - short or long, thick or thin - and at the center of the plate, a single ufo shaped asteroid-image. + +reducing the glass plates to digital data, and then improving the asteroid orbital parameters followed over the next weeks and months - this all took place back in austin, where the center for space research and department of aerospace engineering became involved - their expertise in orbit determination played an important role in the hubble astrometry team. the space age was roughly thirty years old at the time, and members of its first generation led the center for space research - ray duncombe, byron tapley, and bob schutz. + +first, the plates had to be measured using a scanner and minicomputer in the scanning room, hidden behind a nondescript door in the astronomy department library on the fifteenth floor of robert lee moore hall - better known simply as rlm. many hours passed in the scanning room - it was a meditative kind of place, cool and dark, with a steady loud drone from electronics fans. the long back wall was covered with cabinets containing thousands of glass plates, including historic sets of survey plates from palomar and the european southern observatory, alongside many plates from mcdonald. + +black plastic sheets from ceiling to floor formed made kind of cave of the back half of the room, and inside sat the pds microdensitometer. this was a machine for mechanically scanning photographic glass plates - an interesting time capsule of analog-era technology. light from a bulb was focused into a beam shooting downward through a mechanically driven stage with position encoders. a photometer below the stage measured the transmitted intensity while the stage moved in a raster pattern. sampling of the photometer and encoders was done by a very early, mini-fridge sized, rack-mounted sun workstation. + +may or june of ninety was the first observing run at mcdonald - chat among the astronomers was about serious problems with hubble that were repeatedly making headline news - there was still lots of discussion of the high gain antennas, because news of the catastrophic error in the primary-mirror hadn’t yet leaked out - overhearing the veterans during those days at mcdonald was an early revelation about the realities of science and technology. the real world seemed a bit different than the popular science coverage. + +it was an eight-hour drive to west texas from austin - three or four nights were occupied with making plates with the telescope - then came the drive back to austin. texas summer heat was just beginning to get intense, and after a sweltering walk over to rlm it was nice to settle into the cool darkness of the scanning room - that little apartment at mrs zively's house could be uncomfortably warm during the day, even with the air conditioning running full blast. + +the plates were roughly the size and shape of writing paper - the glass was fairly thin and fragile - held up against a background light, the star and asteroid trails were small dark smudges. with the plate secured to the pds scanning stage, and looking across the plate’s surface, dull black trails of photographic emulsion were obvious on the surface of the glass, and the control software on the workstation had to be told which trails to scan. + +this meant moving the scanning beam about the plate, manually steering the stage and noting coordinates - at the top of the pds, roughly at eye level, was a circular glass screen showing a magnified image of the plate illuminated by the scanning beam - individual grains of photographic emulsion were visible, and when the beam was near a star trail it appeared as a fuzzy black worm. the stage was adjusted using two finely geared knobs, and the coordinates of the scanning beam were shown by two sets of red leds on the pds console - the corners of a rectangle about a star trail were the coordinates for a raster scan, and were entered in manually at the workstation keyboard. -once the telescope was ready, camera configuration came next. with the small field of view of the telescope - effectively a high magnification - asteroids moved significantly, relative to the background stars, over an interval of around ten minutes - each asteroid was a bit different, and various orbital characteristics had to be taken into account - the direction and rate of relative motion had already been computed by the nova - now the camera body was rotated in its mounting, relative to the telescope, and programmed to move at the apparent rate of the target asteroid, so it would appear to be motionless. the rear-surface of the image dissector was a round crt screen divided into four quadrants. light from a star, cascading down through the photomultiplier tube, formed a green glow on the screen. a guide-star was found near the asteroid and centered on the screen - with the tracking loop activated, the camera position was updated once per second with a mechanical click, keeping the star at the center of the screen. an asteroid exposure usually began with guide-star tracking - then the steady clicking of the control loop would go silent for a period, and the sky would turn while asteroid-light built up a darker spot on the photograph plate - then the clicking would resume. the result was a dumbbell shape for stars, with two circular peaks connected by a trail - the asteroid was a trail with a circular peak at its midpoint. these peaks and trails became visible the next day when the plates were developed. each plate had many dumbbell shaped stellar trails - short or long, thick or thin - and at the center of the plate, a single ufo shaped asteroid-image. +the workstation was a tall rack standing in the back-right corner and mounting a mini-fridge sized early sun microsystems box - on a table beside the rack was an extremely heavy old crt monitor showing one of the first primitive unix graphical user interfaces, the sunview competitor of x windows - this machine already had the obsolete feel of an earlier era. the hardware seemed especially ponderous and heavy, as if made from scrap steel in an old-school factory - which is probably pretty close to the truth. -reducing the glass plates to digital data and improving knowledge of the asteroid orbits followed over the next days and weeks - this all took place back in austin, where the center for space research and department of aerospace engineering became involved - their expertise in orbit determination played an important role in the hubble astrometry team - the space age was roughly thirty years old, and members of its first generation led the center for space research - ray duncombe, byron tapley, and bob schutz. first, the plates had to be measured using a scanner and minicomputer in the scanning room, hidden behind the astronomy department library on the thirteenth floor of robert lee moore hall - better known simply as rlm. many hours passed in the scanning room - it was a meditative kind of place, cool and dark, with a steady loud drone from electronics fans. the long back wall was covered with cabinets containing thousands of glass plates, including historic sets of survey plates from palomar and the european southern observatory, alongside many plates from mcdonald - black plastic sheets shielded the end of the room from stray light, and at the center of this cave sat the pds microdensitometer. this was a machine for mechanically scanning photographs - an interesting time capsule of analog-era technology. light from a bulb was focused into a beam downward through a mechanically driven stage with position encoders. a photometer below the stage measured the transmitted intensity while the stage moved in a raster pattern. sampling of the photometer and encoders was done by a very early, mini-fridge sized, rack-mounted sun workstation. +a scanning session meant creating a set of digitized raster files, one file for each trail scanned by the pds, archived on 9-track half-inch tape - a group of files, say thirty to fifty for a plate with a good exposure and lots of stars, was created in the filesystem of the workstation and then written to tape using its sibling above on the sixteenth floor, which had the tape drive. -may or june of ninety was the first observing run at mcdonald - chat among the astronomers was about serious problems with hubble that were repeatedly making headline news - there was still lots of discussion of the high gain antennas, because news of the catastrophic error in the primary-mirror hadn’t yet leaked out - overhearing the veterans during those days at mcdonald was an early revelation about the realities of science and technology. it was an eight-hour drive to west texas from austin - three or four nights were occupied with making plates with the eighty-two inch - then came the drive back to austin. texas summer heat was just beginning to get intense, and after a sweltering walk over to rlm it was nice to settle into the cool darkness of the scanning room - that little apartment could be uncomfortably warm during the day, even with the air conditioning running full blast. +the shift over the border from analog to digital took place in the seventies style electronics connecting the pds to the workstation. a few days after scanning those first plates, paul and ray duncombe discussed the next steps in wrw, the aerospace building. it was a short walk from rlm to wrw. overhead was the usual hard blue texas summer sky with little white clouds, and a blazing sun. sweat was running down just seconds after stepping outside the air conditioning. -the plates were roughly the size and shape of writing paper - the glass was fairly thin and fragile - held up against a background light, the star and asteroid trails were small dark smudges. with the plate secured to the pds scanning stage, and looking across the plate’s surface, dull black trails of photographic emulsion were obvious on the surface of the glass, and the control software on the workstation had to be told which trails to scan. this meant moving the scanning beam about the plate, manually steering the stage and noting coordinates - at the top of the pds, roughly at eye level, was a circular glass screen showing a magnified image of the plate illuminated by the scanning beam - individual grains of photographic emulsion were visible, and when the beam was near a star trail it appeared as a fuzzy black worm. the stage was adjusted using two finely geared knobs, and the coordinates of the scanning beam were shown by two sets of red leds on the pds console - the corners of a rectangle about a star trail were the coordinates for a raster scan, and were entered in manually at the workstation keyboard. +during that short walk, lightning struck - exactly which stars were on those plates? how could those stars really, in practice, be identified, in order to determine the position of the asteroid? was there a program on the astronomy or aerospace computers to do that? -the workstation was a tall rack standing in the back corner and mounting a mini-fridge sized early sun box - on a table beside the rack was an extremely heavy old crt monitor showing one of the first primitive unix graphical user interfaces, the sunview precursor to x windows - this machine already had the antiquated feel of an earlier era. a scanning session meant creating a set of digitized raster files, one file for each trail scanned by the pds, archived on 9-track half-inch tape - a group of files, say thirty to fifty for a plate with a good exposure and lots of stars, was created in the filesystem of the workstation and then written to tape using its sibling above on the sixteenth floor, which had the tape drive - the shift over the border from analog to digital took place in the seventies style electronics connecting the pds to the workstation. a few days after scanning those first plates - paul and ray duncombe discussed the next steps in wrw, the aerospace building. there's a clear memory of the short walk from rlm to wrw - stopping in the texas sun - overhead was the typical hard blue summer sky with little white clouds, and sweat running down just seconds after stepping outside the air conditioning - the thunderbolt question has struck from a clear sky - exactly which stars were on those plates? how could those stars really, in practice, be determined, in order to determine the position of the asteroid? was there a program on the astronomy or aerospace computers to do that? the answer was, no - there wasn’t an easy or obvious solution, and helping to figure out a practical method of identifying those stars on those particular plates was the real job - not that an undergrad had any chance of even beginning to find a real solution, but even beginning to be aware of and recognize the magnitude of the problem was a huge step forward - how did one go about recognizing stars - humans could do it, but could an eighties computer system? +the answer was, no. there wasn’t an easy or obvious solution, and helping to figure out a practical method of identifying those particular stars on those particular plates was ultimately the real job. not that an undergrad had any chance of finding a real solution. but just becoming aware of and recognizing the magnitude of the problem was a huge step forward. how are stars recognized? humans could do it, but could an eighties computer system? 2003 - [photos](https://photos.app.goo.gl/ng8Nbxra2RYrbeWA7){:target="_blank" rel="noopener"} -------------------------------------------------------------