[HN Gopher] Skyfield: Elegant Astronomy for Python
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Skyfield: Elegant Astronomy for Python
Author : stefankuehnel
Score : 182 points
Date : 2023-12-01 00:03 UTC (22 hours ago)
(HTM) web link (rhodesmill.org)
(TXT) w3m dump (rhodesmill.org)
| bvan wrote:
| Very impressive. Great job.
| shusaku wrote:
| Looking at the GitHub, there are a lot of non-trivial, yet
| seemingly approachable feature requests. For someone looking to
| contribute to scientific open source software, this seems like a
| great package.
| verandaguy wrote:
| It's been a while since I've seen a project advertise Python
| _2.6_ compatibility.
|
| This looks cool, and most of the code would look nearly right at
| home in a modern code base!
| leetrout wrote:
| I will definitely check this out!
|
| For anyone that could offer thoughts:
|
| I have a ~1985 celestron c8 with the skysensor computer.
|
| The skysensor uses and 1950 epoch and is definitely not y2k
| compliant :D
|
| What is the best way to find a 19xx year that closely matches
| 202x so i can use the GOTO mode? I have been adjusting bright
| stars by some crude guesstimates by looking at average change in
| times between 1950 and 1990 and then again between 1990 and 2023
| and working out the RA and Dec which can get me close.
|
| But it would be nice to figure out if there is a year that would
| match real close. Maybe i can use this library to do a brute
| force search.
| teamonkey wrote:
| One possibility is to replace your SkySensor computer with
| OnStep. This is an Arduino-based system for GOTO scope control.
| It has ASCOM (Windows) and Indi (Linux) drivers so can control
| it from a PC or - if you add wifi - a phone app. It also has
| autoguiding support. It can run on most common microcontrollers
| and even cheap 3D printer control boards.
|
| IIRC the C8 was often sold with a Super Polaris mount, or
| something similar. There are many builds for this mount.[1]
|
| If you're not in to DIYing a solution there are companies that
| sell pre-built conversion kits.
|
| [1] https://onstep.groups.io/g/main/wiki/4414
| leetrout wrote:
| Thank you! I have only done cursory searches around a
| conversion.
|
| I LOVE the retro feel of chonky skysensor so I would love to
| figure out how to keep the original motors and 5 pin plug. I
| have the original manuals and since the circuits are chonky
| too I suspect it would not be hard to make something
| compatible even without a bench scope.
|
| This is a great link, I will dig through and see if someone
| has done what I want already.
| teamonkey wrote:
| It's quite possible that it has a ST-4 style guide port,
| which simply has 4 pins for slewing in each of the 4
| directions + 1 common pin.
|
| https://astrophotosite.com/tiki-index.php?page=ST-4
| leetrout wrote:
| It has two 5 pin DIN ports, one to each motor and an
| RS232C for connecting to a PC so I dont think that is
| compatible.
|
| I appreciate the link since that gives me more to
| research. I am going to have to tear down the mount and
| see if the motors are marked with their ratios and such
| based on what I am reading this morning.
| doctorhandshake wrote:
| Very cool. How does this differ from pyephem?
| JNRowe wrote:
| It is from the same author. He semi-retired pyephem with the
| release of this project1: "The Skyfield astronomy library
| should be preferred over PyEphem for new projects. Its modern
| design encourages better Python code, and uses NumPy to
| accelerate its calculations."
|
| I switched a few toys I'd written from pyephem to skyfield, and
| it felt like a large improvement. (Must note that they really
| were toys though, so the amount of work wasn't huge in my
| case).
|
| 1 https://rhodesmill.org/pyephem/
| sizzzzlerz wrote:
| In many ways. Pyephem uses the ancient xephem linux C library
| for its astronomical calculations for both satellites and solar
| bodies. Skyfield uses the modern NASA SDG4 tables for a more
| accurate calculation of satellite positions and JPL's ephemeris
| tables for planetary positions, yielding much greater accuracy
| and precision. It is written in pure Python and uses Numpy for
| speed enhancement. Finally, its API is completely different so
| knowing pyephem won't be of much help in learning skyfield.
| gammarator wrote:
| Users interested in a broader range of astronomical tools beyond
| coordinate transformations may be interested in
| https://www.astropy.org/ and its affiliated packages.
| thinkmassive wrote:
| Cool, it sounds like Skyfield is intentionally made
| interoperable with AstroPy:
|
| > While Skyfield itself has no dependency on the AstroPy
| library, it's willing to accept AstroPy time objects as input
| and return results in native AstroPy units
| dekhn wrote:
| Thanks- I was wondering if this was a useful tool compared to
| astropy.
|
| I've used astropy for a couple things: 1) to automatically
| locate the angle of the sun in the sky in alt and az, and send
| motor commands to keep my telescope pointed at it for hours
|
| 2) to compute the moon and sun locations around a solar eclipse
| so I could simulate an eclipse in blender
|
| When you use libraries like this you realize you are taking
| advantage of hundreds, if not thousands of years of
| technological development and discovery, turbocharged by modern
| math and software engineering.
| rzimmerman wrote:
| Brandon Rhodes has made such a wonderful contribution to the
| aerospace and python fields with Skyfield, pyephem, his port of
| sgp4, and astropy. Really wonderful helpful stuff.
| nkantar wrote:
| If anyone wants a fun story, Brandon Rhodes is a wonderful
| storyteller, and this talk involves the linked library as well:
| https://www.youtube.com/watch?v=cYHP3oRGjG8
| ngshiheng wrote:
| he is! ive learnt so much from his talks
| vortegne wrote:
| This was great, thank you for posting!
| protontypes wrote:
| The examples and tutorials for these libraries were an ideal
| introduction to me in astronomy, astrodynamics and satellite
| orbits. As part of my Ph.D., I was able to build a multiple orbit
| simulation and validation tools for smaller satellite missions
| thanks to Skyfield.
| thicknavyrain wrote:
| Skyfield is very cool. For my wedding, I wanted to give my
| groomspeople personalised thank you gifts. The idea I came up
| with was to find or ask for precise dates significant to them
| each (their own anniversaries, birthdays, special events...) and
| convert that into an abstraction of the relative positions of the
| planets on that day using Skyfield: https://imgur.com/l7G0att
| (and with the moon's orbit if they wanted:
| https://imgur.com/CYqfLR4).
|
| I then got them engraved onto cufflinks https://imgur.com/bhxJVGo
|
| They were super happy with the result, and we all looked great on
| the day. I wonder if there's a market for these but it feels a
| little niche, I'm glad skyfield exists to help projects like
| these.
| daoboy wrote:
| That is a very cool gift.
|
| While not exactly the same, I got my wife a framed print of the
| stars over our wedding day as an anniversary gift a few years
| after we were married. It may be a little niche, but I think
| there is a market for that kind of thing.
| IanCal wrote:
| Very nice. I love this kind of thing.
|
| I make multispectral Sun images (https://imgur.com/UMQhcw6) for
| people occasionally based on a time & date, I started messing
| around with the idea for my son, and then as a gift for a
| friend and she then helped me get a page up
| https://www.theremarkablz.com/thesun
|
| It's often for sciency people who have just had a kid, because
| with the SDO images you can get really close to the specific
| time of birth.
| dsq wrote:
| I ask as a complete non expert in the field, please be patient:
| Wouldn't this require either downloading and maintaining a large
| database of ephemeri or connecting online to some server, say at
| NASA? Or is everything calculated from first principles.
| d_silin wrote:
| Good question! I use Skyfield library for my project, it does
| require downloading NASA ephemeris, but it is only <200MB,
| unless you want a very long time period and you need to do it
| once every few years.
|
| (DE430 got published in 2014 and most current version is DE440,
| released in 2021.
| dsq wrote:
| That's what I thought must be necessary, thank you.
| mturmon wrote:
| It may be worth adding that the planetary ephemeris are
| computed by NASA (JPL) by integrating the equations of motion
| forward in time numerically.
|
| Then the results (e.g. planet centroid as a function of time)
| are encoded in a file, as noted above.
|
| That file is then read by the ephemeris software to obtain
| the position at the desired time.
|
| I haven't checked in a few years, but there used to be
| multiple files to choose from depending on the time range you
| needed to cover.
|
| It's free -- "your taxpayer dollars at work."
| IanCal wrote:
| That's really cool. I also really like the minimal requirements
| for installing plain python, plus numpy).
| rookderby wrote:
| Lovely project. Ive wanted to do similar for years but never got
| around to it. Now i just need to think of a project to use it
| for. Thank you to the author.
| jfrd wrote:
| Brandon helped me solve an interesting problem during my PhD. I
| was building a sun-tracking sensor for a solar-powered lunar
| rover, and I needed to calculate the vector from the robot to the
| sun.
|
| Brandon showed me how to use skyfield to solve the problem for a
| robot on Earth, and then he went back and forth via email to show
| me how to solve the problem on the moon.
|
| In the end, we used skyfield to generate lookup tables for the
| places and times that we cared about, and it worked out great!
| patrickwalton wrote:
| Skyfield is so well maintained and documented that we actually
| use it to process tracking data for our own satellites and plot
| additional orbit parameters like beta angle, altitude, etc.
| diracs_stache wrote:
| That's really cool, astropy is well baked into our python
| codebase but may need to experiment more with Skyfield since
| it's coordinate transformations and timing and positions
| functionality look good.
| 082349872349872 wrote:
| A question for someone who already knows how to wrangle Skyfield:
| what is its answer for the "dawning of the age of Aquarius" ca.
| 2150?
|
| (see Chap.16 "Of Sky and Time" in "When They Severed Earth From
| Sky", esp. Table 2, for the prevalence of --or at least
| ascription to-- mentions of precession of the equinoxes in
| ancient mythology)
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(page generated 2023-12-01 23:02 UTC)