SkyCruncherLearn
Learn
How starlight becomes a measurement, explained for smart-telescope owners. Notes are short and kept current.
Start here
Four questions, each answered by one page.
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Question 1
Is the picture my Seestar shows me real?
What the app does to your pixels, and the point where a pixel stops being a measurement.
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Question 2
Which files should I keep from a night?
Turn on sub saving before the session starts and keep the FITS subs: they are what a measurement is made from.
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Question 3
Can my Seestar do real science?
Yes, within limits: what I have measured with Seestar frames, what other owners report, and where the data can go.
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Question 4
How do I catch an exoplanet transit?
Pick a planet, plan the night, set up, reduce the frames and send the light curve on.
The exhibit
By topic
Before you shoot
Choices to make before the session starts.
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How long: per sub and per target
Which sub length should I pick, and how long should I spend on a target?
Read noise against sky noise, bright stars, field rotation and rejected subs, and why total time on the target matters more than the length of each sub.
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Alt-az or EQ mode
Should I use EQ mode with a wedge?
Why the star field slowly turns in alt-az mode, what that costs at the corners, and when equatorial mode is worth the extra setup.
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Reading your frames
What the frames and the picture are telling you.
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Why bright stars turn green or purple
Why are my brightest stars green or purple?
Each color stops counting at a different level, so a full star core takes its color from the camera and your software, not the star. What to do about it.
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Is my Seestar image real?
Is the picture my Seestar shows me real light, or processing?
What live stacking and stretching do to your pixels, what a synthetic-sky test showed, and where a pixel stops being a measurement.
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Plate solving
What is plate solving, and why does it sometimes fail?
How four-star patterns find where a frame points, why a match alone doesn't prove a solve, why solves fail, and how often they have worked on my frames.
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S30, S30 Pro, S50
What differs between the Seestar models for science?
Pixel scale and field from ZWO's specs, then what my frames showed: where green clips, how much light a unit collects, and what a stack's corners say. No buying advice.
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Doing science
Turning your frames into data other people can use.
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Can a Seestar do real science?
Can my Seestar contribute anything real to astronomy?
Variable stars, transits, star positions and occultations: what I measured with Seestar frames, what other owners report, and where to send the data.
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How to read a light curve
What am I looking at on a light curve?
Which way is brighter, why every curve is measured against comparison stars, what error bars say, how folding on a period works, and what the variable-stars labels mean.
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Catching an exoplanet transit
How do I catch an exoplanet transit with my Seestar?
Pick a planet your aperture can see, plan a night with a baseline on both sides, set up in EQ mode, reduce against comparison stars and send the result on.
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Submitting to the AAVSO
How do I send my light curves to the AAVSO?
A light curve is a star's brightness over time. This guide covers what you need, what the report file holds, and how to upload it through WebObs, the AAVSO's submission site.
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Under the hood
What happens to a frame between the telescope and a number.
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How calibration works
What do bias, dark and flat frames take off a raw frame?
The math behind calibration, with measurements from a Seestar S30 Pro, and how calibration frames can be built from your own light frames alone.
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Frame receipt format
What is a frame receipt, and how do receipts add up?
A receipt records what was measured on one frame. This Note shows how receipts roll up into sessions and a star database, with a real M 31 frame redrawn from its receipt alone.
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The light map
What is the light map, and why is the sky cut into equal-area cells?
One map of the sky's light on HEALPix cells, with no telescope built in: what each cell holds, how a frame's stars land on it, and how that makes different telescopes comparable.
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Sharing safely
Keeping the right files, and keeping your location out of them.
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What your Seestar saves
Which files should I keep from a night?
Which files a Seestar writes, how to make sure the single FITS subs are saved, what a FITS header records, and how big a night is.
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Before you share
Could my files give away where I live?
The header keys, photo data and file names that reveal an observing site, and what Clean my files and Upload change on your computer before you share.
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On science pages, a thin line beside a passage says how far its claim is proven: measured, planned, illustrative, inferred, and more. Colored numbers carry the same mark. A passage with no line is stated. How claims are marked.
Elsewhere on the site
- See it in our dataResults: living pages rebuilt as data comes in, including the sky map.
- Tools for tonightPlan a night, clean your files and calibrate.
- Dated measurementsExperiments: dated measurement pages, each with the data it used.