A browser-based movie viewer for solar images, built for phones first.
Pick a channel, pick a time window, and the viewer assembles a movie from Helioviewer imagery that you can scrub, loop, pan, and pinch-zoom. The channel list covers the nine SDO/AIA passbands, the HMI line-of-sight magnetogram, and a false-color differential emission measure (DEM) of the last 48 hours.
- Channel chips select the AIA passband and reload the movie.
- Duration / frames / resolution control the time window, the number of frames requested, and the pixel size of each frame. Requesting many large frames can use a lot of memory, so the status line warns when the decoded sequence is likely to exceed what a phone browser will tolerate. The window ends at the newest image Helioviewer has of the channel, which is behind real time by its ingest: tens of minutes for AIA, at times hours for HMI.
- The stamp under the scrubber gives the time of the frame in UT and, under that, in your own time zone, with how long ago it was taken.
- Fit disk resets the view to the full solar disk.
- Sharpen view re-requests the current sequence at the plate scale of the region you have zoomed into, down to the 0.6 arcsec/pixel AIA native scale. Use this after zooming to recover detail rather than magnifying the full-disk frames.
- Track rotation de-rotates every frame to the timestamp of the frame that was showing when you pressed it, so the solar surface holds still and only genuine evolution moves. The view itself does not move, so the limb stays where it is.
- Label regions marks every NOAA-numbered active region on the disk with its number; see below.
- Drag to pan, pinch or scroll to zoom, double-tap to zoom in.
A link can choose what the viewer opens on. ch is a channel by its chip
label (any case), dur the duration in hours and nf the number of frames,
each one of the menu values, and ar=1 turns on the region labels; anything
else is ignored. For example,
https://sun-data.github.io/solar-movie-viewer/?ch=DEM opens on the DEM, and
https://sun-data.github.io/solar-movie-viewer/?ch=171&dur=24&nf=96&ar=1 on
a labeled day of AIA 171.
The labels come from the daily Solar Region Summaries of the NOAA Space Weather Prediction Center, which it publishes for the last 30 days as JSON. Every numbered region is labeled, with or without sunspots, by its full number (NOAA reports 14551 as 4551). A dot marks the reported position and the number sits just north of it.
Each summary gives positions at 24:00 UT, to the nearest degree, so a frame is labeled from the last summary before its UT day, rotated on to the frame time at the same rates as Track rotation. Hence a label can step by a few arcsec at 00 UT when the next summary takes over, a region numbered today is labeled from tomorrow, and a region behind the limb is left off. With tracking on, the labels stay with the de-rotated disk.
The DEM chip shows how much coronal plasma there is at each temperature, as color: hue is temperature, from violet at 0.4 MK through green near 2 MK to red above 6 MK, and brightness is the amount. One fixed scale covers every temperature and every frame, so brightness and color compare across the disk and across the whole window. The key beside or under the disk gives the scale; it hides with the controls.
These frames are not from Helioviewer. A job that runs every 15 minutes
fetches the AIA near-real-time synoptic images from JSOC (six coronal
passbands, 2.4 arcsec/pixel), inverts every 3-minute slot with
utu.dem.plowman, colors the result with colorsynth, and publishes the
last 48 hours as full-disk JPEGs plus a manifest. Hence some differences from
the other channels:
- the window ends on the newest DEM frame rather than now. JSOC posts each image about 11 minutes after it is taken, so that is usually around half an hour behind real time, and more when GitHub runs the job late;
- the frames are a whole number of 3-minute slots apart, so the movie is always evenly spaced, but where the duration over the frame count is not a whole number of slots, it gets more frames than asked for: 120 frames every 3 minutes for 96 frames over 6 hours, 60 every 6 minutes for 48 over 6 hours, and 120 every 6 minutes for 96 over 12 hours. Where frames are missing, as while the job is catching up, it gets fewer;
- the resolution menu chooses between the 512 and 1024 pixel frames, and Sharpen view has nothing finer than 2.4 arcsec/pixel to fetch.
?dem=URL loads the DEM frames and manifest from somewhere else, such as a
local copy, which must send CORS headers.
Tracking remaps each frame rather than sliding it. For every point: screen to helioprojective, to heliographic, advance the longitude by the local rotation rate, project back, and sample there. The rate is Snodgrass (1984) for small magnetic features, converted from sidereal to synodic because the observer rides along with Earth, and the tilt of the solar axis (B0, up to 7.25 degrees) is carried through, so features move vertically as well as horizontally.
Two deliberate approximations. The remap is built from a mesh of small affine patches, because Canvas 2D applies only affine transforms and WebGL cannot touch these frames at all: neither Helioviewer nor the SDO archive sends CORS headers, so the images taint the canvas and cannot be used as textures or read back. And cells touching the limb are drawn unwarped, because the map is singular there and refining the mesh does not converge.
Good to well under a pixel on a zoomed-in region, which is what tracking is for. Not a substitute for a real reprojection if you need to measure something.
The whole viewer is a single self-contained index.html with no build step and
no dependencies. Frames come from the Helioviewer takeScreenshot API (the
DEM from its published JPEGs), are decoded as ordinary images, and are
composited onto a canvas with a view transform tracked in arcseconds so that
pan and zoom stay registered across changes in plate scale.
GitHub Pages serves index.html from the default branch. Pushing to main
publishes.