Find the asteroids and comets in your frames.

Asteroids and comets give themselves away by moving. In one frame an asteroid looks like a faint star; across a sequence it drifts while the stars stay put. This mode works with that motion. It asks an ephemeris service which known asteroids and comets should be in your field at the time of your frames, places them on the image, and measures whether each one is really there. It then subtracts the static sky and looks for anything else that moved in a straight line.

It looks for moving objects. For sources that stay in place and change brightness, use Transient Finder.

• List the known objects in your field. SkyBoT predictions are projected onto your frame, matched to local peaks, and scored. Step 05
• Inspect each one. Predicted and measured positions, motion, magnitude, and a motion-only sky map. Step 06
• Blink and track. Play the sequence while the selected object stays centered. Step 07
• Stack on the motion. Synthetic Track shifts every frame with the object so a faint one sharpens into a point. Step 08
• Align the sequence. Reproject solved frames onto one grid as FITS copies. Step 09
• Search for unmatched movers. Discover links residual detections into tracklets and checks how many known objects it recovered. Step 10
• Label and train. Save your verdict on each candidate and train a local model that scores new ones. Step 12
• Check a candidate. A checklist for deciding what a candidate is, and what reporting needs. Step 13
• Plot the path. Predicted against measured positions, offsets, and SNR over time. Step 14
• See the orbit. A 3D heliocentric view from JPL Horizons with time playback. Step 15
• Export. Images, blink and trail animations, stacks, orbit animations, and CSV tables. Step 16

Images

A folder of subframes of one field taken over time, or a single frame. FITS, XISF, TIFF, PNG, JPEG, and camera RAW files are read. For Discover you need at least three frames of the same filter and exposure; more frames over a longer span make motion easier to see.

Plate solving

Finding known objects works on unsolved frames: CAst solves the current frame when needed. Align and Discover read the WCS stored in each file, so for those every frame must already be plate-solved. For reliable solving, add an astrometry.net key in Settings > Open Settings > General > Astrometry API Key.

Timestamps

Every frame needs an observation time (DATE-OBS) and preferably an exposure time, because predictions are computed at mid-exposure. Times without a timezone are read in Image Timestamp Timezone (Settings > Open Settings > Differential Photometry, under Science Export).

Observing site

Enter your latitude, longitude, and elevation in Settings > Open Settings > Setup. CAst uses them to drop objects below your horizon, and shows them with your telescope and camera in the image information panel.

Internet

SkyBoT, JPL Horizons, IMCCE Miriade, the star catalogues, and astrometry.net are online services. Results are cached where possible.

1. On the mode picker, under SCIENCE WORKFLOWS, click Asteroid / Comet Detection.
2. If CAst is already open in another mode, choose Mode > Asteroid/Comet Detection instead.

The workflow row along the top shows Open and Align, then Trajectory View, Synthetic Track, Discover, and Plots, and on the right the Group and Frame selectors. Below it, the Predicted Objects table is on the left with the Work Log, Inspector, and Sky View tabs underneath, and the image view is on the right. Every control is listed in R1.

1. Click Open on the workflow row.
2. In Select subframe folder for asteroid/comet detection, choose the folder that holds your frames and confirm.

CAst reads every supported image in the folder, sorts the frames by observation time, shows the first one, and starts finding known objects right away (Step 05). The Open button then reads Generate.

There are two other ways in:

• Ctrl + O: File > Open File
• Ctrl + Shift + O: File > Open Folder

Groups and frames

If the folder mixes filters or exposure times, Group lists All plus one entry per combination, for example Filter L | 120 s (100). Blink, Discover, and Synthetic Track work on the selected group, and Discover needs a specific group rather than All. Frame picks the frame shown; it is also the reference frame for Generate, Align, and Discover.

If CAst did not start automatically, or you changed the frame, click Generate. Then watch the Work Log. For the current frame, CAst:

1. Checks the frame's WCS. If there is none, or it disagrees with the mount pointing in the header, it plate-solves the frame.
2. Asks SkyBoT which asteroids and comets are inside the field at mid-exposure.
3. Drops objects that fall outside the image or below your horizon, and asteroids more than 1 mag fainter than the magnitude limit (18.0 by default). Comets are kept whatever their listed magnitude.
4. Places each object at its predicted pixel, looks for a peak nearby, and measures its offset and SNR.
5. Fills Predicted Objects and selects the first row.

The Work Log ends with a line such as Detection complete: predicted 13 objects, likely visible 6, current frame ….

How predictions are made and scored is in R6.

Each row in Predicted Objects is one known asteroid or comet. Highlighted rows are likely visible: CAst found a peak with SNR at least 4 within 8 pixels of the prediction.

1. Click a row. The image centers on the object, and the information panel on the right of the image shows its prediction and the Current Frame Match: offset, SNR, FWHM, flux, and trail.
2. Open the Inspector tab for the same details as text, including the predicted RA/Dec and pixel position.
3. Click Target Marker to draw a marker on the selected object.
4. Change Frame. The predicted position and the match are recomputed for that frame from its own WCS and time.

Predicted against measured

The marker sits on the predicted position. The offset is the distance from there to the peak CAst measured. A small offset with good SNR means the object is where the ephemeris says. A large offset or low SNR can mean the object is fainter than your frame reaches, blended with a star, or that the prediction is off. Plots shows the offset on every frame.

Sky View

The Sky View tab draws only the predicted objects, without stars, so you can see how they move relative to each other. Drag Time to move up to 12 hours either way, click Now to return to the frame time, and Reset View to recenter. Drag to pan, scroll to zoom, and click an object to select its row.

1. Select an object in Predicted Objects.
2. Make sure Track Object is on (it is by default).
3. Click Blink. The first time, CAst preloads the frames of the active group, then plays them.
4. Watch the center of the view: a real mover shifts steadily from frame to frame while the stars stay fixed.
5. Click Blink again to stop.

Center Object centers the selection once and zooms to at least 3×. Hide Info hides the information panel so the field has more room. Use Display to change the stretch, open Curves, or invert the image.

• Mouse wheel: zoom the image
• Left-drag: pan the image

The playback speed is Blink Frame Time in R3.

A faint asteroid may hardly show on any single frame. Synthetic Track moves each frame along with the object and stacks them, so the object adds up into one point while the stars smear into short streaks.

1. Pick a single filter/exposure group in Group if the folder has more than one.
2. Select the object in Predicted Objects.
3. Click Synthetic Track. A progress dialog shows each frame being added.
4. In the Synthetic Tracking window, read the summary line: frames used, Stacked SNR, center offset, and the stacking motion.
5. If the measured peak landed on the wrong spot, hold Ctrl and click the object in the preview. The offset, SNR, peak, and flux are recomputed. Reset to Auto undoes it.
6. Use Overlays to show or hide the Predicted center, Auto peak, Measured peak, and Known objects markers and labels.
7. Click Export Image... to save the stack, or Close.

• Ctrl + click in the preview: set the measured peak by hand

To set the motion yourself, stack the full image, or run on the GPU, see R4. How the shift and stack work is in R8.

Discover compares frames pixel by pixel, so the frames must share one grid. You can align them here once, or let Discover align them each time it runs (Step 10).

1. Set Frame to the frame you want as the reference grid.
2. Click Align. If it is greyed out, hover it: the tooltip names the first frame that has no stored WCS.
3. Wait for the Work Log line Loaded aligned sequence from ….

CAst reprojects every loaded frame onto the reference WCS, refines the shift on stars, and writes FITS copies to an aligned subfolder. Your originals are not changed. The aligned copies are loaded in their place, so run Generate again before Discover.

Discover looks for things that moved but are not on the known-object list. It needs a finished Generate, a specific group, at least three frames, stored WCS on every frame, and a finished blink preload. If the button is greyed out, its tooltip says which is missing.

1. Choose a single filter/exposure Group.
2. Click Discover.
3. If you ran Discover on this group before, choose Restore Last Result to reopen it or Run New Scan.
4. In Discover Pipeline, keep Preset on Detailed search for the most complete search, or choose Fast scan for a quick first pass.
5. Set Alignment to Already aligned if you used Align, otherwise leave Align first.
6. Click Run Discover.

A Discover progress dialog opens with Cancel, and the Discover Results window fills in as each batch finishes. The other options are in R2; whatever you run with becomes the new default.

How Discover finds and links detections is in R7.

The top of Discover Results summarizes the run: Visible Limit (how faint your frame reaches, measured on catalogue stars), Known In Limit, Recovered In Limit, Potential Discoveries, and Borderline Review. The tables are on the left, and the reference image with the selection is on the right.

The two Known tabs are a recovery check. If Discover recovered most known objects within the limit, it was able to see objects of that brightness, so its unmatched list deserves a look. If it missed many, the frames or settings are limiting it.

1. Open Potential Discoveries and click a candidate. The details box lists every frame detection.
2. Click Trajectory... to plot its path (Step 14).
3. Click Synthetic Track... to stack on its motion.
4. Select one or more candidates and click Mark Selected to draw them on the main image.
5. Click Close when done. The result is kept.

Back in the main window, every Potential Discovery appears in Predicted Objects as a row named Candidate C… with Type Potential. Select it to blink and track it, stack on it, or plot it like a known object. Changing Group clears the marks.

Labels record your verdict on each candidate. Once you have a few, CAst can train a model that scores new candidates the way you would.

1. In Discover Results, open Potential Discoveries or Borderline Review.
2. Click Label.... Label Discover Candidates opens with a cutout that blinks through the candidate's frames.
3. Click Real Mover, Artifact, Known Object, Noise, or Unsure. The label is saved and the next candidate appears. Use Previous and Skip to move without labeling, and the speed list next to Auto Blink to change the blink.
4. Back in Discover Results, click Train Model.

You can also label one row at a time with the Candidate Label list and Save Label. After training, the ML Score column shows the model's guess and confidence. Details are in R9.

Most candidates are hot pixels, cosmic rays, satellite glints, noise that happens to line up, or known objects whose prediction was off. Work through these checks before you trust one.

1. Blink it. Select its Candidate C… row with Track Object on and click Blink. A real object is a point source that moves the same distance between equally spaced frames.
2. Look at the path. Click Plots. The measured positions should follow the linear fit with small residuals. Jumps, or a cluster that does not move, point to an artifact.
3. Stack on it. Click Synthetic Track. A real mover sharpens into a point, and its Stacked SNR should be clearly higher than on single frames.
4. Rule out known objects. Look at Known Missed. A known object near the candidate with similar motion is the likely answer. Raise Manual Limit and click Generate again to list fainter known objects.
5. Rule out fixed sources. Open the frame in Sky Explorer to see whether a catalogued star or galaxy sits on the track.
6. Check the Minor Planet Center. Use its online tools to search for known objects at the candidate's position and time.
7. Observe again. Image the field on another night and recover the object where its motion says it should be.

Reporting

Reports of asteroid and comet positions go to the Minor Planet Center. It expects the time, RA, and Dec of each detection from a registered observatory code, normally in ADES format, and a new object usually needs observations on more than one night. CAst does not write MPC or ADES reports. It shows per-frame RA/Dec for a candidate in the Inspector and in Plots, but those come from each frame's plate solution and are not checked for reporting-grade astrometry. Measure the positions in dedicated astrometry software before you submit.

1. Select a row in Predicted Objects.
2. Click Plots, or double-click the row.

A Trajectory - … window opens with four plots and a per-frame table.

A steady offset that grows slowly, as here, usually means the ephemeris and your timing differ slightly. Scattered offsets with low SNR mean the match is unreliable. The toolbar above the plots pans, zooms, and saves the figure.

Plots shows where the object went in your frames. Trajectory View shows where it is in the Solar System.

1. Select one or more known objects in Predicted Objects. Ctrl-click or Shift-click to select several.
2. Click Trajectory View. CAst queries JPL Horizons and opens a 3D View - … window.
3. Drag in the scene to rotate and scroll to zoom. Choose a Camera such as Top-Down or Object Follow.
4. Choose a longer Span, for example 1y, to see more of the orbit. Turn on Planets for context.
5. Click the play button to run time forward, and set Speed. The return button next to UTC goes back to the observation time.
6. Use Objects to show or hide objects, or Nearby Search... to add objects predicted around your field. Click Lookup to add any asteroid or comet by name.

Candidates have no orbit yet, so they are not included. With nothing selected, Trajectory View opens an empty scene that you fill with Lookup. All controls are in R5.

1. Select the object you want in the file name, if any.
2. Click Export above the image and choose:
   • Image... to save the view as shown, as PNG, JPEG, or BMP
   • Blink... to save the active group as a GIF or MP4 blink
   • Trail... to save a GIF in which the stack on the selected object builds up one frame at a time
3. Confirm the file name. The default uses the object, for example (511) Davida_blink.gif, in your source folder.

Other exports live in their windows: Export Image... in Synthetic Tracking, Save in Trajectory View, the save icon in Plots, and Export... in Discover Results for the CSV tables. They are listed with formats in R10.

Workflow row

Open / Generate

Open picks a folder and starts finding known objects. Once a source is loaded the button reads Generate and runs the known-object search on the current frame.

Align

Reprojects all loaded frames onto the current frame's WCS and loads the copies (Step 09).

Trajectory View

3D orbit view for the selected known objects (Step 15).

Synthetic Track

Shift-and-stack on the selected object or candidate (Step 08).

Discover

Searches the active group for unmatched movers (Step 10).

Plots

Path and match plots for the selected row (Step 14).

Group, Frame

Active filter/exposure group and current frame.

Image toolbar

Display

Stretch (Auto Stretch, Linear, Asinh, Sqrt, Log), Curves, Invert, Reset View, Reset Display, Show RA/Dec (live coordinates under the cursor; on by default), Show Grid (off by default), and RA Density / Dec Density for the grid (2 to 12, default 5).

Target Marker

Draws the marker style from settings on the selected object only. Off by default; with it off, no object markers are drawn.

Center Object

Centers the selection once, at 3× zoom or more.

Track Object

Keeps the selection centered while blinking or changing frames. On by default.

Blink

Plays the active group. Preloads on first use.

Export

Image..., Blink..., Trail....

Hide Info / Show Info

Hides or shows the information panel on the image: Frame (time, Moon illumination, filter and exposure, size), Setup, Field, and the selected object's prediction and current frame match.

Lower tabs

Work Log

Timestamped messages from every task, including catalogue and SkyBoT queries and errors.

Inspector

Details of the selected row as text. For candidates it lists every frame detection with pixel position, RA/Dec, and residual score.

Sky View

Motion-only map of the predicted objects with Time, Now, and Reset View.

Drag the splitters to resize or collapse the panels. A collapsed panel leaves a Predicted Objects or Work Log · Inspector · Sky View handle; click it to restore the panel.

Mouse and keyboard

• Ctrl + O: open a file
• Ctrl + Shift + O: open a folder
• Mouse wheel: zoom the image (zooming out stops at the fitted view)
• Left-drag: pan the image
• Double-click a row: open Plots
• Ctrl or Shift + click rows: select several known objects for Trajectory View
• Ctrl + click in the Synthetic Tracking preview: set the measured peak

There are no right-click menus in this mode.

These appear each time you click Discover. The values you run with are saved as the new defaults.

Preset

Detailed search uses your saved defaults at full resolution. Fast scan uses at least 2x2 binning, the temporary cache, Residual Min SNR of at least 6, and smaller overlapping batches. Custom keeps whatever you set below.

Default: Detailed search.

Alignment

Align first reprojects the frames before searching. Already aligned skips that step.

Default: Align first.

Working Binning

Off (1x1), 2x2, 3x3, 4x4. Binning is faster and smooths noise but loses detail.

Default: Off.

Motion Prior Bias

Balanced, Main-belt bias, or Faster near-Earth bias: which motion rates linking prefers. A line below the form shows the typical motion in pixels during one exposure.

Default: Balanced.

Temporary Cache

Writes prepared frames to an auto-cleaned cache.

Default: off.

Residual Min SNR, Residual Max SNR

Drop residual detections below or above a local SNR before linking.

Default: Disabled.

Min Seed Displacement

Minimum start-to-end motion for a track seed. Lower values allow slower movers and more false seeds.

Default: 1.5 px.

Frames per Batch

Splits a long group into overlapping windows.

Default: Whole group.

Single Batch

Run one sampled batch only (10 frames if batching is off).

Default: off.

Retry with detailed search

If no candidates are found, repeat with the detailed full-resolution search. Available with Fast scan and Custom.

Default: off.

Open Settings > Open Settings > Asteroid/Comet. The settings are split into Search, Visuals, and Export tabs. Hover a label for its tooltip.

Search: Estimate Options

Manual Override, Manual Limit

Use manual detection magnitude limit override replaces the default 18.0 mag limit used by Generate with Manual Limit.

Default: off, 18.0 mag.

SNR Threshold, Start Mag, Amount of Stars to Check, Visible Stars Needed

Control the visible-limit estimate shown in Discover Results (R6).

Defaults: 4.0, 15.0 mag, 6, 3.

Annotate Lowest Mag Stars

Marks the faintest confirmed stars after an estimate.

Default: off.

Search: Discovery Advanced

Search Workers

Background workers for Discover and its sweep.

Default: Auto.

Working Binning, Temporary Cache, Frames per Batch

Saved defaults for the matching Discover Pipeline options.

Edge Margin

Ignores residuals this close to the frame border.

Default: 6 px.

Residual Min SNR, Residual Max SNR

Saved defaults for the residual SNR filters.

Default: Disabled.

Point Detection Threshold, Point Detection FWHM

Sigma threshold and expected width for the point-source residual finder.

Defaults: 5.0 sigma, 3.0 px.

Max Residuals / Frame

Caps how many residuals per frame are kept for linking.

Default: 24.

Residual Detector

Hybrid (point + streak), Point-like only, or Streak-aware only.

Default: Hybrid.

Streak Min Area, Streak Min Elongation

Minimum size and length-to-width ratio for streak detections.

Defaults: 6 px, 1.8×.

Minimum Linked Frames

Frames a tracklet must span to be kept. Also the minimum frame count for Discover.

Default: 3.

Potential Deflection RMS, Review Deflection RMS

How straight a tracklet must be for Potential Discoveries, and for Borderline Review. Above the second, it is discarded.

Defaults: 0.9 px, 1.8 px.

Final Synthetic Sweep

Runs a velocity-grid shift-and-stack pass after normal linking. The slowest option.

Default: off.

Sweep Max Motion, Sweep Motion Step, Sweep Angle Step

The velocity grid the sweep tests.

Defaults: 12 px/h, 1.0 px/h, 30°.

Sweep Direction Focus, Sweep Focus Width

All directions (360 deg) or Main-belt direction focus, which tests only directions within the half-width of the motion of known main-belt asteroids in the field.

Defaults: All directions, 45°.

Sweep Min Stacked SNR

Stacked SNR a sweep peak needs to become a tracklet.

Default: 6.0.

Save Sweep Stacks

Writes every tested stack as FITS to synthetic_track in the data folder. Dense sweeps create many files.

Default: off.

Track Crop Radius, Track Integration, Track Weights, Track Rejection, Track Backend, Track Mixed All Group, Advanced Synthetic Track

Synthetic Track defaults, described in R4.

Visuals

Show marked potential discoveries on the main image

Draws candidates you marked with Mark Selected.

Default: on.

Show asteroid/comet name labels on the main image

Labels the selected object.

Default: on.

Marker style

Square aim, Circle, Corner brackets, Open crosshair, Pointer.

Default: Square aim.

Track Object Anchor

Known / predicted position or Detected local match.

Default: Known / predicted position.

Highlight the selected asteroid/comet with distinct colors

Default: on.

Invert also swaps asteroid/comet annotation and text colors

Default: on.

Marker Appearance

Line Color, Accent Color, Label Color, Outline Color, Thickness.

Default thickness: 4.0 px.

Export

Blink Frame Time

Time per frame for Blink and its exports, from 0.05 s to 2.00 s.

Default: 0.05 s.

GIF Resolution, MP4 Resolution

Scale of exported animations, 25% to 400%.

Default: 100%.

GIF Looping

Loop exported GIF playback forever.

Default: on.

Defaults are under Settings > Open Settings > Asteroid/Comet > Search > Discovery Advanced > Preparation.

Track Crop Radius

Radius of the object-centered stack.

Default: 24 px.

Track Integration

Average (unweighted), Mean (weighted), Min, or Max.

Default: Average.

Track Weights

Frame weighting for Mean: PSF signal weight, PSF SNR, SNR, Average signal strength.

Default: PSF signal weight.

Track Rejection

No rejection, Min/Max, Sigma clipping, Winsorized sigma clipping, Averaged sigma clipping.

Default: No rejection.

Track Backend

Auto, CPU only, or GPU when available.

Default: Auto.

Track Mixed All Group

Allow running from mixed 'All' groups.

Default: off.

Advanced Synthetic Track

Open manual one-stack dialog before each run.

Default: off.

Advanced Synthetic Track dialog

With Open manual one-stack dialog on, clicking Synthetic Track opens Advanced Synthetic Track - … first:

1. Choose Stack Scope: Object-centered crop follows the predicted position frame by frame; Full image (manual motion) shifts whole frames by a fixed motion.
2. For a crop, set Track Crop Radius. For a full image, check Motion (px/h) or Motion (arcsec/h) and Angle, which start at the object's motion.
3. Set Integration, Weights, and Rejection.
4. Click Run Synthetic Track.

GPU path

Full-image stacks can run on an NVIDIA GPU through CuPy. With Auto, CAst uses the GPU when CuPy is available and Rejection is No rejection; any other rejection mode runs on the CPU. GPU when available requests the GPU but falls back the same way, and CPU only never uses it. The first GPU run in a session warms the backend up. The Synthetic Tracking window shows which backend ran, for example Compute backend: GPU (CuPy full-frame no-rejection stack), and why it fell back if it did. Object-centered crops always run on the CPU.

Span

Local (45 days either side of your frames), +/-90d, +/-180d, 1y, 5y, or Custom with From, To, and Apply. Changing the span keeps the selected objects.

Planets, Meteor Stream, Periods

Show the planets; show an illustrative debris tube along the orbit of a known meteor-shower parent such as 109P/Swift-Tuttle (a teaching model, not a dust forecast); show orbital periods.

Camera

Orbit Overview, Top-Down, Side View, Object Follow, Earth Follow.

⚙ (Display settings)

Show Labels, Show Sample Points, label Font, Size, Bold, Italic; Asteroids and Comets colors; Meteor Stream Point density, Trail thickness, Orbit guide line, Glow, Animate debris, Drift speed; Sky Track Bayer designations, Star density, Star draw radius, Constellation lines, Fit Trajectory, Entire Sky; and Info panels with Move Up, Move Down, Remove, Reset Layout, and Add Panel.

Info panels

Heliocentric top-down, Sky Track, Magnitude (literature magnitude over the window), and Distance by default. Data, a per-frame table of object and Earth positions and distances, can be added.

Objects (n/m)

Toggles each object's visibility. Nearby Search... opens Nearby Field Search: set Radius and Max predicted mag, click Search Nearby, select rows, and click Add Selected.

Lookup

Object Lookup searches the small-body database by name, designation, or keyword (for example Pallas, 154P, 3I) and adds the rows you select.

Save

Save Trajectory View: choose Trajectory view only or Trajectory view + info panel, a Format (PNG, JPG, GIF, MP4), and for animations a Camera motion (Fixed, Slow orbit, Object chase). An animation covers one pass of the timeline at the current speed.

UTC, Play, Speed, Time, Sample

Type a time, return to the observation time, play, choose 1 h/s to 30 d/s (default 1 d/s), or drag the slider through the samples.

Plate solution

Generate uses the frame's embedded WCS when it agrees with the mount pointing in the header. Otherwise it runs local Gaia matching and astrometry.net at the same time (astrometry.net only with an API key) and keeps whichever solves first.

Ephemeris services

SkyBoT (IMCCE)

Main cone search for asteroids and comets in the field, geocentric, at mid-exposure. The radius is the solved field radius, limited to 0.01° to 10°. A relaxed position-error filter (3600″) keeps objects with uncertain orbits. Server errors and unreadable replies are retried, and failures are written to the Work Log.

JPL Horizons, IMCCE Miriade

Used for the interstellar object 3I/ATLAS, which CAst adds or refreshes from Horizons, with Miriade as the fallback. Horizons also supplies the heliocentric positions in Trajectory View.

Small-body database

Searched by Lookup in Trajectory View.

Magnitude limit

Generate uses 18.0 mag, or Manual Limit when the override is on. Asteroids listed more than 1 mag fainter than the limit are dropped. Comets are always kept, because their listed magnitudes are often unreliable. Pred Mag is SkyBoT's V magnitude: good for triage, not a photometric prediction.

Local match and confidence

Around each predicted pixel, CAst searches a window of about 5 to 18 pixels (larger for faster objects) and measures the peak. SNR is the peak minus the local median, divided by 1.4826 × the median absolute deviation. An object is likely visible when SNR is at least 4 and the offset is at most 8 px.

Confidence starts at 0.1 and adds up to 0.25 for how much brighter than the limit the object is, up to 0.4 for SNR (SNR / 20), up to 0.25 for a small offset (falling to zero at 10 px), and 0.05 if the object trails more than 1.5 px. It subtracts 0.15 near the frame edge, and is capped at 0.99. It is a triage score, not a probability.

Visible limit

Discover measures how faint the frame reaches. It takes catalogue stars in the field (Gaia DR3 to about G 21.5, and, fainter than 20.5 mag, Pan-STARRS north of Dec −30° or DES with SkyMapper as a fallback in the south), steps through 0.5 mag bins from Start Mag, and checks whether at least Visible Stars Needed of Amount of Stars to Check stars per bin are recovered at SNR Threshold. The faintest passing bin is the Visible Limit. Trailing, bandpass, and crowding still change what you can recover in practice.

1. Prepare. Align, bin, and cache the frames as chosen in Discover Pipeline.
2. Model the static sky. Take the per-pixel median of the aligned frames. Stars, galaxies, and anything else that stays put end up in this model; a moving object does not, because it is in a different place on most frames.
3. Make residuals. Subtract the model from each frame. What remains is noise plus anything that moved or changed.
4. Detect. Find residual peaks with a point-source finder, a streak finder, or both. Residuals within 6 px of a known prediction are set aside so known objects are not counted as discoveries.
5. Seed. Pair detections on nearby frames (up to two frames apart) that moved at least Min Seed Displacement at a plausible rate for the motion prior.
6. Link. Fit straight-line motion through the seed, x(t) = a + v_xt and y(t) = b + v_yt, predict where the object should be on every other frame, and pick up detections within about 2.8 px. Refit and repeat a few times.
7. Screen. Keep tracklets with at least Minimum Linked Frames. Measure the RMS deviation from the straight line: up to 0.9 px goes to Potential Discoveries, up to 1.8 px to Borderline Review, and the rest is discarded.
8. Benchmark. A known object counts as recovered when a tracklet follows its predicted path within about 4.5 px, or its catalogue position uncertainty if larger.
9. Sweep (optional). With Final Synthetic Sweep on, stack the residuals along every motion on a grid of rates and directions, and turn stacked peaks above Sweep Min Stacked SNR back into tracklets. This finds objects too faint to detect on single frames.

The method assumes straight, constant-speed motion over the sequence. Very fast near-Earth objects, long sequences with curved paths, and badly trailed objects can fail to link.

Stacking adds signal faster than noise: an object at the same pixel on N frames gains about √N in SNR. Synthetic Track keeps the object on the same pixel by moving the frames with it.

Outlier pixels are rejected if a rejection mode is set, then the stack is combined with the chosen integration. CAst finds the peak near the center and reports stacked SNR, center offset, peak value, and flux. Frames are skipped when the object falls outside them or their time is missing; the window lists each frame and the reason.

If the object really moves at the assumed rate, it builds up into a point. If the motion is wrong, it smears too, and the SNR stays low.

Labels

Real Mover, Artifact, Known Object, Noise, Unsure. Saving a label again for the same candidate replaces it.

Train Model

Fits a Random Forest on every saved asteroid/comet label and the candidate's measured features. It needs at least two labeled candidates with two different labels. With six or more labels and at least two per label, it also reports validation accuracy, precision, recall, and F1 on a held-out quarter.

ML Score

The latest model's predicted label and confidence for each candidate. It does not hide or reorder candidates.

Storage

Labels and models are saved on your computer in %LOCALAPPDATA%\CitizenPhotometry\candidate-training.sqlite3 on Windows.

Default names include the selected object, for example 2015 CU58_trail.gif, and go in the source folder. Discover CSVs are named after the reference frame, for example …_discover_candidates.csv. The candidate CSV holds pixel positions, detection times, and frame paths; per-frame RA/Dec is in the Inspector and Plots. CAst does not write MPC or ADES reports.