Sky map

How to read it

• The whole sky on one oval. It is a Hammer projection, which keeps areas equal, so a crowded patch of the map is a crowded patch of sky. The middle is right ascension (RA, the sky's longitude) 12h; the left and right edges meet at 0h.
• RA runs right to left, as on a sky chart seen from the ground, with hour labels along the celestial equator. Declination (Dec, the sky's latitude) runs from −90° at the bottom to +90° at the top.
• Bigger marks mean more hours. A mark grows with the square root of the target's total exposure time, up to a cap, so the longest-watched targets stand out without hiding their neighbors.
• Shape and color give the stage. Captured, a hollow gray ring: frames of it are in the catalog. Processed, a filled blue dot: at least one of its nights has run receipts (the per-frame record a processing run writes). Published, an amber diamond: an Experiment or Results page about it is out, and the diamond links there.
• Two guide lines. The dashed violet line is the galactic plane, the Milky Way's midline, where nebulae and star clusters crowd. The dotted amber line is the ecliptic, the Sun's yearly path; the planets stay close to it.

Every target

The same targets as the map, as a table. RA is in hours and minutes, Dec in degrees, both for the frame-weighted average pointing of the target's kept frames.

All 125 targets, most hours of exposure first.

What's not on the map

• Comets and other moving targets. An average of where the telescope pointed over a night isn't a position on the sky.
• Frames that aren't single light frames. Darks, biases, flats, calibrated copies and stacks are left out, so each frame is counted once.
• Duplicates and frames with no sky position. A night shared twice is counted once; a frame the catalog can't place is left off, and so is one whose recorded pointing sits on a celestial pole, which is a placeholder, not a real position.
• Names that aren't catalog designations. A field without a designation from a standard catalog (M, NGC, IC, Sh2 and the like) or a short hand-kept list of well-known object names is shown as "Unnamed field", merged with its neighbors in the same patch of sky. Names typed into a telescope can say anything, so only catalog names are shown. Two spellings of one designation ("M31" and "M 31") are one target, and a known alias is shown under one name (Caldwell 5 as IC 342).
• Who, with what, and from where. Nothing about who took a frame, which telescope took it, or where it was taken is in the map or its data file.

Shared nights are on it. Every source is included, nights sent through Share data too: an upload's target, the target's position on the sky, its number of frames and its hours of exposure appear here. Privacy says what that means for you.

Get the data

The map is drawn from one file: /results/data/sky.json, schema skycruncher.sky/1. The page also reads /results/published.json, which turns a target's mark into a diamond as soon as its page is out.

schema

always skycruncher.sky/1

generated

when the file was written (UTC)

catalog_built

the date of the catalog build it was drawn from

snapshot

true when the file is a copy committed with the site, not a fresh build from the catalog

totals

targets, frames, exposure_h, and by_stage counts of captured, processed and published targets

targets[]

one entry per target, sorted by id:

  id

a stable short name, such as ngc-7000

  name

the catalog designation, or "Unnamed field"

  ra, dec

position in degrees, two decimals

  frames

number of kept light frames

  exposure_h

total exposure in hours, one decimal

  stage

captured, processed or published

  link

the page about it when published, otherwise null

Those keys are the whole file: anything else fails the site's publish check. Counts are plain inventory counts with an "as of" date, not measurements; how claims are marked explains the difference.

Credit

Community frames: the Seestar Collective and other contributors. More dated measurements are in Experiments; the other living pages are on Results.