Elbrus plate solver

Upload a picture of the sky and Elbrus tells you where it points: the coordinates of its centre, its orientation and its scale.

In memory of Alfonso Pulido, who wrote Elbrus between 2003 and 2009 and taught many of us not to get lost among the stars. "Better lost than wrongly found."

Drop an image here, or click to choose one
FITS, JPEG, PNG, BMP, TGA, GIF · up to 25 MB

Scale, arcsec per pixel (optional)

or a range: from

Scale helper: focal length, mm

pixel size, µm

Approximate RA (optional)

Approximate Dec (optional)

Search window, degrees

mirrored image

Know nothing about the picture? Leave everything empty: Elbrus solves it blind. Giving the scale and the approximate position makes it faster and more certain.

Try an example

Photos from Wikimedia Commons, under their authors' free licenses. "Solve" fills in sample parameters; "Solve blind" gives Elbrus nothing but the picture.

In memory of Alfonso

Alfonso was a good friend, and an inspiration when I was refining my way of thinking to solve engineering problems. Thank you, Alfonso, and thank you, Galia, for all the good times, and for your patience, your enthusiasm and your rigour.

Alfonso fue un buen amigo y una inspiración a la hora de depurar mi manera de pensar para resolver problemas de ingeniería. Gracias, Alfonso, y gracias, Galia, por todos los buenos momentos, por vuestra paciencia, vuestro entusiasmo y vuestro formalismo.

José Luis Rey

About Elbrus

Elbrus ("Elemento Localizador por BRUjula Sidérea") is the star locator of the Spanish amateur astronomer Alfonso Pulido, written with Galia Pulido. Observers used it to know where their telescopes pointed, for remote observing and to recentre between exposures. In 2008 the IAU named asteroid 66843 Pulido after him for it. Alfonso died in 2023.

This service runs a C++ port of his program, made by his friend José Luis Rey as a tribute. Elbrus keeps the 5 brightest stars of every small box of the sky and the distances between them, finds the distances it measures in your image, builds polygons of matching stars, checks every side against the catalog, and answers only when one polygon wins clearly. The wide-field mode does the same with triangles over the whole sky. And when nothing is known about a picture, groups of four stars are compared by their shape alone, which does not depend on the scale or the orientation; that proposes a scale and a place, and Alfonso's method then has the last word.

Alfonso's pages: astrosurf.com/pulgar ·

REST API

Free and open, no key. Fair use: 30 solves per hour per address, one solve at a time, 60 s per solve. Images are not stored.

curl -F image=@photo.jpg https://cs-miniserver.chronoscan.org/api/elbrus/solve
curl -F image=@m52.jpg -F scale=1.53 -F ra=351.2 -F dec=61.6 https://cs-miniserver.chronoscan.org/api/elbrus/solve
curl -F image=@wide.png -F scale_min=20 -F scale_max=30 https://cs-miniserver.chronoscan.org/api/elbrus/solve
curl --data-binary @image.fit "https://cs-miniserver.chronoscan.org/api/elbrus/solve?scale=2.4&ra=83.8&dec=-5.4"
curl https://cs-miniserver.chronoscan.org/api/elbrus/info

Parameters (form fields or query string)

Name	Meaning
`image`	The image (multipart field), or the raw request body.
`scale`	Arcsec per pixel. Or `scale_min` + `scale_max` to scan a range (max ≤ 4 × min). Optional: with no scale at all the image is solved blind.
`ra`, `dec`	Approximate centre in degrees. Needed for fields under ~2°; narrows the wide search.
`window`	Search window around ra/dec, degrees (default 5; 30 for wide fields).
`angle`, `tol`	Known image angle (position angle of "up", north through east) and its tolerance; otherwise all angles are tried.
`flip`	1 if the image is mirrored (otherwise both are tried).
`mode`	`auto` (default), `1` narrow-field database, `2` wide-field database, `blind` ignore the scale and search by star-quad shapes.
`err`, `stars`, `min_sides`, `min_stars`	Advanced: distance error %, stars used, sides or stars needed to accept a solution.

Answer

solved, failure, blind (found with no hints), blind_matched, database (1, 2, or 3 = star quads only), ra, dec (degrees, ICRS), ra_hms, dec_dms, angle, flipped, scale_x, scale_y (arcsec/px), field_deg, sides, rms_arcsec, matched (x, y, ra, dec, id, resid_arcsec), objects (known objects on the image: name, kind M Messier / D deep sky / S star, x, y, r in pixels, mag), plate (tan_ra, tan_dec and the coefficients P, Q: ξ = P0·px + P1·py + P2, η = Q0·px + Q1·py + Q2 in arcsec, px = x − width/2, py = height/2 − y), image, seconds. Errors answer 400 (bad input), 429 (over the hourly budget), 503 (busy).

Star positions: ESA Gaia DR3. This work has made use of data from the European Space Agency (ESA) mission Gaia (cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC). The star databases derived from it are under CC BY-SA 3.0 IGO. Object names: OpenNGC by Mattia Verga and the HYG database by David Nash, both CC BY-SA 4.0.