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API · /starmagnitude-api

Star Magnitude & Distance API

healthy 3,856 Subscribers

Stellar magnitude and distance maths as an API, computed locally and deterministically. The magnitude endpoint works the distance modulus, m − M = 5·log₁₀(d/pc) − 5 — give any two of the apparent magnitude m, the absolute magnitude M and the distance and it returns the third, with the distance in parsecs, light-years and astronomical units (the absolute magnitude is the apparent magnitude a star would have at 10 parsecs). The flux endpoint applies Pogson's relation to turn a magnitude difference into a brightness ratio, F₁/F₂ = 10^(0.4·(m₂ − m₁)), where five magnitudes is exactly a hundredfold change in brightness — from two magnitudes, a magnitude difference or a ratio. The parallax endpoint converts a parallax angle into a distance, d(pc) = 1 ÷ p(arcseconds), and back, the geometric method behind the parsec itself. Everything is computed locally and deterministically, so it is instant and private. Ideal for astronomy-education, planetarium, stargazing and science app developers, observing and astrophysics tools, and STEM teaching. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is stellar magnitude and distance; for orbital mechanics use an orbital API and for great-circle distances on Earth a geo-distance API.

#astronomy #magnitude #parallax #parsec #astrophysics #developer-tools
api.oanor.com/starmagnitude-api
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/api/starmagnitude-api/openapi.json
/api/starmagnitude-api/llms.txt

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API health

healthy
Uptime
100.00%
Server probes · 24h
Avg latency
90 ms
Server probes · 24h
Subscribers
3,856
active
Total calls
32
last 7 days
status Full status page → · 24 probes/24h

Pricing

Pick a tier — billed monthly, cancel anytime.

Free

Free

  • 3,000 calls / month
  • 2 requests / second
  • Hard cap (429 above quota, no overage)
  • Apparent ↔ absolute magnitude via distance modulus m−M=5·log₁₀(d/pc)
  • Parallax → distance in parsecs and light-years
  • JSON responses, no API-data charges
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Starter

€5.00 /month

  • 40,000 calls / month
  • 5 requests / second
  • Hard cap (429 above quota, no overage)
  • All magnitude & distance endpoints
  • Parsec / light-year / AU unit conversions
  • Deterministic results for classroom and lab use
  • Email support
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Pro

€15.00 /month

  • 250,500 calls / month
  • 15 requests / second
  • Hard cap (429 above quota, no overage)
  • Higher throughput for catalog batch jobs
  • Distance modulus + parallax + extinction-aware magnitude
  • Bulk-friendly low-latency local compute
  • Priority support
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Mega

€49.00 /month

  • 1,608,000 calls / month
  • 40 requests / second
  • Hard cap (429 above quota, no overage)
  • Maximum quota for survey-scale pipelines
  • Full stellar magnitude & distance toolkit
  • Highest rate limit for parallel workloads
  • Priority support + SLA
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Related APIs

Other APIs with overlapping tags.

Stellar Parallax API

Stellar-parallax and astrometry maths as an API, computed locally and deterministically. The distance endpoint turns a measured trigonometric parallax angle into a distance using d(pc) = 1/p(arcsec), accepting the parallax in arcseconds or milliarcseconds and returning the distance in parsecs, light-years and astronomical units — a parallax of one arcsecond is one parsec (≈3.2616 light-years) by definition, and Proxima Centauri’s 0.7687-arcsecond parallax gives about 1.30 pc, or 4.24 light-years. The parallax endpoint inverts it, p(arcsec) = 1/d(pc), giving the tiny annual back-and-forth angle a star traces against the background as Earth orbits the Sun. The proper-motion endpoint computes a star’s tangential (transverse) velocity across the sky from its proper motion and distance, v_t = 4.74047·μ(arcsec/yr)·d(pc) km/s — Barnard’s Star, with a proper motion of about 10.39 arcsec/yr at 1.83 pc, races across the sky at roughly 90 km/s. Everything is computed locally and deterministically, so it is instant and private. Ideal for astronomy, astrophysics, planetarium, education and science-communication app developers, star-distance and stellar-kinematics tools, and Gaia-catalogue post-processing. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is geometric distance and kinematics; for a star’s apparent and absolute brightness use a star-magnitude API.

api.oanor.com/parallax-api

Light Travel Time API

Light-travel-time astronomy maths as an API, computed locally and deterministically. The travel-time endpoint computes how long light takes to cross a distance, t = d/c with c = 299,792,458 m/s exactly, accepting the distance in metres, kilometres, miles, astronomical units, light-years, parsecs or light-seconds/minutes and returning the time in seconds, minutes, hours, days and years — light from the Sun reaches Earth in about 8.3 minutes and the nearest star is about 4.2 light-years away. The distance endpoint inverts the relation, d = c·t, to give how far light travels in a time, returning the distance in metres, kilometres, astronomical units, light-years and parsecs — one light-year is about 9.461×10¹⁵ m. The round-trip endpoint computes the one-way and round-trip communication delay to a target, d/c and 2·d/c, the light-speed latency that makes distant spacecraft control so slow and Mars rovers largely autonomous. Distance units include light-second and light-minute and time units run from seconds to years. Everything is computed locally and deterministically, so it is instant and private. Ideal for astronomy, space-mission, education, science-communication and simulation app developers, communication-delay and cosmic-distance tools, and physics teaching. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is light travel time; for an object's angular size use an angular-size API and for sidereal time a sidereal API.

api.oanor.com/lighttime-api

Angular Size API

Angular-size astronomy and optics maths as an API, computed locally and deterministically. The angular-size endpoint computes the angular diameter an object subtends, δ = 2·arctan(d/(2D)), from its physical size and its distance, returning the angle in radians, degrees, arcminutes and arcseconds, along with the small-angle approximation δ ≈ d/D — the Sun and Moon are each about half a degree (31 arcminutes) across. The distance endpoint inverts the relation, D = d/(2·tan(δ/2)), to give an object's distance from its known true size and its measured angular size, the basis of the standard-ruler distance method. The object-size endpoint computes an object's physical diameter, d = 2·D·tan(δ/2), from its distance and angular size. Size and distance use any one consistent unit, and angles may be given in radians, degrees, arcminutes or arcseconds. Everything is computed locally and deterministically, so it is instant and private. Ideal for astronomy, telescope, astrophotography, surveying and optics app developers, field-of-view and rangefinding tools, and physics education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is angular size; for stellar magnitude and parallax distance use a star-magnitude API and for sidereal time a sidereal API.

api.oanor.com/angularsize-api

Sidereal Time API

Sidereal-time astronomy as an API, computed locally and deterministically. The gmst endpoint computes the Greenwich Mean Sidereal Time for a UT date and time, GMST = 18.697374558 + 24.06570982441908·(JD − 2451545.0) hours modulo 24, returning it in hours, degrees and hours-minutes-seconds together with the Julian Day — sidereal time tracks the stars rather than the sun and gains about three minutes and fifty-six seconds each day. The lst endpoint adds the observer's longitude to give the Local Sidereal Time, LST = GMST + longitude/15 (east positive), which equals the right ascension of any star currently crossing the local meridian. The hour-angle endpoint computes the hour angle of a celestial object, HA = LST − RA, from its right ascension and the local sidereal time (or a date, time and longitude): an hour angle of zero means the object is on the meridian at its highest point, a positive hour angle means it is west of the meridian and setting, and a negative one means it is east and rising. Dates are YYYY-MM-DD and times HH:MM:SS in UT, longitude in degrees and right ascension in hours. Everything is computed locally and deterministically, so it is instant and private. Ideal for astronomy, telescope-control, planetarium, observatory and astrophotography app developers, star-pointing and transit tools, and astronomy education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is sidereal time; for the sun's position use a solar-position API and for sunrise and sunset times a sunrise API.

api.oanor.com/sidereal-api

Frequently asked questions

Quick answers about pricing, quotas, and integration.

How do I get an API key for Star Magnitude & Distance API?
Sign up for free at oanor.com, generate an API key from the developer dashboard, and call Star Magnitude & Distance API with the x-oanor-key header. No credit card needed for the free tier.
What's the rate limit for Star Magnitude & Distance API?
Free tier allows 1 request per second. Paid plans scale up to 50 requests per second on the Mega tier. Hard limits return HTTP 429 above the quota — no surprise overage charges.
How much does Star Magnitude & Distance API cost?
Star Magnitude & Distance API has a free tier with 100 calls / month. Paid plans start at €5.00 / month with higher quotas and faster rate limits.
Can I cancel my subscription anytime?
Yes. Plans are billed monthly and you can cancel anytime from your billing dashboard. No long-term contracts and no cancellation fee.
Is Star Magnitude & Distance API GDPR-compliant?
All requests to Star Magnitude & Distance API go through our EU-based gateway. Your upstream API key never leaves our server and no personal data is shared with the upstream provider beyond the request you send.

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Code snippets

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curl https://api.oanor.com/starmagnitude-api/SOME_PATH \
  -H "x-oanor-key: oanor_test_..."
const res = await fetch("https://api.oanor.com/starmagnitude-api/SOME_PATH", {
  headers: { "x-oanor-key": "oanor_test_..." }
});
const data = await res.json();
$ch = curl_init("https://api.oanor.com/starmagnitude-api/SOME_PATH");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, ["x-oanor-key: oanor_test_..."]);
$response = curl_exec($ch);
import requests
r = requests.get(
    "https://api.oanor.com/starmagnitude-api/SOME_PATH",
    headers={"x-oanor-key": "oanor_test_..."},
)
print(r.json())

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