API · /angularsize-api

Angular Size API

healthy 4,090 Subscribers

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.

#angular-size #astronomy #optics #angular-diameter #field-of-view #developer-tools

api.oanor.com/angularsize-api

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Machine-readable spec so AI agents can integrate this API.

/api/angularsize-api/openapi.json

/api/angularsize-api/llms.txt

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Angular Size API — live data on the oanor API marketplace

API health

healthy

Uptime: 100.00%; Server probes · 24h
Avg latency: 78 ms; Server probes · 24h
Subscribers: 4,090; active
Total calls: 76; last 7 days

Full status page → · 12 probes/24h

Pricing

Pick a tier — billed monthly, cancel anytime.

Free

3,400 calls / month
2 requests / second
Hard cap (429 above quota, no overage)
3,400 calls/month
2 req/sec
Angular size + distance + object size
No credit card

Starter

€6.00 /month

42,500 calls / month
6 requests / second
Hard cap (429 above quota, no overage)
42,500 calls/month
6 req/sec
Radians/degrees/arcmin/arcsec
Email support

Pro

€15.00 /month

234,000 calls / month
15 requests / second
Hard cap (429 above quota, no overage)
234,000 calls/month
15 req/sec
Telescope & astrophotography pipelines
Priority support

Mega

€50.00 /month

1,360,000 calls / month
40 requests / second
Hard cap (429 above quota, no overage)
1,360,000 calls/month
40 req/sec
Platform scale
Dedicated SLA

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Constellations API

The 88 modern IAU constellations as an API — the reference an astronomy app, planetarium or education tool needs. For each constellation: its official IAU abbreviation, English name, the Latin genitive used when naming stars (e.g. "Alpha Andromedae"), a size rank, the approximate centre in equatorial coordinates (right ascension / declination) and the constellation name in roughly 25 languages. Look one up by abbreviation or name, search across every language, find which constellation a sky position falls nearest to, or list them all. Distinct from stars-api (individual stars) — this is the reference for the constellations themselves. Served from memory — always fast.

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Observatory Codes API

The IAU Minor Planet Center list of observatory codes as an API — every site the MPC uses to identify a telescope when it publishes astrometric observations of asteroids and comets. For each of 2,700+ codes: the 3-character code, the observatory name, its east longitude and the parallax constants (rho·cos φ', rho·sin φ'). From those constants the API derives each site's geocentric latitude and a -180..180 longitude, so you can find the observatories nearest any point on Earth with a great-circle (haversine) search. Look one up by code, search by name, list them all, or find the closest sites to a latitude/longitude. Distinct from telescope-api (optics maths) — this is the registry of real observing sites and where they are. Served from memory — always fast.

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Sundial API

Sundial gnomonics maths as an API, computed locally and deterministically — the hour-line, gnomon and longitude-correction numbers a dial maker, horologist or astronomy hobbyist lays a sundial out with. The hour-line-angle endpoint gives the angle of each hour line on the dial plate, measured from the noon line: for a horizontal dial tan(angle) = sin(latitude) × tan(hour angle), and for a vertical south-facing dial cos(latitude) is used instead, where the hour angle is 15° per hour from solar noon. At 50° latitude the 1-o'clock line sits about 11.6° from noon rather than 15° — the lines bunch near noon and spread toward the ends, which is exactly why a sundial's hours are unevenly spaced. The gnomon endpoint gives the style angle: the gnomon's shadow-casting edge must point at the celestial pole, so it rises at the latitude angle on a horizontal dial (50° at 50° N) and at 90° − latitude on a vertical dial — get this wrong and the dial keeps correct time at only one season. The longitude-correction endpoint converts the dial's local apparent time to clock time: 4 minutes of time per degree of longitude, correction = 4 × (reference meridian − local longitude), so a dial at 7.5° E on Central European Time reads 30 minutes slow versus the clock. Everything is computed locally and deterministically, so it is instant and private. Ideal for sundial-design and gnomonics tools, astronomy-education and maker apps, and horology calculators. Pure local computation — no key, no third-party service, instant. Add the equation of time for full clock accuracy. 3 compute endpoints. For the sun's position use a solar-position API; for sunrise and sunset a sunrise API.

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Frequently asked questions

Quick answers about pricing, quotas, and integration.

How do I get an API key for Angular Size API?

Sign up for free at oanor.com, generate an API key from the developer dashboard, and call Angular Size API with the x-oanor-key header. No credit card needed for the free tier.

What's the rate limit for Angular Size 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 Angular Size API cost?

Angular Size API has a free tier with 100 calls / month. Paid plans start at €6.00 / 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 Angular Size API GDPR-compliant?

All requests to Angular Size 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.

AngularSize 3

Meta 1

Pick an endpoint from the list on the left to see its details and try it.

GET /v1/angular-size

Angular diameter

Playground

Parameters

Custom headers

Language: Client:

GET /v1/distance

Distance

Playground

Parameters

Custom headers

Language: Client:

GET /v1/object-size

Object size

Playground

Parameters

Custom headers

Language: Client:

GET /v1/meta

Spec

Playground

Custom headers

Language: Client:

Code snippets

curl https://api.oanor.com/angularsize-api/SOME_PATH \
  -H "x-oanor-key: oanor_test_..."

const res = await fetch("https://api.oanor.com/angularsize-api/SOME_PATH", {
  headers: { "x-oanor-key": "oanor_test_..." }
});
const data = await res.json();

$ch = curl_init("https://api.oanor.com/angularsize-api/SOME_PATH");
curl_setopt($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/angularsize-api/SOME_PATH",
    headers={"x-oanor-key": "oanor_test_..."},
)
print(r.json())

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Angular Size API

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Meteorites API

Constellations API

Observatory Codes API

Sundial API

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