Main-sequence lifetime calculator
Estimate how long a star burns hydrogen in its core: the Sun gets 10 billion years, while a star of two solar masses lives less than two billion. Give the mass, and the luminosity if you know it. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Mass
- 1
- Luminosity
- 1
- Lifetime years
- 10,000,000,000
- Lifetime gyr
- 10
- Solar lifetime years
- 10,000,000,000
- Mass over luminosity
- 1
This main-sequence lifetime calculator estimates how long a star can fuse hydrogen in its core by scaling the solar lifetime of ten billion years with the ratio of stellar mass to luminosity in solar units. The closed form is fully deterministic: lifetime years equals one times ten to the ten times mass over luminosity, where mass is M divided by M sun and luminosity is L divided by L sun. When you omit luminosity, the engine applies the classic mid-main-sequence mass-luminosity relation L over L sun equals mass to the power 3.5, which recovers the familiar lifetime scaling proportional to mass to the power negative 2.5. Well-known checks include the Sun at mass one and luminosity one, which yields exactly ten billion years, and a two-solar-mass star with estimated luminosity near eleven point three solar luminosities, which lives roughly one point eight billion years on the main sequence. The path uses only finite arithmetic with no network calls, no sampling, and no date-dependent shortcuts.
Where main-sequence lifetime fits in study, astronomy, and software
Students meet main-sequence lifetime when a textbook links stellar mass to nuclear timescales, when a problem asks how long a two-solar-mass star stays on the main sequence compared with the Sun, or when they compare high-mass short-lived O stars with long-lived M dwarfs without full stellar-evolution codes. Teachers can pre-generate answer keys for modest mass values without trusting opaque calculator apps that silently switch units or drop scientific notation.
Developers call the same contract from scripts to seed deterministic test vectors for astronomy modules, to normalize user-entered mass before planet-habitability demos, or to satisfy programming-challenge statements that demand a lifetime in years rather than a hand-waved solar value. Contest practice often needs a fast, offline source of mass-scaled lifetimes so solutions can be checked without graphing calculators under time pressure.
Product and education tools use the formula when a learner types a stellar mass in solar units and the UI must show how long that star can burn hydrogen next to comparisons with the Sun.
What you can do with it
Homework and stellar-lifetime checks
Compute main-sequence lifetime from textbook stellar masses (with or without given luminosity) and verify years or Gyr before evolution problems.
Astronomy and education tools
Normalize user-entered solar masses into hydrogen-burning lifetime for star demos, habitability sketches, and interactive lessons.
FAQ
What does the main-sequence lifetime calculator cost?
It is free in your browser on this page.
How is main-sequence lifetime defined here?
τ_MS ≈ 10¹⁰ years · (M/M☉) / (L/L☉). When luminosity is omitted, L/L☉ = (M/M☉)^3.5 (mid-main-sequence mass-luminosity relation).
What happens if mass is zero or negative?
Main-sequence lifetime is undefined for a non-positive mass.
Do I have to supply luminosity?
No. If you omit luminosity, it is estimated as mass^3.5 in solar units. If you supply luminosity, it must be finite and positive.
Does this include post-main-sequence evolution?
No. It only returns the introductory main-sequence scaling from mass over luminosity. Full tracks and isochrones need dedicated stellar-evolution tools.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/astro/main-sequence-lifetime \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"mass":1}'const res = await fetch("https://api.kit.forhosting.com/astro/main-sequence-lifetime", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"mass": 1
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/astro/main-sequence-lifetime",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"mass": 1
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/astro/main-sequence-lifetime", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"mass":1}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"mass":1}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/astro/main-sequence-lifetime", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"mass": 1
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "astro.main_sequence_lifetime",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
What main-sequence lifetime means and what the response contains
The main-sequence phase is the long, hydrogen-burning stage that dominates a star's nuclear lifetime. In introductory astronomy the available fuel scales with mass while the burn rate scales with luminosity, so the characteristic lifetime is proportional to mass over luminosity. Normalizing to the Sun fixes the constant at ten billion years: tau MS approximately equals ten to the ten years times (M over M sun) over (L over L sun). This calculator returns the normalized mass you supplied, the luminosity used (measured or estimated), a boolean luminosity_estimated flag, lifetime_years and lifetime_gyr, the solar scale solar_lifetime_years, the intermediate mass_over_luminosity ratio, precision, the method tag main_sequence_lifetime, a unit string years, and a short formula reminder. When luminosity was estimated from mass, the response also includes mass_luminosity_exponent equal to 3.5. There is no Monte Carlo stellar evolution and no tabulated isochrone library: the engine either builds the finite floating-point lifetime inside the supported magnitude range or rejects the input with invalid_input. Rejected cases include missing mass, non-finite values, magnitudes above the documented ceiling, and any mass that is zero or negative, because the main-sequence lifetime scaling is undefined for non-positive mass.
How mass and luminosity are read and how the lifetime stays reproducible
Optional leading plus signs and scientific notation on numeric strings are allowed when they parse as finite decimals; embedded spaces, hex prefixes, and non-numeric tokens are rejected with a clear message so a bad cell does not become a wrong lifetime. When luminosity is supplied it must also be strictly positive, since division by zero or a negative luminosity is non-physical in this scaling. When luminosity is omitted, the engine sets L over L sun equal to mass raised to 3.5, the standard mid-range main-sequence mass-luminosity exponent used in many textbooks for stars roughly between about half and a few solar masses. The preferred field is mass for stellar mass in solar masses, but aliases m, M, mass_solar, and solar_masses are accepted so spreadsheets, query strings, and typed forms can reuse the same contract. Optional luminosity accepts L, lum, luminosity_solar, and solar_luminosities. Mass must be strictly positive: if mass is zero, negative, or negative zero, the request fails with invalid_input because main-sequence lifetime is undefined for a non-positive mass. An optional precision field, with aliases decimals and dp, chooses how many decimal places to expose for numeric fields, defaulting to ten and capped at fifteen so JSON goldens stay stable. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline without re-implementing the mass-over-luminosity formula yourself.
Where main-sequence lifetime fits in study, astronomy, and software
On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split — free interactive exploration and a priced, identical API — matches the rest of the KIT tier-A catalog and lets you move from a classroom demo to an automated pipeline without changing the mathematical result. Pair it with surface-gravity, absolute-magnitude, or light-travel-time tools when you need related astronomy steps, and with other physics endpoints when you are building a small lab of free, deterministic science helpers.
Integration use cases
Deterministic test fixtures
Generate reproducible mass-over-luminosity lifetimes for unit tests, property checks, and CI assertions on astronomy modules.