IOAA — International Olympiad on Astronomy and Astrophysics
The flagship international olympiad in astronomy and astrophysics, held annually since 2007 with rotating host countries. Each edition combines a theoretical exam, a data-analysis exam and observational tasks, plus a team competition.
- Founded
- 2007
- Host rotation
- Annual, rotating host country
- Level
- International (secondary school)
- Format
- Theory, data-analysis and observation rounds over ~10 days
- Rounds
- Theoretical exam, data-analysis exam, observational exam, team competition
- Eligibility
- Secondary-school students, typically under 20; max 5 contestants plus 2 team leaders per country
- Website
- ioaastrophysics.org
Notable facts
Grew out of the older International Astronomy Olympiad and now draws more than 50 countries. In 2020 it was replaced by the online Global e-Competition on Astronomy and Astrophysics (GeCAA).
Recent editions
| Year | Host |
|---|---|
| 2025 | Mumbai, India |
| 2024 | Rio de Janeiro, Brazil |
| 2023 | Katowice, Poland |
| 2022 | Kutaisi, Georgia |
| 2021 | Bogotá, Colombia |
Typical topics
Past problems
2025
Measuring the Hubble constant
A sample of Type Ia supernovae yields recession velocities for galaxies whose distances were measured independently. From the supplied velocity–distance table, estimate the Hubble constant by a linear fit and derive the corresponding Hubble time in billions of years.
Show solution
A linear fit v = H0·d through the velocity–distance table gives a slope H0 ≈ 70 km/s/Mpc for typical recent data. The Hubble time is t_H = 1/H0 ≈ (1/70) Mpc·s/km ≈ 4.4 × 10^17 s ≈ 14 billion years. The scatter of points about the fit sets the statistical uncertainty: a few percent error in the slope maps to the same percentage error in t_H.
Dark matter in a spiral galaxy
Given a table of circular velocities versus radius for a spiral galaxy, compute the enclosed dynamical mass at several radii and compare it with the supplied luminous-mass profile. Determine the radius beyond which the dark-matter component begins to dominate.
Show solution
At each tabulated radius compute the enclosed dynamical mass from M(<r) = v²r/G. For v ≈ 220 km/s at r = 20 kpc this gives M ≈ 2.2 × 10^11 M_sun, well above the luminous mass at the same radius. Comparing the two profiles, the point where M_dyn first exceeds ~2× the luminous mass — typically just outside the optical disc, near r ≈ 10–15 kpc — marks where the dark halo begins to dominate.
2024
Parallax distance to a nearby star
A Gaia measurement gives the trigonometric parallax of a star as 48.2 ± 0.3 milliarcseconds. Convert this to a distance in parsecs and light-years, then compute the star's absolute magnitude given an apparent magnitude of 7.9, neglecting extinction.
Show solution
With p = 48.2 mas = 0.0482″, the distance is d(pc) = 1/p″ = 1/0.0482 ≈ 20.7 pc, or d ≈ 20.7 × 3.262 ≈ 67.7 ly. The absolute magnitude follows from M = m + 5 − 5 log d(pc) = 7.9 + 5 − 5 log 20.7 ≈ 6.3. The ±0.3 mas parallax error maps to a distance range of 1/0.0485–1/0.0479 ≈ 20.6–20.9 pc.
Luminosity of an accreting black hole
Matter falls onto a 10-solar-mass black hole at a rate of 10^17 kg per year with a radiative efficiency of 10%. Compute the accretion luminosity, compare it with the Eddington luminosity for the same mass, and state whether the flow is super-Eddington.
Show solution
First convert the rate: Ṁ = 10^17 kg/yr ≈ 3.17 × 10^9 kg/s. The accretion luminosity is L = εṀc² = 0.1 × 3.17 × 10^9 × (3 × 10^8)² ≈ 2.9 × 10^25 W. The Eddington luminosity for 10 M_sun is L_Edd = 1.26 × 10^31 (M/M_sun) W ≈ 1.26 × 10^32 W. Since L/L_Edd ≈ 2.3 × 10^−7, the flow is far below Eddington — it is strongly sub-Eddington.
2023
Distance to a Cepheid variable
A classical Cepheid in a nearby galaxy is observed with a pulsation period of 35 days and a mean apparent magnitude of 22.4. Using the supplied period–luminosity calibration and correcting for interstellar extinction, determine the distance to the host galaxy and estimate the uncertainty introduced by the extinction correction.
Show solution
The period–luminosity calibration for a 35 d classical Cepheid gives an absolute magnitude M ≈ −4.6. The distance modulus is then m − M = 22.4 − (−4.6) = 27.0, so d = 10^((m−M+5)/5) ≈ 2.5 Mpc. An uncertainty of 0.1 mag in the extinction correction propagates straight into the modulus, giving Δd/d = (ln 10 / 5)·0.1 ≈ 5%, i.e. d ≈ 2.5 ± 0.13 Mpc.
Exoplanet transit light curve
Contestants receive photometry of a Sun-like star showing three repeated transit events. By folding the light curve on the inferred period and fitting the transit depth and duration, estimate the planet's radius and orbital semi-major axis, then discuss whether the planet lies in the habitable zone.
Show solution
The transit depth yields the radius ratio via δ = (Rp/Rs)²; a ~1% depth on a Sun-like star gives Rp ≈ 0.1 R_sun ≈ 1 R_jup. Folding the three events fixes the period P, and Kepler's third law then gives a = (GM_sun P²/4π²)^(1/3) ≈ 1 AU for P ≈ 1 yr. The transit duration T ≈ P·Rs/(πa) provides an independent consistency check on the scaled orbit. With a ≈ 1 AU around a solar twin, the planet lies inside the habitable zone (~0.95–1.4 AU).