How the olympiad works

Builds on: No earlier section
Reading time: 20 min

On the morning of 28 September 2026, in Hanoi, the contestants of the International Olympiad on Astronomy and Astrophysics opened a five-hour theory paper. The next night they took turns at a telescope under the sky, on 1 October they sat a data-analysis paper, and the day after that they faced the sky projected inside a planetarium dome. Every IOAA follows this pattern of a theory round and a set of practical rounds, and the way each round is set and marked decides how best to prepare. In this section we describe the rounds, how the papers are marked and the medals decided, and what may be used in the exam room.

S1.1The rounds

The olympiad has two parts of equal weight. The theory round gives 50% of the total mark, and the practical rounds give the other 50%, split equally between data analysis and observation.

Round	Length	Share of the total mark
Theory	5 hours	50%
Data analysis	about 4 hours	25%
Observation	set by the host	25%

The theory paper lasts five hours. It normally has five short problems, five of intermediate length and two or three long ones, and together they should cover at least four areas of the syllabus. A short problem usually needs one idea and a few lines of working, while a long one is a chain of parts that build on each other, often around a real observation or a recent discovery. Problems may describe phenomena outside the syllabus, but only if they supply everything needed to solve them.

The data-analysis paper usually lasts about four hours and has two or three problems built on real or realistic measurements. The work is done on paper, with graph paper, a ruler and a calculator. Typical tasks are choosing a model, plotting the data by hand, drawing the best line through the points and estimating the uncertainty of the result. Chapter D teaches these skills.

The observation round tests what a student knows of the sky and how well they use instruments. The host decides its form, which may include naked-eye tasks under the real sky, a session at a telescope, a planetarium round in which the sky is projected inside a dome, and tasks with star maps. At a telescope a student may have to point at a named object, estimate a magnitude or measure a field of view. In the planetarium a student may have to name constellations and stars, mark coordinate lines or work out the latitude and time of the sky being shown. Because the weather cannot be planned, hosts prepare indoor tasks to replace a session under the sky if it is cloudy. Chapters O1, O2 and O3 prepare for this round.

At IOAA 2026 the order was theory first, then the telescope round, then data analysis and finally the planetarium round. Other hosts have used other orders, and the timetable of each year is published by the host before the competition.

S1.2Marking and medals

Every solution must contain an answer and a complete justification. The papers are marked against a detailed scheme that gives marks for each correct step, so a correct method with a slip in the arithmetic still earns most of the marks, and a bare answer without working earns few. Team leaders then see the marking and can ask for a script to be looked at again in a meeting with the markers, called moderation.

Medals are decided relative to the whole field. The organisers first set a reference score $M$ , which is the median total score of all contestants or half of the maximum possible score, whichever is lower. In most years the median is the lower of the two. The bronze line is then placed close to $M$ , the silver line close to $1.3 M$ and the gold line close to $1.6 M$ . Each line is moved slightly to fall in a gap between neighbouring scores, so that two students with almost the same total do not end up with different medals.

ResultReference score and medal lines(S.1)

\begin{aligned} M & = min (median, 50 %) \\ bronze & \approx M, silver \approx 1.3 M, gold \approx 1.6 M \end{aligned}

$M$	reference score, as a percentage of the maximum possible total
$median$	median total score of all contestants, as a percentage of the maximum

The statutes allow a small, controlled adjustment of the lines when the numbers of medals would otherwise be badly out of balance.

The table shows where the lines fall for three medians. In a hard year the lines fall with the median, while in an easy year the reference score stops at 50%, so the lines can rise no further.

Median total	Bronze line	Silver line	Gold line
30%	30%	39%	48%
40%	40%	52%	64%
60%	50%	65%	80%

If the scores are scaled so that the median counts as 50%, the lines fall at 50% for bronze, 65% for silver and 80% for gold. A bronze medal therefore means beating about half of the students in the room. A student who does not win a medal can still receive an honourable mention, which is given for a strong result in the theory round or in the practical rounds alone, judged against separate reference scores for each.

NoteA self-marked score on a past paper cannot be compared directly with these lines, because the lines depend on how every other contestant did in that year. For this reason the mock exams in this course will show medal lines only for years whose real results make the comparison fair.

S1.3In the exam room

The statutes allow drawing instruments and a non-programmable, non-graphing pocket calculator, and a host may be stricter. At IOAA 2026 every contestant was given a Casio fx-82CW, and no other calculator was allowed. Collections of formulas are not allowed, but the organisers supply a table of physical and astronomical constants, and a problem that needs any other value gives it. The Reference section of this course will hold a copy of the most recent table.

Answers are expected in SI units, or the units that the problem uses, with a sensible number of significant figures. The working language is English, and versions of the papers in other languages may also be prepared. At IOAA 2026, phones, smartwatches and other devices were handed in after the opening ceremony and returned only after the last round, and a contestant found with one during the competition could be disqualified.

S1.4How teams are chosen

Each country sends a small team of secondary-school students, chosen through its own national selection. Most countries hold one or more written rounds, followed by a training camp or further tests for the strongest students. The written rounds usually test the same skills as the IOAA theory paper, often with a heavy share of positional astronomy and simple calculations, so the early chapters of this course help from the very first round. The data-analysis and observation skills matter most at the later stages and at the IOAA itself, where a beginner can earn marks in them faster than in any other part of the competition.