An ‘either-or’ key is the solution to a minor puzzle which requires a choice of either one solution or the other. These are generally the harder puzzles within Planetarium. They are represented within the Table of Solutions by a small animation which varies according to which of the choices you selected.

The xiii Forum is a message board only accessible to Planetarium readers in their thirteenth week — that is, readers who have reached the end of the story. You can read messages from readers who have passed through already, exchange comments with those who have finished around the same time as you, or leave your thoughts for readers who will finish later. Because all reader-names expire at the end of the thirteenth week, you only have access to the xiii Forum for at most seven days.

You’ll find links to the xiii Forum at the bottom of most pages in Planetarium.

Some time around the end of your twelfth week in Planetarium, your Table of Solutions will be frozen. This means you will no longer be able to submit or change solutions — it’s the end of the story, and the puzzle, for you. When this happens, you are granted access, during the thirteenth week, to the complete illustrated solutions of all the puzzles in Planetarium. You can see how close you came or what you missed. During your thirteenth week, you also can exchange messages with other Planetarium readers in the xiii Forum.

At the end of the thirteenth week, your reader-name will expire and your time here will be over.

A keynumber is the solution to a minor puzzle, such as a counting problem or number-puzzle, which requires a number answer. All keynumbers are positive whole numbers, no greater than 9999.

A keyword is the solution to a minor puzzle, such as a riddle, which requires a single word answer. All keywords are nouns. If the word you think is the answer may take either a singular or plural form, you should always use the singular.

The Major Puzzle is a puzzle which uses all the solutions from the Minor Puzzles. Nowhere in Planetarium is the Major Puzzle explicitly described — you have to work out for yourself how the solutions to the Minor Puzzles can be used. Of course, there are clues and hints which might prove useful hidden in the story. If any of your solutions to the Minor Puzzles are wrong, your solution to the Major Puzzle will probably be wrong too.

A Minor Puzzle is one of the 36 riddles, problems or puzzles whose solution forms part of the Major Puzzle of Planetarium. Your solutions to the minor puzzles are accumulated in your Table of Solutions. There are three kinds of Minor Puzzles, which each provide a different kind of answer — keywords, keynumbers or an “either-or” key.

Planetarium is in twelve parts, numbered using Roman numerals. Each part contains three minor puzzles, based around a scene in the story and the accompanying text. The text is revealed when you click on the appropriate characters or objects within the part. One part is released each week. It may be that hints or clues to problems are embedded in future parts, in which case you must wait until that part is released before you can find that information.

You need a private password to access Planetarium, because this prevents other people seeing your solutions. It is not part of the puzzle. Passwords are case-sensitive, which means you can and should use a mix of UPPER and lower case letters (as well as numbers if you want) to make it hard to guess. Without your password, you cannot access Planetarium. We do not reissue passwords — if you forget yours, you’ll have to start again.

You need to register to read Planetarium (so it can track your progress). There's no authentication — we just need a reader-name that identifies you so when you come back Planetarium can continue the story. Keep it simple so you can remember it — there are some restrictions but basically choose anything you want using letters (and numbers, possibly with an underscore if you want to break it up a bit). Nobody really sees your username anyway, unless you post in the xiii Forum.

Planetarium access is fundamentally anonymous (optionally, you can provide an email address when you register but that's just for automatic email reminders, and we don't authenticate it in any way). Your reader-name is just a token you can use for a few months — it will be deleted if you don't visit for a month, or when you get to the end of the story. Yes, this means that one day in the future someone else might choose the same reader-name as you did. But then, maybe they already did and you're the unoriginal one. It doesn't matter. Three months from now, more or less, it'll be deleted again anyway.

See also password, which is how Planetarium lets you ensure sure it's just you who is using your reader-name.

Each Planetarium reader has their own private Table of Solutions. This is where you accumulate your own solutions to the Minor Puzzles, and, eventually, your solution to the Major Puzzle. To make sure that you and only you can see your own Table of Solutions, you need to provide a password when you access Planetarium.

Somewhere in Planetarium is an open-ended tiebreaker. You’ll know it when you find it. If you don’t want to wait, then you can see a little more about it here.

Now the competition is over, the tiebreaker no longer serves a function, but we’ve kept it in for fun since it’s something you might like to think about while you are solving the other puzzles.