About Time and Space Science

Free tools and simulators for the things that govern how the world around us works — gravity, motion, time and space — built to be taken apart rather than just read. No app, no account, no sign-up, nothing for sale.

One set of rules, seen from different sides

Almost everything on this site is the same short list of rules, looked at from a different angle each time. A day is the Earth turning. A year is the Earth going round. The seasons are that turn being tilted. The tides are the moon pulling on an ocean. A planet stays in its orbit for exactly the same reason the moon does, and an asteroid does it too. Time zones exist because the Earth is round and turning, and a clock is how we agreed to count that.

Taught separately, those are eight facts to memorise. Seen together, they are one idea with eight consequences — and that idea is much easier to hold on to, because you can watch it happen:

The turnDay and night on a world map — half the planet lit, half dark, and the line between them sweeping west at the speed of the Earth's own spin.

The tiltSunrise and sunset for your town and the Sun, Earth and Moon together — why your longest day is long, and why someone else's is not.

The orbitTonight's moon is a ball lit from one side; the eclipses are the three of us briefly in a line.

The pullTides — the moon's gravity, arriving as water, twice a day, on a coast you can go and stand on.

The balanceWhy nothing falls into the sun — everything out there is falling, constantly, and moving sideways fast enough to keep missing. The asteroid belt included.

The scaleThe solar system on its real orbits and a page for every planet — the same law of gravity at every distance, and the distances themselves, which are the part diagrams usually lie about.

The countingTime zones, a timer, a stopwatch and an alarm clock — measuring time is its own skill, and it is the one every science lesson quietly depends on.

Every figure on those pages is computed, not looked up — worked out in your browser from the real motions, using published orbital elements and standard astronomy. Nothing is fetched from a live feed except the NOAA tide predictions, which say so on the page. Where a picture is not to scale, it prints the factor by which it is wrong. Where a calculation stops being reliable, the page says where. How each number is worked out is a section of its own.

Why I built this

Most importantly, I'm a girl dad to an 11-year-old rockstar. I was a stay-at-home dad until she started school, and we still love working on projects and learning things together. That is a big part of the inspiration behind this site.

My professional background is in business analytics, computer programming and digital marketing. AI is a newer tool in my toolbox, and I've been using it alongside those skills to see what I can create that is genuinely useful. I decided to build a free resource for students and teachers that my daughter and I could also explore and learn from together.

She has already made dozens of good recommendations that have made the site better. Now I'd like to take that same idea much further, by working directly with K–12 teachers and their students.

I want students to help build this

I'd love to work with individual classes, through their teacher: let students explore the site, experiment with the tools, and come up with ideas for making them more useful, more accurate, more engaging or more fun. Children are very good at spotting the moment a thing stops making sense, and they have no reason to pretend otherwise.

If a class comes up with an idea and I build it, the class gets the credit on the page. A line like this, on the tool itself:

This simulator was inspired by an idea from Mr. Smith's 5th grade class at Paradise Elementary School in Paradise, California.

Real school, real class — mine. Paradise Elementary in Paradise, California is where I went, and Mr. Smith taught my fifth grade class there more than thirty years ago. No class has asked for anything yet, so that line is still only an example of the format; it seemed like the right name to hold the place until a real one takes it.

Imagine being a fifth grader, coming up with an idea, and later seeing your class credited on a tool being used by students on the other side of the world. There is something powerful about showing children that their ideas can become real things that other people use.

Nothing about a student is ever published: not a name, not a school email, not a photograph. The credit names the teacher, the grade, the town and the school year, and only if the teacher asks for it — the details are in the privacy policy, and the box is easy to untick.

How working together actually goes → Ask for something for your class

Teachers: bring me a lesson before you teach it

If you see something here that could fit into a lesson, please reach out before you teach it. Tell me what you're trying to teach, the grade level, and how you'd like to use the tool. I'll work with you to improve the tool where it needs it, and to develop the lesson plan, so it can be published for other teachers to use. The teacher, the class, or both can be credited for helping create it.

Work with us sets out how that goes step by step — what to send, what happens next, exactly what a credit line says, and what we will not build. The classroom guide covers the practical side — projector mode, keyboard shortcuts, what works on a school network and what a browser timer genuinely cannot promise — and there are ready-made lesson plans already written against the tools.

I do have some teaching experience: I taught college and graduate-level technology courses for a couple of years. That was more than twenty years ago, and teaching K–12 students is obviously a different job. So I'm genuinely open to criticism. Teachers understand their classrooms and their students in ways I don't. I want help working out what's clear, what isn't, what's missing, and — most of all — what would make a student curious enough to keep going.

The sandcastle part

Becoming a dad changed how I think about teaching. Whether we're building a six-foot sandcastle or diverting a little creek running into the ocean, I turn it into a project and make it fun. What starts as something my daughter and I are doing together often ends up with ten or twenty kids and parents jumping in — asking questions, helping, experimenting, adding their own ideas.

I've realised that's the part I enjoy most. Building something is fun; building something that pulls other people in and gets them curious is much better. That's what I want these tools to do — not just explain something, but hand you the controls and invite you to push them.

Long term, I'd like this to be more than a collection of free tools and lesson plans. I'd like it to be a place where teachers and students contribute ideas, those ideas become new resources, and what one classroom creates helps another classroom somewhere else.

— Lars Estrem

What this site promises

Free to use, with no accountNo sign-up, no email, no paywall on any tool or page — and no plan to put one there. As it stands today there is also no advertising, nothing for sale and no affiliate link anywhere on the site; how it is paid for says what would have to be true if that ever changed.

Nothing collected from childrenAlmost every page asks for nothing at all. The one form with required fields is the class request, and it is for a teacher or another adult to fill in. Don't send us a student's name — we don't want it and we delete it if it arrives. See the privacy policy.

Numbers you can checkFigures are derived rather than typed, so a page cannot disagree with the picture beside it. Outside sources are named. Every simulator says where its model stops being trustworthy, and none of them should be used for navigation, safety or anything where being wrong by a degree would matter.

Corrections, quicklyIf something is wrong, tell us: the report link is at the bottom of every page and pre-filled with the page you're on, and the wrong-date form goes straight to a person. Being corrected is cheaper than being wrong.

Fast, and it works in a browserStatic pages, no app, no install, and the tools run entirely in your tab. That has real limits on a phone and in a background tab — what a browser timer can and cannot promise is written out rather than glossed over.

Independently run, and not affiliated with any device maker, operating system, or other clock, countdown or astronomy product.

How this is paid for

Right now: it isn't. There is no advertising on the site, no affiliate link, nothing for sale and no sponsor. It is paid for out of my own pocket, which is possible because it is genuinely cheap to run — static pages on a content network, with the maths done in your browser rather than on a server I rent.

I'd rather tell you the truth than make a promise I might not be able to keep: at some point this may need to pay for itself. The likeliest shape is a sponsor — an organisation whose work actually belongs next to this one — rather than an advertising network. So instead of swearing "never any advertising", here is the standard anything of that kind would have to meet. This is the part I intend to hold to.

The tools stay free. No account, no paywall, no "sign in to see the rest" — that is the whole reason to take sponsorship rather than charge for it, and it is what I intend for as long as I am running the site. If that ever had to change, this page would say so, in advance, rather than leaving you to discover it.
Nothing that tracks or profiles children. No behavioural advertising, no ad network that builds a profile out of a student's visit, no third-party tracking scripts loaded into a lesson.
Nothing sold to students. A page a ten-year-old is reading is not a shop, and will not become one.
Anything paid for is labelled as paid for, in plain words, next to where it appears. Never dressed up as a recommendation, an explanation, or a search result.
Nobody buys what a page says. A sponsor gets a name and a thank-you, not a say in a number, a conclusion or what gets built. Every figure here is computed and checkable, which is what makes that a testable claim rather than a slogan.
A sponsorship is reviewed every year, however long the agreement runs, and a credit stands only while the agreement does. A long arrangement is welcome — a permanent fixture on the site is not something for sale.
If it changes, this page changes first — saying what changed and when, before you find it somewhere else on the site.

So yes — I am looking for a sponsor. Someone whose work belongs beside this one, who would rather pay for a free thing to stay free than buy an advert on it. If you run a telescope company, a science-kit company, a planetarium, a foundation, a space-education programme, or a district that wants a particular tool built: here is exactly what sponsorship would and would not buy, written down in advance so neither of us has to guess. What I would like best is one sponsor, across the whole site, in something built to last — and structured so that growing the audience is worth something to both of us.

And if you can see a way the standard above fails — a loophole in it, or a place the site already breaks it — I'd genuinely like to hear that too.

Where to start

Start with a question Day & night on Earth Sun, Earth & Moon The solar system Why orbits don't fall in Every planet Sunrise where you are Tonight's moon Tides Work with us Sponsor the site For teachers How the site works

💡 Question, problem or idea? Tell us →