How big is the Universe? And how small is it?

The observable Universe is some 93 billion light years across, about 900 yottameters. The yottameter is the biggest unit of length in the International System of Units (SI). The smallest SI unit is the yoctometer, 10^-24 m. That's a number with 24 zeros between the decimal point and a "1". It's actually rather big to describe the quantum foam that's the basis of the fabric of the universe. The quantum foam is smaller than the Planck Length, and 60 billion Planck Lengths would fit comfortably into a yoctometer.

Writing about long numbers is easier than comprehending them. But one way into them is to explore relative sizes and changes of scale rather than trying to grasp the size of a yottameter. This is what Cary and Michael Huang try to do on “The Scale of the Universe 2” website.

Good features of the website

• Available in several languages.


• Interactive. Unlike watching a video, you can choose to increase or decrease the size, or linger over something that interests you.


• Easy to use.


• Shows the scale of what you're viewing in different ways: in powers of ten notation, in meters, in SI units, and visually, as a series of labeled circles with objects on the same scale grouped inside.


• Graphics that are accurate, attractive and interesting.

A few quibbles

• You can click on the objects for more information. This is a good feature and some of the information is quirky and funny. But some of it is quirky without being informative.


• Could use a bit of updating.


• Some of the graphics are puzzling.

Astronomy
Although I found the whole website interesting, I concentrated on what related to astronomy.

Things I liked
I found seeing the scaled drawings made an impact. For example, I know that neutron stars – what remains after a supernova explosion – are very small. But it was still startling to see a neutron star smaller across than the USA's smallest state, Rhode Island.

The drawings show that Voyager 1, despite having traveled for more than three decades and passing well beyond the Kuiper Belt, is still not even one light-day from the Sun. (A light-day is the distance light travels in one day.) It's in interstellar space where the solar wind no longer dominates, but it's still in the Solar System.

The Oort Cloud is the most distant part of the Solar System, its frozen bodies still held by the Sun's gravity, but almost halfway to the next nearest star. As you enlarge the distance on the website, you can see the distance between Voyager 1 and the Oort Cloud. NASA scientists reckon it will be at least another 15,000 years before the craft passes through the Oort Cloud and truly leaves the Solar System.

And - wow! - the size of the Tarantula Nebula was astonishing. It's one thing to read that it's 600 light years across, but another to see it compared to other Galactic distances.

I also liked the little details on the drawings. There are volcanoes on Jupiter's moon Io, Uranus is on its side, variable stars pulsate, and the nebula drawings are modeled on the wonderful pictures from space telescopes.

A few changes?
Despite the generally impressive accuracy of the presentation, knowledge progresses, and two things are particularly worthy of updating. One is the Large Hadron Collider. It's found the Higgs boson now and Peter Higgs has even won a Nobel Prize. The second is Voyager 1. Since it's moving, the distance keeps changing, and it wouldn't make sense to be perpetually changing that on the presentation. Nonetheless it's quite significant that the craft is officially the first human-made object in interstellar space.

The little jokes in the information boxes are fun, but I think that they should also all be informative.

I am puzzled by all the twinkling going on out in the nebulae, dwarf galaxies and beyond. Messier 54, the Omega Centauri globular cluster and the dwarf galaxies look like Christmas decorations. Is this supposed to represent unspecified variable stars? It seems somewhat odd.

Recommended?
The website is an excellent creative achievement. I'd recommend it to anyone who's curious about the Universe.

But I would particularly commend it to educators and students. The idea of size and scale is quite important to a number of disciplines and I think it's helpful to present it in such an interesting way. The presentation includes elements of astronomy, geography, biology, physics, chemistry and math. It could be a useful and flexible learning resource.

Some notes, August 2018
I've checked the website and "The Scale of the Universe 2" is still at https://htwins.net/scale2/index.html. It's still good, though in need of some updating, which I don't think it's going to get.

You need Adobe Flash to run it. It looks as though there's an app for it too, but I didn't pursue that.

The website doesn't use https, so the Chrome browser won't open it. But Firefox does.