scale – Christian Ready

28 October, 201330 October, 2013

Proxima Centauri is Far, Far Away

Space is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space.

Douglas Adams, The Hitchhiker’s Guide to the Galaxy

Today an archive Hubble Space Telescope image of Proxima Centauri was released. It’s a beautiful image that shows Proxima as a small red dwarf star about one-tenth the radius of our Sun. As it’s name suggests, Proxima is close by – a scant 4.243 light years away, nary a stone’s throw across the universe.

But “close” is a very relative term here. In fact, the only way we can begin to comprehend the ridiculous distance to the closest star is to scale it down to something we might be able to better comprehend.

Let’s say for the sake of argument I got past security and managed to place a volleyball-sized scale model of our Sun on the top of the Capitol Building in Washington, DC, like so:

The Sun, shrunk down to the size of a regulation Volleyball (radius of about 10.5 cm) placed atop the Capitol Building in Washington, DC. Image from Google Earth — The Sun, shrunk down to the size of a regulation Volleyball (radius of about 10.5 cm) placed atop the Capitol Building in Washington, DC. Click to embiggen. Image from Google Earth

That shrinks our Sun down to a radius of about 10.5 centimeters. Proxima is 4.243 light years away, which on this scale equates to a distance of 6025 km. That means on this scale, Proxima could lie anywhere along this ring around our volleyball sun in DC:

A 6,025km-radius ring drawn around a volleyball-sized Sun atop the Capitol building in Washington, DC. Click to embiggen. Image from Google Earth.

Proxima’s parent star, Alpha Centauri, lies about 155km beyond on this scale, so let’s place both at their respective distances in France:

The Sun in Washington, DC, Proxima Centauri in the French countryside and Alpha Centauri in Paris. Click to embiggen. Image from Google Earth

So there you have it. If the Sun were a volleyball atop the Capitol Building in Washington DC, our nearest stellar neighbor would be about 1.5 centimeters in radius – about the size of a large ball bearing – somewhere in the French countryside.

Space is freakishly, mindbogglingly big!

3 December, 2012

A galaxy in perspective

One of the things that’s very difficult to appreciate is the relative sizes and distances of celestial objects. After all, their sizes and distances aren’t remotely small enough for us to appreciate. As a result, everything we see looks in some way compressed – one object in an image may just as easily be twice as distant, or ten times as near, as another with little way of knowing the difference.

But if we apply a little knowledge to these images, the relative distances seem to jump out at us, like this:

ESO 318-13 as imaged by the Hubble Space Telescope using its Advanced Camera for Surveys. Image credit: NASA/ESA & Hubble

This is a Hubble Space Telescope image of ESO 318-13 taken with Hubble’s Advanced Camera for Surveys. ESO 318-13 is an irregular-shaped galaxy. That is, a galaxy that has no formal structure such as spiral arms or even a well-defined central nuclear region.

It’s a beautiful image, but what I really love about it is that in one shot we can discern a tremendous amount of perspective and depth. Let’s start with the nearby stuff and work our way outward.

The brightest objects are foreground stars in our own Milky Galaxy. Coincidentally the foreground star in the middle right of the image happens to line up with the middle of ESO 318-13, but keep in mind that the galaxy is itself a collection of stars millions of light years beyond.

If you look at the full-resolution version of the image, you’ll see individual stars within ESO 318-13. And if you look toward the right-edge of the galaxy you’ll spot a beautiful face-on spiral tens of millions of light-years in the distance behind the galaxy. For all of their grandeur, galaxies are mostly empty space, and can be transparent enough to allow background galaxies to easily be seen through them.

Pan around the image and you’ll see a lot more galaxies in the background, including a giant elliptical galaxy in the upper right-hand corner of the image. ESO 318-13 is a dwarf galaxy and may contain a few tens of millions of stars. But the elliptical galaxy in the background is a cosmic titan containing several hundred billion suns!

The distances to objects in this image are all relative – there isn’t anything that tells us exactly how far away they are just by looking at them. To get those measurements we need to use indirect methods such as spectroscopy. But in one image we can begin to get an idea of the sheer scale of the cosmos – keeping in mind that this is still a fairly local region of the universe!

26 September, 201226 September, 2012

The deepest view of the universe: the Hubble eXtreme Deep Field

How deep into the universe have we looked? As of today, this deep:

This is the Hubble eXtreme Deep Field, (XDF), and it’s a masterwork ten years in the making*. What you’re seeing is what you get when you take a very long exposure with two of Hubble’s best cameras of a region of the sky that contains no known stars – an ocean of 5,000 galaxies! And it’s a very deep ocean, indeed. More than 5,500 galaxies are crammed into a field of view just a fraction of the size of the full moon.

The galaxies are arranged at varying distances from us. Some are relatively bright and even have spiral arms as seen in nearby spiral and elliptical galaxies:

But others, way, way, waaaay in the background, don’t appear to have any structure at all. Instead, they just look like little blobs of stars and gas:

Portion of the HUDF — A portion of the HUDF. The tiny points of light are primordial clumps of newly formed stars, gas, and dust that would combine to form modern-day galaxies.

So what’s going on here? It turns out that these fainter galaxies are so far away, their light took billions of years to reach us. In other words, we’re seeing these galaxies as they were several billion years ago when the universe was only a few hundred million years old!

To put that into perspective, it helps to think of the XDF as a kind of “core sample” of the cosmos; the deeper into the field we look, the farther back into the universe’s past we can probe:

heic1214c — The XDF, separated by the distances of objects within it. The most distant objects within the XDF are more than 95% of the way back to the Big Bang.

Our universe is 13.7 billion years old. Thanks to Hubble, we can see what galaxies looked like in the current era, what they looked like in its earlier years, and what they looked like a relatively short time after the Big Bang.

And so, in just one image, we can trace the evolution of galaxies over time – from small embryonic building blocks of fluff to beautiful spirals, to giant ellipticals that are the relic of collisions of multiple galaxies. It’s the story of the universe, writ in a single image.

I’ll never tire of looking at this image, and marveling at just how far we’ve come in our understanding of the universe in so short a time.

But what really gives me goosebumps is what’s left to discover.

* I realize in retrospect I didn’t explain this elsewhere in the post. XDF is actually part of the Hubble Ultra Deep Field, which was made with Hubble’s Advanced Camera for Surveys (ACS) from September 2003 through January 2004. But this new image was made with additional ACS images taken since then, as well as Hubble’s new Wide Field Camera 3 (WFC3) which was installed in 2009. WFC3 is sensitive to near-infrared, allowing even fainter, more distant proto galaxies to be imaged. Hence my comments about this image being ten years in the making, as well as the deepest view ever!

10 September, 201214 September, 2012

Magnifying the Universe

“Space,” it says, “is big. Really big. You just won’t believe how vastly, hugely, mindbogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space, listen…” The Hitchhiker’s Guide to the Galaxy, by Douglas Adams

Now that we’re up, up and away, a little orientation of the universe seemed like as good a way as any to get started. The problem is that the sheer scales of even the most trivial objects in the universe are so beyond our day-to-day experiences is that it is very difficult to get our heads around them.

That shouldn’t surprise us. After all, we evolved to survive on a planet that happened to be of a certain size. Perhaps if we were some sort of interstellar whales we might have a more intuitive sense of the sizes and distances of everything from small asteroids to the largest stars. But even then we might have a hard time contemplating the relative sizes of galaxies and the vast distances between them.

Fortunately, such scales are not beyond our mathematics, nor beyond our ability to express them in a convenient infographic courtesy of the folks at numbersleuth.org. Be sure to click for the full size as it’s worth a fun little read.

However…

While I trust that their scales check out, some of the imagery used is incorrect or misleading. For example, the image of the solar system chosen only goes out to the orbit of Jupiter. It’s much larger than that, of course. The first two images of the poster for the Observable Universe and the Observed Universe should be switched and labeled differently. Still, it’s a pretty fun way to get a handle on the scales of these things.

But wait, there’s more!

As an added bonus, the same folks were kind enough to organize the infographic into a handy zoomable interactive:

Enjoy zooming around!