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Episode 144 - Why We Know About Things Far Away but Not Nearby, and Lots of New News

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Recap: A close examination of why astronomers claim that they know about things on the other side of the universe, but they can't figure out what's going on in our own backyard. Since this episode comes out two months after my previous, there are also three New News stories where I discuss a recent exosystem mystery, space law, and, conveniently, the new most-distant known object in our solar system.

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Episode Summary

Claim: As I begin to emerge from a giant mountain of work to crawl under a slightly smaller one, I’m going to return to basics for this episode’s shorter main segment and look into a claim that I’ve heard more frequently than I would like, and it goes something like this:

“The solar system is anywhere from one to two light-years in diameter, it’s enormous. We have no idea what’s out there. We really— we talk about these solar systems that are, I don’t know, 20 light-years, 200 light-years away, it’s-it’s— it’s absurd to me. Because th-th-they’re talking about, you know, these perturbations on-on orbits and things like that. To me, I don’t even take it seriously anymore. Because we don’t know what’s in our own solar system.”

In other words, astronomers seem so certain about things far away, but we don’t seem to even know what’s going on in our own backyard. And if that’s the case, then how can we possibly know what’s going on so far away?


This is a case where we really do know what’s going on far away, but we have trouble with some close stuff. In other words, the person who said that, and other people who make similar claims, are incorrect, and the reason is one of those things that once you understand it, you’d wonder how you could possibly have ever been confused in the first place. And conspiracists will drop their conspiracies and we’ll all have world peace and feed the hungry, too.

When I was trying to think of an analogy to this situation, the first thing that came to mind is something I’ve discussed with Apollo Moon Hoax claims, specifically the one where people point out that pictures are rectangular or the big crosshair in the center isn’t in the center, and it’s at an angle. Conspiracists and anomaly hunters make a huge deal about this, claiming that since NASA says the big crosshair is always supposed to be in the center of the square film, then these pictures prove NASA is lying and therefore they’re lying about everything.

But the answer is so simple: Rotate & crop. The square pictures were rotated so that something like the horizon line is straight horizontal, and then the picture is cropped to give a more photogenic scene, like removing a bunch of black sky. When pointed out, it’s so simple that you’d wonder why you ever could have thought that this was evidence for the moon landings being a hoax.

Similarly, there’s this claim about knowing about far away stuff but not nearby stuff, and if we don’t know about nearby stuff then we couldn’t possibly know about far away stuff.

Here’s what I’d suggest: If you’re driving, look out the front windshield, which you already should be doing anyway, so get off your phone and stop txting. If you’re not driving and you have a window nearby, look out the window. Otherwise, do this when you can see outside.

Pick some big feature that’s far away. For me, there are some mountains perhaps 30 miles or 50 km away from me. Those mountains are really big, really obvious. I know they’re there because they’re a big, major feature. But, if I then come back to the foreground, I have absolutely no idea now many pieces of dirt are on the ground right in front of me, or if you’re driving, how many rocks there are right beside your car right now.

And that’s really all there is to this: Astronomers, just like you in this thought experiment, are good at picking out big, obvious structures that are far away. We’re less good at picking out relatively tiny things close by. For us, it all has to do with two very basic things: How big something is on the sky (it’s angular size), and how bright it is as seen from Earth.

Big and Bright vs Small and Faint

Let’s think about something like a galaxy, one that we’re not in. For fun, let’s pick the Andromeda Galaxy, also known as M31, which is the biggest close galaxy to us and one that will eventually collide with ours in a few billion years.

The Andromeda Galaxy is about 2.5 MILLION light-years away. Or, 1.5*10^19 miles, or 2.4*10^19 kilometers. Really far away. But it’s gigantic. In our sky, while it’s core is perhaps half the size of the full moon, its full extent as seen from Earth is about 6 full moons long by 3 full moons wide. It’s also visible to the unaided eye if you know where to look and aren’t in a city. It shines with the light of about 1 trillion stars, which is around 3 times as many as are in our own galaxy.

Now, compare that with the asteroid that passed by Earth on October 31, 2015. The asteroid, known officially as 2015 TB145 but which I’ll call “The Great Pumpkin,” spends most of its time a bit past Mars. It’s 600 meters, or 2000 ft across. It passed Earth about twice as far as the moon’s orbit. It was discovered on October 10, 2015, when it had a brightness magnitude 20, meaning that it was about 1 to 10 MILLION times FAINTER than the Andromeda Galaxy. When it passed closest to Earth, it had an apparent magnitude of 10, meaning that it was “only” about 500 times fainter than the Andromeda Galaxy.

This is an excellent example of how we didn’t know about this object until three weeks before its closest approach to Earth, and it got as close as twice as far away as the moon. But at that time, it was 500 times fainter than the Andromeda Galaxy and it covered about 0.009% the size of the full moon, as seen at that time from Earth.

Big, bright, and far is a lot easier than small, faint, and close.

As another example, exoplanets are still big in the popular culture. The primary way to detect them now - with the success of the Kepler mission - is the transit method, whereby the planet goes in front of its parent star, as seen from Earth, and we see this as a slight change in the brightness of the star’s light because the planet blocks part of the star’s disk. They are much too far away to resolve the system and see the actual disk of the star and the planet pass in front of it, but we effectively get a graph with a steady line of total star brightness that quickly and briefly drops down a bit when the planet passes in front.

Because area goes as diameter squared, if we see a 1% reduction in light, then the planet was 10% the diameter of the star. This would be like Jupiter passing in front of the sun. If we see a 0.01% reduction in light, then the planet was 1% the diameter of the star, which would be like Earth passing in front of the sun.

These days, with CCD chips and very basic computer software, these things are somewhat easy to detect, at least the big ones that go in front of their star often so you don’t have to stare at them for a long time hoping for a transit when the star may not even have a planet. Incidentally, that’s why the majority of known exoplanets orbit their stars in just a few days — those are the easiest to detect because it’s something you can do with just a month of observing time.

Contrast that with what conspiracy people say about a possible hidden Planet X in our solar system. And I’ll revise that statement: It’s not just conspiracy people. I’ve said on this program and elsewhere, as have other astronomers, that it is entirely possible that there is a planet-sized object out there in the cold reaches of the solar system, still in orbit around the sun, that we just haven’t seen yet.

But how could that possibly be the case if we can see planets around other stars, gagillions of times farther away? How could we not know if there’s more planets in our own solar system? Or, since we don’t know if there are other planets in our solar system, then doesn’t that mean that we couldn’t possibly know if there are other planets around other stars?

No. The reason is that they are completely different things. It’s easier to tell if a bug passes in front of a porch light - if you’re watching it - than if there’s a bug somewhere in the same room as you when that room is lit by one lamp that you’re somewhat close to.

To tell if there’s a bug in front of the porch light, you just see the light dim a tiny bit very briefly. Since many bugs are attracted to light, you’ll likely see the light’s output appear to flicker as the bug continuously passes in front of it and then to the side or behind. Just like an exoplanet around its star, though a bit more haphazard.

But then let’s go back to your room. You have a lamp in the middle, and you’re reading a book so you’re somewhat close to the lamp. For those listeners under the age of 20, a book is a thing with words printed on paper, where paper is that stuff that comes out of your printer.

To tell if there’s a bug in the room with you, assuming you don’t hear it, then you have to do a very careful, methodical search all around the room, looking carefully all around you. And if the bug is big, you may see it. If the bug is tiny, then maybe you need to get binoculars to do your search. Which will then take longer because you have to search more slowly because you can’t see as much of the room with the binoculars as your eye.

In other words, to get back to the science and away from the analogy, this is a case where it’s not just as simple as one thing is big and bright and far away versus small and faint and close - like the Andromeda Galaxy versus The Great Pumpkin - but it’s also because the entire method of finding things within our own solar system can be different from the method for finding the same kind of thing in a different solar system.

Wrap Up

I started out by presenting a claim that may seem, on its face, to make some sense and you may start to wonder how we can know anything. Just like the idea that it took two parents to make me, two parents each to make them meaning 4, two each to make those so you have 8, and by the time you get to my great-great-great grandparents, there must have been 32! So how could the population of the world be increasing now, since there must’ve been a near-infinite population back then to give rise to all the people today, right?!

Well, no. As I then explained, it’s just a simple, straight-forward factoid that you’re missing and, once it’s explained, hopefully that initial claim, that initial misconception, is shown to be nothing but giants gently turning in the wind.

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