Wednesday, October 26, 2011

Weird Worlds: Kepler 16

I have talked about the Kepler exoplanet-finding mission in the past (planet spotting, Kepler 11, KOI 730). Today I'm going to look at a planet Kepler has found in a binary star system: Kepler 16(AB)b and next week I'll talk about Kepler 14b which is also in a binary system but in a different configuration.

A binary star system is where two stars are close enough together to be in orbit around each other, instead of individually orbiting the centre of the galaxy. Instead they orbit the centre of the galaxy together, much the same way as the Earth and the moon orbit the sun together. Also sort of like on Tatooine from Star Wars.

Kepler 16b

Artist's impression of the Kepler 16 system.
Credit: NASA/JPL-Caltech/R. Hurt
Basic stats for the Kepler 16 system are somewhat unartistically presented here. I'll go over some of them below.

As far as we know, there are three bodies in the Kepler 16 system: the two stars which are designated Kepler 16A and B (and together Kepler 16(AB). As per usual convention, the more massive star will be A while the smaller will be B. The usual convention, for non-binary systems, is that the star is designated Whatever-a and planets in order of discovery then mass (so mass when several are discovered simultaneously) are designated Whatever-b, Whatever-c etc. The lower-case a for the stars is a bit redundant here, though. Masses and distances for the system are as follows:
  • Star A:
    • Mass: 0.69 solar masses
    • Size: 0.65 solar radii
    • Temperature: 4450 Kelvin (about 4180º C or 7600º F)
  • Star B:
    • Mass: 0.20 solar masses
    • Size: 0.23 solar radii
  • Stars AB together:
    • Orbital period: 41 days
    • Orbital separation: 0.224 AU (for comparison, Mercury's orbit is 0.387 AU from the sun)
  • Planet Kepler 16(AB)b:
    • Mass: 0.33 Jovian masses
    • Size: 0.75 Jovian radii
    • Orbital period: 229 days
    • Orbital radius: 0.70 AU (Venus is 0.72 AU from the sun)
It's not possible to separate out and measure the temperature of star B because it is completely overwhelmed by the light from star A. We can only make guesses based on it's spectral type which is determined from its chemical make up. Also note that the distance measurement for the planet is from the centre of mass of the two stars -- the barycentre.

For a bit of fun, let's work out how big and bright each star would be from the planet, relative to the sun. I should note that this is a gas giant planet and so any possible light would be more likely to exist on one of its moons, not the planet. The suns would appear the same size from a moon, though.

First, how big would the suns appear? (See this post for details on the calculation.) Remember for comparison that the sun (and moon) have an angular diameter of about 0.5º. So, sizes:
  • Star A as seen from planet on average: 0.49º, so about the same as the sun
    •  Range: 0.43º to 0.59º
  • Star B as seen from planet on average: 0.18º, which is about a third of the diameter of the sun
    • Range: 0.15º to 0.21º
Now, how much light would reach the planet from the two suns? Or how brightly would the stars illuminate the planet? This is a slightly more complicated calculation which you can read about here (and for comparative purposes, about 1400 Joules of energy hit each square metre of the Earth from the sun each second). Remember, also, that sometimes star B will pass behind star A, sometimes they will appear next to each other and sometimes B will be in front of A, blocking out some of A's light but contributing its own. I'm just going to calculate them separately.
  • Star A: 410 Joules per square metre per second, which is a bit less than a third of the light energy the Earth gets from the sun. It is also going to be redder light, thanks to the cooler temperature of the star.
  • Star B: assuming its temperature is about 2500 K which is within the plausible range for M type stars (star A is K type, if you're curious), I get about 5 Joules. That's 3-4% of the light from the sun hitting Earth. On the other hand, it's still a lot brighter than the full moon in Earth's sky (and significantly redder). About 1400 times brighter, in fact. And about as bright as 260 100 Watt light bulbs at a distance of 10 m. Except it would probably feel dimmer thanks to the redness.
Finally, let's suppose that there is an Earth-like moon of this gas giant planet Kepler 16b. How warm would the suns make it? The calculations are discussed in this post on the habitable zone. Since most of the warming comes from star A, I'm going to ignore star B for this calculation. The average temperature I get is about 190 K which is about -85º C or -121ºF. So a little bit too cold for life, but not too hot, which is a harder problem to solve. Maybe throw in a bit of greenhouse warming and a lot of snow gear and you have yourself a snowball planet with two suns. Not just cold, but pretty cool.

And if you want to read more, here is a nice New Scientist article about it. And, below, a video from APOD:

Friday, October 21, 2011

Bunch of links, mostly outdated

First up, square Earth anyone? Forget realism, let's just have a think about what an Earthlike planet would be like if it were a cube. Puts me in mind of the planet builders in Hitchhikers' Guide to the Galaxy. Brought to you by Discovery News.

Second, the Planetary Habitability Laboratory talks about brightnesses of the various planets in the solar system and also of exoplanets. An interesting read, particularly if you enjoyed my old How Bright is the Night? post.

Martian moons eclipse the sun in these NASA photos from the Opportunity rover:
Credit: NASA/JPL/Cornell

Enceladus pics from Cassini. Enceladus is one of Saturn's moons, most famous for it's ice geysers.

Proposed space robot to cannibalise old satellites which have previously been boosted up to "graveyard" orbits. Many mentions of zombie satellites and grave robbing associated with this one ;-p . From New Scientist.

And finally, laser driven fusion in California. From New Scientist again.

Happy weekend, gentle readers!

Wednesday, October 19, 2011

Propulsion: Not just rocket science

Spaceships: something's gotta make them go. Even if you have made up a nice way of going faster than light -- wormholes, warpdrives, hyperspace, improbability drives -- there are going to be bits when your characters have to travel more mundanely. You can't go into orbit when you're travelling faster than light. Unless you happen to be inside the event horizon of a black hole, but then you have other problems.

This post is about relatively non-relativistic (yeah, I did that on purpose, so shoot me) methods of propulsion. To be used in local space only (or if you want to throw your characters into suspended animation or trap them on a generation ship, or something).


OK, it's pretty much mandatory that I start with rockets since they are what got us into space in the first place. Specifically chemical rockets, since the term has come to be used more broadly in some circles.

Space shuttle Endeavour taking off.
Credit: NASA
The basic premise is: set things on fire explosively, direct the explosion away from where you want to go, and conservation of momentum does the rest. Why conservation of momentum? In the greater scheme of the universe, momentum must be conserved. It cannot be created spontaneously and it cannot be destroyed. It's one of those immutable laws. So, the only way to move is by exchanging momentum with something else. Say you sit on a particularly good wheeled chair. If you throw your heavy, laptop-filled bag away in front of you, the chair will move backwards a bit. Assuming you were stationary to begin with, when you threw the bag, you imparted it with momentum. (Momentum, by the way, is just the product of mass and speed, nothing too mysterious.) But momentum has to be conserved, so to compensate, you and your chair moved backwards with momentum exactly equal and in the opposite direction to that of the bag. Of course, this example isn't perfect since the wheels of the chair are also slowed down through friction, but ideally, your mass plus the chairs mass, multiplied by how quickly you moved backwards, would be equal to the mass of the bag multiplied by the speed at which you threw it.

In a frictionless environment, such as space, throwing something as small as an apple (also, congrats on smuggling an apple onto your space station) would propel you backwards noticeably. This is what most fuels do, in essence. They throw something backwards as hard as they can so that they can go forwards.

Commonly, rockets (that take off from Earth) have two tanks, one filled with liquid oxygen and one with liquid hydrogen. When combined they react very quickly and exothermically* which leads to a rapid release of energy and water. Because water is what you get when you put a lot of hydrogen near a lot of oxygen. (Really, putting a lot of hydrogen near a little bit of oxygen also ends explosively.) And water is what you get when you burn hydrogen (and if you're wondering "burning" something is just a colloquial way of saying "oxidise rapidly" or "react with oxygen"). The good news is that launching rockets doesn't have a large carbon footprint (because no carbon is involved in the actual launch process); building them is another matter.

Back to the point, oxygen/hydrogen are used as propellants because they give off the most energy of any practical combination of chemicals. Somewhere, probably on the internet, I once came across a table of effectiveness of different fuels. I would love to link to it now, but that was several years ago and I could not find it again. The closest I got was this table in Wiki, which is more a table of different propulsion methods.

* Exothermic reactions are reactions that release energy. Conversely, endothermic reactions consume energy.

Ion drives

Ion drives are a term that gets bandied around in both science fiction and "future of science" type discussions every now and then. There are actually a few different ways to build an ion drive (see aforementioned table in Wiki for details). The basic premise is that instead of using a chemical reaction to push something out the back of the spacecraft, you use electric fields to push ions (atoms with either a positive or negative charge; positive one are being pushed out, usually) away from the spacecraft. (Which you might have ionised with a laser or similar.)

The main downside is that the accelerations generated are fairly low, so it would take a long time to get anywhere. Unlike chemical rockets, however, ion drives would generally take a lot longer to run out of fuel. It might also be possible to scoop up stray atoms from space, ionise those and use them as propellant (this part, completely untested right now; ion drives in principle have been constructed though). So, although you start off slowly, if you keep accelerating constantly over a long period of time, the ion drive could leave you with considerable speed by the time you arrive. On the other hand, now that I think about it, they probably wouldn't work for decelerating suddenly, nor for manoeuvring.

Really, ion drives are just another way of throwing things backwards to make you go faster.

To read more, go look at the NASA Deep Space 1 page, a mission powered by an ion drive.

Solar sails

Solar sails, on the other hand, work on a slightly different principle. Instead of bringing fuel along on the trip and throwing it out, a solar sail works, well, similarly to a sail on a boat. You throw your fuel at it to make it go forwards.

Just as wind pushes boats along by the sails, so does light push solar sails along.

Light can't push things! I hear you exclaim. (Or is that the sleep deprivation talking?) Actually, yes it can. Photons, particles of light, have a momentum associated with them. It is calculated a little differently to momentum for objects/particles which do have mass; instead of mass times velocity it's Planck's constant divided by wavelength (exactly why is a bit complicated. Quantum is involved).

So a solar sail works by "collecting" the momentum of the light that hits it. The source of that light could be the sun or it could be a giant laser. The advantage of the sun is that it's free, but the disadvantage is that sunlight is a little dilute from an Earth's distance away so the acceleration would be fairly slow. A laser would start off more concentrated and impart a lot more initial acceleration, but once the sail was out of range you'd be left with a giant laser and nothing to point it at. (I suppose some people wouldn't see this as a disadvantage.) Perhaps some combination of the two would be best, but in the real world, we're not up to that sort of testing.

Below is a picture (CGI sadly. I so wanted this to be a photo taken from the ISS or something) of NASA's NanoSail-D which they recently deployed. From memory, there was a bit of trouble getting the thing to unfurl properly (definitely can't launch with those sails fully extended) and then after a few days it magically worked. Here is more info from NASA.

NanoSail-D. Pic from NASA via APoD.

So there you have it, a few ways for your characters to travel mundanely, mainly within a system.

Wednesday, October 12, 2011


Rimmer from Red Dwarf. He went mad in his
astronavigation exam and wrote "I am a fish"
four hundred times. It's not actually that hard.
If you want to include space travel in your story, then at some point, some of your characters will need to know about navigating through space. Even if a computer/AI does the actual controlling of the ship, someone probably needs to know the basics. Unless, of course, you want all your characters to fail astronavigation (repeatedly) like Rimmer from Red Dwarf. Not to mention, computerfail is a common plot device.

To the stars and beyond*!

*Not actually very far beyond.

The Stars

The first, conceptually basic method is by looking at the positions of the stars. This is a bit different to sailors navigating by the stars.

The Earth rotates about its axis once ever 24 hours. That means over the course of a night, stars appear to move across the sky; the stars aren't actually moving, it's the planet. But if you know the time and where the stars should be at that time, you can use that information to navigate fairly accurately. Even if you don't have precise instruments, the Southern Cross or the North Star can point you in the general direction of south and north. (These two point to or are located close to the southern and northern celestial poles, respectively. The celestial poles are located along the line where the Earth's rotational axis extends into space. As stars move across the sky at night, they will appear to circle one of these points. Unless you're at the equator, in which case they will move straight from east to west.)

If you're in interstellar space, the rotation of the Earth is supremely irrelevant. However, if you know the exact locations (in the galaxy) of at least three stars and can measure their directions relative to you with precision, then you can use that information to triangulate your position.

The tri in "triangulate" gives you the hint that you only need three stars to be able to pinpoint your position but, because there's only so much accuracy with which directions can be measured, the more stars you use, the more accurately you can determine your location. Another good reason to have more than three reference stars is so that you (or, y'know, the computer) can still navigate when you're on the other side of the galaxy and can't see them any more.

As far as re-identifying stars goes, the spectra of normal regular stars are a bit unique. That is, the temperature of the star combined with the exact concentrations of various elements that make up the outer layers of a star are like a fingerprint and (usually) don't change very rapidly. So if you find yourself coming out of a mysterious wormhole, and you have a spectrograph on board, you could take some spectra, find enough reference stars and get the computer to work out your location for you. Yay.

(One final note: you would want a computer to take all the spectra and do the comparisons. Really, you would. I mean, the calculations of stellar positions are at least possible by hand but if you don't already know what stars you're looking at, there is no way you want to be comparing those squiggly lines by hand. Trust me on this.)

Astronavigation 101, unit 1: pass.

Speeding stars

OK, so what if you know more or less where you are, but you're not sure how fast you're going? First, I need to point out that speed is entirely relative. It is impossible to determine an absolute speed for anything. On Earth, we tend to measure speed relative to the ground or, sometimes, relative to the wind. However, the Earth is spinning and hurtling around the sun at about 30 km/s. The sun is, in turn, careening around the centre of the galaxy at about 220 km/s. The galaxy is streaking through space at about 550 km/s relative to the CMB (cosmic microwave background radiation).

And yet, here we sit in front of our computers/smartphones/iPads and (with the possible exception of those of you reading this on your phone on public transport) it feels like we're sitting still.

The moral of the story is that we can't feel speed. What we can feel when we're on a moving train, or taking off in an aeroplane, or in a car going around a corner is actually acceleration. And it's not just us, Einstein's equivalence principle tells us that (assuming there isn't some window for us to look out of) there is no possible way to tell the difference between sitting still and hurtling through space at eight hundred kilometres per second. We can make devices that detect acceleration (those of you who have ever had a smartphone or a camera change the LCD image when you turned it sideways have experienced this). What we can't do is build a device to determine absolute speed. Because speed is relative.

The good news is, there are lots of ways to determine speed if we can see where we're going. On a train, for example, you might look out the window and get an idea. In space, at reasonably non-relativistic speeds, the stars don't stream past you like they do in that old Windows screen-saver. The distances between them are so vast that they would not appear to be moving at all.

This is where your trusty spectrograph comes in handy again. All stars have some recognisable elements in them. Notably hydrogen, helium, maybe oxygen and carbon but depending on the star, these may not be present in sufficient quantities for our purposes. Every element has a unique set of emission/absorption lines. The wavelengths at which these lines are found are based on quantum mechanics and immutable. However, when you're moving towards or away from the source of the lines (ie, a star), the Doppler effect will come into play. The Doppler effect makes the wavelength of light that you (or your spectrograph) see appear to be slightly longer or slightly shorter, depending on whether you're moving away from or towards the source. So you can take a spectrum, compare the wavelength of the hydrogen (for example) lines with what they should be, then you can work out how fast you're moving relative to that star.

Incidentally, this wouldn't be a particularly tedious calculation to do by hand, assuming you had reference tables at hand and maybe some sort of (basic scientific) calculator. Also, if you remembered the equation.

So there you have it. Your characters can now work out where they are, and how fast they're going. Don't worry, though; they won't violate Heisenberg's uncertainty principle. They're not quantum particles. (And the uncertainty on the position will be too big.)

Astronavigation 101, unit 2: pass.

Friday, October 7, 2011

Winds of Change finally available for (online) purchase

As the title suggests, it is now possible to purchase Winds of Change, the latest Canberra Speculative Fiction Guild anthology, featuring my short story "Time Capsule". There is a PayPal/credit card button on the CSFG website here.

Table of contents and book trailer are also at that link, and I've blogged about them before here and here, respectively.

Wednesday, October 5, 2011

Let's talk seasons

Depending on where you live, you probably experience two or four seasons a year. Does this have to be the case on planets other than Earth? What causes Earth's seasons and what else might cause seasons on other planets? Read on!


Earth spins about an axis that runs approximately from the North Pole to the South Pole. It completes one rotation per day (and, indeed, a day is defined by the period of rotation). the degree of tilt of the axis never changes. This is because one of the fundamental laws of physics is that angular momentum must always be conserved. If the angle of tilt changed then the direction of the angular momentum would also change and this isn't possible without some sort of external influence (like an asteroid, which isn't quite something we want to happen).

What is this angle of tilt relative to? Well, it's the amount by which the axis of rotation differs from making a 90º angle with the plane of Earth's orbit around the sun. Hopefully the image below helps.

Nabbed from Wiki. Credit: Dennis Nilsson, NASA.
As I said, the tilt doesn't change, so for part of the year the northern hemisphere is more exposed to the sun and for another part of the year, six months later, the southern hemisphere is more exposed to the sun. In temperate climates, these periods of greater exposure are called summer while the periods of least exposure are called winter. The in-betweens, as I'm sure you're aware, are spring and autumn. Here is another diagram to illustrate this:
Light and heat from the sun is hitting more of the southern hemisphere than the northern hemisphere.
Hot and/or tropical regions, which tend to lie close to the equator, experience two seasons: the wet season and the dry season. Similarly, the other extremes of the planet, the poles, also experience two seasons: polar day and polar night. This is because during winter the sun never rises the poles and never sets during summer. Within the polar circle but away from the actual rotational poles, there will be a period of transition between the two seasons (of varying length, depending on distance from the poles).

The greater the axial tilt, the more pronounced the differences between summer and winter will be (see the bit about Uranus at the very end for a very extreme case).

OK, so axial tilt causes Earth's seasons. What else can cause seasons?

Near and Far

Another possible cause of seasons is an elliptical orbit. This occurs when for part of the year a planet is noticeably closer to its sun than for the rest of the year. So when the planet is physically closer to the sun, the whole planet experiences summer (not just one hemisphere). During the more distant part of its orbit, the whole planet would experience winter.

On Earth, key seasonal dates, such as the solstices and equinoxes, are defined by the length of daylight (shortest day/night of the year and equal day and night respectively). On a planet with an elliptic orbit the key dates would be defined by significant points in the orbit. The equivalent of the summer solstice would be the periastron, the point of the planet's closest approach to the star. The winter solstice would be replaced with the apoastron, the time when the planet is furthest from the sun.

An interesting thing to note is that, thanks to Kepler's second law, a planet will move more quickly in its orbit when it's closer to its star than when it's further away. (If you follow that wiki link, there's a nice little animation which sort of explains it.) The result is that summer on such a plane will be briefer than winter. The more eccentric (non-circular) the orbit, the greater the difference between the lengths of summer and winter (and the closer the planet will be to its sun during summer). Could make for an interesting cultural interpretation of the seasons.

Pulsing star?

Some stars vary their brightness. Cepheid variables, for example, pulse with a regular period (which can be anywhere from one day to a few months). Theoretically, this could induce a seasonal variation for any surrounding planets. However, there is a problem when it comes to life evolving on such a planet. These stars are unstable and won't last very long (on an astronomical scale) in their pulsing state. This makes it a bit more difficult to justify having an inhabited planet around them. Maybe a planet with a colony that's studying the star. Anything more natural probably wouldn't last or might not have enough time to have evolved (depending on the size of the star). Of course, there's no rule saying impending doom couldn't be central to a plot.

Wacky planets

Uranus is sideways. (Also, the rings aren't
really red, just coloured that way for emphasis
here.) Credit: Lawrence Sromovsky, (Univ.
Wisconsin-Madison), Keck Observatory.
via APOD
Uranus is an interesting case. It's axis of rotation lies almost in the plane of it's orbit. So for part of the year the south pole points directly towards the sun and part of the year the south pole points directly away from the sun. In between is a transition similar to the type of seasons Earth experiences, but with more extreme beginning and end.

Of course, Uranus is too large and with too dense an atmosphere to support life as we know it. However, it's possible that a rocky planet more suitable for human habitation could also have this kind of extreme tilt. Everywhere except on the equator there would be periods of multiple days of darkness. Even on the equator, polar summer and winter would be spent in perpetual twilight.

I suspect this sort of configuration could also cause interesting weather/climate issues, but I think that would depend a lot on the atmosphere as well. Could be problematic.

Tuesday, October 4, 2011

More on Terra Nova

I had a few comments on my last post (and a surprisingly large number of hits--who knew writing about something so topical would be so popular?). Although I addressed the questions in the comments section there, I'm not convinced anyone will see them, so I thought I'd repost and expand my responses here.

Stars, not moon

The first comment pointed out that geeky girl in Terra Nova blamed the expansion of the universe for the stars in the sky being in different places, not the moon. My mistake. She's still wrong, though. The stars we see in the sky are all part of the Milky Way and hence too close to be expanding away from us (or more accurately, because they are gravitationally bound to the galaxy). They would still look different 85 million years ago, however. This is because all these stars, including our sun, are orbiting the centre of the galaxy. It takes the sun about 250 million years to orbit the centre of the galaxy. Even in 85 million years it, and all the other stars, would have all orbited part way around and be in different positions. The sun would actually have moved about a third of the way around it's orbit, but different stars closer or further in have different circumferences and would appear to have gone further or less far around.

The second commenter also raised a good point about the characters remembering the constellations, though. If the parents were young when they last were able to see the moon, it seems unlikely that they would ever have seen the constellations. Perhaps geeky girl studied them in class? (The parents don't actually mention the stars, just that the moon looks different and that they were young last time they saw it.)

Runaway moon?

The commenter two asked how, if the moon is moving away from us by 2 cm a year, has it not moved too far away by now?

Laser Ranging Retro Reflector, used to measure the exact distance
between Earth and moon, and how much this distance is changing.
Deployed by Apollo 14 astronauts.
Credit: NASA Johnson Space Center (NASA-JSC)
First, let me say that from bouncing lasers off reflectors left on the moon by Apollo astronauts, we know that right now the moon is moving 3.8 cm away per year. However, various theories suggest that the moon was moving away at different rates in the past. This makes sense since the Earth's gravitational influence becomes weaker as the moon moves further away, and because things like ice-ages would influence how much water was available for tidally sloshing around and influencing the moon.

In Terra Nova, the girl actually says the moon is moving away half a centimetre a year. I chose 2 cm when explaining it by accident, but it turns out this is roughly what palaeontological estimates predict the average may have been over that time (link and citations within).

A recession of 2 cm a year over 85 million years gives us a moon less than 2000 km closer 85 million years ago. Given that the moon varies more than that as it moves through closer (perigee) and further away (apogee) parts of its orbit now (at perigee it appears about 15% larger than at apogee), the real question is would the moon really be that noticeably bigger? If you're keen, you can use what I wrote in this blog post to work it out.

Of course, it might be. We only have theories and models for how the moon's rate of recession changes. But even using the present-day value of 3.8 cm/year, it would still only be 3200 km close 85 million years ago, which is less than a percent closer on average.

Saturday, October 1, 2011

Eureka & Terra Nova pilots: Sciencefail rant

You know what I really hate? Big budget productions with characters who are supposed to be geeky/nerdy/knowledgeable that say things that are wrong. When you have spent piles of money on special effects, isn't it in your best interests to make sure the dialogue isn't made of fail? As I'm sure you've probably guessed, this really annoys me. And, unfortunately, I've come across two pilot TV episodes in as many days that had a "smart" character explain something erroneously (where the fact it was an error wasn't part of the plot).


First up was Terra Nova, a show where colonists from a over-polluted future travel back in time 85 million years to where the air is fresh and dinosaurs roam the Earth. One of the important characters is a geeky girl whose main function so far has been to explain backstory in a sciencey and geeky way. Fine.

The moon looked bigger 85 million years ago because it was closer to the Earth. True story.
(Screen capture from pilot of Terra Nova.)
So back in 85 million years ago, they look up at the night sky and are amazed to see the moon because in their time the sky is too smoggy. The one of the parents says something like, "Was it always this big?" And geeky girl answers, "No, it moves two centimetres further from the Earth each year." So far so good. But then she says that it's because of the expansion of the universe.

That was when I died a little bit inside. The expansion of the universe is a large scale effect. Over cosmologically small distances gravity dominates. Like a lot. I touched on this in one of my galaxy posts when I said that the Milky Way and Andromeda will eventually merge. Basically, yes the universe is expanding, but it's only really far away things that are moving away from us. Even the nearby galaxies are being pulled gravitationally closer to us. Galaxies are made up of stars. Stars have planets around them and planets have moons. Our moon is much to close to the Earth for the expansion of the universe to pull it away.

So what is really causing the moon to drift away? Tidal forces, something else I've mentioned in the past. The moon causes tides on Earth by pulling water in the oceans towards it slightly, making it bulge out (and a bulge also forms on the opposite side to balance it). However, the Earth is rotating faster than the moon is orbiting it, so the bulge gets dragged along with the ground as it spins and in turn exerts a slightly different gravitational pull on the moon, pulling it forwards along its orbit. This causes an angular momentum exchange between Earth and moon--the Earth's rotation is slowing down and the moon's orbit is becoming wider (it's actually moving more slowly though...). Fun fact, that means tides would have been a bit higher back in the day, too.

There you have it. 85 million years ago, the moon was closer to the Earth because it hadn't had as much time to steal angular momentum from the Earth and hence widen its orbit. It has nothing to do with with the expansion of the universe.

Speaking of the expanding universe...

In the beginning there was the big bang. We don't know what caused it and for the purposes of my next rant, it doesn't really matter. At one point, everything was in the same place. Then it exploded.

I am going to digress slightly and talk about everyday explosions. (Well, hopefully things don't explode in your everyday life, but you know what I mean.) When something explodes, for simplicity let's say a bomb, then a sudden burst of energy--be it chemical or nuclear--pushes the material of the bomb (the outer casing or what have you) away from the centre. Depending on location and conditions, this material will fly through the air or water or whatever. In this sense, the big bang wasn't an explosion.

Matter, the stuff the universe is made of, did not explode out from a single location. It did not explode into anything because the universe is everything. There is nothing physically accessible outside it (M-brane theory notwithstanding). A common metaphor is this: imagine an un-inflated balloon with a bunch of galaxy clusters stuck onto its surface. The balloon part of the balloon is the universe. When you inflate it, the universe-balloon stretches and the galaxy clusters all move further away from each other. It's the space between the clusters that's expanding. You could make the balloon very small in its un-inflated form to get everything coming from one point. Then, at that point, everything was in the same place; all the space was together at the origin. Then it expanded. There is no single point that was once the origin, all the points were at the origin.

Imagine my frustration, then, when a genius scientist in the pilot episode of Eureka is looking for the origin point of the universe. It made me very angry. The fact that the MacGuffin of the plot hinged on his research was also a bit annoying. That he was trying to use an optical telescope to look for the beginning of the universe is just hilariously ridiculous (he would need to use very long wavelength radio waves, not visible light to do that--but I'll write a proper blog post about telescopes some time soon). It also really, really didn't help that the genius in question was a massively arrogant prick, but would it have killed the writers to make him a scientifically accurate prick? That would have mitigated my annoyance somewhat (not that much because the show is more sexist than it should be, but that's not a rant for this blog).

The moral of the story

If you don't take the time to get someone to check your facts (or if you do--and I know many Hollywood studios do--and then ignore the expert), you will piss geeks off. If you are making science fiction and geeks are a chuck of your target audience, why would you want to annoy them?

(And if you're wondering, I did actually like Terra Nova, it was just one line that irritated me. Eureka on the other hand, continued to annoy me with episode 2, even if irritating scientist prick wasn't in it.)

End rant.

PS You can read a bit more about the Terra Nova part of this (with more science and slightly less rant) in this post.


Related Posts Plugin for WordPress, Blogger...