Astroquizzical is one year old today!
Thanks to everyone who has read along, both old and new, and my particular thanks to all of you who have submitted your questions!
Here’s to many more questions and answers to come!
Astroquizzical is one year old today!
Thanks to everyone who has read along, both old and new, and my particular thanks to all of you who have submitted your questions!
Here’s to many more questions and answers to come!
What kinds of meteorites are there?
Unlike the shooting stars we see in meteor showers, which burn up entirely in our atmosphere, meteorites are the fragments we find that have made it all the way down to the ground. Like anything that enters our atmosphere, meteorites have also been burned by the friction of our air, which means that the pieces that we find are only a fraction of the original object; the rest of it was burnt up as a colourful vapor in our sky, like the pieces of grit that make up a meteor shower.
Meteorites are usually made of a combination of one of two substances: rock, or iron. With the infinite inventiveness of astronomers, we duly called them stony, iron, or stony-iron, if they’re a relatively even blend of the two. Stony meteorites can (and often do) contain some small fraction of iron, but only those meteorites which are almost entirely metal are classified as iron meteorites. The vast majority - over 90% - of meteorites that fall to earth are stony, leaving less than 10% of all meteorites as primarily iron. However, the iron ones are a little more well known, and that’s because for a long time, the iron ones were much easier to identify as meteorites.
Stony meteorites look like stones (see the picture just below), so unless you know exactly what you’re looking for, they can be hard to spot. In certain parts of the world, they can be a little easier to pick out - the deserts of Africa or the high deserts of Chile will let unusual-looking rocks stand out a little more. The best place to look for stony meteorites, however, is the glaciers of Antarctica. The ice there is so old and so slow-moving that meteorites that fall there will stay put for a long time. Meteorites are also quite easy to spot there, since anything dark will stand out for miles against the white ice.
That said, even though they look like one of many other stones on our planet, they are still fantastically interesting to scientists. Some of these stony meteorites are some of the oldest untouched rocks in the solar system, and they give us a sense of what the early solar system was made of and how it built itself up.
We also have some stony meteorites which have been blasted off of other worlds. In particular, we have a little collection of about 30 different meteorites which were originally part of Mars, one of which is shown just below. These are chunks of the surface of Mars which were flung so far away from the surface after another impact that they never fell back to the surface, and wandered the solar system until they encountered the Earth. These martian meteorites tend to be much younger than the rest, and are composed of a different set of elements and minerals, so we can pick them out without too much trouble.
Iron meteorites are much easier to spot than the stony ones. This is partially because it’s relatively unusual to find weathered chunks of iron sitting on the ground, so they are more easily recognized as out of place. As with the stony meteorites, they are most easily found in deserts and in the glaciers of Antarctica, where they are likely to stand out more starkly from their background, but they can also be relatively easily picked out in other places. Iron meteorites don’t wear down as much by erosion as the stony ones do, so they’re also more likely to stay around for a longer period of time. The iron meteorites are not actually completely made of iron, but contain a significant fraction of nickel, and this blend of metals is part of what makes them unique.
This one has been sliced in half and polished to show off the metal crystals inside it - but without this extra treatment, they look much less dramatic.
Opportunity, one of our Mars rovers, discovered a basketball-sized iron meteorite on Mars in 2005, which people got very excited about. The discovery of that meteorite was the first time we’d found a meteorite on a planet other than our own. This is much more what iron meteorites tend to look like before being sliced in half.
Iron meteorites and stony meteorites also tend to behave a little differently as they come through the atmosphere. Stony ones tend to be a little more fragile against the force of the atmosphere, and as a result, they can shatter more easily before they hit the ground. Iron meteorites are a little more resilient; heating up the outer layers of a metal lump doesn’t create enough stress to fracture them the way the stony ones would.
The Chelyabinsk meteor that exploded over Russia a little over a year ago also left behind some pieces for us to examine; the largest of the pieces were extracted out of a lake. One of the confirmed pieces is shown at the top. The meteorite pieces confirmed that the object that came through our atmosphere was a stony type meteor. It had already been suspected of being stony since it had exploded so brilliantly in the air.
Both iron and stony meteorites give us a fascinating look at the early solar system, and help us to understand how the planets formed and when, so finding more and more meteorites helps us to understand the variety that was present when the planets were first being formed.
Thanks for your patience while my thesis was being completed, everyone!
This is a quick announcement to say that your Astroquizzical astronomer is currently in the final stages of writing a Ph.D thesis and as a result, posts may be a little more sporadic than usual.
Please continue to send in your questions! I will get to them all as promptly as I can. As always, questions can be submitted anonymously through the sidebar, the ask page, or less anonymously through Facebook or twitter!
Thank you for continuing to make Astroquizzical a success!
If we were trying to reach out to somewhere outside of our universe, what would our overall universal address be? The closest I’ve come is this: (personal address), state. USA North America, Earth, Solar System, Global Cluster, Milky Way, Local Group, Virgo Cluster.
This is a surprisingly tricky thing to work out, but the difficulty lies in being able to locate ourselves in three dimensions on large scales more than anything else.
Your addressing scheme (as far as you’ve written it) is pretty accurate up to the Virgo supercluster, which itself is really a conglomeration of other clusters, both small and large, shown above. (This is distinct from the Virgo Cluster, which is about 65 million light years away from our local group.) But that address would really only help people if they know where to look for the Virgo supercluster. The next step up from the supercluster is a loose affiliation of other superclusters, so if you could get everyone in that supercluster affiliation to look at the right supercluster, they might be able to zoom in from there and find us using your address.
We have dealt with this problem on a much smaller scale before. Both the Pioneer and Voyager spacecrafts tried to relay our position in the unlikely event that they were ever encountered and picked up by another intelligent race of beings. The Pioneer plaque showed the location of our planet within our solar system, but it (and the Voyager Golden record) also gave a map that would be useful to someone else within our galaxy. The set of lines radiating out from a single point on the left hand side of the Pioneer plaque and the Voyager record is this map. This gives the positions and frequencies of a set of pulsars - incredibly rapidly spinning objects that beam light out into the cosmos like a lighthouse. Each pulsar has its own unique frequency - the number of times per second it flashes in our direction. Pointing out the distances and frequencies of 14 pulsars, as we’ve done here, should allow someone else, observing the same set of pulsars, to triangulate our position.
However, this can only be scaled up so far. If you’re trying to tell someone outside our universe where we are - or really, anyone sufficiently far away in our own universe - you swiftly become tangled in a different problem, which is that the more distant from our planet you would like to map out for our faraway friends, the more you travel back in time. At some “distance” from our planet, our exploration becomes one much more of time than of space. Even just the Virgo supercluster (a tiny corner of the universe) is some 110 million light years across. Undoubtably, between light leaving that side of the cluster and our receiving it, things have changed over there in the intervening 100 million years. If our visitor happened to be at a 90 degree angle to the line that connects us to the other side of the cluster we observe, they would receive light from both of us at the same time. This means that particular observer wouldn’t have the same time delay that we observe between our current time and the time that light left the other side of the cluster. They would have a different, but equal, delay on their observation of both of us. They might see a structure that looks a little different from the way we understand it, as a result.
This becomes an increasingly disruptive problem the further back in time we go. At some point, we are looking at structures and objects that no longer exist. Many things can happen in a couple billion years, and they usually do, so using those objects on our map isn’t very useful for an inter-universe traveller.
So what can we use as a universal reference frame? Unfortunately, one of the fundamentals tenets of cosmology tells us that there are no “preferred” or “special” perspectives on the universe. This means that there’s no overall zero point everyone can agree on, which makes it difficult to give directions. I’ve talked about this total lack of a universe-wise reference frame once before, and there’s no easy solution at hand.
The best thing we may be able to do right now is to create a really good map of our little local set of superclusters, and tell our visitors to stop by if they happen to see something that matches it in their travels.
Is it possible that maybe dark matter may be the reason why there is gravity? That is, the more mass takes its place, the more it tends to squeeze mass therefore creating gravity? If so, can we invent something that contracts this dark matter by making it think that there is something very heavy then release it so that we skip a portion of space and keep repeating the process to reach a consistent speed?
With regards to fast travel, you’re actually not that far off from something that was proposed in 2011 by NASA employee Harold White!
It seems there’s a bit of confusion about dark matter and gravity, though. The phenomenon we call gravity is really just a distortion of space and time. Both dark matter and regular matter interact in the same way with space; the more of it there is, the more space bends. Dark matter is five times as plentiful but impossible to observe directly, so we have less of an intuitive grasp on it. But both dark and regular matter warp space, and the more heavily distorted space is, the ‘stronger’ the gravitational pull is. It’s true that in places with a lot of dark matter, you also tend to collect normal matter (this is how we think galaxies begin to form). And while collecting a little bit of normal matter will increase the overall amount of mass in a given region, thereby deepening the pucker in space we’re looking at, neither the dark matter nor the regular matter are responsible for ‘causing’ gravity. The combination of both forms of matter are responsible for causing the distortion in space and time that causes things to feel a gravitational pull.
As far as we know, we can’t make dark matter do much of anything, since it seems to only interact with other things in the universe through its disturbing affect on space (i.e., via gravity). However, what you’re after with your proposed method of travel is, fundamentally, a way to distort space, compressing the part in front of you, and releasing it once you’re past. This is precisely what every proposed (mathematically plausible) warp drive is trying to achieve. Since you create an expansion of space behind you, as the image above shows, you can almost surf space-time on an artificial distortion.
The main distinction is that instead of proposing to bend space by moving heavy objects around, it’s more efficient to bend space using the energy equivalent of that mass. Space does not like to bend, and the math used to predict how much energy this would require had always indicated that you would need to convert a mass the size of Jupiter entirely into energy in order to make it work. (Jupiter, for the record, is 317 times the mass of the earth, which weighs it in at 1.9 x 10^27 kilograms.) Hauling Jupiter masses around with your spacecraft is hugely unfeasible, so this idea had been mostly discarded. This is why people got very excited about Dr. White’s modification to the math in 2011. He found that changing the geometry of the bubble of surfable space would drop the energy required to force the distortion by factors of many thousands and into the range of plausibility. He’s currently trying to design a miniature version in the lab to make sure that his idea can work at small scales.
For the moment, even Dr. White’s model is still science fiction. Even if it does work, there may be other tangles to work out - a few theoretical physicists have worked out that this kind of travel might trap high energy particles inside the warp bubble, releasing them outwards in a potential death ray when you arrive at your destination - not quite ideal.
Does the sun cast shadows on itself?
You can try this one at home. Get an incandescent light bulb, switch it on, and try to use the light from the bulb to cast a shadow on the bulb.
The problem you’ll run into is that every point on the surface of the light bulb is actively producing light, and in order to form a shadow, you need the surface to be dark, blocked from the light. It’s easy for a bulb or a star to cast shadows outwards; simply place a solid object at some distance from the light. A piece of paper or your hand will suffice for a light bulb; something on the opposite side of your hand will be deprived of the light from the bulb.
The shadow casters around stars tend to be planets and moons. Solar eclipses are the most dramatic proof of this. If you stick the Moon in the way of the Sun, some parts of our planet will be placed in the shadow of the moon. Lunar eclipses, show us the colour of the Moon when it travels through the shadow of the Earth. Like shading your eyes from the sun with your hand (yet another way of forming a shadow around our star), the Earth blocks the light travelling towards the Moon, plunging it into darkness.
Because every point on the Sun’s surface is glowing with light, there’s no way to deprive it of light by casting a shadow. Even if you put another source of light near the surface of the sun (for instance, a glowing filament as shown above), it doesn’t change the fact that the main surface of the sun is still glowing. Any attempt to put an object between the filament and the surface of the sun in order to cast a shadow would simply result in both sides of the object being illuminated! And very likely, said object would subsequent vaporize, given the 5500 degree Celsius temperatures near the surface of the sun.
Can light exist without darkness?
To the great dismay of the great existentialist thinkers, scientifically speaking, this is not that difficult a question to tackle.
From a physics perspective, “light” is just a series of particles zooming through space, a little beam of radiation heading outwards in the cosmos. An individual particle of light usually doesn’t care whether it’s surrounded by lots of other photons, or whether it is off on its own in the universe, travelling a unique path.
Darkness is usually described simply as the absence of light; this description also works pretty well as a physical description. By this standard, “light” and “darkness” are just a binary toggle between “radiation” or “not radiation”.
The question here is asking if you can have only radiation - only light - and skip the “no radiation” part entirely. If you remove darkness, could you still have light? If you’re thinking about darkness and light in terms of a yes/no toggle, then this is perfectly possible. You just hold the toggle at “yes” at all times. The individual light particles won’t care that they’re not letting “not radiation” not have its times - they’re simply travelling forwards.
The ways that our universe produces light are also independent on a lack of light nearby. Stars form light as a byproduct of the incredible pressures at their centers, and are most often formed in clusters - with tens to hundreds of other stars forming nearby. New stars only unveil themselves to our eyes by using the light they give off to burn away the dust and gas that hid them in darkness.
There are two major reasons for darkness in the universe. The first is to be in shadow. The physical blocking of light by an object is an easy way to be in darkness. That’s all night is on Earth, after all - you’re in the shadow of the planet. The second is that the universe hasn’t existed for an infinite amount of time. If the universe had already existed for an infinite amount of time, our skies would be brilliant with light both day and night, as the light from every star in the universe streamed towards us, brightening our skies. In that case, the only sources of darkness would be the shadows.
In that universe, perhaps we would be asking the question the other way around - is there any darkness without the light?
How are gamma ray jets being generated from black holes?
There are two ways to create gamma rays from a black hole, and the two are distinguished by the size of black hole that creates them. The first is called a Gamma Ray Burst, and is sometimes formed during the creation of a “stellar mass” black hole, as a star collapses at the end of its life. Gamma Ray Bursts are the most intense bursts of gamma radiation in the universe, but are pretty rare and therefore hard to spot. These bursts happens over the period of less than a minute - incredibly short, especially given the lengthy timescales that astronomy usually operates on. They are created during what’s called a hypernova - the amped up cousin of a supernova, where the original star is at least 15 times the mass of our sun. In addition to the high mass of the star, in order to get the gamma rays out, you also need to have the star rapidly rotating before it explodes & collapses.
The second way that black holes can produce gamma radiation is via objects we call quasars - an abbreviated form of a “quasi-stellar object”. This is a remnant from the days in which we kept finding these super bright, point-like objects (like stars) but had really bizarre spectra (definitely not like stars). They were dubbed “quasi-stellar” in nature due to them looking like a star, but not behaving like a star. We now believe that quasars are the signature of supermassive black holes at the centers of galaxies that are currently attempting to grow by inefficiently pulling in material from a rapidly spinning disk of material that surrounds the black hole.
The formation of gamma rays in both Gamma Ray Bursts and in quasars occurs in a very similar manner. For a Gamma Ray Burst, the rapid rotation of the dying star twists up the magnetic field of the dying star, and means that the easiest means of escape for any of the particles being produced in the supernova is along a very narrow ‘beam’ at the poles of rotation, since the magnetic field can’t get as tangled in that direction. However, many of the particles being given off are electrons, not photons; getting from a beam of electrons to a beam of gamma ray photons requires a few transfers of energy. There are a couple of ways of doing this. One method of energy transfer happens when electrons travel along the untangled magnetic field lines extending outwards along the beam. The magnetic field causes the electrons to travel in a helix, as though they were tracing the path of an extremely long spiral staircase. These spiraling electrons give off high energy particles of light; if the electrons are moving fast enough, they can spit out gamma rays. The other way you can create gamma ray photons is more straightforward: via collision. If you take a extremely speedy electron and crash it into a photon, the photon can gain enough energy to become a gamma wave. The end result of both of these processes is a pencil beam of gamma radiation speeding outward in two jets at the north and south poles of the spinning star. These jets are only stable for a few tens of seconds before the black hole forms, and they vanish.
Getting gamma radiation out of a quasar happens in a very similar way to the Gamma Ray Burst. We believe there must be a magnetic field surrounding the disk of material surrounding the black hole (called the accretion disk), and this disk must be rapidly rotating. The black hole itself may also be rapidly spinning, but that depends on which theoretical physicist you speak to. The rapid spin of the accretion disk, in combination with the magnetic field, produces jets, which can accelerate particles (again, largely electrons) all the way up to gamma ray energies. These quasar jets, in contrast to those produced by Gamma Ray Bursts, are very stable, and can reach lengths of hundreds of thousands of light years. If we are able to spot them, it means that that quasar just so happened to have been aimed in our direction as it shot a bright beam of light across the cosmos.
Does life exist in other planets?
We can’t think of a single good reason why it shouldn’t, if the conditions are right!
The hardest part is getting the right conditions. On Earth, the biggest requirement for life is water. Our planet is very good at growing things in every possible location, so long as it’s near or in liquid water. Life arose extremely quickly after the formation of the earth, which seems to indicate that if once the Earth had a surface with liquid water on it, there were not a lot of other stumbling blocks to overcome before life could spring forth.
Having liquid water usually means that the planet has to be in a relatively narrow distance window away from its star, and have a surface upon which the water can rest. Effectively, we need rocky planets at exactly the right distance from the sun such that all the water doesn’t freeze solid or evaporate away. Outside of that distance band in a solar system which allows for liquid water, there are precious few opportunities for liquid water to exist, except in unusual cases like Enceladus, a moon of Saturn, and Europa, a moon of Jupiter. Both of these moons are thought to have an ocean of liquid water under their icy surfaces. These small moons can maintain liquid water because the tidal forces from the massive planets they orbit are constantly stretching the rock at the cores of the moons. This stretching heats up the rock, and that heating provides the energy required to maintain liquid water, even though these moons are far too distant from the sun to keep liquid water on their surfaces. As a result, planetary scientists are very excited about the prospect of being able to find life on Europa and Enceladus, but in order to go check, we’ll have to send a craft to those moons to look directly.
Also within our solar system, we are currently looking for evidence that life once existed on Mars. The information coming back from our Mars rovers tells us that Mars was once warmer and wetter than it is now, which means that it should have been a good place for life, back when it was able to hold liquid water. However, since Mars has become very cold over the years, we don’t expect to find evidence of life currently thriving there.
Looking for planets outside our solar system becomes much more difficult than looking within it; for starters, it’s much more difficult to find the planets to start with. We then need to filter out only the ones that fall within this magic range of distances from their star where liquid water can exist. The technology to find rocky planets in the liquid water zone has only recently been developed. These planets are extremely hard to detect, and push the boundaries of the sensitivity of our telescopes. The Kepler satellite has begun to push into this realm of extrasolar planets, and the massive amount of data it took before the end of its mission is still being analyzed. It seems, from the data that’s been studied so far, that about 20% of all stars like our sun have a planet around it like the Earth - a rocky planet near enough to the star to have liquid water.
Proving that liquid water does in fact exist on those planets is more difficult still - you have to detect the signature of water in the atmosphere of a planet that is light years away. Proving the existence of life will be an even more difficult task, but once we begin to find lots of planets with liquid water on their surfaces, the odds are pretty good that one of them will contain life of some form. It will be much easier to search for life within our own solar system, since we can actually go to these places and see what’s there directly.
No matter where it might be - the search is on.
Could you see a spaceship or station in orbit by day, if it were the size of an aircraft carrier?
In order to figure this out, we need to know the size of an aircraft carrier, how much light it would reflect, and have something to compare it to.
Going in order - the largest aircraft carrier I can find is technically a supercarrier, and measures 77 meters wide by 333 meters long. This gives us a reflecting area of 25641 square meters (2.56 square kilometers - this thing is massive).
In order to know how much light it would reflect, we have to know what it would be made of - on earth a lot of our marine craft are made of steel, which reflects 58% of the visible light that hits it. However, spacecraft don’t need to follow ocean rules exactly, so I’ve also considered the amount of light reflected off of aluminum, which is one of the most reflective metals out there; it reflects 91% of the light that hits it.
So, now to compare to something concrete. Fortunately, we have a space station to compare to - the International Space Station. The ISS is 72 meters wide and 108 meters across, which gives it a total surface area of roughly 7776 square meters, or 0.7 square kilometers. Comparing this to the surface area of the supercarrier, we find that the supercarrier is 3.3 times larger in reflecting area.
However, this doesn’t mean that the supercarrier is automatically 3.3 times brighter, since we haven’t taken into account how much light the ISS reflects relative to how much our supercarrier reflects. The ISS is designed to reflect as much light as possible, in order to try and best insulate the space station. The space station, on average, reflects about 90% of the visible light that hits it - the solar panels are slightly less reflective than the main body of the station, since they’re trying to absorb sunlight to power the station.
We’re going to want to compare the brightness of the ISS to the brightness of an object made of a different material, so we need to scale the brightness of the ISS by the fraction of light that’s reflected off of steel and aluminum. Aluminum reflects 91% of the light that hits it - the ISS reflects 90%: supercarrier divided by ISS will give us how much brighter (or fainter) aluminum is when compared to what the ISS is made of. These numbers are almost the same, so we should expect this factor to be almost exactly one, and it is: 1.01. Steel reflects much less light than aluminum, so we find that a steel space station would be only 64% as reflective as the ISS.
Now we can scale the brightness of the ISS by both reflectivity and size - for steel, we find that an object 3.3 times larger, but 64% as reflective gives us an object that reflects 2.12 times the amount of light that the ISS does. For an aluminum spacecraft, it would reflect 3.36 times the amount of light that the ISS reflects.
What does this mean in terms of visibility? A spacecraft the size of a supercarrier would be easily visible at night - it’s between 4.8 times (steel) and 7.7 times (aluminum) as bright as Venus. It would appear as an extremely bright star moving relatively quickly through the night sky. It’s also above the visibility threshold for daytime viewing. You can see Venus in the day if you know where to look, and since the supercarrier would be at least four times as bright as Venus, you should be able to spot the space craft during the day as well. However, it’s nowhere near as bright as the sun or the moon, so it wouldn’t necessarily stand out if you weren’t already looking for it.
Is there a universal addressing scheme for the universe? (e.g. Quadrants… etc.) If so, what is the central reference point, or zero?
We’ve come up with a few different coordinate systems for the Universe, but none of them are really “universal”. By that, I mean that you wouldn’t be able to use them no matter where you are in the universe - most of them only work conveniently from Earth.
Starting small, we’ve got one coordinate system to describe our solar system, with our sun at the center. This coordinate system is easiest to visualize as if you had a birds eye view of our solar system, watching all the planets go around the sun. Every coordinate system needs three coordinates to describe a location - normally we think of up/down, right/left, and forward/back. The three coordinates here are distance outwards from the sun (in any direction), the position of the object in a circle around the sun at that distance (usually measured as an angle from a line drawn from the position of the Earth in September to the sun), and distance away from the plane described by the orbits of the planets. Perhaps unsurprisingly, this is only really a useful coordinate system for objects in our solar system.
We also have a galactic coordinate system, which is not centered on the center of the galaxy as you might expect, but instead, it’s still centered on the location of the sun. The second coordinate here is the distance “up” out of the disk of the Milky Way, and the third is distance from the sun once again. The disk of the Milky Way is not in line with the disk of our solar system, which you can spot if you go outside in a dark sky. The Milky Way usually goes North-South in the sky, and all the planets (and the moon) will always be found in a line that goes East-West. This coordinate system is generally considered to be confusing to work with, and is mostly not used, unless you’re trying to map the Milky Way itself.
By and large, what astronomers use to describe the locations of things in the sky is actually a projection of the Earth’s latitude and longitude lines onto the sky. Take the line between the north and south poles, and extend them out into the sky - those are the northern and southern celestial poles. (The north celestial pole points almost exactly to the North Star.) The equator, expanded outwards in a plane from the surface of the earth, describes the Celestial Equator. The units we then use to describe the positions of objects are right ascension, declination, and distance (if we have it). Declination is similar to latitude - it describes the angle above or below the celestial equator. Right Ascension is like longitude, but instead of being measured in degrees, is measured in hours, minutes, and seconds. We do this because we know how fast the earth rotates - 360 degrees in 24 hours. This means that the earth rotates through 15 degrees in an hour, and we can easily tell how long we need to wait for another object to be overhead. If an object at the 0 hour coordinate is overhead right now, objects at the 3 hour line will be overhead in three hours. This coordinate doesn’t tell you anything about the absolute position of an object in the Universe, but it’s very good at describing where that object appears to be placed in the sky.
Using the earth as the zero point starts to make more sense once you start looking at things that are very far away, because at that point, you start looking increasingly far back in time. Looking very far away in the universe is looking backwards through shells of time, and since we are observing from Earth, those shells are by definition centered on the Earth - the objects that we see as five billion years old are being viewed at that age because it took light that long to get here. The speed of light is the same in every direction, so you’ll see the same age in every direction at that distance, from the perspective of the Earth. This would be true of anyone observing from anywhere in the universe, but they might see a slightly different set of galaxies.
Because we only have coordinate systems that are centered on the earth or the sun, if you were elsewhere in the galaxy, or elsewhere in the universe, you’d have to constantly convert your location into where you would appear to be (from the perspective of the earth or the sun) if you wanted to use one of these systems. I suspect that whenever we do start exploring outside our solar system, we will come up with another coordinate system that’s convenient for keeping track of our spacecraft, but we’ll keep all the old ones we’ve come up with “for historical reasons”.
Have your own question? Something here unclear? Feel free to ask! Or submit your questions via the sidebar, Facebook, or twitter. Astroquizzical is now also on Google+, if you’re a Google+ person.
How hot are brown dwarf stars when they are burning deuterium?
A few definitions are in order!
Deuterium is hydrogen, plus a neutron. Most hydrogen in the universe, and on Earth, is one proton, one electron, and no neutrons. It’s the simplest atom out there, and hydrogen in this form is the most abundant atom in the universe. Deuterium, with its one proton, one electron, and one neutron, is much less common than its simpler counterpart - it’s only 0.016% of all the hydrogen out there. That’s approximately 160 atoms of deuterium for every million standard hydrogen atoms.
The other fun fact about deuterium is that it’s effectively not produced by any ongoing natural process. Stars don’t create it - in fact, they actively destroy deuterium. So, we think all the deuterium in the universe was created in the Big Bang, and we’ve been slowly eating away at it ever since.
Brown dwarfs, meanwhile, are little balls of gas that didn’t quite make it to being a star. They don’t have enough mass to create the temperatures and pressures in their cores needed to start burning hydrogen the way our sun does. Brown dwarfs are typically so much smaller than the rest of the stars in the universe that instead of being weighed in units of “stellar masses”, which are multiples of or fractions of the mass of our sun, we use “Jupiter masses”. Brown dwarfs tend to come in somewhere between 13 times the mass of Jupiter and about 83 times the mass of Jupiter. The upper limit here is the mass required to ignite hydrogen burning - in different units, this is 0.08 times the mass of the sun. The lower mass limit is a bit fuzzier, and that’s when you tend to run into the issue of “Is this a really large planet or is it a star”, particularly if it’s hanging around another star that is much larger than it is. You can have brown dwarfs that are smaller than 13 Jupiter masses, and planets larger than 13 Jupiter masses - it depends what’s going on inside of the object.
By definition, brown dwarfs can’t burn hydrogen, but it turns out that they can burn deuterium. Deuterium burns at lower temperatures and pressures, so if the brown dwarf is above the 13 Jupiter-mass cutoff, the internal pressure of a brown dwarf can trigger the start of deuterium burning. The temperature at which this happens is about 10^6 Kelvin - one million degrees. Keep in mind that this is the temperature at the very core of the star, not at the surface! By the time you get to the surface of the star, you’re down to somewhere between 2000 degrees Kelvin and 750 degrees Kelvin, depending on the size of your brown dwarf.
Remember that there are still only 160 atoms of deuterium per million atoms of hydrogen - these brown dwarfs are made of this same mixture. This means of course, that there is not a lot of deuterium around in the star to be burned. Most brown dwarfs race through their deuterium in about 100 million years - a flash, in cosmic time. (By comparison, our sun will be stable for about 8 billion years.) Once the star has burned all the deuterium it can reach, it’s burning days are over. The heat it built up through burning deuterium will slowly fade away, and the dwarf will truly be a “failed star”.
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What would happen to a cat’s hair in space?
Back in the early days of the space program, every country who was developing rockets to send up to space needed to test the survivability of those rockets. Instead of sending up people right at the start, pretty much every country in the space racer was sending up animals as a lower-risk alternative. There were a couple of cats sent up to space, but dogs and monkeys were preferred, generally because they could be better trained than cats. The French sent a cat called Félicette into low orbit on October 18th, 1963; Félicette had a successful 10 minute flight (5 minutes of which were without gravity) and survived her round trip.
Cats, in general, do not like zero gravity, as this video from the Air Force of yesteryear proves. They find it just as disorientating as people do in their first time in zero gravity. But if you were to put a cat in space, their hair should behave more or less the same as people’s hair in space.
On the ground, the force of gravity helps pull all hair - short or long - towards the ground. As you might expect, this is particularly noticeable for long-haired cats and long-haired people. People and cats with short hair would be less inclined to say that their hair points downward, and might notice less of a change. In both long and short haired cases, the lack of gravity will mean that each hair will float freely away from your head. This doesn’t usually change the appearance of people with very short hair by very much, but people with medium to longer hair notice a dramatic change in the way their hair behaves - their hair will tend to expand outwards into a cloud around them.
This is Marsha Ivans, an American astronaut, in space, and the most dramatic case of space-hair I could find. (Normally, she looks like this.) If you apply the same principle to cats, your medium to long haired cats will come out looking much more Pomeranian-y than usual, as their hair puffs out around them. Short haired cats will look a little bit fluffier, but it won’t be as extreme a change.
As far as how loose cat hair would behave once shed in space, we can once again look to how the astronauts take care of their own hair. Astronauts have to use a vacuum as part of their shaving routine to make sure that sharp pieces of hair don’t start floating around the space station, and they also have to be careful when washing their hair to not let the loose hairs escape their towels. There are two reasons for this precaution. First, wandering hairs can clog up the intake of the air filtration system on the space station. To keep the filters clean, the astronauts would have to be very conscientious about vacuuming out the filters, and they would probably need replacing more frequently, given the way that cat hair can work its way into fabric. Secondly, and more of a direct problem for the health of the astronauts, loosely floating hairs can float directly into the eyeballs of the astronauts, causing significant irritation. They can also be inhaled. Neither eyeballs nor lungs like foreign particles very much, and the irritation from either of those could keep the astronauts from doing all the science they have to do while in orbit.
So both the cats and the astronauts will probably be happier if we leave them safely on the ground. The cats will be much happier with gravity around, and the astronauts will be happier without cat hair in their eyes.
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Are stars different colors?
Stars come in an extremely wide range of colors! Our universe provides everything from bright blue supergiant stars, to deep magenta dwarf stars, to bright red-orange giant stars, to our own yellow-green star and everything in between.
There are two ways to think about the color of a star. First, there’s the color of light that the star produces the most of. Each star produces a broad variety of colors of light, but there is always a peak in that range - one color will always be produced more often relative to the rest. This is usually the color that astronomers use when they are talking about a given star - this particular color can be useful to find out other things about the star, like the temperature on the surface.
However, this ‘most commonly produced color’ is not always the color it would appear if you were to sit at a telescope and look at it directly, or if you could zoom around in a spaceship and look at it up close. This difference is due to the way that our eyes process light. If the star were only producing light at the “most commonly produced” wavelength, then our eyes would mostly register a color that matches that wavelength. But when more than one color of light is coming at us, our eyes effectively take an average of all the colors of light that the eyeball is sensitive to.
For instance, if you look at the sun (carefully), it appears white to our eyes. ‘White’ light is simply how our eyeballs process the mixture of the rainbow of colors produced by the sun. The red, orange, yellow, green, and blues blend together to make white, even though there’s more ‘yellow-green’ being produced than any other color. You can see all the colors produced by the sun in a rainbow - but since each color is split into a different part of the sky, your eye no longer has to average the colors coming in, and you can spot the yellows and greens.
It’s a very interesting feature of our eyeballs and the range of colors produced that means we will not see stars that look “green” to us. We can spot yellow stars, red stars, and blue stars, but when stars produce green light more frequently than any other color, our eye averages the colors together and makes white. It will do this over a pretty broad range of most commonly produced colors, until there’s either enough extra blue light to give the white light a blue tint, or enough red that our eyes process the light as yellow or orange.
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How many stars live in our galaxy?
This is actually a surprisingly tricky question to answer. The current wisdom suggests we have somewhere between 100 and 400 billion stars in our galaxy. You’ll notice that this is not very precise. 300 billion stars is a pretty sizable number of stars to be able to throw around, even by astronomical standards, which are notoriously wobbly. Why is this measurement so hard?
Fundamentally, it comes down to the simple fact that we’re inside the thing we’re trying to measure, and that the galaxy is a very complicated place.
We can’t just go out into the sky and count the number of stars we see, add them all up, and get the right answer. As a first problem, that would take way longer than anyone is willing to spend counting stars. If you were to spend one second counting each star, and we’re right that there are at least 100 billion stars to count, you’d have at least ~3,180 years worth of work laid out in front of you. On top of that, the galaxy is full of a bunch of pesky gas and dust, which blocks out light from stars behind it. The gas and dust tends to be most dense within the disk of our Milky Way, which is exactly where we’re sitting. Any time we look along the disk of the Milky Way, our view is heavily obscured, so we’d be missing a large fraction of the stars just because their light never reaches us.
So other than counting all the stars, what can we do? There are a couple methods left. A very crude way of counting is to take very detailed images of a few (hopefully low dust and low gas) patches of the sky - by proxy this is looking at a few patches of the Milky Way - and try to statistically piece the galaxy together. Look away from the disk, and how many stars do you see? How much area in space should look like that region? Multiply your density of stars by the area, and you’ll get out a number of stars in that area. Do the same thing again for a region of the galaxy near us, and near the center of the galaxy, and you can - approximately - work the number out, or at least get a sense of how big the number is likely to be.
You can also take the total amount of light that is given off by the galaxy and try to work backwards to figure out how many stars you need to have to create that much light. We will again have the problem of gas and dust blocking out some of the light, but certain wavelengths of light allow us to see through gas and dust to some extent, and we can use information from those other wavelengths to try and correct for the dust. The bigger problem at this stage is that working from total light to a number of stars, you need to know how many of each size star you expect to make. If your galaxy is good at forming very big stars, these stars are also extremely bright, so you need fewer stars to produce the same amount of light than if the galaxy is good at making very small stars, which tend to be dim. You can add quite a few very small dim stars into the galaxy before you change the amount of light produced by the galaxy by a significant amount - which is part of why the total number of stars in the galaxy that we calculate out could vary by so much. Galaxies produce stars of all sizes, but the exact ratio of small to large stars is still something astrophysicists are trying to understand - or tell if indeed it is a single number. We use the stars very near to us to get a general idea of what the distribution is like, but the small faint stars are (unsurprisingly) hard to spot, so this is still a difficult thing to look for.
Given how hard these measurements are to make, it’s perhaps less surprising that we have 300 billion stars worth of wiggle room in our numbers. Whether the answer be 100 billion or 400 billion, this is still an astounding number of stars, and given that we’re finding planets around almost every star, an even more astounding number of planets.
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