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It seems I've been neglecting this space recently. Well, some of it has been spent playing around with Celestia, a free program which bills itself as a 'universe simulator'. Although the user can explore space from the perspective of an imaginary spaceship capable of ludicrous acceleration, I'm sure you all know what The Guide has to say about space: "Space," it says, "is big. Really big. You just won't believe how vastly hugely mindboggingly big it is. I mean you may think it's a long way down the road to the chemist, but that's just peanuts to space
When you start up the program you find yourself facing Earth from a distance of about 30,000 kilometres and the sun directly behind you (and the program is synchronised with your computer's clock, so if it is daytime where you are, you will find yourself looking down on your home). Another thing you might notice is, because of the tilt of our axis the planet is not oriented as you would expect from looking at a map. Actually, since it is only about a week since the equinox this is about as close as it will get and maybe it only looks odd to me, what with having so much landmass in the northern hemisphere.
The function keys map to the various preset speeds of your spaceship and the numpad steers. I think the spaceship controls are a bit fiddly and there are easier ways to navigate in Celestia but those are what I want to talk about now. So. F1 to stop. F2 will accelerate you towards the Earth at a glorious 1 km/s. Watch in awe as nothing happens. Well, some of the numbers will start changing, slowly.
F3 codes for 1,000km/s. Earth swells in your field of view pretty quickly at that rate and soon it will fill the screen, so better stop.
You can go just about anywhere you like in Celestia and right now I recommend the Moon. Good ole Diana. Just press Enter, type 'moon' and hit enter again to find it quickly, and 'c' to centre the screen on our silver neighbour. She'll be hard to see as I write this; she's just past New right now (solar eclipses always happen at New Moon for very good reasons). All I see is a very faint, small sliver in the centre of my screen. F3 again and pay her a visit.
Anyone who just tried that should have noticed very little change on their screen. That's because Luna is more than 300,000kms away and it would almost six minutes to get there at F3 speed. F4 lets you travel at the speed of light, c. The Moon practically leaps into view and if you are not careful you will overshoot it, as I just did. For me, it is pretty awe inspiring to imagine traveling at lightspeed. One could zip around the solar system at that speed, right?
Venus is the nearest planet (after beloved Earth) right now so let's pay her a visit (locked onto same way as the Moon just before – press 'f' too if you don't want her drifting away once you get there. Or just press '2' to select the second planet). And once again I find myself staring at an unchanging screen. It will take a number of minutes to get there at the speed of light so I'm letting it travel as I type this. Good thing I did not select a more distant planet, such as one of the ice giants, or I could be waiting hours. Of course, once I come to the end of the journey it is going to be fast and if I blink once Venus is near enough to show a disk I may miss it.
...And it took me a few more minutes of waiting after I finished that paragraph but at least I have a near precision stop to show for it.
Now let's try Mars. F5 is 10c, so it should be much quicker getting to him, even though he's twice as far as Venus was. Yup, much quicker. In fact I overshot him by more than 170,000 kilometres. I did not actually note the time of either journey but math tells me Venus-Mars took roughly 1/5th the time of Moon-Venus as it was twice the distance at ten times the speed. It certainly felt shorter.
For the next stop on our tour I have chosen Pluto. At more than 32 Astronomical Units (AUs) away, it would take more than 26 minutes at 10c to get there (or nearly four and a half hours at the speed of light). Fortunately by pressing F6 we can accelerate to the heady speed of 1AU/s, about 500c. So now it only takes half a minute to reach Pluto (Incidentally Pluto's two most recently discovered moons are not present in Celestia, however they can be downloaded as an add-on).
If we want to go any farther (lets say Proxima Centauri)we run into problems again. Proxima is 4.2 light years (ly) from Pluto so if we travel at 500c we're going to be sitting in front of the screen for more than three days. That is very impressive, traveling to the stars in the same time it took the Apollo astronauts to reach the Moon, except I doubt anyone has the time for it so long as the journey is purely imaginary.
And yet if we press F7 (hands up if you saw F7 coming) we run into another problem. F7 means 1ly/s, which means you reach Proxima in 4.2 seconds and are almost guarranteed to overshoot it, and by a large enough margin to make approaching it even at 500c a tedious prospect.
So let's put this thing to a more serious test. Let's aim for one of the most distant (and luminous) stars in the night sky: Deneb. Deneb is almost a kiloparsec away (~3000 light years) and puts out far, far more radiation than our sun.
Each of those points of light drifting by is a star. They can all be selected, visited and inspected. If you want more information on any of them you can right-click (I suppose that Mac and Linux versions of Celestia use a different command) and select info and you will be taken to a web page containing more information. And now, if anyone has actually been following along with this tour I recommend you reduce speed to zero because it will take most of an hour to reach Deneb at 1ly/s and there are no more preset speeds to try. But there is a much faster way. Just press 'g' for go. Or you can hold down 'a' to accelerate to whatever speed you find practical. Be careful though. If you go too fast you risk leaving the galaxy entirely.
If you look back to the sun from Deneb and especially if you have Celestia set to label prominent stars, you will see most of them are clustered around Sol.
Celestia does include space outside the Milky Way. Try locating Sculptor – a small satellite galaxy orbiting our own – and paying it a visit. Looking around from here you can see the Milky Way and the two Magellanic Clouds hanging in space. But if you tell Celestia to stop displaying galaxies and turn the visible magnitude up to maximum you will see something else. You will see every star in Celestia's sky, all clustered together in the distance.
Press 'h' and 'c' to centre on the sun and then try playing with the 'home' and 'end' keys to move back and forth to have a look at the swarms of stars surrounding us. Notice that they are sparse at the edge but as you zoom closer more and more become visible in the centre until the screen is almost white. This is because stars are generally easier to see the nearer they are and consequently most of the stars we have charted are in our own neighbourhood. Notice also that Deneb, despite lying almost beyond the stars we know, is actually only a third of the way to the edge of Celestia's starmap. Almost all the stars we see in our sky are also relatively nearby – even though we also see mostly only the brightest ones and many of those visible are hundreds of light years away, that is still nearby at this scale.
Celestia gets its stars from the Hipparcos catalogue, named for the satellite that collected the data which in turn was named for the ancient Greek astronomer, famous for his star catalogue. Hipparcos (the satellite, not the man) was sent up there to collect stellar parallaxes with very high precision and that is just what it did. Remind me to write another post about Hipparcos and parallax later. I'm tired and winding down now.
Anyway, Celestia uses the Hipparchos catalogue and contains around 100,000 stars. There is an add-on available for download which uses the less accurate Tycho catalogue and can bring the total up to one or two million stars for the user to visit, if desired. The Milky Way is fairly large, as galaxies go, and contains an estimated 200 to 400 thousand million stars. So even the largest catalogue available for Celestia contains no more than 0.001% of the galaxy.
If you tell Celestia to display galaxies again and reduce the visible magnitudes to a sensible level, I recommend going to M32, a small satellite of the Andromeda Galaxy (Andromeda is the largest of the three major galaxies in our local clustor, the other two being M33 [Triangulum] and the Milky Way itself). From here it is possible to rotate the view and look through Andromeda and back at your home across two million light years (it will look like a bright sparkly wisp of cloud). And to think that in a few thousand million years these two will collide and merge into a monster elliptical.
I wonder what will happen to all our satellites and globular clusters? The space surrounding the two galaxies is practically swarming with their entourages (and it makes me wonder about the swarms of satellite galaxies surrounding others we have not detected because they are too distant).
So far the most distant galaxy I have found in Celestia was 232Mpcs (Megaparsecs – that's million parsecs for those who don't know their prefixes and a parsec is 3.26 light years for reasons I will explain if I ever get around to that Hipparchos post), which is still nearby on the cosmic scale. I haven't found any quasars yet but nor have I looked very hard. If it comes to it I know I can download more galactic catalogues for Celestia, catalogues which definately do contain some. I want to see how they are rendered.
Anyway, this is Summer Snow saying "Goodnight"
~_~
It seems I've been neglecting this space recently. Well, some of it has been spent playing around with Celestia, a free program which bills itself as a 'universe simulator'. Although the user can explore space from the perspective of an imaginary spaceship capable of ludicrous acceleration, I'm sure you all know what The Guide has to say about space: "Space," it says, "is big. Really big. You just won't believe how vastly hugely mindboggingly big it is. I mean you may think it's a long way down the road to the chemist, but that's just peanuts to space
When you start up the program you find yourself facing Earth from a distance of about 30,000 kilometres and the sun directly behind you (and the program is synchronised with your computer's clock, so if it is daytime where you are, you will find yourself looking down on your home). Another thing you might notice is, because of the tilt of our axis the planet is not oriented as you would expect from looking at a map. Actually, since it is only about a week since the equinox this is about as close as it will get and maybe it only looks odd to me, what with having so much landmass in the northern hemisphere.
The function keys map to the various preset speeds of your spaceship and the numpad steers. I think the spaceship controls are a bit fiddly and there are easier ways to navigate in Celestia but those are what I want to talk about now. So. F1 to stop. F2 will accelerate you towards the Earth at a glorious 1 km/s. Watch in awe as nothing happens. Well, some of the numbers will start changing, slowly.
F3 codes for 1,000km/s. Earth swells in your field of view pretty quickly at that rate and soon it will fill the screen, so better stop.
You can go just about anywhere you like in Celestia and right now I recommend the Moon. Good ole Diana. Just press Enter, type 'moon' and hit enter again to find it quickly, and 'c' to centre the screen on our silver neighbour. She'll be hard to see as I write this; she's just past New right now (solar eclipses always happen at New Moon for very good reasons). All I see is a very faint, small sliver in the centre of my screen. F3 again and pay her a visit.
Anyone who just tried that should have noticed very little change on their screen. That's because Luna is more than 300,000kms away and it would almost six minutes to get there at F3 speed. F4 lets you travel at the speed of light, c. The Moon practically leaps into view and if you are not careful you will overshoot it, as I just did. For me, it is pretty awe inspiring to imagine traveling at lightspeed. One could zip around the solar system at that speed, right?
Venus is the nearest planet (after beloved Earth) right now so let's pay her a visit (locked onto same way as the Moon just before – press 'f' too if you don't want her drifting away once you get there. Or just press '2' to select the second planet). And once again I find myself staring at an unchanging screen. It will take a number of minutes to get there at the speed of light so I'm letting it travel as I type this. Good thing I did not select a more distant planet, such as one of the ice giants, or I could be waiting hours. Of course, once I come to the end of the journey it is going to be fast and if I blink once Venus is near enough to show a disk I may miss it.
...And it took me a few more minutes of waiting after I finished that paragraph but at least I have a near precision stop to show for it.
Now let's try Mars. F5 is 10c, so it should be much quicker getting to him, even though he's twice as far as Venus was. Yup, much quicker. In fact I overshot him by more than 170,000 kilometres. I did not actually note the time of either journey but math tells me Venus-Mars took roughly 1/5th the time of Moon-Venus as it was twice the distance at ten times the speed. It certainly felt shorter.
For the next stop on our tour I have chosen Pluto. At more than 32 Astronomical Units (AUs) away, it would take more than 26 minutes at 10c to get there (or nearly four and a half hours at the speed of light). Fortunately by pressing F6 we can accelerate to the heady speed of 1AU/s, about 500c. So now it only takes half a minute to reach Pluto (Incidentally Pluto's two most recently discovered moons are not present in Celestia, however they can be downloaded as an add-on).
If we want to go any farther (lets say Proxima Centauri)we run into problems again. Proxima is 4.2 light years (ly) from Pluto so if we travel at 500c we're going to be sitting in front of the screen for more than three days. That is very impressive, traveling to the stars in the same time it took the Apollo astronauts to reach the Moon, except I doubt anyone has the time for it so long as the journey is purely imaginary.
And yet if we press F7 (hands up if you saw F7 coming) we run into another problem. F7 means 1ly/s, which means you reach Proxima in 4.2 seconds and are almost guarranteed to overshoot it, and by a large enough margin to make approaching it even at 500c a tedious prospect.
So let's put this thing to a more serious test. Let's aim for one of the most distant (and luminous) stars in the night sky: Deneb. Deneb is almost a kiloparsec away (~3000 light years) and puts out far, far more radiation than our sun.
Each of those points of light drifting by is a star. They can all be selected, visited and inspected. If you want more information on any of them you can right-click (I suppose that Mac and Linux versions of Celestia use a different command) and select info and you will be taken to a web page containing more information. And now, if anyone has actually been following along with this tour I recommend you reduce speed to zero because it will take most of an hour to reach Deneb at 1ly/s and there are no more preset speeds to try. But there is a much faster way. Just press 'g' for go. Or you can hold down 'a' to accelerate to whatever speed you find practical. Be careful though. If you go too fast you risk leaving the galaxy entirely.
If you look back to the sun from Deneb and especially if you have Celestia set to label prominent stars, you will see most of them are clustered around Sol.
Celestia does include space outside the Milky Way. Try locating Sculptor – a small satellite galaxy orbiting our own – and paying it a visit. Looking around from here you can see the Milky Way and the two Magellanic Clouds hanging in space. But if you tell Celestia to stop displaying galaxies and turn the visible magnitude up to maximum you will see something else. You will see every star in Celestia's sky, all clustered together in the distance.
Press 'h' and 'c' to centre on the sun and then try playing with the 'home' and 'end' keys to move back and forth to have a look at the swarms of stars surrounding us. Notice that they are sparse at the edge but as you zoom closer more and more become visible in the centre until the screen is almost white. This is because stars are generally easier to see the nearer they are and consequently most of the stars we have charted are in our own neighbourhood. Notice also that Deneb, despite lying almost beyond the stars we know, is actually only a third of the way to the edge of Celestia's starmap. Almost all the stars we see in our sky are also relatively nearby – even though we also see mostly only the brightest ones and many of those visible are hundreds of light years away, that is still nearby at this scale.
Celestia gets its stars from the Hipparcos catalogue, named for the satellite that collected the data which in turn was named for the ancient Greek astronomer, famous for his star catalogue. Hipparcos (the satellite, not the man) was sent up there to collect stellar parallaxes with very high precision and that is just what it did. Remind me to write another post about Hipparcos and parallax later. I'm tired and winding down now.
Anyway, Celestia uses the Hipparchos catalogue and contains around 100,000 stars. There is an add-on available for download which uses the less accurate Tycho catalogue and can bring the total up to one or two million stars for the user to visit, if desired. The Milky Way is fairly large, as galaxies go, and contains an estimated 200 to 400 thousand million stars. So even the largest catalogue available for Celestia contains no more than 0.001% of the galaxy.
If you tell Celestia to display galaxies again and reduce the visible magnitudes to a sensible level, I recommend going to M32, a small satellite of the Andromeda Galaxy (Andromeda is the largest of the three major galaxies in our local clustor, the other two being M33 [Triangulum] and the Milky Way itself). From here it is possible to rotate the view and look through Andromeda and back at your home across two million light years (it will look like a bright sparkly wisp of cloud). And to think that in a few thousand million years these two will collide and merge into a monster elliptical.
I wonder what will happen to all our satellites and globular clusters? The space surrounding the two galaxies is practically swarming with their entourages (and it makes me wonder about the swarms of satellite galaxies surrounding others we have not detected because they are too distant).
So far the most distant galaxy I have found in Celestia was 232Mpcs (Megaparsecs – that's million parsecs for those who don't know their prefixes and a parsec is 3.26 light years for reasons I will explain if I ever get around to that Hipparchos post), which is still nearby on the cosmic scale. I haven't found any quasars yet but nor have I looked very hard. If it comes to it I know I can download more galactic catalogues for Celestia, catalogues which definately do contain some. I want to see how they are rendered.
Anyway, this is Summer Snow saying "Goodnight"
~_~
