Would the stars really look like that?

January 16, 2007 4:37 AM

Would the stars really look like that?

I was watching Star Trek: The Wrath Of Khan last night and during the opening credits, the names appear in what was probably a futuristiic-looking font in the 80s, and as the credits progress, the stars seem to slip past the screen, starting out from the center and then progressing offscreen without passing through the center again.
Would it really look like this? How fast would one have to be going for it to look like that? Wouldn't some of the stars be larger than the others from the p.o.v. of the viewer's spaceship?

posted by eustacescrubb to science & nature (9 comments total)

To see a star field move in such a recognisable way you'd have to be moving fairly slowly and just viewing a massively speeded up time-lapse of points in the journey (maybe you'd like to upload your brain to a machine and have it run you at 1 second per century). If you were moving fast enough to zoom past stars like that from the perspective of a "real-time" traveller, you'd be at velocities at which relativistic effects are compressing your view of the universe into, well:

To see stars fly by like in certain sci-fi series, she would have to travel much faster, on the order of light years per experienced ship second. This corresponds to the actual velocity of 0.9999999999999994c, or (1 - 6x10-16)c. At this extremely high ultra-relativistic velocity, radiation from the universe would emanate from a single point in the direction of travel, and all radiation, even the cosmic background, would be Doppler shifted out to gamma ray wavelengths or far radio, with next to nothing in between.
posted by Freaky at 5:16 AM on January 16, 2007 [1 favorite]

If you travelled close to the speed of light, the stars would only be visible directly to the front and back of your spacecraft; in front the stars would look blue and behind they'd be red.
The reason for the colours is that you're going so fast towards the light from the stars in front that the wavelength of the light is effectively compressed (blue light has a shorter wavelength), and the wavelength of the light from the rearward stars is lengthed (red light has a longer wavelength). This is called the Doppler effect (and specifically in astronomy the change in colour of light is called 'blueshift' and 'redshift') and is the same as when emergency vehicle sirens sound higher pitched as they race towards you (soundwave being compressed = shorter wavelength = higher pitch) and lower pitch after they've passed you and are moving away (soundwave being stretched = longer wavelength = lower pitch).
I can't remember why the visible stars bunch up in front and behind you, but I'm sure someone else will explain that.

Disclaimer: The above is based on reading lots of sci-fi and my highschool physics knowledge, so it's probably not entirely accurate.
posted by EndsOfInvention at 5:26 AM on January 16, 2007

Nobody really knows what it would look like to be traveling faster than light using a "warp drive" that works by an unspecified mechanism. Similarly, nobody knows what hyperspace smells like.

If they had specified a clear mechanism that warp drives used, a physicist should be able to figure out what it might look like, if anything, from the inside. ISTR that people have figured out what it might look like to be in a ship using an Alcubierre drive.
posted by ROU_Xenophobe at 6:35 AM on January 16, 2007

In Vernor Vinge's book "A Fire Upon the Deep", travelers get a windows-screensaver-like moving starfield because their FTL drive works by performing a series of teleportations. Each one can't go very far (fractions of a light year to a few light years), and each one takes a moment to 'set up', but they're instantaneous. The conscious observer only sees real-space, and is never moving at any real velocity at all (or only whatever negligible velocity they started out with), but the stars shift as they move closer and closer towards their destination.


The program Celestia is nice for getting some idea of the velocities involved in making the stars appear to move.
posted by dmd at 6:57 AM on January 16, 2007

(N.B. that Celestia behaves like I described with the Vinge book - there are no relativistic or doppler effects. Your viewpoint may be moving, but your speed is zero as far as the rendering is concerned.)
posted by dmd at 7:00 AM on January 16, 2007

To add to EndsOfInvention's answer, here is a great clip from Carl Sagan's Cosmos documentary series illustrating what near speed of light travel would look like to the traveler (using an italian motorbike! How awesome!)
posted by nelleish at 7:06 AM on January 16, 2007

Did the Eames' "Powers of 10" film do this accurately? I seem to remember that, at a certain point (at the most blown-out perspective), the stars stopped "moving."
posted by Alt F4 at 7:13 AM on January 16, 2007

If you travelled close to the speed of light, the stars would only be visible directly to the front and back of your spacecraft; in front the stars would look blue and behind they'd be red.

I'm not so sure about that. It's true that the light of stars ahead of you would be "blue-shifted" and the light from stars behind you would be "red-shifted." For the stars ahead of you, for example, the light which is visible light to a stationary observer would be shifted towards higher frequencies for you--some of it would be shifted into the ultraviolet part of the spectrum, and some into the higher-frequency part of the visible spectrum (towards the blue/violet end). But at the same time, light which is infrared, and thus invisible, to the stationary observer gets shifted to higher frequencies, filling in the lower part of the visible spectrum. So I suspect that the stars would still appear mostly white.

When we say that we can tell distant stars are moving away from us because their light is red-shifted, it's not that the stars appear more red to the naked eye, it's that characteristic absorption lines are shifted towards the red end of the spectrum.
posted by DevilsAdvocate at 7:18 AM on January 16, 2007

A word about listening to sirens at the side of the road.

The pitch of the (hypothetical single frequency) siren falls continously the entire time you are listening to it, from the time you notice it approaching to the moment you can't be sure you hear it receding. The farther you are from the road, the more gradual the decline in pitch, and you hear the siren at its resting frequency at the instant it is closest to you.

But this doesn't really fit anyone's experience because the siren actually emits a spread of frequencies and because the small doppler effect is overwhelmed by another phenomenon: higher frequencies of sound are much more strongly absorbed by the atmoshere than lower ones are-- which is why distant thunder rumbles and lightning nearby rips.
posted by jamjam at 8:22 AM on January 16, 2007