Boost Stars Yale Bright Stars Nearby, random Nearby, red Nearby, blue Radii Colors Circles Density Limiting Mag Projection Stereo Equal Area Equi-Rect Behrmann Hammer Animate Running Time

### How Stars Appear From a Spacecraft

Effects to look for:

• a large number of "new" dim stars appear in the direction of motion. Those stars were there all along, but were initially too dim to be seen. They are brightened by the boost.
• most stars in the direction opposite to the direction of motion disappear from view.
• in some cases, a star behind you can disappear at lower value of β, and then reappear again later at higher β (example, watch closely at the edges).
• for high β, the stars as a whole begin to resemble the appearance of a large globular cluster. This thing is so big, beautiful, and glorious, it deserves a name. Let's call it the relativistic supercluster.
• a core of bright, blue stars in the center, changing to white away from the center, and then generally redder and dimmer at the edges (this example exaggerates the effect). For the human eye, this effect would be visible, but perhaps a bit subtle, since human perception of the colour of stars is not strong. (Photographs would show it more plainly.)
• the change in brightness of a star depends on the doppler factor, and on its color/temperature/spectral class. See this diagram for more details.

### Explanatory Notes

An excellent reference for this sort of calculation is the paper of McKinley and Doherty (1979).

Stars
The most realistic choice is the Yale Bright Stars, which is a catalog of stars brighter than magnitude 6.5, as seen from Earth. The view shown is towards Polaris, the North Star. If you look closely, you will be able to see the Big Dipper just to the left of center (it's tiny).

The other choices for stars:

• Nearby, random: generate stars randomly within 10 parsecs of the Earth. These stars are assigned colors and brightnesses according to typical relative frequencies.
• Nearby, red: generate a uniform field of spectral class M stars (3050°, absolute magnitude 10.0, distance of 0.5 parsecs).
• Nearby, blue: generate a uniform field of spectral class A stars (8750°, absolute magnitude 2.0, distance of 10 parsecs).
To generate more such stars, just increase the density setting.

Applies to the half-sky views only. Turn this setting on to see the half-sky radius (contains 'half the sky') and the neutral radius (where the doppler factor D=1).

Colors
This simulation makes the rough approximation that the light from the stars is identical to a black body spectrum, which is characterized by a single number - the black body surface temperature. Different surface temperatures have different colors, from reddish-orange (coolest), to white, to bluish-white (hottest).

The perception of the colour of starlight by the human eye is weak. The colors shown here are more like the colors you would see in a photograph of the stars, instead of by the human eye.

At the high density of stars you would see at high values of β, there should be visible a graduated color effect, with blue stars in the center, changing to white away from the center, and then red stars towards the edge.

Circles
Turn this off if your browser slows down. The animation does a lot of processing, and sometimes your computer may have trouble keeping up. Drawing stars as small squares instead of circles can sometimes help.

Density
The number of stars per cubic parsec. This is used only for the randomly generated sets of stars, and not for stars from the Yale Bright Star Catalog. Increase the density a bit if you want to see more stars.

Limiting Magnitude
The cut-off point for showing stars, according to brightness. A higher limiting magnitude means you will see more stars.

There can be many stars in these simulations, but you usually won't see them all. There's a good reason for having stars in the simulation that you can't see all the time. Due to relativistic effects, stars can increase in brightness. So, stars that are initially not visible (and are below the limiting magnitude), can often become visible later on.

Projection
Stars on the celestial sphere need to be projected onto the flat plane of the screen. Various star map projections are provided. You can select the one that you prefer. Some show half the sky, and some show the whole sky. In each case, the center corresponds to the direction of motion.

Note that with the whole-sky projections, some of the motions of stars along the edge of the view are an artifact of the map projection being used.

Brightness Index
Roughly equivalent to the number of Vega-like stars that would produce the same amount of apparent radiant energy produced by the visible stars. This is a measure of the total brightness of all the stars visible in the sky, as seen from the spacecraft. It includes only those stars that are brighter than the given limiting magnitude. It's calculated using a formula that relates differences in magnitude to differences in luminosity. Here, 1 unit of brightness is equivalent to 1 star of magnitude 0. The bright star Vega has magnitude 0.03, so this is roughly the equivalent number of Vegas that would produce the same apparent radiant energy. On the same scale, a full Moon is about 125,000 units.

### Limitations

Some limitations of this simulation:
• the Milky Way is not included.
• stellar radiation is modeled as black-body radiation. For individual stars, this is only a rough approximation of their actual spectrum.
• the reddening of starlight by interstellar dust isn't included.
• only typical starlight radiation is included. At extremely high β, the stars become dimmer, and eventually drop below the limiting magnitude for human vision. Presumably other forms of radiation, such as that from interstellar dust (infrared) or even the cosmic microwave background (microwaves) would eventually dominate the view.
• the stars are limited to those in the Yale Bright Star Catalog, brighter than magnitude 6.5. If this simulation used the Tycho-2 catalog, which goes to magnitude 11.0, then the effects you see here would be even more exaggerated. In terms of the number of stars seen, there's a peak at a speed of β~0.993, where relativistic effects would make thousands more dim stars visible to the human eye, all concentrated into a central cluster of radius ~28°. That would be a glorious sight. (I wonder if we'll ever photograph it...)