The View from an Interstellar Ship

Imagining the famous ‘starbow’ phenomenon of relativistic speeds

Moving at speeds comparable to those of light can lead to strange sights — including speculations of a rainbow of color-shifted stars. Image of a starbow by Spaceway.

There is an image of a derelict starship slipping through the vast gulf of empty space. The gulf is an all-encompassing darkness with little in the way of comfort. Within the ship itself the metal whines and its passengers are long dead, the onboard computers having gone dark from their efforts to monitor a depleting fuel supply. Communication does not find and does not leave the ship. It is, like a treehouse in the backyard of an abandoned country home, the kind of sight that makes your stomach turn. On occasion a rocky piece of debris will scrape the metal, leaving an unloving indentation on one side; if the debris is large or violent enough it will change the starship’s course. But it doesn’t matter. The distance between galaxies is unfathomable and will take centuries to traverse no matter which direction the ship faces. It has now become a relic lost somewhere out there in a lewd kind of limbo.

Unlike ships that ride the briny oceans, our vessels of space won’t always be able to use the stars for navigation. For thousand of years stars were pronounced the lighthouses of the sky — helping sailors position themselves by their particular brightness and patterns. The constellations are not only artful and dreamy, they are still used for navigating outside of Earth’s atmosphere today. Celestial navigation was used in the Apollo program to help mankind leave its first etchings on the moon. But to a spaceship of the future moving at blistering relativistic speeds, the constellations are unrecognizable. They’re mangled by the starship’s journey. Fainter stars become distinct, they mingle with the others which were once brighter.

Before it was lost in the thickets of the cosmos, the starship left its home system to explore another. The machinery clicked, twinkled, and buzzed. A crew member pressed their face to the window and left a milky fog with the warmth of their breath. What would they have seen, moving at near the speed of light?

An artist’s concept shows a generation starship aboard which some people would spend their entire lives. It is a kind of ark carrying humans and their descendants. Strange effects aren’t seen until a vessel reaches around 10% the speed of light. If the future of interstellar travel lies in generation starships — which will likely only tumble along at around 2% the speed of light and which aren’t as concerned with time — typical navigation tools like the ones we use today could still be helpful in charting a course to new destinations. Image by NASA.

In the 1960’s the existence of the starbow is proposed by the Journal of the British Interplanetary Society. It begins at 15% lightspeed.

The original host star behind the ship will become redshifted as the destination star in front of the ship gleams brighter than before. The red-shifting effect — in which the wavelength of the light is stretched — causes yellow stars to become orange. Orange stars meld into red and originally red stars disappear altogether as the wavelength of their light enters the invisible spectrum. The ship speed increases and the stars ahead come together in beady clusters while those at the rear of the ship are thinned out and slowly dim until they blend into the background.

It’s at 37% lightspeed that both the origin and destination star disappear into the invisible part of the electromagnetic spectrum, each becoming a pupil-like circle of darkness. These circles of darkness continue to grow until, at 50% the speed of light, they are each enormous breadths of black at the front and at the back of the starship. But a small area of space around the ship is still freckled with visible stars. They have all been shifted into a sensational new spectrum. From the front of the ship to its stern the sight of the stars gradate from a glacial blue-white to luscious greens, yellows, and summery orange-reds at the very back. The sight is divine; it is a rainbow of stars breaking two solid stretches of darkness before and behind the ship.

Using the stars to navigate has no longer become an option. To slow down, observe, calculate an accurate position, and then re-accelerate to relativistic speeds will require a lot of fuel. In a situation like this a ship is in danger of entering a cosmic tundra outside of the galactic plane, an emptiness where any signal can no longer reach the death-bound crew.

A starship capable of incredible speeds is still only as successful as its navigation system.

According to the original proposition from the 60’s, the starbow will become a circular band of colorful stars at around 99% lightspeed. At the rear of the ship will be nothing but darkness and the front cone of darkness will have been reduced to a small circle surrounded by the starbow, as shown above.

But as beautiful as this picture of the starbow may be, later studies by scientists in the 70’s concluded that this is all it was — a beautiful picture and nothing more.

The original starbow proposition made the mistake of assuming that all light radiation from stars came in a single wavelength. In reality stars radiate in a variety of wavelengths and at different temperatures. These stars are strewn altogether in the sky, giving us a mixture of blues, yellows, oranges, reds, and whites but not in the neat strips of a rainbow and not in the purples or greens of science fiction novels. Because the whole spectral energy of a star is shifted, some parts of it — like the infrared — may burnish a star redder or the light may extend into the ultraviolet spectrum where we won’t be able to see it at all.

But it’s not only the color of the surroundings that change. Relativistic speeds compress the field of view in front of the ship. Objects that are behind the starship still appear as if they are before it. The stars do cluster together, more and more looking like one singular blue-shifted ornament ahead. At 99% lightspeed almost all stars are blue-shifted. They are confined to a small pond of space about 10 degrees in size.

The cosmic background radiation will also be shifted toward the blue part of the spectrum, eventually coming to dominate the field of view as the other stars peak and fade into that inky, silky blackness of the universe. It is certainly an unfamiliar sight.

To navigate in a situation like this might require ships of the future to undergo dead reckoning. It’s a technique which goes against our instincts to peer out those windows, point, and say, “Our destination is over that way. Chart the course.” Instead, dead reckoning is unconcerned with the view from our interstellar ship. It requires only that a navigator track a ship’s velocity and direction, using an artificial map of the heavens to frequently update the starship’s position.

Images by Oikofuge.

At faster than light speeds — if possible — the CMB would grow into a looming white glow and the ship would feel a pressure from the x-ray radiation of blue-shifted stellar light. The above gallery shows what a realistic view would look like from a spaceship traveling at relativistic speeds. The simulation begins at a stationary 0% lightspeed and ends at 99% lightspeed. The last image is of hyperspace travel showing the blinding glow of the CMB.

But today we are nowhere near relativistic speeds and the challenges they bring. To navigate interstellar space NASA is still offering those familiar lighthouses: their new SEXTANT (Station Explorer for X-Ray Timing and Navigation Technology) aims to use pulsars to triangulate positions in space. The idea is simple. A series of pulsars are positioned around you. As you move closer to one pulsar, its signal will arrive a little earlier and when you move away from it, the signal will arrive a little later. The technology has already been successfully used in experiments on the ISS.

Sextant is a poetic name for it. A sextant is an old navigational tool that uses the angles between two objects to give us a ship’s position on a chart. The rosy horizon of the Earth and a body in the heavens — perhaps a star, or a planet, for example. We have used sextants to wander the sucking and heaving of the seas. We’ll use them now to wander through the cosmos. Knowing our way to new worlds — that is, learning the winding body of the cosmos — is as important as the vessel we’ll take to arrive there. As for the demise of the starbow, the scientists lamented that they, “have nothing so poetic to offer as its replacement. Only better physics”.