Center of the Cosmos

Center of the Cosmos

Where is the center of the Cosmos? Is there an edge to the Universe? What lies beyond that? In a two-dimensional universe, curved through a third dimension, there is no center – at least not on the surface of the sphere.

The center of such a universe is not in that universe; it lies, inaccessible, in the third dimension, inside the sphere. While there is only so much area on the surface of the sphere, there is no edge to this universe. The universe is finite but unbounded. The question of what lies beyond is meaningless. Flat creatures cannot, on their own, escape their two dimensions.

Increase all dimensions by one, and you have the situation that may apply to us: the universe as a four-dimensional hyper-sphere with no center and no edge, and nothing beyond.

The center of the Cosmos is not in our universe (quotations from Megan Jorgensen). Image: © M. Jorgensen (Elena)

Why do all the galaxies seem to be running away from us? The hyper-sphere is expanding from a point, like a four-dimensional balloon, being inflated, creating in every instant more space in the universe.

Sometime after the expansion begins, galaxies condense and are carried outward on the surface of the hyper-sphere.

Orion Nebula

Orion Nebula

We can ask the computer to run a constellation forward into time. Consider Leo the Lion. The zodiac is a band of twelve constellations seemingly wrapped around the sky in the apparent annual path of the Sun through the heavens.

The root of the word Zodiac is that for zoo, because the zodiacal constellations, like Leo, are mainly fancied to be animals. A million years from now, Leo will look still les like a lion than it does today. Perhaps our remote descendants will call it the constellation of the radio telescope – although I suspect a million years from now the radio telescope will have become more obsolete than the stone spear is now.

The stars flash on and wink off like fireflies in the night (quotations from Megan Jorgensen). Image © Meg Jorgensen (Elena)

The nonzodiacal constellation of Orion, the hunter, is outlined by four bright stars and bisected by a diagonal line of three stars, which represent the belt of the hunter. Three dimmer stars hanging from the belt are, according to the conventional astronomical projective test, Orion’s sword. The middle star in the sword is not actually a star but a great cloud of gas called the Orion Nebula, in which stars are being born.

Many of the stars in Orion are hot and young, evolving rapidly and ending their lives in colossal cosmic explosions called supernovae. They are born and die in periods of tens of millions of years. If, on our computer, we were to run Orion rapidly into the far future, we would see a startling effect, the births and spectacular deaths of many of its stars, flashing on and winking off like fireflies in the night.

Appearance of the Constellations

Appearance of the Constellations

The appearance of the Constellations changes not only in space but also in time; not only if we alter our position but also if we merely wait sufficiently long. Sometimes stars move together in a group of cluster; other times a single star may move very rapidly with respect to its fellows. Eventually such stars leave an old constellation and enter a new one.

Occasionally, one member of a double-star system explodes, breaking the gravitational shackles that bound its companion, which then leaps into space at its former orbital velocity, a slingshot in the sky.

In addition, stars are born, stars evolve, and stars die. If we wait long enough, new stars will appear and old stars vanish. The patterns in the sky slowly melt and alter.

Time is important. (quotations from Megan Jorgensen). Image : © Megan Jorgensen (Elena)

Even over the lifetime of the human species – a few million years – constellations have been changing. Consider the present configuration of the Big Dipper, or Great Bear. Our computer can carry us in time as well as in space. As we run the Big Dipper backwords into the past, allowing for the motion of its stars, we find quite a different appearance a million years ago. The Big Dipper then looked quite a bit like a spear. If a time machine dropped you precipitously in some unknown age in the distant past, you could in principle determine the epoch by the configuration of the stars : if the Big Dipper is a spear, this must be the Middle Pleistcene…

Constellations

Constellations

Despite the efforts of ancient astronomers and astrologers to put pictures in the skies, a constellation is nothing more than an arbitrary grouping of stars, composed of intrinsically dim stars that seem to us bright because they are nearby, and intrinsically brighter stars that are somewhat more distant.

All places on Earth are, to high precision, the same distance from any star. This is why the star patterns in a given constellation do not change as we go from, say, Quebec, to Australia. Astronomically, Canada and Australia are the same place.

Dark Deep Space Reflective. Image in public domain

The stars in any constellation are all so far away that we cannot recognize them as a three-dimensional configuration as long as we are tied to Earth. The average distance between the stars is a few light-years, a light year being, as you remember, about ten trillion kilometres. For the patterns of the constellations to change, we must travel over distances comparable to those that separate the stars; we must venture across the light-years. Then some nearby stars will seem to move out of the constellation, others will enter it, and its configuration will alter dramatically.

Voyages of Exploration and Discovery

Voyages of Exploration and Discovery

Launched on August 20, 1977, Voyager 2 moved on an arcing trajectory past the orbit of Mars, through the asteroid belt, to approach the Jupiter system and thread its way past the planet and among its fourteen or so moons.

Jupiter is surrounded by a shell of invisible but extremely dangerous high-energy charged particles. The spacecraft must pass through the outer edge of this radiation belt to examine Jupiter and its moons close up, and to continue its mission to Saturn and beyond.

However, the charged particles can damage the delicate instruments and fry the electronics. Besides, Jupiter is also surrounded by a ring of solid debris, discovered by Voyager I, which Voyager 2 had to traverse. A collision with a small boulder could have sent the spacecraft tumbling widely out of control, its antenna unable to lock on the Earth and its data lost forever.

Voyage to Earth. These voyages of exploration and discovery are the latest in a long series that have characterized and distinguished human history. Carl Sagan, Cosmos Image : © Megan Jorgensen (Elena)

Just before encounter, the mission controllers were restive. There were some alarms and emergencies, but the combined intelligence of the humans on Earth and the robot in space circumvented disaster.

Voyager’s passage by Jupiter accelerated it toward a close encounter with Saturn. Saturn’s gravity has propelled it on to Uranus. After Uranus it plunged on past Neptune, leaving the sloar system, becoming an interstellar spacecraft, fated to roam forever the great ocean between the stars.

Voyager relies on a small nuclear power plant, drawing hundreds of watts from the radioactive decay of a pellet of plutonium. Its three integrated computers and most of its housekeeping functions – for example, its temperature-control system – are localized in its middle. It receives commands from Earth and radios its findings back to Earth through a large antenna, 3.7 meters in diameter.

There are many scientific instruments – ultraviolet and infrared spectrometers, devices to measure charged particles and magnetic fields and the radio emission from Jupiter – but the most productive have been the two television cameras, designed to take tens of thousands of pictures of the planetary islands in the outer solar system.

Most of the scientific instruments of Voyager are on a scan platform, which tracks Jupiter or one of its moons as the spacecraft hurtles past.