Marianne O'Hagan

The Cosmos

If we consider the Earth, the Moon, the Solar System, the Sun and the Universe as a whole, nothing is immobile.

Our Solar System consists of our Sun, and eight planets that are bound to it by gravity: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune, followed by the Plutons: Pluto, Chiron (Pluto’s largest Moon), Xena, Ceres and possibly Sedna which do not qualify as planets.

On the 24 August 2006, the International Astronomical Union (IAU) changed the definition of “planet” and Pluto did not qualify. Consequently there are officially only eight planets in the Solar System.

Of course, the change in terminology does not affect the magnetic fields in space. It is not important as to how we classify the various celestial objects in our Solar System, but how much we learn from their magnetic fields.

If we ask the question, “How fast is the Earth moving?” we have to remember what Einstein said, “You can’t measure the speed of an object by itself; it has to be measured relative to something else”.

The Earth orbits the Sun in three hundred and sixty-five days, five hours, forty-eight minutes and forty-six seconds in one tropical year, and it turns on its axis every twenty-three hours, fifty-six minutes and four seconds. The Earth is not a perfect sphere owing to the gravitational attraction of the Sun and Moon on the equatorial bulge of the Earth which causes the axis of the Earth to continually wobble. This unique motion results in the precession of the equinoxes. Over a period of one year, when the Sun returns to the vernal equinox, the Earth is fifty seconds of arc behind its last position, equal to about one degree of arc every seventy-two years. It completes a retrograde circle of the twelve constellations in approximately 26,000 years. This journey in time is known as the Great Year. A cosmic month is approximately 2160 years which is the approximate time it takes for the vernal point to move through one constellation as measured against the fixed stars.

The Solar System is located in the outer reaches of the Milky Way Galaxy, which is a spiral galaxy. The Milky Way Galaxy contains roughly 200 billion stars. Most of those stars are not visible from Earth. Almost everything that we see belongs to the Milky Way Galaxy. The Sun is about 26,000 light years from the centre of the Milky Way Galaxy, which is about 80,000 to 120,000 light years across. We are located out towards the edge of its spiral arms. It takes our Sun, and our Solar system, roughly 200 – 250 million years to orbit once round the Milky Way. In this orbit, we, and the rest of the Solar System are travelling at a velocity of around 155 miles/sec (250km/sec).

The cosmos comprises of three fundamental aspects of nature: motion, matter and energy. Motion is the starting point where everything moves, from the atoms in stationary objects, to the most distant galaxies.

Ancient observers founded the science of astronomy by charting the motions of the Sun, Moon, stars and planets in detail. Today, our telescopes and observing equipment are sophisticated enough to detect planets around other stars. We have learned that the movements of celestial objects are ever-changing. Any slight alterations in their paths through space could have disastrous consequences. For that reason we observe space for any comets and/or asteroids that could fire towards Earth.

Our Universe consists almost entirely of hydrogen and helium with a minute amount of heavier elements. On Earth, we are accustomed to seeing matter within a narrow framework of temperatures and pressures that make life possible. Such conditions are rare elsewhere, just a few atoms drift here and there in cold spaces between the stars and galaxies.

When matter is put in motion, it emits energy. Energetic outbursts throughout the cosmos give us insights into objects we would not otherwise detect.

For example, a star explodes somewhere once every second, blasting light and particles called neutrinos into space. Gas plunges into black holes at the centre of galaxies, releasing waves of x-rays. The Sun is a constantly churning ball of charged gas, lacquered with magnetic fields that writhe and snap, propelling dangerous flares towards Earth. We have devised clever ways to see these elusive waves, from giant radio receivers on the ground, to x-ray and gamma-ray telescopes in orbit.

Some of the questions at the frontiers of cosmological science today seem extraordinarily hard to address. For example: “Have matter and energy combined to create life elsewhere?”, “What are the essential ingredients of matter?”, “Does a single theory of physics describe the behaviours of all forces and particles in the Universe?”, “What sparked the birth of the Universe?”

As far as the future is concerned, we have found hints that a force of repulsion permeates the Universe, forcing it to expand more quickly as time passes by, and we are confident that the principles of physics which govern the nature of Earth also apply throughout the cosmos.

Basic quantities such as the strength of gravity; or the charge of an electron remain the same within the limits of our ability to measure them, no matter where one is. Atoms shine or decay radioactively in a laboratory on Earth in much the same manner as they do billions of light years across space. Magnetic fields exist everywhere and these magnetic fields affect charged particles in the same way everywhere.

Our Sun is an ordinary star, like billions of others in the Milky Way. Our galaxy is much like other spiral galaxies in the Universe. It is quite likely that our planet is just one of countless rocky planets orbiting stars at habitable distances; not too hot, not too cold.

Five hundred years ago, Nicolaus Copernicus voiced the notion that there is nothing special about our place in the cosmos. The Copernican principle still holds today. It gives us the freedom to apply what we know about Earth, the Sun and the Milky Way to any other location in the cosmos because (we are led to assume) the laws of nature here are quite ordinary.

On the largest scale of all, we are finding that the Universe looks the same in every direction. Any cosmic space contains galaxies arrayed in similar design as any other cosmic space. The faint remnants of heat left over from the explosive origin of the Universe are smooth across the entire sky to within one part in one hundred thousand. We refer to this large-scale uniformity of the Universe as the cosmological principle: matter, motion and energy.
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