Exploring our Universe I

Milky Way, the large, disk-shaped aggregation of stars, or galaxy, that includes the Sun and its solar system. In addition to the Sun, the Milky Way contains about 400 billion other stars. There are hundreds of billions of other galaxies in the universe, some of which are much larger and contain many more stars than the Milky Way. The Milky Way is visible at night, appearing as a faintly luminous band that stretches across the sky. The name Milky Way is derived from Greek mythology, in which the band of light was said to be milk from the breast of the goddess Hera. Its hazy appearance results from the combined light of stars too far away to be distinguished individually by the unaided eye. All of the individual stars that are distinct in the sky lie within the Milky Way Galaxy.

From the middle northern latitudes, the Milky Way is best seen on clear, moonless, summer nights, when it appears as a luminous, irregular band circling the sky from the northeastern to the southeastern horizon. It extends through the constellations Perseus, Cassiopeia, and Cepheus. In the region of the Northern Cross it divides into two streams: the western stream, which is bright as it passes through the Northern Cross, fades near Ophiuchus, or the Serpent Bearer, because of dense dust clouds, and appears again in Scorpio; and the eastern stream, which grows brighter as it passes southward through Scutum and Sagittarius. The brightest part of the Milky Way extends from Scutum to Scorpio, through Sagittarius. The center of the galaxy lies in the direction of Sagittarius and is about 25,000 light-years from the Sun (a light-year is the distance light travels in a year, about 9.46 trillion km or 5.88 trillion mi).

Moon is the name given to the only natural satellite of Earth. The Moon is the second brightest object in Earth’s sky, after the Sun, and has accordingly been an object of wonder and speculation for people since earliest times. The natural satellites of the other planets in the solar system are also sometimes referred to as moons. Telescopes have revealed a wealth of lunar detail since their invention in the 17th century, and spacecraft have contributed further knowledge since the 1950s. Earth’s Moon is now known to be a slightly egg-shaped ball composed mostly of rock and metal. It has no liquid water, virtually no atmosphere, and is lifeless. The Moon shines by reflecting the light of the Sun. Although the Moon appears bright to the eye, it reflects on average only 12 percent of the light that falls on it. This reflectivity, called albedo, of 0.12 is similar to that of coal dust. The diameter of the Moon is about 3,480 km (about 2,160 mi), or about one-fourth that of Earth. The Moon’s mass is only 1.2 percent of Earth’s mass. The average density of the Moon is only three-fifths that of Earth, and gravity at the lunar surface is only one-sixth as strong as gravity at sea level on Earth. The Moon moves in an elliptical (oval-shaped) orbit around Earth at an average distance of 384,403 km (238,857 mi) and at an average speed of 3,700 km/h (2,300 mph). It completes one revolution in 27 days 7 hours 43 minutes. For the Moon to go from one phase to the next similar phase—as seen from Earth—requires 29 days 12 hours 44 minutes. This period is called a lunar month. The Moon rotates once on its axis in the same period of time that it circles Earth, accounting for the fact that virtually the same portion of the Moon (the “near side”) is always turned toward Earth.

This series takes a fascinating new look at a very old universe. Fifty years after man first ventured into outer space, we examine the greatest secrets of the heavens. Each episode outlines how humans have explored the universe, and scrutinises the discoveries they have made. We look at hi-tech space telescopes which record the violent birth of stars, robotic rovers which glimpse the red surface of Mars, and sophisticated NASA probes which delve into the mysterious make-up of comets. As the earth churns ominously with the effects of global warming, this is a revealing and prescient journey into the heavens. From the planets to the stars and out to the edge of the unknown, history and science collide in this epic exploration of the Universe and its mysteries.

If we hope to truly ascertain our place in such a vast and bewildering universe, we must take a look far, far away into the realm of Alien Galaxies. Our galaxy is just one of hundreds of billions in the universe. The Milky Way consists of more than a billion stars, our sun being only one of them. In Alien Galaxies, we take a view of the universe through the Hubble Space telescope and go back almost all the way to the Big Bang. Cutting-edge computer graphics are used to bring the universe down to earth. We show what life would be like on other planets, and to imagine what life forms might evolve in alien atmospheres.

The Sun is the closest star to Earth. The Sun is a huge mass of hot, glowing gas. The strong gravitational pull of the Sun holds Earth and the other planets in the solar system in orbit. The Sun’s light and heat influence all of the objects in the solar system and allow life to exist on Earth. The Sun is an average star—its size, age, and temperature fall in about the middle of the ranges of these properties for all stars. Astronomers believe that the Sun is about 4.6 billion years old and will keep shining for about another 7 billion years.

For humans, the Sun is beautiful and useful, but also powerful and dangerous. As Earth turns, the Sun rises over the eastern horizon in the morning, passes across the sky during the day, and sets in the west in the evening. This movement of the Sun across the sky marks the passage of time during the day (see Sundial). The Sun’s movement can produce spectacular sunrises and sunsets under the right atmospheric conditions. At night, reflected sunlight makes the Moon and planets bright in the night sky.

As the earth churns ominously with the effects of global warming, this is a revealing and prescient journey into the heavens. From the planets to the stars and out to the edge of the unknown, history and science collide in this epic exploration of the Universe and its mysteries. Ignited by the power of the atom, and burning with light, heat and wrath, stars are anything but peaceful. They collide, devour each other, and explode in enormous supernovas - the biggest explosions in the Universe. Using cutting-edge computer graphics, never-before-seen satellite images, and interviews with the world’s leading astronomers, take a front row seat at the most amazing light show in the cosmos.

Finding life on other planets (Aliens!) is a tantalising prospect that occupies our daydreams. And yet with the constant onslaught of new technology are we fast approaching a time when it could become a reality? To humans, the idea of being alone in a Universe at least 10 to 13 billion light years across is disconcerting. The philosophical ramifications of being alone in such an overwhelming expanse of spacetime cannot be overstated. Given everything we know about the current rate of star and planetary formation, however, it would seem illogical that we should be the only sentient beings in the Universe. And given what we do know about the structure of life here on Earth and of molecules found thus far in the interstellar medium, it would appear that carbon could be the key to life's development anywhere in the Universe. While we can only continue to speculate about the extraterrestrial development of life and intelligence, we do know that carbon production is based on the rate of star formation. Estimates by the Hubble Space Telescope strongly suggest that carbon production peaked almost 7 billion years ago. Given the time span necessary for biological evolution as we know it, some theorists now believe that it is highly unlikely that the Universe could have seen the first carbon-based intelligent life any sooner than 3 billion years ago, or when the Universe was already more than 10 billion years old. In other words, the evolution of extraterrestrial intelligent life could be a very "recent" cosmic phenomenon. In fact, as Mario Livio from the Space Telescope Science Institute and Charles Lineweaver from the University of New South Wales in Sydney have both pointed out, the Universe may only just be awakening to an epoch of intelligent life. As Lineweaver has noted, at this stage in our own development, it is impossible to know whether we have come late or early to the cosmic party, but in the long history of our Universe, we might be relative newcomers.

The Big Bang theory is an effort to explain what happened at the very beginning of our universe. Discoveries in astronomy and physics have shown beyond a reasonable doubt that our universe did in fact have a beginning. Prior to that moment there was nothing; during and after that moment there was something: our universe. The big bang theory is an effort to explain what happened during and after that moment.

According to the standard theory, our universe sprang into existence as "singularity" around 13.7 billion years ago. What is a "singularity" and where does it come from? Well, to be honest, we don't know for sure. Singularities are zones which defy our current understanding of physics. They are thought to exist at the core of "black holes." Black holes are areas of intense gravitational pressure. The pressure is thought to be so intense that finite matter is actually squished into infinite density (a mathematical concept which truly boggles the mind). These zones of infinite density are called "singularities." Our universe is thought to have begun as an infinitesimally small, infinitely hot, infinitely dense, something - a singularity. Where did it come from? We don't know. Why did it appear? We don't know.

After its initial appearance, it apparently inflated (the "Big Bang"), expanded and cooled, going from very, very small and very, very hot, to the size and temperature of our current universe. It continues to expand and cool to this day and we are inside of it: incredible creatures living on a unique planet, circling a beautiful star clustered together with several hundred billion other stars in a galaxy soaring through the cosmos, all of which is inside of an expanding universe that began as an infinitesimal singularity which appeared out of nowhere for reasons unknown. This is the Big Bang theory.

In The Search for ET, we explore the possibilities of alien life on other planets. In a galaxy filled with a billion stars, and in a universe filled with a hundred billion galaxies, are we alone? SETI (the Search for Extraterrestrial Intelligence) is a privately funded project using radio telescopes and optical telescopes to scan the stars for signals. NASA is planning missions to Mars, Jupiter’s sixth moon, Europa, and Saturn’s largest moon, Titan, to look for primitive, microbial life in ice concentrations. Whether we discover primitive or intelligent life, how will that knowledge impact humankind’s view of itself? Cutting-edge computer graphics are used to bring the universe down to earth to show what life would be like on other planets, and to imagine what kind of life forms might evolve in alien atmospheres.

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