Mysteries About Our Solar System

Mysteries About Our Solar System The universe The Universe is very large and possibly infinite in volume, the observable matter is spread over a space at least 93 billion light years across. For comparison, the diameter of a typical galaxy is only 30,000 light-years, and the typical distance between two neighboring galaxies is only 3 million light-years. As an example, our Milky Way Galaxy is roughly 100,000 light years in diameter, and our nearest sister galaxy, the Andromeda Galaxy, is located roughly 2.5 million light years away. There are probably more than 100 billion (1011) galaxies in the observable universe. Typical galaxies range from dwarfs with as few as ten million (107) stars up to giants with one trillion (1012) stars, all orbiting the galaxy's center of mass.

A light-year is a unit of distance. It is the distance that light can travel in one year. Light moves at a velocity of about 300,000 kilometers (km) each second. So in one year, it can travel about 10 trillion km. More precisely, one light-year is equal to 9,500,000,000,000 kilometers. Why would you want such a big unit of distance? Well, on Earth, a kilometer may be just fine. It is a few hundred kilometers from New York City to Washington, DC; it is a few thousand kilometers from California to Maine. In the universe, the kilometer is just too small to be useful. For example, the distance to the next nearest big galaxy, the Andromeda Galaxy, is 21 quintillion km. That's 21,000,000,000,000,000,000 km. This is a number so large that it becomes hard to write and hard to interpret. So astronomers use other units of distance.

All About the Milky Way The Milky Way is simply the common name for the galaxy that encompasses our solar system. The phrase Milky Way came from the band of white light that can be seen across the celestial sphere visible from Earth. This celestial sphere contains a host of various stars and other solar matter. The discovery of the Milky Way is credited to the ancient Greek philosopher Democritus, who was the first person in recorded history to make the assumption that the Milky Way existed and was made up of billions of distant stars.

The Milky Way is believed to be more than 13 billion years old, which is estimated to be virtually as old as the entire Universe itself. The Milky Way galaxy is actually just one of billions of galaxies contained within the Universe, although very little is currently known about its seemingly infinite galactic counterparts. The Milky Way galaxy has a whopping circumference of roughly 250-300 thousand light years! Within the main body of the Milky Way there are estimated to be between 200 and 400 billion stars. The Earth’s solar system is believed to exist very close to the Galaxy’s galactic plane, due to the fact that the Milky Way essentially divides the night sky into two virtually equal hemispheres. Scientists now estimate that in roughly three billion years, the Milky Way galaxy will actually collide with the Andromeda Galaxy, which is very slowly working its way towards us at a modest speed of about 1,800 kilometers per minute.

Our Solar System The Solar System consists of the Sun and those celestial objects bound to it by gravity, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The Sun's retinue of objects circle it in a nearly flat disc called the ecliptic plane, most of the mass of which is contained within eight relatively solitary planets whose orbits are almost circular. The four smaller inner planets; Mercury, Venus, Earth and Mars, also called the terrestrial planets, are primarily composed of rock and metal. The four outer planets, Jupiter, Saturn, Uranus and Neptune, also called the gas giants, are composed largely of hydrogen and helium and are far more massive than the terrestrials.

The Solar System is also home to two main belts of small bodies. The asteroid belt, which lies between Mars and Jupiter, is similar to the terrestrial planets as it is composed mainly of rock and metal. The Kuiper belt (and its subpopulation, the scattered disc), which lies beyond Neptune's orbit, is composed mostly of ices such as water, ammonia and methane. Within these belts, five individual objects, Ceres, Pluto, Haumea, Makemake and Eris, are recognized to be large enough to have been rounded by their own gravity, and are thus termed dwarf planets. The hypothetical Oort cloud, which acts as the source for long-period comets, may also exist at a distance roughly a thousand times beyond these regions.

Within the Solar System, various populations of small bodies, such as comets, centaurs and interplanetary dust, freely travel between these regions, while the solar wind, a flow of plasma from the Sun, creates a

bubble in the interstellar medium known as the heliosphere, which extends out to the edge of the scattered disc. Six of the planets and three of the dwarf planets are orbited by natural satellites, usually termed "moons" after Earth's Moon. Each of the outer planets is encircled by planetary rings of dust and other particles.