The Outer Space

The Sun is our nearest star and the central member of the Milky Way galaxy, thanks to this, we can study it better than any other star. The Sun is a yellow dwarf star, which means it is a medium size star. You can believe me or not, the Sun is just a star, just like those we see twinkling at night. The Sun, however, is so much closer to us on Earth that it looks much bigger, much brighter, and we can even feel heat coming from it. Compared to these other stars, the Sun is actually quite average. Many of the stars that appear so small in the night sky are actually much bigger than our Sun. Others, however, are quite tiny in comparison. Some are much hotter, and some are so cool and dim we can barely see them. But for us on Earth, the Sun is just right!

The Sun is a yellow main sequence star comprising about 99% of the total mass of the Solar System. The Sun is made of hot gases, containing many of the same materials we find here on the Earth. These materials, called elements, include hydrogen, helium, calcium, sodium, magnesium, and iron. You can find all of these on any periodic table of elements. The Sun does not have a definite boundary as rocky planets do, and in its outer parts the density of its gases drops approximately exponentially with increasing distance from its center. Nevertheless, it has a well-defined interior structure, described below. The Sun's radius is measured from its center to the edge of the photosphere. This is simply the layer above which the gases are too cool or too thin to radiate a significant amount of light, and is therefore the surface most readily visible to the naked eye. The solar core comprises 10 percent of its total volume, but 40 percent of its total mass. The solar interior is not directly observable, and the Sun itself is opaque to electromagnetic radiation.

The sun is made up of extremely hot, gaseous material. The middle of the Sun is at least 10 million degrees. The "surface" of the Sun (what we see) is only 5800 degrees. This is cool for the Sun, but is actually about 16 times hotter than boiling water. The outer atmosphere of the Sun (which we don't really see with our eyes) gets extremely hot again, about 1.5 to 2 million degrees. These huge temperature changes are very interesting to scientists.

The Sun is very very huge. Even though it looks small in the sky it is actually bigger than you might imagine. It only looks small because it is 93 million miles away. (That's about 150 million km.) The Earth is very tiny compared to the Sun. In fact, if you think of the Sun as a basketball, the Earth would only be the size of the head of a pin -- a mere speck. The Earth is about 13 thousand kilometers (8000 miles) wide, whereas the Sun is roughly 1.4 million kilometers (900,000 miles) across. This means it would take more than 100 Earths to span the width of the Sun. If the Sun were a hollow ball, you could fit about one million Earths inside of it!

Our central star - the Sun, is extremely far from Earth. In fact, it is 93 million miles away. (That's about 150 million km.) If the Sun were the size of a basketball, and Earth the size of the head of a pin, the basketball and the pin would be separated by about 100 feet -- a third of a football field (30.5 meters). If you were standing at the basketball (and didn't have a telescope to help you), you wouldn't even be able to see the pinhead Earth. Another way to understand the distance is to think of driving to the Sun in a car. If you actually could do this, and drove really fast, say 60 miles an hour (80 km/hr), it would take you 176 years to get there. Light from the Sun takes about 8 minutes to reach the Earth. If you understand how fast light travels, you can recognize that the Sun must be very far away.

Although we cannot actually weigh the Sun with a scale, we can compute its weight by studying the way it affects other objects, like the Earth. We do know that it contains virtually all the mass in our solar system! We can also understand this better by making some comparisons. Since the Sun is so much more massive than the Earth (over 300,000 times heavier) its gravitational pull is also much larger. A child that weighs 75 pounds on Earth would weigh about a ton on the Sun. The weight increases by a factor of 30. (Of course, we cannot really stand on the Sun, for it is too hot and has no solid surface.)

The Sun is about 4 1/2 billion years old. Humans have only been around for a tiny, tiny fraction of this time. As a comparison, if you think of 4.5 billion years as the length of a 12 inch ruler, then the time humans have existed wouldn't even be the width of the lines marking the inches. (Metric equivalent is 30.5cm and it would still be just the width of the markings.) The Sun will remain more or less the way it is now for about another 5 billion years. After that, it will exhaust the hydrogen it currently "burns" and will enter a new phase of existence. During this phase the Sun will begin "burning" helium and will expand to about 100 times its current size and become what is called a red giant. Once it runs out of helium it will collapse into a much smaller object called a white dwarf.

Remember one moment: Never look directly at the Sun, even with sunglasses! The human eye is not made to look at an object that bright. It is so bright it could easily blind you in just a few seconds. Have you ever looked at a bright light bulb and then had to look away after a short time? Well, the Sun is about a million times brighter than a household light bulb. This is why you can injure your eyes: if you look directly at the Sun, the inside of your eyes can burn severely and may never heal again. You could lose your sight permanently. In order to study the Sun, scientists look directly at the Sun only with the aid of special instruments that are made to tolerate the extreme brightness. The Sun also emits harmful ultraviolet (UV) radiation, which can damage your skin and eyes. In fact, any tan is a sign of damage to your skin. A sunburn may hurt for a while, but damaging your skin over many years can cause many problems, including skin cancer. That is why you should always wear sunscreen of SPF 15 or higher when you will be out in the Sun for more than a few minutes. This applies even for cloudy days -- though not as bright as sunny days, much of the harmful UV light still comes through. Note that having a tan is little protection from skin damage, providing an SPF of only about 2. To help protect your eyes, use sunglasses that filter 100% of UV light. When you buy glasses, check for labels that say 100% UV Protection. People who do not protect their eyes when they are young run the risk of loss of sight when older and even of getting cataracts.

First of all, let's talk about the general concepts and try to understand how this mysterious space looks like. The Outer space, or better known as the space, consists of the relatively empty regions of the universe outside the atmospheres of celestial bodies. And here goes some new terms, the Universe is identified as everything that physically exists: the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and constants that govern them. However, the term "universe" may be used in slightly different contextual senses, denoting such concepts as the cosmos, the world or Nature. And the second term - celestial bodies, or Astronomical objects, are a significant physical entities, associations or structures which current science has confirmed to exist in space. This does not necessarily mean that more current science will not disprove their existence. Some astronomical objects, such as Themis and Neith are, in light of more recent findings, considered not to exist at all. Others, like Pluto and Ceres, prove to be of an entirely different nature than first expected. In these cases, the scientific community must come to a consensus as to the new status of these objects. Astronomical objects thought to exist based on indirect scientific evidence are considered hypothetical. Astronomical objects can be easily confused with astronomical bodies. The term "body" indicates a simple object, such as a planet. On the other hand, an astronomical object could be an asteroid belt. These terms differ from "celestial objects" and "celestial bodies" only in that the latter terms do not include the Earth. The table below lists the general categories of objects by their location or structure.

Astronomical observations point out that the universe is 13.73 ± 0.12 billion years old and at least 93 billion light years across. The theoretical event that started the universe is called the Big Bang. At this point in time all matter and energy of the observable universe was concentrated in one point of infinite density. After the Big Bang, the universe started to expand to its present form. Since special relativity states that matter cannot exceed the speed of light, in a fixed space-time, it may seem paradoxical that two galaxies can be separated by 93 billion light years in 13 billion years; however, this separation is a natural consequence of general relativity. Stated simply, space can expand with no intrinsic limit on its rate; thus, two galaxies can separate more quickly than the speed of light if the space between them grows. Experimental measurements such as the redshifts and spatial distribution of distant galaxies, the cosmic microwave background radiation, and the relative percentages of the lighter chemical elements, support this theoretical expansion and, more generally, the Big Bang theory, which proposes that space itself was created ex nihilo at a specific time in the past. Recent observations have shown that this expansion is accelerating, and that most of the matter and energy in the universe is fundamentally different from that observed on Earth and not directly observable (cf. dark matter and dark energy). The imprecision of current observations has hindered predictions of the ultimate fate of the universe.

Going further, the term outer space is used to distinguish it from airspace and terrestrial locations. Contrary to popular understanding, outer space is not completely empty (that is a perfect vacuum) but contains a low density of particles, primarily hydrogen plasma, as well as electromagnetic radiation. Theoretically, it also contains dark matter and dark energy. The term "outer space" was originally recorded by a famous science fiction novel writer H. G. Wells in 1901. In point of fact, the shorter term space is much older, being initially used to mean the region beyond Earth's sky in John Milton's Paradise Lost in 1667.