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The Moon is Earths only known natural satellite, and the fifth largest satellite in the Solar System. It is the largest natural satellite of a planet in the Solar System relative to the size of its primary, having a quarter the diameter of Earth and 1⁄81 its mass. The Moon is the second densest satellite after Io, a satellite of Jupiter. It is in synchronous rotation with Earth, always showing the same face <- Moonwalk
Space is bigger than the human mind can imagine, it is impossible to measure so no one knows how big space really is. All we know is thatearth is in space and it is also home to many other planets. Space doesn’t have a colour but some people believe that it is black. Space is the void that exists beyond any celestial body, including the Earth.It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos. In the space between galaxies, matter density can be as low as a few atoms of hydrogen per cubic meter
Earth formed 4.54 billion years ago, and life appeared on its surface within one billion years.The planet is home to millions of species, including humans. Earths biosphere has significantly altered the atmosphere and other abiotic conditions on theplanet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earths magnetic field, blocks harmful solar radiation, permitting life on land. The physical properties of the Earth, as well as itsgeological history and orbit, have allowed life to persist during this period. The planet is expected to continue supporting life for at least another 500 million years.
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. Of the many objects that orbit the Sun, most of the mass is contained within eight relatively solitary planets whose orbits are almost circular and lie within a nearly flat disc called the ecliptic plane. 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, the gas giants, are substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are composed largely of ices, such as water, ammonia and methane, and are often referred to separately as "ice giants".
Think you know everything there is to know about stars? Think again! Here’s a list of 10 interesting facts about stars; some you might already know, and few that are going to be new 1. The Sun is the closest star Okay, this one you should know, but it’s pretty amazing to think that our own Sun, located a mere 150 million km away is average example of all the stars in the Universe. 2. Stars are made of the same stuffAll stars begin from clouds of cold molecular hydrogen that gravitationally collapse. As they cloud collapses, it fragments into many pieces that will go on to form individual stars. The material collects into a ball that continues to collapse under its own gravity until it can ignite nuclear fusion at its core. 3. Stars are in perfect balanceYou might not realize but stars are in constant conflict with themselves. The collective gravity of all the mass of a star is pulling it inward. If there was nothing to stop it, the star would just continue collapsing for millions of years until it became its smallest possible size 4. Most stars are red dwarfs If you could collect all the stars together and put them in piles, the biggest pile, by far, would be the red dwarfs. These are stars with less than 50% the mass of the Sun. Red dwarfs can even be as small as 7.5% the mass of the Sun. 5. Mass = temperature = color The color of stars can range from red to white to blue. Red is the coolest color; that’s a star with less than 3,500 Kelvin. Stars like our Sun are yellowish white and average around 6,000 Kelvin. The hottest stars are blue, which corresponds to surface temperatures above 12,000 Kelvin. So the temperature and color of a star are connected. Mass defines the temperature of a star. The more mass you have, the larger the star’s core is going to be
6. Most stars come in multiplesIt might look like all the stars are out there, all by themselves, but many come in pairs. These are binary stars, where two stars orbit a common center of gravity. And there are other systems out there with 3, 4 and even more stars. Just think of the beautiful sunrises you’d experience waking up on a world with 4 stars around it. 7. The biggest stars would engulf SaturnSpeaking of red giants, or in this case, red supergiants, there are some monster stars out there that really make our Sun look small. A familiar red supergiant is the star Betelgeuse in the constellation Orion. It has about 20 times the mass of the Sun, but it’s 1,000 times larger. But that’s nothing. The largest known star is the monster VY Canis Majoris. This star is thought to be 1,800 times the size of the Sun; it would engulf the orbit of Saturn! 8. The most massive stars are the shortest livedI mentioned above that the low mass red dwarf stars can sip away at their fuel for 10 trillion years before finally running out. Well, the opposite is true for the most massive stars that we know about. These giants can have as much as 150 times the mass of the Sun, and put out a ferocious amount of energy. 9. There are many, many stars Quick, how many stars are there in the Milky Way. You might be surprised to know that there are 200-400 billion stars in our galaxy. Each one is a separate island in space, perhaps with planets, and some may even have life. But then, there could be as many as 500 billion galaxies in the Universe, and each of which could have as many or more stars as the Milky Way. Multiply those two numbers together and you’ll see that there could be as many as 2 x 1023 stars in the Universe. That’s 200,000,000,000,000,000,000,000. 10. And they’re very far With so many stars out there, it’s amazing to consider the vast distances involved. The closest star to Earth is Proxima Centauri, located 4.2 light-years away. In other words, it takes light itself more than 4 years to complete the journey from Earth. If you tried to hitch a ride on the fastest spacecraft ever launched from Earth, it would still take you more than 70,000 years to get there from here.
COMETS are members of our Solar System. But unlike the Earth and other planets, which always stay at approximately the same distance from the Sun, most comets are great travelers that spend most of their time on the outskirts of the Solar System (way beyond Pluto!) and then wisk in briefly for a close pass near the Sun. The comets that pass close to the Sun originally came from one of two places: either the Oort Cloud or the Kuiper Belt. You can think of the Oort Cloud as a giant spherical shell surrounding the Sun thats filled with about 1 million million comets The Kuiper Belt refers to a roughly disk-shaped region that extends from just beyond Plutos orbit out to about twice Plutos orbit. It is often not very easy to tell whether a comet originally came from the Oort Cloud or the Kuiper Belt. For example, Halleys comet has a period of only 76 years, but many astronomers believe that Halley was once in the Oort Cloud.
At the center of a comet is the NUCLEUS, which is typically only about 1 to 10 miles across. Except when various spacecraft flew near the nucleus of Comet Halley in 1986, no one has ever seen a comet nucleus directly.As the nucleus moves closer and closer to the Sun, it gets warmer and warmer, which causes its ices to evaporate. When the ices evaporate, they drag DUST particles off of the surface of the comet. Sunlight reflecting off of these dust particles produces a COMA, which is primarily what you see when you look at a comet.The dust particles leaving the nucleus are pushed by light from the Sun into a DUST TAIL. The gas molecules (like water, carbon monoxide, and carbon dioxide) that evaporated from the ices are ionized by sunlight (the sunlight tears off one of their electrons) and are pushed by the solar wind into an ION TAIL.