The Moon is Earth's 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
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 that
earth 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
Up Mercury Saturn
Naming Venus Uranus
Planets Earth Neptune
Mars Pluto (ish)
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. Earth's biosphere
has significantly altered the atmosphere and other abiotic conditions on the
planet, enabling the proliferation of aerobic organisms as well as the formation of the
ozone layer which, together with Earth's magnetic field, blocks harmful solar
radiation, permitting life on land. The physical properties of the Earth, as well as its
geological 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 stuff
All 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 balance
You 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 multiples
It 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 Saturn
Speaking 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 lived
I 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
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 that's filled with about 1 million million comets
The Kuiper Belt refers to a roughly disk-shaped region that extends from just beyond Pluto's
orbit out to about twice Pluto's orbit.
It is often not very easy to tell whether a comet originally came from the Oort Cloud or the
Kuiper Belt. For example, Halley's 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.
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