Let's Understand About Space
We often refer to our expanding universe with one simple word: space.
But where does space begin and, more importantly, what is it?
Space is an almost perfect vacuum, nearly void of matter and with
extremely low pressure. In space, sound doesn't carry because there
aren't molecules close enough together to transmit sound between them.
Not quite empty, bits of gas, dust and other matter floats around
"emptier" areas of the universe, while more crowded regions can host
planets, stars and galaxies.
From our Earth-bound perspective, outer space is most often thought to
begin about 62 miles (100 kilometers) above sea level at what is known
as the Kármán line. This is an imaginary boundary at an altitude where
there is no appreciable air to breathe or scatter light. Passing this
altitude, blue starts to give way to black because oxygen molecules
are not in enough abundance to make the sky blue.
Spaceships
The station was designed between 1984 and 1993. Elements of the
station were in construction throughout the US, Canada, Japan, and
Europe beginning in the late 1980s.
The International Space Station Program brings together international
flight crews, multiple launch vehicles, globally distributed launch
and flight operations, training, engineering, and development
facilities, communications networks, and the international scientific
research community.
Moon
The Moon is Earth's only natural satellite. It orbits at an average
distance of 384,400 km (238,900 mi), about 30 times the diameter of
Earth. Tidal forces between Earth and the Moon have over time
synchronized the Moon's orbital period (lunar month) with its rotation
period (lunar day) at 29.5 Earth days, causing the same side of the
Moon to always face Earth. The Moon's gravitational pull – and to a
lesser extent, the Sun's – are the main drivers of Earth's tides.
Earth's Moon is the brightest and largest object in our night sky. The
Moon makes Earth a more livable planet by moderating our home planet's
wobble on its axis, leading to a relatively stable climate. It also
causes tides, creating a rhythm that has guided humans for thousands
of years.
Nebula
A nebula is a giant cloud of dust and gas in space. Some nebulae (more
than one nebula) come from the gas and dust thrown out by the
explosion of a dying star, such as a supernova. Other nebulae are
regions where new stars are beginning to form. For this reason, some
nebulae are called "star nurseries.
Nebulae are made of dust and gases—mostly hydrogen and helium. The
dust and gases in a nebula are very spread out, but gravity can slowly
begin to pull together clumps of dust and gas. As these clumps get
bigger and bigger, their gravity gets stronger and stronger.
Eventually, the clump of dust and gas gets so big that it collapses
from its own gravity. The collapse causes the material at the center
of the cloud to heat up-and this hot core is the beginning of a star.