ASTROPHYSICS OR SPACE PHYSICS
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ASTRO PHYSICS OR SPACE PHYSICS
Space Physics is the science of what the Universe is, how
it came to be this way, what its fate is, and what it's made up of.
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GALAXY
called a galaxy.
A group of billions of stars and planets is
POINTS TO REMEMBER
a. Galaxies are each made up of many billions of stars.
b. The Sun is a star in the galaxy known as the Milky
Way.
c. Other stars that make up the Milky Way are much
further away from the Earth than the Sun is from the
Earth.
d. Astronomical distances can be measured in light-years,
where one light-year is the distance travelled in (the
vacuum or space) by light in one year.
e. One light-year is equal to 9.5 × 1015 metres.
f. The diameter of the Milky Way is approximately,
100 000 light-years.
This means that light would take 100 000 years to
travel across it.
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Stars are luminous astronomical objects
comprising of gases in the plasma state which are held
together by their gravity.
DARK MATTER
Dark matter seems to be the scaffolding on
which galaxies are built or considered as a glue
between the galaxies.
Researchers’ best guess is that dark matter is made up
of particles that do not absorb, reflect or emit light. So they
cannot be directly observed and detected using
electromagnetic radiation.
DARK ENERGY
Dark energy is the name given to the
mysterious force which accelerates the rate of
expansion of our universe.
It acts against the gravitational force, which tries to
bring the universe together. Dark energy can escape a black
hole because dark energy is not affected by gravity.
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OUR SOLAR SYSTEM
Our Solar System is the gravitationally bound system of
the Sun and the objects that orbits it.
• The SUN is a star that radiates energy and light
• The Earth is a planet that orbits the Sun
• There are 8 planets and several dwarf planets which orbit
round the Sun.
• The Moon is a satellite that orbits around the Earth.
. Other constituents of our solar system are
asteroids, meteors, comets and space dust.
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COMET
ASTEROID
METEOR
COMETS
COMETS can be called space snowballs, filled with
frozen gas (ice), rock and dust, formed along with our solar
system. They also orbit around the Sun, but in very
irregular, highly elliptical orbits. When they move towards
the sun, the dust and ice vaporize to form a comet’s tail.
ASTEROIDS
ASTEROIDS are rocky pieces left out after the
formation of the planets in our solar system. They are
mostly found in the asteroid belt formed between Mars and
Jupiter, orbiting the sun. [Seen in the inner solar system]
METEORS
When a meteoroid approaches closer to the surface of
Earth and enters the atmosphere, it vaporizes to form a
METEOR, which is visible to us as a streak of light. We often
call them the “shooting stars”.
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METEOROIDS
METEOROIDS are small rocky or metallic body in outer
space like asteroid, but significantly smaller than asteroids
METEORITES
When meteoroids do not vaporize completely in the
atmosphere and land on the Earth’s surface like a rock
piece, it is known as METEORITES. It can cause much
damage.
PLANETS
A PLANET is a non-stellar astronomical body
that is massive enough to be rounded by its own gravity,
that directly orbits a star, and that has cleared its orbital
zone.
CONDITIONS NECESSARY FOR A BODY TO BE A PLANET
1. Should orbit the star
2. Should have enough mass that its gravity
pulls it into a spherical shape
3. Should have large enough gravitational force to
clear its orbit.
[ ie. to clear away any other object of
a similar size near its orbit around the Sun]
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PLANETS IN OUR SOLAR SYSTEM
We have got 8 planets in our solar system.
Planets which can be seen with our naked eye:
Mercury, Venus, Earth, Mars, Jupiter
Name of the planets in the correct order from the Sun :
1. MERCURY
2. VENUS
3. EARTH
4. MARS
5. JUPITER
6. SATURN
7. URANUS
8. NEPTUNE
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The four planets nearest the Sun are
rocky and small and the four planets furthest from
the Sun are gaseous and large.
Pluto was considered as a tiny planet till 2006.
Pluto failed the third condition due to another
dwarf planet called ERIS close to Pluto. Now
Pluto is considered as a dwarf planet.
DWARF PLANETS
DWARF PLANETS are objects in the
solar system which orbits the Sun. They are
large enough that their gravity caused them to
form a spherical shape, but they may not be able
to clear their orbit.
Example: Pluto, Eris, Ceres etc..
It is believed to have more than
200 dwarf planets in our solar system.
SATELLITES
A satellite is an object in space that
orbits or circles around a bigger object.
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EARTH, SUN, MOON
DAY AND NIGHT
Day and Night are caused by the spinning of
the Earth on its axis.
[Axis is the imaginary line between the poles, and
it is tilted through an angle of 23.50]
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The Earth takes 24 hours [23hours 57
minutes] for one complete spin or rotation.
It has anticlockwise rotation.
Sun appears to move from east to west,
but the fact is that the Earth moves from west to east.
Venus and Neptune are exceptionshaving clockwise rotation.
What is DAY and NIGHT?
The side of the earth
facing the Sun experiences light and we call it day
while the other side experiences darkness and we call
it night. As the Earth rotates, the other side of the
Earth become day and opposite side becomes night.
EQUINOXES AND SOLSTICES
SOLSTICES_ longest and shortest days
June 20th or 21st and December 21st or 22nd
EQUINOXES_ Day and night are equally long.
March 21st and September 23rd
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[Longest day for northern hemisphere and
shortest day for southern hemisphere on June 20th
or 21st
AND
longest day for southern hemisphere and shortest
day for northern hemisphere on Dec 21st or 22nd]
Land of midnight Sun – NORWAY
SEASONS
The seasons occur because of the tilt of the
Earth`s axis and due to the rotation and
revolution of the Earth.
The Earth`s axis is tilted through an angle
of 23.50.
This tilting remains in the same direction
throughout its revolution.
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The Earth orbits the Sun, and it takes 365 days to
complete one orbit or one revolution. So, there will be 365
spins in one year, for the Earth. That means, there are 365
days and nights in one year.
So, when the axis points towards the
Sun, northern hemisphere gets direct sunlight,
and it is summer there and winter in the
southern hemisphere.
When the axis points away from the
Sun, northern hemisphere will have winter
and southern hemisphere will have summer.
At midpoints, axis will be 900 away from the
Sun, though it is tilted sideways. This causes
equinox, and northern hemisphere and
southern hemisphere will have spring and
autumn.
Countries at the equator do not
experience seasons because the Sun`s rays
always hit them at the same angle.
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PHASES OF THE MOON
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Phases of the Moon means, the different
ways the Moon looks, when viewed from the Earth
over a period of one month.
The moon is a rocky sphere which we only
see when it reflects light from the Sun. The moon
orbits (revolves) round the Earth and it takes 27.5
days for one complete revolution. [Also, for one
complete rotation.]
As the Moon orbits the Earth, half of the
Moon that faces the Sun will be lit up by the Sun. As
the Moon moves, the shape of the lighted part of the
Moon which can be seen from the Earth changes. So,
we see the Moon in different shapes, and we call it
different Phases of the Moon.
When the Moon completes one revolution
or when all the phases of the Moon are completed in
27.5 days, we consider it as one month.