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Class Notes: Objects in the Universe

Major components of the universe include

Galaxies

Black Holes

Nebulae

Stars

A galaxy is a large grouping of stars and interstellar gas and dust. These components are
held together in the galaxy by their gravity.

A black hole is a dense body thought to have zero volume but infinite density, which forms
an intense gravity well in space

A nebula is a hot cloud of gas and dust. Stars are formed in the nebula as its materials
slowly condense into regions of higher density due to gravity.

a star is a large ball of gas or plasma that is held together by its own gravity.
Universe, Galaxy, Solar System
How do we define the term
“universe” ?
 Universe:
commonly defined as the totality
of existence, including planets, stars,
galaxies, the contents of intergalactic
space (areas between galaxies), and all
matter and energy
Galaxies
 Galaxies:
massive, gravitationally
bound systems consisting of stars,
stellar remnants, an interstellar
medium of gas and dust, and dark
matter
Solar System
Solar
System: The Sun together
with the group of planets and
other celestial bodies that are
held by its gravitational attraction
and revolve around it
There
is a wide range of galaxy shapes
and sizes. There are four classifications of
galaxies, based on their shapes:
 elliptical
 spiral
lenticular (lens-shaped)
irregular.
Our
galaxy, the Milky Way, is a spiral
galaxy.
Astronomical bodies

Planets

Stars

Moons

Asteroids

Nebulae

Galaxies

Dwarf planets

Comets
Distance
 There
are enormous distances between
objects in space. We use the idea of light
years and scientific notation to help us grasp
these large distances
A
light-year-How far a beam of light travels in
one year
In
one year light travels 9.4607 × 1012 km
Or

you can think about it in miles
6 trillion miles
Stars
Stars radiate energy through the
process of fusion in which two
hydrogen atoms are combined to
form a helium atom, and large
amounts of energy are released.
Some of the energy generated by
the star is in the form of visible light.
Stars

The size and composition of a star determine the
amount of gravity (more mass generates more
gravity) and energy it emits.

Scientists use the Hertzsprung-Russell diagram to
understand the relationship between a star’s
brightness and its surface temperature.
Where are most of the stars?
 On
the Hertzsprung-Russell diagram there is a
band known as the main sequence which
contains about 90% of all stars. This shows that
there is a strong relationship between a star’s
brightness and its surface temperature.
 The
other 10% of stars are special types
(supergiants, giants, and white dwarfs), and each
group falls in a specific area on the diagram.
Hertzsprung-Russell diagram
A
B
S
O
L
U
T
E
Scientists use the
Hertzsprung-Russell
diagram to understand
the relationship between
a star’s brightness and its
surface temperature.
The physical properties of stars:
 Apparent Magnitude (brightness)
 gives the brightness of an object, observed
from any point.
 Absolute brightness (Luminosity)
 gives the brightness of an object as seen from
10 parsecs away.
 Temperature
 color
 Size
 Apparent
magnitude gives the
brightness of an object, observed
from any point.
 Absolute magnitude gives the
brightness of an object as seen from
10 parsecs away.
Brightness
 The
closer and object is to earth the
brighter it looks to the human eye.
 Closer=brighter
 More
distant=fainter in its brightness
Absolute Magnitude
 The
absolute magnitude of an object is
defined as the brightness of an object at a
distance of 10 parsecs away from it.
(A parsec is a unit used to measuring
distances between stars. A parsec is about
3.26 light years, and the distance between
the Sun and Proxima Centauri, the closest
star to the Sun is about 1.3 parsecs).
How do I actually Use this?
The law of Universal Gravitation

Key concepts:

Gravity is a force of attraction between two or more masses.

The Sun, as the most massive object in our solar system, determines the motion of all
other bodies in the system by the force of gravity.

Bodies of the solar system remain in their orbital paths due to a balance between
gravitational forces and the constant forward motion of the celestial bodies.

Strength of the gravitational attraction depends on the mass of the objects involved
and on the distance between them. Gravitational attraction exhibited by an object
increases with increasing mass. If the distance between objects increases,
gravitational attraction between the objects decreases.
Spectrograph-Scientists uses these to
determine the elements found in
stars. It breaks light into colors and
produces an image of the resulting
spectrum
Background Info

All of the celestial bodies in the solar system move in predictable
patterns known as orbits, and this motion is controlled by gravity.
Every celestial body (including Earth) is surrounded by its own
gravitational field, which exerts an attractive force on all objects.
The Sun’s massive gravitational field causes the entire solar system to
orbit around it. Earth’s gravitational field attracts the Moon and
holds it in orbit. The Moon’s gravitational field has attracted
numerous meteorites that made impact craters, and so on.
Gravity in SpaceMASS and DISTANCE

Everything that has mass has gravity.

The more mass an object has, the stronger its
gravitational pull on other objects.


For example, Earth has more mass than the Moon, so its gravitational
field is stronger.
As the distance between two masses increases,
the gravitational attraction between them
decreases

So gravity depends directly on the mass of the objects and inversely on
how far apart they are:
What would happen if there was
no gravity in space?

Earth’s orbit around the Sun is determined by the balance of the
Sun’s gravitational pull on Earth and Earth’s forward momentum as it
travels around the Sun. Without the Sun’s gravitational pull, Earth
would not move in a circle around the Sun, but would continue
moving in a straight line through the Milky Way. Without Earth’s
momentum, the Sun would pull Earth into itself. If an object does not
have enough orbital speed or momentum to resist the pull of
gravity, then it will be pulled into the surface of the larger object.
That is why meteorites crash into the surface of moons and planets.
That is also why the Moon does not crash into Earth; it is orbiting at
just the right speed and has just the right forward momentum to stay
in orbit around Earth.
Planets that orbit the sun
The
Planets Eight major planets
orbit the Sun. They fall into two
main categories:
Inner Planets
Outer Planets
Inner Planets
 The
inner planets:
 Mercury, Venus, Earth, and Mars.
 “terrestrial” (“like Earth”)
 rocky planets
 small and have a dense, solid core and
surface, which we could stand on
Outer Planets

The outer planets

Jupiter, Saturn, Uranus, and Neptune

“Jovian” (“like Jupiter”) planets or gas giants

large and have extensive atmospheres.

Trying to stand on their visible surfaces would be
like trying to stand on a cloud.
Pluto

Pluto is a special case. It used to be called the ninth planet, but after
the discovery of several objects similar to Pluto further out in the Solar
System—the largest of which is larger than Pluto—the International
Astronomical Union decided in 2006 that Pluto belongs to a new class
of objects called dwarf planets, and is not an actual planet.

It is small, like the terrestrial planets, but unlike them, is made of a
mixture of ice and rock.
Comparing Objects in our Solar
System-Review and New Content

The Sun is at the center of our solar system, and its strong gravitational pull
holds eight planets, asteroids, and other celestial objects in orbital paths
around it.

Planets in the solar system revolve around the Sun in an orbital path and can
be either rocky, terrestrial objects, or large and gaseous. Each planet rotates
(spins) on an axis. The inner planets of Mercury, Venus, Earth, and Mars are
mostly solid with minerals similar to those on Earth. The outer planets of Jupiter,
Saturn, Uranus, and Neptune are gaseous masses with rocky cores surrounded
by liquids.

Moons are smaller celestial objects that orbit planets.
Sun
 Is
a medium-sized star
 The most massive object in our solar system
 It is an extremely hot, dense mass of gases, which
radiates visible light and charged particles.
 Located at the center of our solar system, the Sun
rotates (spins) on its axis and does not have a solid
surface.
 Planets in the solar system revolve around the Sun in
an orbital path
Electromagnetic Spectrum
The electromagnetic spectrum is a range of all types
of electromagnetic radiation ranging from very short
wavelengths, including gamma and x-rays, to very
long wavelengths, including microwaves and radio
waves.
 Radiation is energy that travels and spreads through
space.


By studying wavelengths of the electromagnetic
spectrum that reach Earth from stars and other bodies
in the universe, scientists have been able to analyze
properties, distances, and motion of objects in the
universe.
Electromagnetic Spectrum

All objects in the universe emit electromagnetic
radiation. By measuring the wavelengths or
frequencies of light coming from objects,
scientists can infer some of their physical
properties.

The amount of radiation emitted at each
wavelength indicates the temperature of the
object. Therefore, scientists can estimate the
temperatures of faraway celestial bodies based
on the wavelengths of radiation they emit
Technology

Until space travel becomes more commonplace,
scientists must depend on electromagnetic radiation to
bring them information about distant objects in space.

New technologies developed in the late 20th century and
early 21st century allow scientists to use many regions of
the electromagnetic spectrum to explore and measure
the universe. Using devices that are sensitive to light that is
not detectable by human eyes, scientists can “see” by
using computer image-processing techniques that assign
arbitrary color values to the light.
EM Spectrum

Longest wavelength: Radio Waves

Shortest wavelength: Gamma Rays

LONGEST----RMIVUXG-----SHORTEST
Visible Light (ROYGBIV)
The only region in the electromagnetic spectrum that human eyes
can detect is called the visible region. Visible light includes the
colors of the rainbow: red, orange, yellow, green, blue, indigo, and
violet. Within the visible light region, red light has the longest
wavelength and violet light has the shortest.
Jupiter
 Jupiter’s
diameter is roughly 11 times that of
Earth, and 2.5 the mass of all the other planets
in the Solar System combined.
Mercury
The
smallest planet in regards to both mass
and volume is Mercury—this tiny planet is
nearly 20 times less massive than Earth, and its
diameter is about times 2 ½ smaller. In fact,
Mercury is closer in size to our Moon than to
Earth.

Grapefruit

Peppercorn

Large blueberry

Pea

Watermelon

Apple

Lime

Cherry Tomato
A size comparison of the planets in our solar system.
In order of increasing distance from the Sun:
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.