Space Flashcards
About Astronomy
Astronomy is the study of the universe and the objects in it
An astronomer is a person who studies astronomy
Celestial Objects
Objects in the universe are called celestial objects
Star - any massive self-luminous celestial body of gas that shines by radiation
derived from its internal energy sources
Planet - a large, rounded astronomical body that is neither a star nor its remnant
Solar System - the Sun together with all the planets and
other celestial objects that are held by the Sun’s gravitational
attraction and orbit around it
Galaxies - a system of millions or billions of stars, together with gas and dust, is
held together by gravitational attraction
Light takes time to travel
When astronomers study celestial objects, they are not seeing
the celestial object as it appears now, but as it appeared in the
past
BECAUSE…
Light takes time to travel!
And nothing can travel faster than the speed of light in a vacuum
according to Albert Einstein’s theory of special relativity
Science of Astronomy
Astronomy involves both empirical and theoretical research.
Scientific theories are explained and supported based on
empirical evidence. Empirical evidence is the data obtained
through direct or indirect observation and experimentation.
Geocentric Model Theory
The belief that the Earth sat at the center of the Universe and the sun,
the moon, and 5 known planets revolved around it
Stars were thought to be fixed to the inside of the “Celestial Sphere”
These beliefs were suggested by the teachings and views of Plato,
Aristotle and Ptolemy
Theory was based on observations of the night sky to explain the
movement of celestial objects from our perspective
Disproving Evidence: Noticed the retrograde movement of planets
across the night sky
Heliocentric Model
Polish astronomer Nicholas Copernicus revived the idea that the Sun was
the center of the universe and Earth and the planets orbited around it —
triggered a revolution in astronomy
In the heliocentric model, each planet orbits the Sun at a different distance.
A planet’s distance from the Sun is called the planet’s orbital radius
The shorter the orbital radius, the faster the planet moves in its orbit due to
distance and gravitational pull
The farther an object is from the Sun, the weaker is the effect of the Sun’s
gravity on that object
For example, Earth, which is closer to the Sun than Mars, orbits the Sun more
quickly than Mars does.
German Mathematician, Johannes Kepler discovered that the orbits of
the planets were ellipses and not circles called elliptical orbits
Supporting Evidence: Technological and scientific advances helped
prove Copernicus’ theory of the model including discoveries made by
Italian scientist, Galileo Galilei using his first telescope — convicted
and placed under house arrest
While disproven in its belief that sun is the center of the universe, the
heliocentric model for our solar system is supported by all
astronomical observations
Galaxies and Expanding Universe
Wilhelm Herschel made important observational advances in
identifying clusters of stars as a galaxy
American Edwin Hubble studied the universe in the 1920’s and
confirmed that galaxies existed beyond the Milky Way
Hubble’s finding suggested that the universe is expanding, the
galaxies are moving away from each other at an accelerated rate —
but Earth is not getting bigger or moving away from objects in the
solar system due to gravity
Hubble’s work and ideas remain the foundation of modern
understanding of nature and formation of the universe — The Big
Bang Theory
The Big Bang Theory
The Big Bang Theory states that the universe formed when an infinitely
dense point suddenly and quickly expanded in a single moment — most
widely accepted theory
As the universe expanded, it cooled and energy was converted in various
subatomic particles which eventually formed simple elements like
helium and hydrogen
This eventually led to the formation the earliest stars, galaxies, and
planets
All of the energy and matter that exists today is the result of this moment
13.8 billion years ago, and marks the beginning of space and time!
Evidence for the Big Bang Theory
Abundance of Elements: The large amount of Hydrogen and
Helium in outer space
Hubble’s Law: The expansion of the universe (cosmological
redshift)
Background cosmic radiation detected (the energy left over from
the massive expansion of the universe 13.7 billion years ago) – echo
from the Big Bang
Observable Universe
Everything you can see, and everything you could possibly see right
now is the observable universe
Light has a finite speed, the farthest we can see comes from the
cosmic microwave background, a time 13.8 billion years ago when
the Big Bang happened — information beyond that hasn’t had time
to reach us
Cosmologists typically assume that our observable universe is just
the nearby part of a greater entity known as “the universe” where
the same physics applies
Theories that our universe is part of a greater multiverse
Measure distance in Solar System
In the solar system, distances become so large it is hard to envision.
Astronomers have developed a unit of measurement for these large distances called an
astronomical unit (AU) to measure distances within the solar system
1 astronomical unit is equal to the distance of Earth to the Sun which is 150 000 000 km!
150 000 000 km is a large number so, we use scientific notation to convert it into a much more
manageable figure that is easier to work with and interpret!
Measure distance beyond the solar system
Outside the Solar System, distances become even larger and AU is no longer
appropriate to use
Astronomers have developed a unit of measurement for these much larger distances
called a Light Year (ly) to measure distances outside the solar system
Light takes time to travel a certain distance and Light Year is the distance light travels
in one year — 9.5 trillion kilometers!!
The Sun
At the center of the solar system is the Sun, which is
a star
A star is a hot ball of plasma, an electrically charged
gas, which shines because nuclear fusion takes place
in it
Nuclear Fusion
Nuclear fusion is the process in which the nuclei of
atoms fuse and release huge amounts of energy
In the Sun’s core, four hydrogen atoms fuse to form
a helium atom
Inner Solar System
A planet is a celestial body that 1) is in orbit around a star 2)
assumes a spherical shape 3) clears the neighbourhood around
its orbit
The planets closest to the Sun are called the Inner Planets
These planets are smaller than some of the other planets in
our solar system and are rocky
Inner planets include Mercury, Venus, Earth, and Mars
Outer Solar System
Between Mars and Jupiter, there is an asteroid belt, a region
of rocky debris that forms a ring around the Sun and separates
the inner planets from the outer ones
The asteroid belt contains rocks of all sizes from tiny as sand
particles, to very large (1000 km across)
The Outer Planets are very large, and made out of gas, and
are often called the gas giants.
Jupiter, Saturn, Uranus, and Neptune are the outer planets
Moon
A moon is a natural satellite that orbits a planet, dwarf planet,
or small solar system body – there are over 200 moons in our
solar system
The Earth has one moon, visible by reflected sunlight, and it
rotates on its axis and revolves around the Earth in the same
amount of time (about a month) so, we only see one side of
the moon
All planets in the solar system have one or more moons
expect Mercury and Venus
Dwarf Planet
Dwarf planet is a celestial body that orbits the sun,
has enough mass to assume a nearly round shape,
BUT has not cleared the neighborhood around its
orbit and is not a moon.
Pluto, Eris, Makemake, and Haumea are some of
the dwarf planets
Other Minor Bodies
Other minor bodies in the Solar System include:
Kuiper Belt Objects (including dwarf planets): a region of the solar
system beyond the orbit of Neptune, believed to contain many
comets, asteroids, and other small bodies made largely of ice
Oort Cloud Objects: a spherical layer of icy objects surrounding our
Sun
Comets: a celestial object consisting of a nucleus of ice and dust
and, when near the sun, a “tail” of gas and dust particles pointing
away from the sun
Asteroids: a small rocky body orbiting the sun
Interplanetary dust and ice
Interstellar Space
Beyond our solar system, the heliosphere, we enter
interstellar space which is the space between star systems.
Beyond our Milky Way is intergalactic space which is the
space between galaxies. All of the astronomical objects and
structures outside of the solar system can be generally
referred to as being in the distant regions of outer space or
deep space.
Galaxy
Galaxy is a huge collection of gas, dust, stars, and their
stellar systems
All galaxies contain stars, planets, dust, and dark matter
held together by gravity
Galaxies tend to occur in groups called galaxy clusters
Galaxy clusters form groups called super clusters
Nebula
Galaxies with more dust than others tend to produce more
new stars, because stars form from dust and gases present
in nebulae
A nebula is a giant cloud of gas and dust in outer space
which gravity pulls together to form stars
Some galaxies, thought to be ancient, have almost no dust
because it has all been used up in star-making
Spiral and Barrel spiral
Looking from the side, a spiral looks like a thin disc
New stars form in the dusty regions of the disc
Widening near the core called central bulge which is
mainly made up of old stars
New stars do not form here due to lack of dust and
gas
Surrounding the central bulge is the galactic halo
which is made up of individual stars
Elliptical
Elliptical galaxies are almost spherical to long and
cylindrical
Such galaxies are formed when other galaxies, such as
spiral galaxies merge
Largest galaxies in the universe are elliptical
Contain very little dust and have fewer young stars than
spiral galaxies
Many of the stars in elliptical galaxies are extremely old
Irregular
Galaxies without a regular shape are called irregular galaxies
Distorted forms of an irregular galaxy may result because the
galaxy collided with another galaxy
OR it got close enough that the gravitational force from the other
galaxy drew stars away
Black Holes
A black hole forms when massive stars collapse at the end of
their life cycle
It is a region of space where gravitational pull is so strong that
nothing, not even light, can escape
After it forms, black holes continue to grow by absorbing mass
of surrounding stars
Each large galaxy contains at least one supermassive black
hole at its center, including the Milky Way
A Quasar is an extremely luminous, active supermassive black
hole
Dark Matter
Dark matter refers to the matter in the universe that is invisible.
It does not emit or absorb light or any other kind of radiation, so cannot be directly
seen with telescope
It makes up about 25% of the universe while celestial objects in space make up less than
10% of the total matter in space
Most of the gravity in the universe is thought to be produced by dark matter
Dark Energy
The remaining 65% of the universe appears to be
made up of a mysterious, invisible force called Dark
Energy that repels gravity
The proposed reason to explain why galaxies are
moving farther away and why the universe is
expanding at an accelerating rate
Composition of Stars
Light is a form of energy that travels in
wavelengths called electromagnetic radiation
Each different colour of the visible spectrum has its
own wavelength and each element has a unique
spectral signature
Stars often have characteristic spectral lines and
analyzing absorption spectral lines indicates which
elements are in a star
Star Clusters
A star cluster is a concentration of
stars in a small region of space (in
a galaxy)
There are two types: Open
Clusters and Globular Clusters
