Post on 16-Apr-2020
Astronomy, Stars and Galaxies (2019)
1. Introduction to Astronomy
Humans have been fascinated by objects in the sky for thousands of years.
Different cultures developed different explanations for the existence of
cosmological objects, how they formed, and our place in the universe. The
understanding of the Earth's place in the universe improved over time as humans
become more scientifically advanced. Better instruments allow scientists to make
better observations leading to better models of the earth-sun relationship. The
most popular model and the model you are probably most familiar with is the
Copernican Model show below:
Astronomy is not to be confused with astrology. Astronomy is based on theories
and hypothesis. On the other hand astrology is based on the premise that the
date of birth defines the kind of person you are.
https://youtu.be/FmGBS1Q91RI
Big Bang Theory The most current theory of how the Universe formed is called the Big Bang
Theory which hypothesized that all matter and energy was compressed into one
tiny mass. In one instance the original mass exploded spewing subatomic
particles, and unleashing the four fundamental forces (gravity, strong nuclear
force, weak nuclear force, and electromagnetism) into the space. Within a very
short period of time after the explosion matter moved incredibly high speed to fill
the empty space. As time passes the subatomic particles combined and interact
with each other via the four fundamental forces to form new atoms, stellar
matter, stars, solar systems, and galaxies to occupy the Universe.
Evidence of the Big Bang
The Big Bang Theory is supported by observations. Firstly, the
electro-magnetic energy of quasars is highly red-shifted, as is the light from all
galaxies outside our local group. This red-shift caused Edwin Hubble to rightly
conclude that all galaxies are moving apart, and that the universe is
expanding. Scientists conclude that if all galaxies are moving apart today, then
at some point in the past they were all together.
Secondly, there is ambient level of cosmic radiation that seems be uniformly
spread out in space. Presumably this is the left over of the energy resulting
from the explosion.
Future of the Universe
What the future holds for the universe depends on the balance or competition
between gravity (pulling the universe back in) and momentum (pulling the
universe outwards):
● If the force of gravity wins then the universe is said to be "closed" and
will collapse in what some call the "Big Crunch". This could potentially
lead to a second Big Bang and Big Crunch, repeating forever in what is
called the Oscillating Universe Theory. It is possible that the most recent
Big Bang is not even the first, it could be anywhere from the first to the
43rd billionth!
● If momentum of the galaxies exceeds gravity's ability to slow, stop and
reverse them then the universe is said to be "open" and will expand
forever.
https://youtu.be/sZ59mBnWUEY
3. Studying the Universe
Astronomy would not be possible without scientific observations
made using the naked eyes. Civilizations throughout human
history have used these observations to record the passage of
time and to predict future cosmological events. As scientific
knowledge and technology improve, our understanding of the
properties of the cosmos also improve which helps us to
appreciate our place in the universe.
In this chapter you will be looking at various instruments that
help astronomer study the cosmos.
Optical Telescopes
Telescopes: Eyes to the Universe
Observing stars is done with many instruments. The most popular of which is an optical telescope. Optical
telescopes extends the power of the human eye as it gathers light from cosmological objects, resolves it, and
magnifies it making objects from outer space appear bright, in high contrast, and as large as possible.
Read about the
● history of the telescope.
https://www.nasa.gov/audience/forstudents/9-12/features/telescope_feature_912.html
● the locations of the world's largest optical telescopes.
https://en.wikipedia.org/wiki/List_of_largest_optical_reflecting_telescopes
●
Types of Telescopes
Optical telescopes are classified as refractors or reflectors. Each uses the properties of light and it interaction
with mirrors and lens to bring images of distant object to observable range.
Refractors:
Refractor telescopes make use of lenses to collect light and magnify it
The refracting telescope is basically a tube with a lens on each end as shown in the
link below, each part is important and you should be able to describe the shape
and purpose of each part. Some important notes are included with the diagram so
be sure to read those through.
Reflectors:
Reflector telescopes use mirrors to collect light and lenses to magnify it
A reflecting telescope uses two mirrors in its tube to collect and bend light. Again
a diagram is provided and you are responsible to determine the parts.
Because of the high cost of making perfect mirrors, and any tiny flaw will make the objective in a reflector
useless, many new telescopes use many smaller mirrors to collect the light. These are known as MMT or
multiple mirror telescopes. Each smaller mirror is specially shaped to collect the light and reflect it to the
same focal point. The main advantage is an enormous cost savings on making more small mirrors rather than
one big one.
Maximizing telescope clarity
Various conditions are required for an optical telescope to operate
well; as a result only certain locations are good for placing an
optical telescope. Some of the conditions include: stable night
temperatures, clear weather or being above the weather, far from
the background light of cities and as little atmosphere to block
the light from stars as is possible. As a rule high mountains and
deserts make good locations for optical telescopes.
Hubble Telescope
The Hubble Space Telescope is capable of viewing all wavelengths
and is stationed in orbit around the earth. Because it is in space
its temperature is constant, there is no light pollution in image
from cities, no light is blocked by cloud, no light is absorbed by
the atmosphere and it is always able to point to night somewhere
in space. The Hubble gives excellent image all day every day.
While it is nearing the end of its useful lifetime new technology
will see us one day place a new observational satellite in space
and on the International Space Station.
https://youtu.be/joDtVFGa1-g
Radio Telescopes
Need for Radio Telescopes
Notice that visible light is a very very narrow band of the full electromagnetic
spectrum. Using optical telescopes only, astronomer would miss out on a HUGE
amount of information emitting from stars, galaxies in the non-visible range.
Additionally, a star's maximum brightness is based on temperature. As energy
increases in a star its temperature also increase causing its brightness to increase
as well. However, a star's brightness only shows the visible wavelengths of the
EM. Besides visible light, stars also emit EM waves NOT in the visible range
A radio telescope detects the radio waves given off by stars
and can "see" things our eyes can't. Radio waves can pass
through the atmosphere easily. Unlike visible light which is
lost in daylight, radio waves can be measured 24 hours per
day. Radio telescopes are satellite dishes which collect radio
waves given off by stars and galaxies.
Radio Telescope Array
A radio telescopic array makes use of many satellite dishes
over a long baseline but the multiple dishes can make for a
clearer image. Other telescopes that collect and view X-rays,
gamma rays, infra-red and ultra-violet rays but are not used
on the surface of the Earth due to absorption of these waves
by the atmosphere.
3.3. Other Instruments
Non Optical Telescopes
The Electromagnetic Spectrum
Visible light is characterized by its energy, wavelength and frequency. Light is
only a small part of what is known as the electromagnetic, or EM, spectrum.
Other forms of electromagnetic waves are not visible to human eyes. Some
you may have heard of such as infra-red, ultraviolet, microwaves and X-rays.
The EM spectrum diagram below shows the energy, frequency and
wavelength of each type of EM wave.
All stars produce light. Using a spectroscope to observe their spectra closely
we see dark lines. These are caused by specific elements in the star absorbing
energy at certain wavelengths. Looking closely at the dark lines and their
wavelength we can determine what sort of elements are in the star. Spectra
with dark lines are called absorption spectrum as the light from the spectrum
has been absorbed (leaving black lines) at certain wavelengths. An example of
the absorption spectrum of a gas is below.
Astronomers take the absorption spectra and compares it the emission
spectra to determine the elements in the star.
This is the absorption spectra of
a star which has an unknown
element.
The absorption spectra is
compared to this emission
spectra of a known element.
Using this comparison
astronomers can determine the
elements in the star.
The Spectroscope
You have probably seen a picture similar to one below in which white light is pass through a prism which
breaks down visible white light into seven bands of colours. Astronomers use this principle in an instrument
called the spectroscope to determine the elements in a star.
Emission Spectrum
All atoms and elements will emit light when they are highly energized. Viewed through a spectroscope,
the light generate a pattern called an emission spectrum. Each element will generate a unique emission
spectrum.
In the lab supercharged gases to generate a emission spectrum. The diagram below shows the emission
(bright line) spectra of hydrogen, sodium, helium, neon and mercury.
Absorption Spectrum
All stars produce light. Using a spectroscope to observe their spectra closely we see dark lines. These
are caused by specific elements in the star absorbing energy at certain wavelengths. Looking closely at
the dark lines and their wavelength we can determine what sort of elements are in the star. Spectra
with dark lines are called absorption spectrum as the light from the spectrum has been absorbed
(leaving black lines) at certain wavelengths. An example of the absorption spectrum of a gas is below.
Astronomers take the absorption spectra and compares it the emission spectra to determine the
elements in the star.
This is the absorption spectra of a
star which has an unknown
element.
The absorption spectra is
compared to this emission spectra
of a known element.
Using this comparison astronomers
can determine the elements in the
star.
Cameras
Cameras and CCD (charge coupled devices) are used
to capture film and digital images of stars for later
study. They can also be used to determine
variations in brightness and position from hour to
hour or night to night. A digital camera set on a
time long exposure can capture star trails.
Blue and Red Shifting
We know when a sound source is moving towards or away from us its volume changes. We also know that its pitch changes in a phenomena call The Doppler Effect. Light exhibit a similar
behavior called Blue shifting or Red shifting.
You'll learn more about these later on.
https://youtu.be/Kg9F5pN5tlI
3.4. Modern Space Exploration
In 1957 Sputnik I was the first artificial satellite launched into space by the USSR.
The satellite was small, battery powered and could barely manage to send a radio
signal back to Earth. Later that same year the USSR sent the first dog, Laika, into
space on Sputnik II. In 1958 Gordo the monkey was launched by the USA into
space aboard a rocket. Unfortunately when his craft landed in the ocean it sank
and Gordo was never to be seen again. 1959 saw the USSR send an unmanned
rocket around the Moon and brought back the first images of the far side (recall
from last lesson that the same side always faces Earth).
Human's first ventured into space was in 1961 when the USSR sent Yuri Gagarin
around the Earth in a rocket. The early 1960's saw several unoccupied probes land
on the moon, the first woman in space. In 1967 the USSR landed Venera probes
on Venus, sending back images of Venus beneath the clouds. 1969 saw the USA
successfully land Neil Armstrong and Buzz Aldrin of the Apollo 11 mission on the
surface of the moon. Budgetary cut backs in both the USSR and USA saw space
exploration slow to a crawl but the two countries staged joint meetings and
research on Skylab and Salyut space stations in orbit.
During the late 1970's and 1980's space research focused on launching
communication satellites, spy satellites, and research into space based weaponry.
The invention of the space shuttle changed the path of exploration by allowing
re-usable spacecraft and rockets to drop costs and re-initiate opportunity.
Satellites were used to carefully map and measure the Earth. With increasing
ultraviolet, infra-red, and radio wave technologies in the EM spectrum we were
able to look at and view the Earth differently from above.
The invention of the Global Positioning System, GPS, by the US military in the
1990's was made possible with the use of 24 satellites in fixed orbits above the
earth. Any ships, aircraft, tanks, personnel and supplies across the surface of the
Earth with a GPS transponder can calculate its distance from any 3 satellite. Then,
comparing the three measurements it can locate itself on Earth's surface to within
2 meters.
Most recent advances include the Mars rovers, unmanned, robotic explorers we
have landed on Mars, the Cassini and Huygens probes for studying Jupiter, the
Hubble Space Telescope, satellite probes showing desertification, ozone layer
holes, weather systems, hurricane structure, carrying telephone and television
signals to name a few.
Space exploration is not without risk. Financially, billions of dollars every year
from many governments around the world are spent on telescopes, rockets,
space stations, astronaut training, probes etc. Additionally, 21 people have lost
their lives over a period of 50 years. Notably, in the 1967 Apollo 1 disaster, a fire
onboard the rocket killed three USA Apollo astronauts. Then in 1986 the space
shuttle Challenger blew up when it launched, killing the seven astronauts aboard.
https://youtu.be/4s4AlG44EKc