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
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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
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