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BTEC APPLIED SCIENCE UNIT 16 - Learning aim B
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B: Observing and Recording Astronomical Objects Grade Distinction
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Emilia HawkinsUnit 16: Astronomy and Space Science
B: Observing and Recording Astronomical Objects
Section 1:
Optical telescopes
Optical telescopes use light from visible light from the electromagnetic spectrum. It is able to gather
much more light than the human eye to create a magnified image. There are three main types of
optical telescope; refractor, reflector and catadioptrical optical designs. They can be distinguished by
looking at the objective or the part of the telescope that gathers light. The objective used by a
refractor telescope is a glass lens and the objective used by a reflector telescope is a mirror.
Refractor telescopes use lenses to gather and focus light. As the light enters the telescope and
passes through the lens it focuses the light onto a single point at the eyepiece. Refractor telescopes
were the first telescopes made and are commonly used on earth. For example, the largest refracting
telescope ever made was built for the great Paris exhibition of 1900. Refactor telescopes have a
relatively simple design, are easy to use and more reliable due to their optics being permanently
aligned. The glass lenses inside the tube are sealed from the atmosphere meaning that there is very
little maintenance involved as the lenses don’t need to be cleaned. Refracting telescopes are more
expensive as they require high-quality lenses that are difficult to produce without any imperfections.
They also suffer from an effect called chromatic aberration that causes a rainbow of colours to
appear around and distort the image.
Reflector telescopes use a mirror to gather and focus light. The telescope uses parabolic mirrors to
focus the parallel light rays that come from celestial objects. It focuses these light rays onto a single
point to produce high quality images. Reflector telescopes can be used to view celestial objects from
space. For example, the Hubble telescope is a reflector telescope that was launched into space in
1990 that is able to capture more clear observations due to it being above the clouds and earth’s
atmosphere. Reflector telescopes cannot suffer from chromatic aberration due to all wavelengths of
light reflecting off the mirror in the same way. They are also cheaper and easier to produce as light is
only reflecting off one side of the telescopes and therefore only one side has to be perfect. It is much
easier to get the optics of a reflector telescope out of alignment and due to the tube being open to
the outside it regularly needs to be cleaned. When a secondary mirror is used it can cause diffraction
effects such as bright objects having spikes.
Catadioptrical telescopes use components from both refracting and reflecting telescopes to produce
an optical system that has a wider field of view and are easier to manufacture.
Radio telescopes
Radio telescopes use radio frequencies to analyse astronomical objects by using an antenna to
detect radio waves from each spot in the space around an object and storing the information in
pixels. A computer can then turn the information stored into numbers. To increase the field of
search on an object, radio telescopes can be electronically linked together. Some frequency bands
used by radio telescopes are channel 37, hydrogen line and the waterhole.
, Emilia Hawkins
Solar telescopes
Solar telescopes are used specifically to observe the sun at near-infrared and ultraviolet
wavelengths. They can only be operated during the day and when the sun is visible and are usually
located on the top of a tall, white structure. Due to the solar telescope having large amounts of light
to observe, the challenge is being able to control that light so that it doesn’t damage the telescope
and being able to turn the light into something that can be observed.
Infrared telescopes
Infrared telescopes are used to detect astronomical objects that are very far away, by detecting the
infrared radiation that is emitted. Due to most infrared radiation being blocked from earth by its
atmosphere, many infrared telescopes are in space. Infrared telescopes have special cameras which
are constantly kept at temperatures below -150 oC because every hot celestial body emits infrared
radiation.
Ultraviolet telescopes
Ultraviolet light is also blocked from earth by its atmosphere and can therefore only be observed
from space. This allows distant stars and galaxies to be observed more closely because stars that are
in the early or late stage of their life release more UV radiation and are therefore more visible to this
telescope. Most other start only emit infrared and visible wavelengths which means they are
insignificant when looking at ultraviolet light. The first telescope that was able to look at ultraviolet
light was put onto the surface of the moon in the Apollo 16 mission in 1972.
X-ray telescopes
X-ray telescopes are designed to look at extremely distant objects in X-ray frequencies. These
telescopes also have to be launched into space due to X-rays being blocked from reaching earth
because of its atmosphere. X-ray telescopes use mirrors to gather radiation and focus it onto
specialised detectors. The distance between the mirrors and the detector must be roughly a few
meters in order to focus correctly.
Microwave telescopes
Microwave telescopes are put into space due to the earth’s atmosphere absorbing most of the
microwave radiation. Cosmic background radiation is the oldest electromagnetic radiation in the
universe as it was caused by the big bang.
https://www.rankred.com/different-types-of-telescopes/
http://www2.phy.ilstu.edu/~bkc/astronomy/telescop/telescpa.htm
Refractor telescopes
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