Methods of observation
historically, stars, planets, comets and the Moon have been discovered and plotted with the naked eye
distant stars can be seen because they're so hot and powerful emitters of electromagnetic radiation (e.g. visible light)
optical telescopes
earliest types used to examine the universe
detect visible light and convex refracting lenses and concave reflecting mirrors are used in their construction
the bigger the diameter of the objective lens, the better the quality of the image
the greater the optical quality of the lenses, the better the resolution
mirror-based reflecting telescopes
thee bigger the diameter of the concave mirror, the more light gathered and the better the quality and res of the image
better light-gathering power than the naked eye
anything that changes and reflects or emits visible light can be detected and by using long-time exposures you can detect very faint very distant objects
problems with observations
problems with optical telescopes
absorption of light by Earth's atmosphere
light pollution
the Earth's atmosphere absorbs + scatters light coming from an astronomical resource
reduces the quality of the image
air pollution (e.g. dust) can also absorb/scatter light, diminishing the quality of any image
solutions to the problems
observatories using optical telescopes can be sited high up on mountains in dark places
atmosphere is less dense (thinner), especially in remote places where there is little light/air pollution
how a reflecting telescope works
uses a concave mirror
collects as much light as possible from a distant astronomical object (e.g. star)
by using a magnifying lens in the eyepiece tube, you can produce a clear, focused and greatly magnified image
collected light is reflected by a small plane mirror at ~45° into an eyepiece/camera to record the image
the bigger the telescope, the greater the resolution of the image produced
bigger telescopes can gather more electromagnetic radiation for a computer to produce an image
you can also see further into space
from the 1940s onwards, radar technology collects information EM waves cannot
e.g. radio waves can penetrate through star dust that scatters visible light so we see other features of star systems like detecting stars being born
Infrared radiation penetrates gas and dust, for seeing objects behind the 'stellar debris'
the visible light emitted depends on the age and type of star
used to examine near objects and galaxies
ultraviolet is also used to study young star development and the shapes of galaxies + identifies elements from uv spectral lines
x-ray telescopes give information on very high energy particle interactions happening at the highest temperatures
e.g. when the temperature is many millions of degrees centigrade in the violent explosions of supernovae