•A refracting telescope has two converging (convex) lenses of different POWERS set in line with each other. The lenses can be moved closer or further away from each other to focus the image. The smaller lens is called the EYEPIECE and the larger lens is called the OBJECTIVE LENS. The light gathering power of the telescope is given by D which is the DIAMETER of the lens. REMEMBER: when using angles, the angle of incidence always equals the angle of refraction!
•The reflecting telescope is made up of a large concave mirror to collect reflected light from a distant object like a planet in our solar system. The concave mirror also converges the light to a small plane mirror for the observers eye. The eye lens acts like a magnifying glass to increase the size of the virtual image. Reflecting telescopes have the advantage over refracting telescopes of having bigger mirrors without the image disorting.
The Hubble Telescope is in a fixed position outside the earth's atmosphere. The benefit of it being outside the earth's atmosphere is that the atmosphere absorbs and refracts some of the radiation given out by the stars; so placing a telescope outside the atmosphere ensures that all of the radiation emitted reaches the telescope thus giving a much clearer image.
CONVERGING LENSES AND APERTURE!
A converging lens is one that can focus parallel light rays into a single point. It is important to remember that converging lenses can be fat or thin, and the fatter the lens - the more it will refract the light passing through it. A fat lens that can refract a large amount of light is said to have a short focal length and a HIGH power.
•CONVEX LENS --> CONVERGES LIGHT TO A FOCUS
•CONCAVE LENS --> DIVERGES LIGHT
An aperture of a lens, is the diameter of the OBJECTIVE lens. The LARGER the aperture, the BRIGHTER the image!
RADIO TELESCOPES & LIGHT POLLUTION!
Radio telescopes are used to study naturally occurring radio emission from stars, galaxies, quasars, and other astronomical objects between wavelengths of about 10 meters and 1 millimetre. Radio telescopes are often very large because the galaxies that emit the radio waves they collect are very far away for Earth.
When an astronomer is looking through a telescope and there is a lot of light it is refracted from the lower part of the atmosphere and this will show in the telescope which will reduce the quality. This is called light pollution.
LUNAR & SOLAR ECLIPSES!
A lunar eclipse is when the Moon blocks the Sun’s light falling on Earth’s surface. During the eclipse, the moon takes on a reddish appearance, because red light from the Sun’s rays are refracted around the Earth’s surface.
In a solar eclipse, the Moon blocks the Sun’s light falling on Earth’s surface.
The parallax method is a way of measuring distances of far-away objects. Astronomers use parallax to measure the distance to stars.
Using the Parallex method:
When the Earth moves from one side of the sun (June) to the other (December) every six months. When seen through a telescope based here on Earth, a nearer star will shift its position against the position of a more distant star. The nearer the star the greater the shift. Scientists can therefore work out using this method how far away each star in the night sky is from planet Earth.
A star's brightness depends on two different things. First of all, it depends on the star's surface temperature and second of all, it depends on the size of the star.
Most stars burn at a steady rate, but there are a few which don’t. These stars that don't are called 'Cepheid variable stars'. These stars vary in brightness. Over a period of time they go from bright to dim and back again. These stars are actually expanding and contracting which then changes its luminosity and temperature. The length of time (called a single period) it takes to change brightness and back to it's original brightness is important as this information can be used to calculate its luminosity. The time it take to go dim and then return to original brightness is called the period of variation.
The Sun is the closest star to Earth and formed over four and a half billion years ago. The Sun’s surface is called the photosphere. The temperature of the photosphere is about 6,000° centigrade. Its core is under its atmosphere. The temperature at the core, or very middle, of the Sun, is about 27 million° centigrade.