Category Science

How do scientists know the distance of the nearby stars?

The stars lie millions of times farther away than the sun, so astronomers have to use different techniques to establish their distance. The most important is the method of Parallax, which involves measuring the angle of the movement of a star between two points and relating it to the Earth’s orbit.

A simple experiment illustrates the method. Hold a finger in front of your face; in relation to the background. Now close that eye and open the other. The finger seems to have moved. The nearer the finger is to your face, the greater distance it seems to move.

In astronomy, the finger is the nearby star whose distance is being measured. Astronomers observe its position relative to very distant stars, looking at it from two different positions in the Earth’s orbit. By measuring the angle of the stars apparent movement between these two positions, also known as the Parallax angle, and knowing the diameter of the Earth’s orbit, astronomers can calculate the distance.

The Parallax angle is measured in arc seconds. One arc second is 1/3600 of a degree in the sky, or roughly 1/2000 the apparent size of the moon. The distance to a star in light-years is 3.26 divided by the Parallax angle. The result is given in parsecs, which is the unit of distance that corresponds to a parallax of one second of arc, or 3.26 light years. Using this method, astronomers have found the distance to hundreds of the nearest stars. For example, the nearest star to the sun is a faint one called Proxima Centuari, which lies 4.22 light years away or 1.2 parsecs. The brightest star in the sky, Sirius, is 8.6 light years away, or 2.64 parsecs.

 

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How do scientists know the distance of the Sun?

Radar cannot be used to work out the distance of the sun because it is not solid. Instead, astronomers base their calculations on the law of planetary motion. This is the third law discovered by the astronomical Johannes Kepler (1571-1630) in 1618. It states that the square of the time it takes for a planet to complete a journey around the sun (the orbital period) is equal to the cube of the planets mean distance from the sun.

Using Kepler’s law, astronomers could calculate the average distance of the earth from the sun. This value is now known to be 92,955,630 miles (149,597,870km). The Earth-Sun distance is defined as one unit, called an astronomical unit, or AU. Astronomers use this unit to calculate how far the other planets are from the Sun. First they must find the distance from the Earth to the planet. To do so they can use either Parallax or radar.

Using radar, it is possible to tell, for example, that the distance of Venus from Earth, when the two are at their closest, is 26,000,000 miles (42,000,000 km). But astronomers also know that it takes Venus 224.7 days (or .615 of the year) to orbit the sun. According to Kepler‘s law, then, Venus’s distance from the sun is .72AU (since .615 of a year’s equals .72AU cubed).

 

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How do scientists know the distance between the planets?

When it comes to the planets in the solar system, astronomers don’t have reflectors to return pulses of light. Instead, they use radar. Before radar was available they used the speed of light and the Parallax method to calculate the distance of planets. Today, however, they send a pulse of radio waves towards a planet, and wait for the faint echo to return after the waves have bounced of the planets rocky surface. Radio waves travel at the speed of light, so the calculation is the same as for measuring the distance to the Moon.

Radio astronomers have picked up radar reflections from all the planets with rocky surfaces – Mercury , Venus and Mars – and even from the rings of Saturn, which are made of billions of tiny lumps of ice. They cannot detect a radar echo from Saturn itself, or Jupiter, because both consist of gases and do not reflect radar.

 

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What is Stereophonic sound?

Stereophonic sound helps to give a sense of direction and feeling of depth to radio broadcasts or recordings. When you hear an orchestra playing on the radio, for example, you can tell where the violins, woodwind and drums are positioned.

Many  VHF radio programmes are now broadcast in stereophonic sound system pioneered in the United States by Zenith and General Electric in 1961. The program is recorded using a number of microphones, and edited to produce sounds from the right and left of the broadcast studio on two separate tracks.

The transmitter sends out two sets of radio signals over the air. One set carries the combined output of the microphones so that it can be received on ordinary (mono) receivers. The other set carries coded signals for a stereo receiver. It has a decoder that can sort out the coded set into left and right channel signals. These are amplified separately, and fed to separate left hand and right hand loudspeakers.

 

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How does magnetism relate to electricity?

Iron and its alloys, such as steel, are naturally magnetic. They draw other magnetic substances towards them if they are within a certain range, known as the magnetic field. All magnets have a north and south pole, and it is opposite poles that attract each other.

The magnets attractive power relies on the arrangement of its atoms. All the atoms are tiny magnets formed into groups, known as domains. The magnetic strength is increased if the domains are induced to fall into line by the action of another magnet.

A bar of iron placed inside a coil of wire carrying an electric current will be magnetised for as long as the current flows. This is because an electric current has a magnetic field that act at right angles to its direction of flow in the same way as naturally occurring electromagnetic radiation. The strength of the magnet depends on the strength of the current.

These electromagnet can be much stronger than ordinary magnets, and can easily be magnetised or demagnetised by switching the electric current on or off.

Conversely, moving a magnet in and out of a coil of wire will set up an electric current in the wire for as long as the magnet is moving. This was how the first electric generator was produced after the principle (electromagnetic induction) was discovered by an English man, Michael Faraday, in 1831.

 

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What does the electron beam do?

Miniaturized information storage will be a boon to such establishments as libraries who have to store great number of bulky books, newspapers and reports. At present, the British Museum adds an estimated 8 miles (13 km) of books to its library shelves every year.

Scientists at Cavendish laboratory, Cambridge, are used an electron beam to generate patterns of dots to form both microscopic pictures and lettering in aluminium fluoride. In this way they can reduce printed words to a density of 10 million words per square millimetre.

Since the beginning of electron-beam welding on an industrial scale at the end of the 1950s, countless electron-beam welders have been designed and are being used worldwide. These welders feature working vacuum chambers ranging from a few liters up to hundreds of cubic meters, with electron guns carrying power of up to 100 kW.

An electron microscope uses a controlled beam of electrons to illuminate a specimen and produce a magnified image. Two common types are the scanning electron microscope (SEM) and the transmission electron microscope (TEM).

 

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