Category Science

What are “Red Shift” and “Blue Shift” with reference to a star’s spectrum?

A shift of pattern towards the red end of the spectrum indicates that the star is moving away from us. A “Blue Shift” indicates a movement towards us.

What is colour temperature?

As a star’s temperature rises, its predominant colour changes from infra red through ultraviolet.

How are spectral patterns of the stars classified to indicate the temperature of the stars?

spectral patterns of stars are classified in descending order of star temperature as  O, B, A, F, G, K, M, R, N and S (O stars are blue and M stars are red).

What are drive systems for modern astronomical telescopes?

Instead of turning mounts manually, they can be driven automatically. And although normally electrically driven, more sophisticated computer drives are now available.

What is the apparent magnitude of a star?

Apparent magnitude is the apparent brightness of a star as seen from Earth. Star magnitudes are denoted by numbers 1 to 6 where 1 refers to the brightest stars and 6 to the faintest star visible to the unaided eye. The scale is logarithmic. Hence magnitude 2 stars are 2.512 times fainter than magnitude 1 stars. Magnitude 3 stars are 6.310 times fainter than magnitude 1 stars.

Celestial objects brighter than magnitude one may have zero or negative magnitude. Celestial objects fainter than magnitude six may have higher values of magnitude. The lower the apparent magnitude, the brighter is the star.

What is the absolute magnitude of a star?

The absolute magnitude of a star is a hypothetical concept and is the apparent magnitude the star would have if it were located at a standard distance of 10 parsecs from the Earth.

The absolute magnitudes of stars provide a measure of their relative luminosities, by comparing the apparent brightness which stars would have if they all lay at the same distance. If the Sun was at a distance of 10 parsecs, it would be a faint star of absolute magnitude +4.8.

What is the altazimuth type of telescope mount?

Any instrument with a magnification beyond 7 must have some form of mounting for precision. For small telescopes and more powerful types of binoculars, the altazimuth mount is commonly used, permitting vertical and horizontal movements simultaneously. The altazimuth mount is fine for low-power wide-field work, but it becomes increasingly difficult to keep objects inside the narrow field of view of a large telescope, and both axes of the mount require constant adjustment.  

What is the equatorial type of telescope mount?

To overcome the problems of the altazimuth mount, astronomers generally prefer the equatorial types of telescope mount, which permits an object to be followed by the adjustment of one axis only. It has two axes-polar and declination placed at right angles to each other. The polar axis is permanently pole. Once the mount is set up, both axes are used to bring an object into the field of view. The declination axis is followed by slowly turning the telescope tube around the polar axis.

Astronomical telescopes produce inverted images. Why are the images not corrected to look normal as in the case of terrestrial telescopes?

All Telescopes first produce an inverted image. In a terrestrial telescope, an erecting prism is used to make the make the image look normal. However, such a prism causes a slight loss of brightness undesirable in observing the faint light from the stars. Hence, astronomical telescopes tolerate inverted images.

How do astronomers observe the Sun without damage to their eyes?

Instead of observing the Sun directly through dark glasses, astronomers view the image of the Sun projected on a screen by a telescope.

What is the magnification of a telescope?                                   Focal length of the objective

Magnification of the Telescope =  ——————————–?

   Focal length of the eyepiece

For example, with an objective of focal length 1 meter and an eye piece of focal length 10 mm a telescope will give a magnification of:

1000/10 = 100

Since the focal length of the eyepiece does not very much in actual practice, the focal length of the objective is of paramount importance in determining the magnification of the telescope.

What units do astronomers use to measure distances in the Solar System?

Since distances are appreciably large, astronomers use a unit of distance called ‘astronomical unit’. One a.u. is equal to 149,600,000 km which is the average distance between the Earth and the Sun. The Earth is at a distance of 1 a.u. from the Sun. Mercury and Venus is less than 1 a.u. from the Sun since they are nearer to the Sun than Earth. The other planets are more than one a.u. from the Sun since they are farther from the Sun than the Earth.

How precise were ancient Indian astronomers?

According to the 4000 years old Rigveda, the solar year was 364.24675 days, the Sun was 108 Sun diameters from the Earth and the Moon was 108 Moon diameters from the Earth.

Name the five important observatories in India?

Kodaikanal, Hyderabad, Ooty, Nainital and Kavalur.

What is a “Jantar Mantar”?

A Jantar Mantar is an ancient observatory used for observing the heavens before telescopes were invented. They are found in India, Arabia and North Africa. The Jantar Mantars in Jaipur and Delhi are well known.

How do astronomers measure large distances in space?

Distances in space are measured by the method of trigonometrically parallax based on the displacement in the apparent position of an object viewed from two different positions. In principle, two observations are possible for a star, separated by a time interval of six months during which the observer on Earth moves through a distance equal to half the orbit of the Earth around the Sun. Due to parallax, the star then appears to trace out a small ellipse while the Earth’s orbit repeats another ellipse in space. Knowing the magnitude of the parallax, the Sun-star-Earth triangle can be mathematically solved to arrive at the distance of the star.

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