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Category Astronomy

What are the main differences between astronomy and astrology?

In astrology (dating back to ancient times), only heavenly phenomena and movements visible to the naked eye are considered. Hence the planets beyond Saturn that can only be seen with telescopes do not figure in astrology. Astrology also places great importance on the visual pattern (constellations) of the heavenly objects in the night sky, whereas they are of least significance to astronomers. The heavenly objects recognized by astrologers also include objects like “Rahu” and “Ketu” considered non-existent by astronomers. The movements of the heavenly objects are believed by astrologer’s manner, whereas according to astronomers such a contention has no scientific basis and any astrological correlations are considered purely coincidental.

The Universe

What is meant by “Apogee” and “Pergiee”?

Apogee (Aphelion with reference to solar orbits) is the point in the elliptical orbit at which the orbiting body is at its farthest distance from the body around which it orbits.

Perigee (Perhelion with reference to solar orbits) refers to that point where the orbiting body is closest to the body around which it orbits. For example, in the case of an artificial satellite moving in an elliptical orbit around the Earth, its distance from the Earth would fluctuate during each orbit from a maximum at apogee to a minimum at perigee.

 

 

What is a nebula?

A nebula (Plural: nebulae or nebulas) is a vast cloud of gas and dust floating in space. Nebulae are usually detected in the night sky as bright or dark patches against the background of stars.

The Universe

What are galaxies?

Galaxies are clusters of stars. The Sun and the Solar System are part of a star cluster called the Milky Way galaxy visible as a cloudy white area in the night sky and commonly called “Akash Ganga” in India.

How many galaxies are there in the Universe?

It has been estimated that there are about a hundred billion galaxies in the Universe.

What are spiral, twin spiral, and multiple spiral patterns of galactic discs?

The spiral, twin and multiple spiral patterns refer to the number of ‘arms’ of the spiral.

How are galaxies classified?

Galaxies are classified as elliptical, spiral and irregular depending on the nature of distribution of stars on the galactic disc.

The more common types have a regular structure. Elliptical galaxies arre denoted by the letter E followed by a numeral having values from 0 to 7 depending on the degree of flattening of the ellipse. Spiral galaxies arre denoted by Sa, Sb, Sc, Sba, SBb or SBc according to the pattern of the spiral arms. Barred spiral galaxies are denoted by Sba, SBb and SBc. SO denotes a class intermediate between elliptical and spiral. Irregular galaxies arre denoted by Irr.

 

 

 

 

What is Gravity?

“Gravity” or “Gravitational Force” or “Gravitation” refers to the natural force of attraction between objects in space. For example, we fall down when we jump up, because our bodies are attracted by the Earth’s gravity. The Moon orbits the Earth because the Earth’s gravity holds it in place in its orbit. The Earth, the planets and the other objects in the Solar System orbit the Sun due to the gravitational force exerted on them by the Sun. It plays a vital role in the behavior of the Universe.

 

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The Universe

 

 

 

 

 

 

 

 

 

What are asteroids?

Asteroids are tiny heavenly bodies that move around the Sun. Most of them occur in the region between Mars and Jupiter. They are thought to be fragments left over from the formation of the solar system.

 

What is trajectory?

Trajectory is a general term for the path of any object moving in a force field such as a gravitational field that exerts a force on the object. Hence, the term trajectory can be applied to the path of space probe moving in a gravitational field.

 

 

 

 

What is an orbit?

When a small heavenly body moves around a larger one, the smaller body is said to orbit the larger one and the path followed by the smaller body is called its orbit around body. For example, the Earth orbits the Sun.

 

 

 

What are comets?

Comets are small heavenly bodies which orbit the Sun but regularly come close to the Sun. They are partially vaporized by the Sun’s heat and glow brightly for a short time when near the Sun. A comet consists of a central nucleus a few kilometers across and can be mixed with dust.

 

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The Universe

What is a natural satellite?

A natural satellite is a smaller natural heavenly body that moves around a planet. For example, the Earth has one natural satellite (the Moon), Mars has two and Venus has none. Natural satellites that orbit planets are also called the moons of their planets.

What is the difference between natural and artificial satellites?

Nowadays man-made objects can be launched into space from the Earth. Today, the satellites circling the Earth in space include the Moon as well as such man-made objects. Satellites such as the Moon are called natural satellites and man-made ones are called artificial satellites.

 

The Universe

What do we mean by the Solar System?

The solar system refers to the Sun and the various heavenly objects that move around the Sun.

Name the heavenly bodies that move around the Sun?

Planets, satellites, asteroids, comets etc.

What is a planet?

A planet is a major heavenly body. For example, the Earth is a planet and so are Venus and Mars.

What is a star?

A star is a massive heavenly body which emits enormous quantities of energy and appears to be glowing.

How many stars are there in a galaxy?

On an average, there are about a hundred billion stars in each galaxy.

How many stars are there in our galaxy, the Milky Way?

About four hundred billion stars.

Which star is nearest to the Earth?

The Sun.

How many stars are bigger in magnitude than the Sun?

In the Milky Way galaxy alone, there are five billion stars larger in magnitude than the Sun.

which heavenly body is nearest to the Earth?

The Moon.

 

The Universe

What is the universe?

The Universe consists of everything one can cognize through one’s senses and through observations using instruments.

The Sun and the Moon are components of the Universe one can easily observe but some objects too faint or too far away can easily only be observed through instruments like telescopes.

What are the main components of the Universe is general terms?

 The Universe consists of a vast emptiness called space with unknown boundaries, containing matter and energy in various forms.

In what forms does matter exist in the Universe?

Matter exists in the form of stars, plants, comets, satellites, meteors, asteroids, galaxies etc.

In what forms does energy exist in the Universe?

Energy exists in the form of heat, light, X-rays, microwaves, gamma rays, radio waves etc. What the eyes detect is only a minute range of wavelengths and frequencies (visible light) from a vastly broader spectrum of electromagnetic radiation. The heat and light from the Sun is a part of the energy can be detected only through instruments.

Does the Universe remain steady and unchanging?

No. The Universe is constantly changing with the passage of time.

 

What is the weight of our atmosphere?

            Our Earth is surrounded by a blanket of air from all sides. This enveloping blanket is called atmosphere. The atmosphere consists of a mixture of more than ten gases. In terms of volume, 78.05% of the atmosphere is nitrogen, 20.94% is oxygen and nearly 1% carbon dioxide. The remaining gases include argon, helium, neon, carbon monoxide, ammonia etc. The atmosphere also contains water vapour and dust particles, hydrocarbon, hydrogen oxide and sulphur compounds in variable amounts.

            Since all these gases are different forms of matter, they exert a downward force on the surface of the Earth and are regulated by the force of gravity. Man is rarely conscious of this weight since it presses on him from all directions, and his body is fully adjusted to it. The weight of the atmosphere can be determined by taking into account the masses of these gases and the force of gravity (weight = mass x gravity). We know that one mole of nitrogen weighs 28 gm. and that of oxygen 32 gm. Mole is the basic unit for measuring the amount of any substance in terms of atoms and molecules. 

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How do astronauts walk in space?

          It appears strange but true that astronauts can walk in the space. This is so because in ordinary walking we rest our feet on the surface of the earth and the force of earth’s gravity pulls us towards it. But when there is nothing in the empty space – neither any surface to walk on nor any gravitational force to pull the feet down onto the ground – how does an astronaut walk in the space?

           Space walking by astronauts is quite different from the normal walking. To walk in the space the astronauts take the help of hand rockets which provide them the force to move. The hand rockets follow the principle of rocket propulsion. In rockets, the ejection of gas with a great force from the backside pushes the rocket forward with an equal thrust. This working principle is based on Newton’s third law of motion which states, ‘To every action there is always an equal and opposite reaction’. Similarly in hand rockets when the engine is powered the exhaust thrust pushes the rocket in the opposite direction and the astronaut walks along with this force as he carries the hand rocket with him. In fact, it is not ‘walking’ in the strict sense as there is no surface in the space to rest the feet but rather ‘floating’ – to express more accurately.

          But why do the astronauts walk in the space? Apart from experimental reasons, sometimes they are required to shift from one spacecraft to another or need to carry out a repairing work on the outer surface of the craft. During such operations they use the specially designed hand rockets and the direction of the exhaust outlet is pointed opposite to the desired direction of walking.

          The first spacewalk was made in March 1965 by a Soviet astronaut, A. Leonov, who stayed outside the aircraft for 24 minutes. Another important walk was made in 1973 when the American satellite Skylab was to be repaired for damage in the heat shield that made the craft dangerously hot. 

Could you ever see an eclipse of the Moon in daylight?

Yes, though only for a few minutes, and only if the eclipse is occurring just as the Moon is rising and the Sun is setting, or the Moon is setting and the Sun rising. A total eclipse occurs when the Earth is between the Moon and Sun, which are directly opposite to each other in the sky.

 Seeing both the Sun and eclipsed Moon at the same time would appear to be a geometrical impossibility, but because the atmosphere has a lensing effect, it raises the images of both the rising Moon and setting Sun above the horizon for a few minutes.

For the same reason, day and night are not exactly equal at the time of the fall equinox, because the day is artificially lengthened a few minutes at each end by the refractive effect of the atmosphere, for a total of seven minutes. It is not until three or four days later that the day equals the night.

It is easier to see the scallop of a partial eclipse above the horizon at sunrise or sunset than it is to see a total eclipse, because the Sun is so much brighter than the Moon.