My Science School

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.

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.

 

Continue reading "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.

 

Continue reading "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.

 

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.

 

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.

 

          The cosmic year is related to the motion of a galaxy. A galaxy is a large system of stars held together by gravitational force. There are millions of galaxies in the universe. The size of a galaxy is measured in Light Years. The diameters of different galaxies range from a few thousand Light Years to 500,000 Light Years.

          There are three main types of galaxies depending on their shapes: spiral galaxies, elliptical galaxies and irregular galaxies. The spiral galaxies are generally disc-shaped with curving arms extending from a centre bulge. The elliptical galaxies are shaped like spheres or flattened spheres. The irregular galaxies have no definite shape. 

 

 

          The Milky Way or Akash Ganga as described by ancient Indian astronomers is a spiral galaxy. The Milky Way belongs to a cluster of some 24 galaxies called ‘The local group’. Our solar system belongs to this galaxy. Sun is one of about 100,000 million stars located in the Milky Way. The modern estimates place the Sun at a distance of about 32,000 Light Years from the centre of the galaxy.

          The Milky Way is not stationary. It is rotating round an axis passing through its centre. This is the real reason for its flat disc-like shape. The whole disc of the galaxy rotates about its galactic centre —but not at a uniform speed. The rate of rotation decreases with increasing distance from the centre. The galaxy does not rotate like a solid wheel.

          Each star revolves around the central nucleus in an elliptical or circular orbit, just like the planets revolve round the sun. The stars near the centre move faster than the stars farther away. Sun moves round the centre of galaxy at a speed of 250 km per sec. It takes about 225 million years to complete one revolution around the galactic nucleus. This period is known as the cosmic year or the galactic year.

          There is evidence of galactic rotation in observations that in general stellar motions are not random, but in preferential directions. The Dutch astronomer J.C. Kapteyn first observed this effect in 1904.