My Science School

What are Kepler’s Laws of Planetary Motion?

Kepler’s Laws of Planetary Motion state:

1. The orbit of a planet is an ellipse with the Sun as one focus of the ellipse.


2. The planet moves in its orbit at such a velocity that its radius vector sweeps out equal areas in an equal interval of time.


3. The orbital period squared is proportional to the mean distance from the Sun cubed.

These laws apply to all the planets including Uranus, Neptune and Pluto,

Planets discovered long after Kepler’s death.

Do Kepler’s laws equally apply to comets and asteroids also?

Yes. According to Kepler’s law comet spends most of its time moving very slowly and bursts into high speed only during its perihelion passage.

 

How far away are the moons Phobos and Deimos from Mars.

The moons are very close to Mars. Deimos is about 20,000 km away and Phobos is less than 6,000 km away.

Name the English satirical writer who predicted the existence of the moons of Mars?

Johnathan Swift predicted the existence and the characteristics of the moons of Mars in his book Gullivers Travels, 142 years before the moons were discovered.

What is unusual about the period of revolution of the two moons of Mars?

Phobos orbits once in 7 hours and 40 minutes and Deimos once in 30 hours. The inner moon Phobos orbits the planet faster than the spinning motion of the planet. The outer moon Deimos remains above a given landscape for nearly three days passing through all its phases twice.

Phobos not only rises in the sets and in the east but it rises and sets twice each day. It is thought to be an asteroid captured by Mar’s gravity.

What is the synodic orbital period of a planetary moon?

The synodic period of a planetary moon is the period from one new moon to the next. For the moons of Mars it is 7 hours 39 minutes and 21 minutes for Deimos.

 

 

Continue reading "The Planets"

 

 

What is the problem in observing features on the surface of Venus?

Venus is permanently covered with a cloak of dense clouds of sulfuric acid drops and carbon dioxide. Hence no features on the surface are visible on visual observation. However, such features can be observed by instruments.

 

 

 

 

 

 

 

Which planet is known as the ‘Red planet’?

Mars. The colour is caused by large deposits of red iron oxide on the surface of the planet.

How hot is it on the surface of Mars?

The temperature on the surface of Mars can vary from 250 C at night.

 

 

What is the obvious snag in locating features on the gas giants Jupiter, Saturn, Uranus and Neptune?

Being gaseous planets, the rotation of the equatorial zone is faster than at the higher latitudes. Also there are no fixed reference points in the constantly shifting clouds of gas.

Is the size of a planet related to its rotation?

No. For example, Jupiter’s day is only 9 hours 50 minutes even though it is by far the largest planet.

How big is Jupiter, in general terms, as compared to the other planets of the Solar System?

If Jupiter was hollow, all the other planets of the Solar System could be accommodated within it. It is the largest in the Solar system. Its equatorial diameter is 142,800 km and it has a mass more than twice that all the other planets combined.

Why was the astronomer Galileo persecuted by the Catholic Church?

 Viewing Jupiter through his telescope, Galileo discovered it had four moons revolving around it. This went against the Church doctrine of that time that all heavenly bodies revolved around the Earth which was held to be the centre of the Universe.

Which planet has a permanent large red spot on its surface which keeps changing and shifting?

Jupiter. The spot is believed to be an area of permanent turbulence.

What are the Galilean Moons?

The four moons of Jupiter discovered by Galileo are called the Galilean moons.

How powerful a telescope is required to observe the Galilean moons of Jupiter?

The Galilean moons of Jupiter can be seen with a good pair of modern binoculars.

 

Why does the Sun rise in the east and set in the west on the Earth? Does the concept hold equally good for all the planets in the Solar System?

The Earth spins on its axis from west to east. Hence the sky appears to move from east to west. In the case of the other planets, the Sun will rise in the east to west. In the case of the other planets, the Sun will rise in the east and set in the west, when viewed from the surface of that particular planet, only if that planet is spinning in the same direction as Earth, with respect to the Sun. In all the planets the Sun rises in the east and sets in the west. In the case of Venus, Uranus and Pluto, the Sun rises in the west and sets in the east, since the planets spin in the west and sets in the east, since the planets spin in the opposite direction.

 

 

 

 

 

 

Are all planets oblate spheroids?

All the planets exhibit oblate spheroidness to some degree, the extent of which increases with increasing speed of spinning and decreases with increasing density. Consequently, a gaseous planet with a rapid axial rotation like Saturn exhibits a very high degree of oblate spheroidness. For example, Jupiter whose day is less than 10 hours has its diameter over 140,000 km at the Equator and less than 133,000 km at the poles.

 

Do all planets have satellites?

Mercury and Venus have no satellites. Earth has one satellite (the Moon), Mars and Neptune have two satellites each. Uranus has five satellites. Jupiter and Saturn have a large number of satellites. Pluto has one satellite.

 

 

 

 

 

 

Can a satellite be larger than a planet?

A satellite is much smaller than the planet around which it revolves. However, a large planet is capable of having a large satellite. Titan, one of the satellites of Satum, and Triton, a satellite of Neptune, are larger than the planets Mercury or Pluto.

 

 

 

 

 

 

 

 

Does the period of spinning remain the same for all the planets?

The day of each planet is different. For example, the period of one day for Mercury is 59 Earth days; for Venus, it is 243 Earth days and for Mars, it is about 24-1/2 Earth hours. Thus a large variation in the period of spinning is due to random collisions with comets and asteroids over very long periods.

Can all the planets be seen from Earth with the naked eye?

Neptune and Pluto can be seen only with telescopes. The other planets, including a faint Uranus, can be seen with the Naked eye.

Astronomers in ancient times were hence unaware of the planes beyond Saturn since they did not have telescopes.

When the planets beyond Saturn were first discovered?

In 1781, Sir William Herschel discovered the Existence of the planet Uranus. It is twice as far out as the sixth planet Saturn.

Which planet is farthest from the Earth?

The eccentric orbit of Pluto regularly brings it closer to the Sun than Neptune. Hence Neptune and Pluto will take turns to be the farthest planet from time to time.

Do all the planets have an atmosphere similar to that of the Earth?

Mercury and Pluto have no atmosphere. The other planets have atmospheres containing different gases. Earth’s atmosphere, containing mainly nitrogen and oxygen, is unique. Venus has a carbon dioxide atmosphere. The atmosphere of Mars is mainly argon and carbon dioxide. Jupiter, Saturn, Uranus and Neptune have thin atmospheres containing hydrogen, helium and methane.

Why are Mercury, Venus, Earth and Mars Called “Terrestrial” planets?

“Terrestrial” means Earth-like. All the terrestrial planets have large, solid, metallic cores surround by a rocky outer layer. All of them have atmospheres.

Why Jupiter, Saturn, Uranus and Neptune are called “Gas Giants”?

The gas giants or Jovian planets do not have any significant solid cores and are almost entirely composed of gases or liquefied gases. They are also enormous in size compared to the other planets.