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# Tag Archives: sun

## Why does the sun appear to rise and set though it is actually not moving?

Why does the sun appear to rise and set though it is actually not moving?

First of all I would like to remind you that it is incorrect to say that “sun is not moving”. Sun is also moving. But the question here is, “Sun appears to rise and set not because of its motion”.

Sunset and sunrise are caused by the rotation of earth. When earth rotates, the position of sun appears to change and it seems as if the sun is revolving around the earth; just like we feel that the ground is revolving around us when we are looking out from a rotating merry-go-round.

## Parallax Method

How to use it to calculate the distance between two astronomical objects?

Parallax  is the change in the apparent position of an object due to change iv view point.

The parallax method is a way of measuring distances of far-away objects.

## Parallax Method to determine the distance of stars

WHAT IS THE WAY TO MEASURE THE DISTANCE OF DISTANT OBJECTS LIKE STARS WITH THE HELP OF PARALLAX METHOD

Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.

Astronomers use the principle of parallax to measure distances to celestial objects including to the Moon, the Sun, and to stars beyond the Solar System.

See the animation below to understand the parallax method for determining the stellar distances

http://spiff.rit.edu/classes/phys240/lectures/parallax/parallax.html

is it the same method that we use in trigonometry ?
Parallax is a different concept, though we are using the principle of trigonometry to solve problems based on it.

## Doubt in Law of Gravitation

According to law of gravitation
F=g*(m1*m2)/r^2
If we bring two objects close to each other say our hands then the distance will be zero and the force of attraction will become infinite because r will we zero. Therefore F will become infinite but this is not the case.
When we touch our both palms together we can easily pull then away.

When we consider the distance, it is between the center of mass of the two bodies under consideration. When we bring our hands together the distance between their CM is not zero.

Other wise, the two particles under consideration must be point masses.

Then if you consider two atoms or two nuclei, the forces that come into play will be different if we decrease the distance between two atoms or nuclei. The attraction will turn into strong repulsion when the limits are exceeded.

## A question from Gravitation.

“Sun have high gravitational energy ,then why planets of solar system doesn’t colloid with sun?”

“The planets are moving around the sun and the gravitational force is used in providing the necessary centripetal force (The force required by a body to move in a circular path). As long as the planets are in motion, they will not move towards the sun. A similar explanation hold good for moon going around earth also.”

## Spaceship and gravity – a problem

A spaceship is launched and starts moving directly towards the Moon. At what distance from the earth will the pull of the Moon on the spaceship exceed the pll of the Earth? Ignore the effect of the sun in this calculation

## Why Earth does not collide with the sun?

If our earth rotates around sun in discrete orbits, then why it doesn’t collide with Sun because of gravitational force acting between both bodies ?

Earth is moving around the sun in such a way that the distance to be traveled TOWARDS sun is compensated by its circular motion. Therefore, instead of “falling towards” the sun, earth “falls around” and never reaches the sun.

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