How Star help us to find Direction and time

Stars help map-makers, pilots,and sailors find directions and
locations. For example - the North star serves as a guide to the
direction north because this star always appears to be in the same
place over the north pole. The earth's spinning motion makes the sky
seem to rotate each night. Observers who are north of the equator see
the star rotate around a point that is above the north pole. The north
stare is near this point in the sky and so seems to moves very little.

The north star can also be used to measure latitude. A sextant issued
to measure the angle at which the star appears above the northern
horizon. This angle is same as that of latitude. For example : at 45
degree north latitude, the north star is at an angle of 45 above the
northern horizon.

Pilots and sailors measure their position by means of celestial
navigation. The method depends on the idea that a star is directly
over some point on the earth's surface at a given time. The earthly
position of a star changes as the star appears to move from east to
west.
A book called an almanac lists the earthly position of various
stars at different times.

To determine their location, observers measure the angle of the star
with a sextant and note the exact time of the measurement. Then thay
look up the star's earthly position in an almanac. They use the angle
of star to determine how far their location is from the star's earthly
position. By repeating the process with two more stars, they can find
their lacation.

Human eye :structure and functions

Human eye : structure and functions

Every person thinks that how i see anythings from my eyes. So let us know how our eyes works.

The human eye is optically very similar to camera. An enclosure,the eye ball itself ,contains a lens-shaped organ whose focal length can be shortened by ciliary muscles capable of squeezing it into a thicker shape. The cornea is a curved transparent membrane in the front of the eye ball. Refraction takes place here. A watery fluid in front of the lense and a jelly behind it contribute to the refraction producing an image on the ratina is inverted. The ratina contains millions of delicate nerve endings whose sensations are carried to the brain. The iris is a variable-sized diaphragm controlling the amount of light entering the eye through the pupil, and thus protects the retina from damage.

The images of the objects at different distances from the eye are brought to focus on retina cy changing the focal length of the eye-lense. The ciliary muscles change the thickness of the eye-lens.

A thicker lens has lesser radius of curvature and hence smaller focal length. In this manner, by changing the focal length of the eye lens, the images of object at different distance are brought to focus on the retina.

Hence , in this way , we see an objects ,and various things those are lies in our surroundings.

Difference between Hypothesis, axioms and models

We should not think that everything can be proved with physics and mathematics. All physics and also mathematics is based on assumptions, each of which is variously called a hypothesis or axiom or postulate, etc.
A hypothesis is a supposition without assuming that it is true. It would not fair to ask anybody to prove the universal law of gravitation, because it cannot be proved. It can be verified by experiments.
An Axiom is self-evident truth while a Model is a theory proposed to explain observed phenomena.