# Aberrations; a lecture in Optics. 4

Optical systems are studied under two assumptions

object point does not lie far away from the axis of the optical system.

rays taking part in image formation make a small angle with the axis of the optical system.

The domain of optics where above two assumptions are valid is called as Paraxial optics. Paraxial systems are highly idealized and in reality do not perfectly represent the situation. The consequential errors in image reconstruction are known as aberrations.
The paraxial assumption can be represented by truncating at the first term of the polynomial expansion of the sin function by the Maclaurin series. More…

# The angular parameters of celestial mechanics ! Reply

Define an Hour Circle.

Its a bit tricky to define some astronomical parameters and not run into innocent looking misrepresentations of facts. One needs to cool his amber more times than there are parameters, then one gets a feel where and how to begin and give a good description.

Hour Circle is a GREAT Circle, on a celestial sphere ** that, at the same time, passes through one of the celestial poles. Hence it passes through both of the celestial poles*.

A great circle is a circle that passes on a sphere, so that its radius (or diameter) equals to the radius (or diameter ) of that sphere.

If the great circle goes through one of the poles (– so both poles as an imminent condition of this definition) its also called a meridian and this circles’s angular reference wrt one of all possible meridians is called a longitude angle, or simply longitude. More…

# Star Motion, an interesting star concept. Reply

To budding astronomers.

A difference between true velocity and proper velocity. Proper velocity (proper motion) is the motion of a star apparent to the center-of-mass of the solar system. That is, how fast any object (a star) is moving wrt the sun’s position. (in terms of its center-of-mass)

So if a star is close to sun, its true velocity might be as much as it is, but proper velocity can be larger. Proper velocities are often larger when stars are closer, an useful fact in Astronomy.

(How proper velocity is eg useful in Astronomy, should be a good essay type question in Indian University exams, in the course of astronomy, but rather its more useful to remove essay type questions from Exams of University and such essay should be written by students as blogs, and the best blogs can be rewarded, Change should be brought to our education system by innovative thinking and not just by lecturing on outdated spiritual discourses) More…

Soon India will launch its navigation satellite on October 10. Its the 3rd of the 7 that India will set on voyage above Indian Nation’s geo-spatial surface, all of which will be set to function in their orbit by next year. India has taken its strides into space.

“This will provide terrestrial, aerial and marine navigation accurately and help disaster management, vehicle tracking and fleet management, mobile phone tracking, mapping of terrain as well as air and sea navigation.”

Despite of the fact that theoretically we have better than mm range accuracy … More…

# Update to: I solved Flyby anomaly of Galileo-I !! Reply

This article is a compilation of technical results that I obtained through my research. The ideas of this article thus will be comprehended mostly perhaps by only an expert of satellite technology and/or a general Physicist, nevertheless only after he/she also goes through preceding analysis and descriptive-content, the last one is linked below.

Flyby-Anomaly for Galileo-I, solved.

I had missed one unit earlier (– see below) in the computations I had carried out, this anomaly is explained by Theory of Relativity contrary to what was claimed so-far. More…