# Episode Eleven – Newton’s Achievements

One major advantage of a reflecting telescope is that it is free from the severe chromatic aberration of refracting telescopes.

A chromatic aberration is caused by the failure of the lenses in refractive telescopes to properly focus all colors of light to the same point. This results in a blurred image and colored edges.

Such as that shown below:

See the purplish chromatic aberration.

Newton realized that the lens of any refracting telescope would suffer from the dispersion of light into colors. Which is what causes chromatic aberration.

So, he invented the reflective telescopes, using mirrors to correct this problem.

Most telescopes used today are reflecting telescopes. This is because they are not subject to chromatic aberration, although they do suffer other problems.

They also can be used to help combat the disruptive effects of atmospheric turbulence, which is great for Earth-based telescopes.

It is also easier and cheaper to produce the mirrors used by reflecting telescopes than it to make the lenses used by refractive telescopes.

They are also generally more portable and compact.

They have other advantages, as well as disadvantages. Their disadvantages include the fact that their mirrors require more careful handling than their refractive counterparts. As well as the fact that their mirrors may need occasional readjusting.

But, by and large, reflective telescopes are very commonly used. Various space agencies, including NASA have employed many reflecting telescopes and they are very popular among amateur telescope buyers.

## Newtonâ€™s Law of Cooling

This theory provides an empirical formula for calculating the rates of cooling. The law states that the rate of cooling of a body is directly proportional to the temperature difference between the body and its surroundings.

This can be used to find the rate of cooling of objects or how long it will take to reach a certain temperature.

You could for instance calculate the temperature of a cup of tea. Or how long it would take an ice cube to melt given its initial temperature.

If finding the temperature of cups of tea or figuring out how long it takes to melt ice do not sound very important, then the Law of Cooling has many other more interesting and important applications.

For instance, it has been used in forensics in estimating the time of death of a body some time after death. It is used to help maximize the efficiency of designs of heating/cooling systems such as solar heating systems. And many other things where it is important to understand changing temperatures over time.

This too involves elements of calculus and is yet another example of the myriad uses of calculus. And the kind of relationship you can discover using calculus and some careful reasoning.