## Friday, 29 January 2010

### Why do we always see the same side of the Moon?...

This is due to the effect known as 'Gravitational Locking'. The Earth's gravitational field slowed the Moon's spin over time and now the Moon spins about its axis at a rate such that the time to rotate once on its axis is exactly equal to the time it takes to go round the Earth. The diagram (click on the figure to see it clearly) explains how this results in effectively the same side of the Moon facing the earth all the time.
Gravitational Locking is observed in the case of other planets as well whose satellite moons are locked in the same way as the Moon is locked to the Earth.

## Sunday, 17 January 2010

### Units in Cosmology...

In the study of cosmolgy, one encounters distances and masses which are extremely large compared with what we can easily comrehend.

It would be fair to say we can judge numbers that are a few hundred times a billion. We hear of companies worth 100 billion pounds etc. and appear to be comfortable with such statements, but a million billion will be difficult to understand.

Average distance of the Sun from the Earth is 150 million km and the diameter of the Milky Way galaxy is about a million million million km.
Mass of the Sun is 2000 billion billion billion kg and the numbers get bigger as we study the galaxies.

Therefore in astronomy we talk about a different set of unit.

Unit of mass is one solar mass = 2000 billion billion billion kg
Rest of the heavenly bodies are weighed relative to the Sun.
The situation about length is not so simple. There are three different units used depending on the context. These are:

1. The astronomical unit or AU:
1 AU ~ 150 million km = 149,597,871 km
An Astronomical Unit is approximately the mean distance between the Earth & the Sun.
AU is used when discussing distances of planets and other objects in the Solar System.

2. The light Year or Ly:
A Ly = about 10 million million km
A light year is the distance traveled by light in vacuum in one year.
It takes light 8.32 minutes to travel from the Sun to the Earth.
Ly is a big unit, it is about 63,000 astronomical units.
Diameter of the Milky Way galaxy is about 100,000 Ly
and the size of the observable Universe is measured in billions of Lys!
Light Year is the most commonly used unit when one is talking about galaxies and the Universe. It is also starightforward to understand.

3. Parsec or pc:
One parsec = 31 million million km or 210260 AU or 3.26 Ly
Parsec is based on the change of angle in a star's position when viewed from the Earth as it revolves round the Sun. We shall not use this unit in our discussions.

## Saturday, 16 January 2010

### In Cosmology one deals with big numbers...

Writing numbers that are very big or very small ...
In science, you will encounter numbers that are very big or extremely small. These can be rather inconvenient to write out in the normal notation.
Powers of ten is a useful shorthand method of writing very large or very small numbers.

For example:
One thousand (1000) is 103 ; reads 'ten to the power 3' and is 1 followed by 3 zeros
One divided by 1000 is 0.001 or 10-3 ; reads 'ten to the power minus 3'

And that is it -

the positive power on ten tells us how many zeros are after 1.
negative powers of ten tell us the position of the 1 after the decimal point.

Distance of the Sun from the Earth is 150 million km or 150,000,000 km or 15 x 107 km.
Diameter of an atom is 0.0000000002 m or 2 x 10-10 m.

Multiplication and division of powers of ten numbers is very easy...

When you multiply two numbers powers add

When you divide two numebrs powers substract.

Example: Multiply 2 million by 4 million

Longhand: 2,000,000 x 4,000,000 = 8,000,000,000,000

Powers of ten: 2 x 106 x 4 x 106 = 8 x 1012

### Exploring the Cosmos

Dr Ravi Singhal
Free Science Talks for Secondary Pupils & Adults
No Science Background Needed

11 am to 12 noon on Saturdays
30 January; 6, 13, 20 and 27 February 2010
James Watt Auditorium, E.K. Technology Park, G75 0QD

(Ample free parking on site)
In Partnership with: Glasgow University and Scottish Enterprise, Lanarkshire

The size and complexity of the Universe is truly astounding. The Sun is but one of more than 200 billion stars in the Milky Way galaxy and the observable Universe could contain 100 billion galaxies. It takes light a hundred thousand years to travel across the Milky Way. The Universe
is populated with strange and bizarre objects like the white dwarfs, neutron stars, black holes; the true nature of which we are now beginning to understand. Prodigious amount of energy is produced by the heavenly bodies – the Sun produces a million times more energy in one second than we consume globally in a year!

Human curiosity has always wondered about the nature of the Universe we live in and attempted to rationalise what could be observed. Our understanding has enormously improved due to technological advances of the last century. However, many questions remain unanswered…..

Have you ever wondered how the distance, size, motion, temperature, composition of a star are measured? How are stars formed and how do they die? A frequently asked question is - How do they know? Exploring the Cosmos is a programme of ten talks, five of which are being announced at this stage. Come along to the talks to find out.
The fifth talk will discuss the search for extraterrestrial life.

Talks are free to attend; e-mail ekTalks@yahoo.co.uk to confirm interest. Please check http://ektalks.blogspot.com for updates.

The Science for All programme is a community education initiative. The talks are aimed at the general audience and no prior background in science is assumed. The talks are also suitable for secondary school pupils. The presentation promises to be visually attractive and highly informative.