Twinkle twinkle little star…

Stars seem to twinkle because we see them through th layers of the Earth’s atmosphere. As light passes through these layers, it is distorted so that the amount we actually see changes constantly. The stars nearest the horizon appear to twinkle the most because the light is passing through a greater depth of atmosphere. Stars do not twinkle when viewed depth of atmosphere. Starts do not twinkle when viewed from space, which is why telescope in space, such as the Hubble, give the best possible view of distant stars and galaxies.

Star facts
A star is a luminous body of gas, mostly hydrogen and helium. Stars generate light, which makes it possible for us to see them with a telescope or the naked eye. They also release energy from nuclear fission reactions in their core.

Brightest
Not counting the Sun, the brightest star as seen from Earth is Sirius, known as the dog star, in the constellation of Canis Major. It has a diameter of 149,598,020km and is more than 24 times brighter than the Sun. The star Cygnus OB2 No 12, discovered in 1993, is so far away that it cannot been seen from Earth. It may be the brightest star in the galaxy – up to six million times as bright as our Sun.

Heaviest
HDE 2698 10 is a star in the Large Magellanic Cloud – 170,000 light years from Earth (a light year is the distance light travels in a year). It has been discovered by the Hopkins Ultraviolet Telescope to be 190 times as heavy as our Sun.

Largest
The largest star is the M-class supergiant Betelgeuse, or Alpha Orionis. It is the top left star in the constellation of Orion, which is 310 light years away. It has a diameter of 700 million km, which is about 500 times greater than that of the sun.

Nearest
Proxima Centauri, discovered in 1915, is 4.22 light years (39,953,525,879,212km) from Earth. A spaceship moving at 40,000km/h – which is faster than any human has yet traveled in space – would take more than 114,000 years to reach it.

Supernovae
These are vast explosions in which a whole star is blown up. They are extremely bright, rivaling for a few days the combined light output of all the stars in the galaxy. Supernovae are rate – the last one in our galaxy was seen in 1604 by the German astronomer Johannes Kepler.

Quasars
Quasars are extremely distant radio galaxies – galaxies giving out large amounts of radio energy – and the brightest objects in the Universe. Even those near the most distant edge of the observable Universe are easily detected by small radio telescopes. Their radio emission is typically 1,000,000 to 100,000,000 times greater than that of a normal galaxy, and they are as bright as or brighter than the brightest radiogalaxies.

Black holes
A black hole is a star that has collapsed into itself. It has a surface gravity so powerful that nothing can escape from within it.

Time tellers

The following are some landmarks in the history of telling the time.
1500-1300BC
Sundials are used in Egypt: as the Earth rotates, the gnomon - the upright part of the sundial - casts a shadow which moves to indicate the time.

c 400 BC
Water clocks are used in Greece: as water drains from a container, each level it reaches represents a period of time.

c 890
In England people use candles marked with time intervals.

12th century
The hourglass, familiar to us as an eggtimer, is used by monks to show times of prayer.

1325
The first clock with a dial is installed in Norwich Cathedral, England.

1335
The first clock to strike the hours is made in Milan, Italy.

1350
The oldest known surviving alarm clock is made in Wurzburg, Germany.

1364
Clocks are first used in people's homes.

1386
Salisbury Cathedral's clock is installed. This is the world's oldest clock in working order.

1462
The earliest descrition of a watch is written in Italy.

1641
The idea of the pendulum clock is proposed by Vincenzio Galilei, son of the famous astronomer Galileo.

1657
The first pendulum clocks are made in Holland.

c 1665
The first watches with minute and second hands are made.

1759
John Harrison's marine chronometer is made. Accurate timekeeping at sea is important for calculating position, but previously the rolling of a ship had made it impossible.

1880
Greenwich Mean Time becomes the standard from which time around the world is set.

1880
The first practical wristwatches are made for the German navy.

1928
The first quartz crystal clock is made.

1949
The first atomic clock is built.

1957
The first battery watches are marketed in the USA.

1969
Quartz wristwatches are first sold in Japan.

1970
Digital wathces and displays become widely used and can be made and sold cheaply.

2006
40 radio clocks around the world transmit signals that enable people to set their clocks and watches accurately.

The Universe in a year!

The American astronomer Carl Sagan (1934-96) first suggested a "cosmic calendar" as a way of helping people understand the history of the Universe. he put everything into the scale of calendar year: the galaxies are formed over nine months and the Earth appears in September. All human history is crowded into the last five minutes of the last dayof the year. Recent time has to be divided into seconds and fractions of a second. So everything that happened over the fractions of a second. So everything that happened over the last 475 years place in less than the last second of the last minute of the year.

The World in a single day
In one day (24 hours or 1440 minutes or 86,400 seconds) the world turns once on its axis. During that time, on average:

358,522 People are born
155,012 People are die
203,510 are added to the world's population.

Hour:minutes:second/fractions of second
11:59.50.487 pm Great Pyramid is built (2520 BC)
11:59.55.333 pm Great wall of China is built (215 BC)
11:59.56.785 pm Roman Empire falls (AD 476)
11:59.58.026 pm Battle of Hastings (1066)
11:59.58.921 pm Columbus lands in America (1492)
11:59.59.128 pm Shakespeare writes his first plays (1588-90)
11:59.59.874 pm World War II ends (1945)
11:59.59.891 pm Mount Everest is climbed (1953)
11:59.59.924 pm Man lands on the Moon (1969)
Midnight Today

Date/time Event
1 Jan (midnight) Big Bang-Universe forms
15 Mar First stars and galaxies form
1 May Milky Way galaxy forms
8 Sep Sun forms
9 Sep Solar system forms
12 Sep Earth forms
13 Sep Moon forms
20 Sep Earth atmosphere forms
1 Oct Earliest known life on Earth
7 Oct Earliest known fossils
18 Dec First many-celled life forms
19 Dec First fish
21 Dec First land plants; first insects
23 Dec First reptiles
24 Dec First dinosaurs
26 Dec First mammals
27 Dec First birds
28 Dec First flowering plants
28 Dec Dinosaurs extinct
31 Dec Homo sapiens (modern human) appears

A Pair of Palindromes

Multiply 21978 by 4
Now see if you can find a pair of palindromes.


Ans: 1) 4 x 21978 = 87912. The number is reversed.
2) 49

Brothers and Sisters

A family I know has several children. Each boy in this family has as many sisters as brothers but each girl has twice as many brothers as sisters.
How many brothers and sisters are there?

Ans: Since the boys have as many brothers as sisters, there must be 1 boy more than the number of girls. If we try 2 and 1,3 and 2, and 4 and 3, we will find that 4 boys and 3 girls is the solution to fulfil the requirement that each girl has twice as many brothers and sisters.

Tall Men Next Door

Next door to me live four brothers of different heights. Their average height is 74 inches, and the difference in height amongst the first three men is two inches. The difference between the third and the fourth man is six inches.
Can you tell how tall is each brother?

Ans: The first brother is 70 inches tall, 72, the third 74 and the fourth brother 80 inches tall.

Rule of Three

What is meant by the rule of three?

Ans: The rule of three means proportion.
In the words if there numbers are given when four numbers are in proportion, this is a method of finding one of them.