Astronomy

Eratosthenes

275

Eratosthenes 275 BC - 195 BC
Born in Cyrene.
Greek Mathematician
Created a map of the world based on the information of his geographical location.
First person to calculate the circumference of the earth with 2% error.
The angle of elevation of the sun is one fiftieth of a circle during a solstice.
He determined the distance between Alexandria and Cyrene to be 1 stadion (39690km)
He also calculated the tilt of the earth and discovered the leap year.

Nicholaus Copernicus

Feb 19, 1473

Nicholaus Copernicus 1473 - 1543
Born in Royal Prussia, Poland.
Renaissance astronomer.
His work suggested that the sun was at the centre of the universe and other celestrial bodies rotated around other sun. This is referred to as the heliocentric model.
He discovered that the earth rotates daily on its axis and the earth's motion affected what people saw in the heavens.
The Earth's axis tilted relative to the sun and annual rotations about the sun brings the seasons.

Tycho Brahe

Dec 14, 1546

Tycho Brahe 1546 - 1601
Born in Knutstorp Castle, Sweden.
Greek astronomer and alchemist.
Did not accept the Copernicus model and believed in the Heliocentric model.
He made the most precise observations that had yet been made by devising the best instruments available before the invention of the telescope.
He also made observations on planetary motion, particularly that of Mars.
In 1572, he discovered a supernova which suddenly appeared where none had been before and was visible for 18 months

Galileo Galilei

Feb 15, 1564

Galileo Galilei 1564 - 1642
Born in Pisa Italy.
Italian physicist, mathematician, astronomer and philospher.
He pointed the telescope towards the sky and used it to observe the stars.
Was the first to obeserved the moon and drew sketches of it showing that the moon was not smooth.
He published his findings and stopped by the church as it went against its teachings
His observations supported copernicus's theory.
Discovered that Jupiter had moons which orbited around it.

Johannes Kepler

Dec 27, 1571

Johannes Kepler 1571 – 1630
Born in Baden-Württemberg, Germany
German mathematician, astronomer and astrologer.
Witnessed a lunar eclipse at the age of 9
Developed the Laws of Planetary motion which state that:
1.Planets must travel in an elliptical pattern orbiting the sun.
2.The speed of the planets vary according to its distance to the sun. It travels faster when closer to the sun and slower when further away.
3.The further away a planet is from the sun, the longer it must orbit.

Alexander Friedmann

Jun 16, 1888

Alexander Friedmann 1888 - 1925
Born St Petersburg, Russia
Russian cosmologist, mathematician and physicist.
Developed a model which explains the development of the universe.
1. A closed universe where it will first expand and then contract back to singularity
2. A flat universe where it will expand forever but eventually approach at a rate of zero.
3. A open universe where it will expand forever at a rate that will reach a positive constant value.

Edwin Hubble

Nov 20, 1889

Edwin Hubble 1889 - 1953
Born in Marshfield USA.
American astronomer.
In 1924 he notices a particular type of pulsating star in the Andromeda nebula. Showed that the andromeda was really a separate galaxy.
This was the first evidence to suggest there were other galaxies other than our own, found 24 other galaxies.
In 1929, hubble discovered that the universe is expanding, and from this hubble's law was formed.

Henrietta Swan Leavitt

Oct 16, 2011

Henrietta Swan Leavitt
Born in Lancaster, Massachusetts.
American Astronomer.
Her observations led her to finding a special kind of star located in the Large and Small Magellanic Cloud which later were known as Cephids.
Cephid a member of a class of luminous variable stars
Her most notable achievement is observing a linear relationship between the luminosity and the pulsation period of a star.

Ptolemy

Mar 2, 2022

Ptolemy 85 AD - 165 AD
Born in Ptolemais Hermios
Mathematician, astronomer, geographer and astrologer.
Believed in a Geocentric model.
The model he created could predict the position of planets within 2 degrees
The Ptolemaic system of astronomy placed the Earth at the center of the universe and explained all the observed motions of the Sun, Moon, planets, and stars with a system of uniform circular motions.

Aristotle

Mar 2, 2022

Aristotle 384 BC - 322 BC
Born in Northern Greece.
Greek philosopher, logician and scientist.
Believed in the Geocentric Model.
All the the planets and stars had a perfect sphere shape.
The moon planets sun and star orbited the earth in a simple circular motion.
Deduced that earth was a sphere much smaller than the star in the sky.
No technology was available at the time so everything was seen by the human eye.

Hipparchus

Mar 2, 2022

Hipparchus 190 BC – 120 BC
Born in Nicea
Greek astrologer, astronomer, geographer and mathematician.
He worked on the epicycle which was a geometric model that help explain the variations in speed and direction of the moon, sun and planets.
He devised the epicycle system which stemmed into the ptolemaic system. This system allowed planets and the moon to follow its particular orbit.