SCIE 3001
1 - Nature of Living Things
1.4 Human Organ Systems and Health
4 - Cycles and Seasons
5 -Structure of the Earth, and Earth Movements

Unit 2 - Cycles and Seasons

How was the Universe conceptualized?


1. The ancients understood that stars remained in groups called constellations which moved in the sky as groups. This helped them, for example, to predict the seasons for successful agriculture. These constellations are stars which people imagined formed patterns. Sometimes supernatural properties were assumed leading to Astrology.

2. There were 'wandering stars' (planets) - i.e. bright points of light which moved among the background stars.

3. The Greeks, for example, knew these planets as Mercury, Venus, Mars, Jupiter and Saturn. They also considered the Moon and Sun to be planets. This led to the days of the week being named after these seven gods.

4. Not all Greeks believed these planets moved around the Earth (called a geocentric theory). Aristarchus of Soamos believed that the Sun was at the centre (called a heliocentric theory), but his ideas were ignored by the traditions of the geocentric theory.

5. European scholars prized Greek sources of knowledge and thus the Church and Scholars adopted the Aristotlean and Ptolomic geocentric model.

6. Astronomers and those who depended on their prediction were faced with certain anomalies in the movement of the plantets.

7. One major problem is called the retrograde motion of the planets. Usually planets shift slightly eastward from night to night against the backdrop of stars. However, from time to time they move in the opposite direction for a few months before resuming the usual motion.

The motion from B1 to B2 is eastward, however, B2 to B4 is westward or retrograde and then it follows B4 to B5 which is eastward.

8. When the heliocentric theory (planets revolving around the Sun) was revived by Copernicus and Kepler in the 16th. century it was satisfactorily explained. When the Earth (E1) passes the outer planet (P1) it is seen at B1 against the stars. As the Earth moves to E2 and the planet to P2, it appears to have moved all the way to B2. When the Earth moves to E3 and E4 the planet to P3 and P4, the planet appears to be moving backward to B3 against the stars (retrograde motion). As the earth moves from E4 to E5 and the planet from P4 to P5 it once again appears to be moving in the direction of B4 to B5.



9. As astronomy began confronting the inaccuracies in eclipse prediction and navigation at sea, Copernicus introduced the heliocentric model with the Sun as the fixed point in the solar system. This made the understanding of planetary orbits simple.

Johannes Kepler use of Tycho Brahe's observational data to develop mathematical equations for planetary motion and Issac Newton's gravity theory gave further support to this heliocentric theory.

10. Albert Einstein's work on gravity further developed the model and thus we are able to navigate the cosmos today.
2300 BCE
Chinese astronomers start to observe the sky.
1800 BCE
Babylonians begin to keep astronomical records.
585 BCE
Greek philosopher, Thales of Miletus predicts a solar eclipse.
450 BCE
Greeks postulate that other worlds might exist.
270 BCE
Aristarchus (Greek) says that the Sun is the centre of the solar system, but he is ignored.
Idea of a heliocentric universe...
Nicholas of Cusa and Giordano Bruno dispute the solar system is unique. Bruno is burned at the stake in 1600 for claiming that there are other solar systems beside ours.
1543 Nicolaus Copernicus suggests that the Earth and other planets orbit around the sun.  
1550 - 1650 Tyco Brahe made extensive observations of celestial bodies which Johannes Kepler used to develop laws about how planets moved.  
1609 Galileo Galilei uses the telescope to observe the moons of Jupiter. Proof that there are other world beside the Earth.
1698 Christian Huygens speculates about life on other planets in a book called Cosmothermos  
1750 Thomas Wright postulates that the Milky Way may be a massive disk of stars and some of the objects in the sky may be stars like our Sun.  
1781 William Herschel discovers Uranus, first new planet discovered since ancient times  
1855 Capt. W.S. Jacobs finds anomalies in the orbit of a binary star which begin the search for extra solar planets.  
1925 Edwin Hubble uses the Hooker 100" telescope in California to examine galaxies.. Galaxies are groups of stars like the Milky Way.
1990 Launch of Hubble Telescope. Discovery of exo planet - Gas giants.
1992 Aleksander Wolszczan and Dale Farrel discover two rock exo-planets. Discovery of two rocky planets. Unfortunately the condition are too harsh for organic life as we know it.
1995 Michel Mayor and Didier Queloz discover a large planet orbiting a main sequence star.  
1999 Researchers of SanFrancisco State University and the Harvard-Smithsonian Center for Astrophysics discover planets in the Andromeda constellation Andromeda is the closest galaxy.

Teams using the Hubble telescope discover a planet with sodium, hydrogen, carbon and oxygen.

Another team finds a planet in the 'habitable' zone (distance and temperature where liquid water can exist) around a star.

Important elements in the nature of living things.
2003 Spitzer and Canadian Space Telescope launched Spitzer can detract infrared light.
2006 French CoRoT telescope launched. can detect planets as they transit their stars.
2007 Spitzer detects water on an exoplanet  
2008 Hubble Space telescope detects organic molecule on an exoplanet Alien life???
2009 Kepler mission launched. Kepler can observe thousands of stars at once trying to detect transiting Earth-like planets.  

Rotation, Revolution and Orbit

Rotation occurs when something is spinning around an axis e.g. a fan blade

Revolution – the motion of a body around another body so the axis of rotation is outside the body. e.g. a stone on a string.

Orbit – the path that is followed around another body in space

What are some examples of things that rotate?

Tops, Fans, Figure skaters, cyclones, Tornadoes, CDs, Earth.

star trails

How do we know that the Earth rotates?

  1. Star trails- trails made with time exposure photography are circular paths. The Earth is moving and the stars are relatively stationary.
  2. Winds curve because of the Earth’s rotation.
  3. Moving objects in north curve to the right in the northern hemisphere, and to the left in the southern hemisphere.
night and day

Night and Day

What causes night and day?

  1. The rotation of the Earth
  2. The side of the Earth that is facing the sun has daylight, the side of the Earth away from the sun has night.
  3. It takes about 24 hours for the Earth to complete one rotation.
  4. The Earth is tilted on it’s axis at a 23.5 degree angle.
  5. The Earth’s tilt is always in the direction of the North Star also called Polaris
  6. This tilt is what causes our days to get longer in the summer and shorter in the winter.
  7. Because of the Earth’s rotation the sun appears to rise in the east and set in the west.
night and day  


What two things cause the difference in the seasons?

  1. The Earth rotates on its axis (imaginary vertical line around which Earth spins) every 23 hours & 56 minutes.
  2. One day on Earth is one rotation of the Earth.
  3. Day on Earth is when our side of the Earth faces the sun.
  4. Night on Earth is when the side of Earth we are on faces away from the sun.
  5. It takes the Earth 365 days (or rotations) to travel or revolve around the Sun once. This is called a year.
  6. The Earth’s orbit around the sun is NOT a perfect circle. It is an ellipse.
  7. Seasons are not caused by how close the Earth is to the sun.
  8. In fact, the Earth is closest to the sun around January 3 (Winter in the Northern Hemisphere) and farthest away from the sun around July 4 (Summer in the Northern Hemisphere).
  9. Seasons are the result of the tilt of the Earth's axis.
  10. Earth’s axis is tilted 23.5°. This tilting is why we have SEASONS like fall, winter, spring, summer.
  11. The number of daylight hours is greater for the hemisphere, or half of Earth, that is tilted toward the Sun

Summer is warmer than winter (in each hemisphere) because the Sun's rays hit the Earth at a more direct angle during summer than during winter.

Warmer in Summer

  1. We are tilted toward the Sun (23.5deg)
  2. Sun is visible for more hours= more total energy  
  3. ·More direct (intense) sunlight

Chimborazo in Ecuador

Chimborazo in Ecuador is almost on the equator but is snow capped...

Chimborazo in Ecuador

Land adjacent to the red currents are warmer and colder near the blue currents

Factors affecting weather & climate

The following natural factors influence the weather and climate of different places around the world

  • Ocean currents - the movement of water at different temperatures through the oceans. Cold currents like the Humbolt causes the west coast of South America to be at a lower temperature than what is expected at similar latitudes.
  • Amount of water (clouds) and dust in the atmosphere. Water is a greenhouse gas and traps sunlight in cloudy areas leading to higher surface temperatures. Dust reflects sunlight leading to lower surface temperatures.
  • Prevailing winds - the direction that winds usually blow from. Warm winds can warm the air above the ground and similarly cold winds can lead to the opposite)
  • Altitude - height above sea-level. The higher one goes up the colder it gets.
  • Latitude - distance from the equator. The angle of sun's rays and effect on day length and so determines the amount of energy incident on the ground.
  • Distance from the sea. Water has a high specific heat capacity and thus moderates warming or cooling.
  • Aspect - Slopes facing the sun may get more energy and hence are warmer than slopes facing away from the sun.

Humans can also affect climate by

  • Deforestation
  • the amount of carbon dioxide produced by human industry and communities
  • the amount of methane produced by human industry and farming
Concept by Kishore Lal. Programmed by Kishore Lal... Copyright © 2015 Kishore Lal. All rights reserved.