Science Lesson 4.2

• Earth is the only planet in the solar system that sustains life. This is the planet that has an atmosphere suitable for organisms. The shape of Earth is oblate spheroid


  which means that it is flattened at the poles and bulges at the equator. The equator is an imaginary line at the center of a celestial body such as planet Earth. Earth’s equator divides the planet into the Northern Hemisphere and the Southern Hemisphere. The equator is equidistant from its poles at 0 degree latitude.
• Earth is spinning but we do not really feel this movement. Earth rotates on its axis


  an imaginary line that runs through the center from the North Pole to the South Pole in a counterclockwise movement or from west to east. Earth is slightly tilted on its axis at 23.5 degree angle. Because of this tilt many places on Earth do not have an exact 12 hours of day and 12 hours of night. Aside from that seasons happen on Earth because of this tilt.
• The length of one complete rotation

  or the movement of Earth on its axis is 24 hours or one day.
• The rotation of Earth makes day and night. As Earth turns


  the other half is facing the sun; so one half of the planet is experiencing daytime.
• The sun does not move around Earth. In fact


  the rotation of Earth on its axis makes it look as if the sun was moving. Our planet rotates very slowly all the time. Its movement is also smooth and at constant speed.
• Shadows - are formed when an opaque object blocks the source of light. Shadows are visible when there is a light source such as when the sun is shining. The sizes of shadows depend on the position of the sun. Shadows are the shortest at the middle of the day because the sun is at its highest position in the sky.
• The rotation of Earth also affects the wind or moving air. If it did not rotate


  the wind would only blow from north to south and vice versa. As Earth rotates counterclockwise the winds between the equator and the poles move in a circular pattern. The south-to-north flowing air over the equator gradually flows to the east.
• As Earth rotates on its axis


  it also moves around the sun through an imaginary line called the orbit. It takes about 365 and ¼ days or one year for Earth to complete one full revolution around the sun.
• The regions in the equator always experience a warm climate because the sun always experience a warm climate because the sun always get high in the sky. The Philippines is located near the equator


  which is why we have a tropical climate. Many places on Earth experience four seasons.
• The four seasons:
• The revolution of Earth around the sun

  the tilt and how high the sun gets into the sky are factors that contribute to the occurrence of the different seasons.
• The universe is infinite. It is made up of galaxies, planets, asteroids, meteoroids, and other celestial bodies
• General kinds of galaxies

  • Elliptical
  • Spiral
  • Irregular
• The Milky Way – a spiral type of galaxy, is where our solar system is located
• The sun, the planets, and other celestial bodies that orbit around the sun make up our solar system. Everything is held together by the force of gravity
• Our solar system orbits the center of the Milky Way at 828,000 kilometers per hour
• Astronomy


  The branch of science that deals with the study of space, celestial objects, and phenomena outside the atmosphere of Earth
• Astronomers


  Scientists who study celestial bodies
• Astronauts/cosmonauts


  People trained by a human space flight program to man, pilot, send commands, or serve as crew members of a spacecraft mission
• Planets orbiting the sun in the solar system

  • Mercury
  • Venus
  • Earth
  • Mars
  • Jupiter
  • Saturn
  • Uranus
  • Neptune
• Groups of planets


  • Terrestrial planets
  • Jovian planets
• Terrestrial planets


  • Inner planets
  • Physically look like Earth
  • Made up of rocks or metals with a hard surface
  • Have a molten core
  • Have one or a few satellites (moons)
  • Have topological features such as volcanoes, craters, and valleys
• Mercury


  • The nearest planet to the sun and the smallest planet in the solar system
  • Approximately two-fifths the size of Earth
  • Named after the Roman god of travel who is known for his speed and who also served as the messenger to the other Roman gods
• Mercury has a diameter of 4,878 kilometers and is about 57 million kilometers away from the sun. It is also known as the fastest planet, as it makes one complete revolution around the sun for 88 Earth days only
• Mercury has a very thin atmosphere. Because of this, the planet's surface can reach up to 467 degree celsius when the sun's ray are directly facing it. Although it is the closest planet to the sun, it is not the hottest because its thin atmosphere cannot trap the heat for a long time. So, Mercury can also have very low temperatures, which can sometimes reach as low as -187 degrees celcius for the parts that cannot retain the heat
• Mercury is also a dense planet because it is composed mainly of iron and nickel with an iron core, making it really heavy. This planet does not have any moons. Its magnetic field is only about 1% that of Earth
• Mercury's surface is very dry. Because it has a thin atmosphere, its surface has plenty of craters covered by a thin layer of silicates. In 2012, scientists discovered evidence of organic compounds, the building blocks of life, and water in the form of ice in craters shaded from the sun
• Venus


  • The second planet from the sun
  • Named after the Roman goddess of love and beauty
  • Has almost the same size as Earth, which is why it is often called the sister planet of Earth
  • Does not have any moons
• Venus has a diameter of 12 104 kilometers and is approximately 108 million kilometers away from the sun. Venus spins slowly in a clockwise direction, which is a direction opposite from most planets
• Venus's atmosphere is mainly composed of carbon monoxide and carbon dioxide. This toxic layer of atmosphere traps heat from the sun, making Venus the hottest planet in the solar system. The temperature on this planet reaches 460 degrees Celsius, which is hot enough to melt lead. It takes 224.7 Earth days for Venus to make one complete revolution around the sun
• Because it reflects sunlight, Venus can also be the brightest object in the sky
• Venus


  The brightest planet in the solar system
• Venus is located at the east of the sun


  It shines in the evening, thus earning the name "evening star"
• Venus is located at the west of the sun


  It rises before the sun, making it known as the "morning star"
• Surface of Venus


  • Mostly made of volcano marks and deep canyons
  • Some of its volcanoes are still active
• Only a few spacecraft have entered Venus' thick gaseous atmosphere and survived
• Life is impossible on Venus due to its extreme heat and toxic atmosphere
• Earth


  Our home planet, the third planet in the solar system and the largest terrestrial planet
• Earth is the only planet that has its unique name, not adapted from any Greek or Roman god or goddess
• Earth's rotation and revolution

  1. Rotates on its axis for 24 hours or 1 day

  2. Revolves around the sun at 365 ¼ days in a counterclockwise direction