Why does Earth have day and night?
Day (light) and night (dark) are caused by Earth's spin on its axis. Earth turns or rotates one time every 24 hours. The part of Earth that is facing the Sun experiences day, and the part facing away from the Sun experiences night. Earth spins counterclockwise, so daylight moves across the globe from east to west.
 

What is our Solar System?

Graphic from Aerospace.Web

The mass of the sun is so great that its gravity is able to hold the planets in an orbit around it.

• The planets orbit the sun.

• The Earth is the 3rd planet from the sun.

• The Earth takes 365 days (1 year) to orbit the sun.

• The Earth rotates (spins) on its axis one time every 24 hours as it goes around the sun.

The mass of the Earth is so great that its gravity is able to hold the moon in an orbit around it! It takes about 28 days for the moon to orbit the Earth.

Graphic

therefore...

The moon orbits the Earth as the Earth orbits the Sun.

Earth: It's JUST RIGHT for living things!

• 75% of Earth's surface is covered with water
• Earth has a blanket of breathable air

NASA - "As seen from space, one of the most unique features of our home planet is the water, in both liquid and frozen forms, that covers approximately 75% of the Earth's surface. Believed to have initially arrived on the surface through the emissions of ancient volcanoes, geologic evidence suggests that large amounts of water have likely flowed on Earth for the past 3.8 billion years, most of its existence. As a vital substance that sets the Earth apart from the rest of the planets in our solar system, water is a necessary ingredient for the development and nourishment of life."

Other characteristics:

• Earth is spherical
• Earth is tilted on its axis by 23.5 degrees

Earth has a tilted axis. Because of this tilt, the different hemispheres sometimes get direct rays (more energy: summer) and sometimes get indirect rays (less energy: winter). Close to the equator, the Earth gets direct rays year-round. The tilt causing the direct/indirect rays is the reason for the seasons!

The pinpoints of light that we see in the night sky are stars. Stars are giant balls of gas in space that shine through the darkness. Our ability to see the stars depends on how bright they are, their size, and also how far away they are from our solar system. We can only see the stars at night because our own star, the sun, is so bright during the day when our half of the Earth is facing it.

The Sun is the only star in our solar system. It is an average star. Earth and all the planets in our solar system orbit it.

"Powers of Ten" (Video) 

Our star, the sun ("Sol"), shines brightly as the only star in our solar system, preventing us from seeing other stars during the day. It is relatively close to Earth compared to the other stars of the universe.

 

Most of the universe is empty space: SPACE! To get a look at the vast distance of space see the video above.

"Planets and Stars: A Size Comparison" (Video)
 

Our star, the sun ("Sol") is an average sized star.
Planets and stars come in very different sizes.

 Reduce, Reuse, Recycle!

Some resources like fresh water, air, wildlife, and trees rely upon us to use them wisely. If we do, they will be available for our use. If we don’t use them wisely, we are in danger of limiting their supply.

• The amount of water on Earth never changes, but we might change the amount that we can use in a certain area. We might pollute it to the point that we can’t use it, or pump too much out of a large underground reservoir that took thousands of years to build up that supply.
• The air in our atmosphere must be protected from pollution that harms living things.
• Wildlife can be impacted by our choices. If an animal species is over-hunted or if its habitat is destroyed, its population may decline or it may become extinct. It is our responsibility to make wise decisions on how to protect animals and their habitats.

Graphic from Princeton Ecology Education

Graphic from FactMonster.com

Graphic from Princeton Ecology Education

Examples of ecosystems include forests, deserts, rainforests, grasslands, arctic, freshwater, marine, and more. An ecosystem in a warm wet rainforest is very different from an ecosystem in a cold, dry desert. An ecosystem in salty ocean water is different from one in a freshwater lake. Different kinds of organisms live in different kinds of ecosystems but the organisms in each ecosystem find the food, water, temperature, shelter, and space that they need.

All ecosystems have a limited amount of resources. The organisms living there must compete for what they need. Competition helps to keep populations steady and helps to maintain a balanced environment.

When organisms do not get enough food, space, or light from their ecosystem, they respond by reproducing less, moving, adapting, or dying out.

• beneficial
  • Worms aerate the soil.
  • People plant trees.
  • People set aside areas of land as parks
• detrimental
  • Swarms of grasshoppers can eat huge amounts of grasses and other plants, including farmers’ crops like hay or corn.
  • Humans use very large amounts of resources, such as water and trees.
  • People build towns and cities where once there were once forests and prairies.
  • People bring plants and animals into new areas where they compete with native species and sometimes cause them to die out.

   

Temperature is the measure of thermal energy. It measures how fast particles are moving in matter.

Know the difference:
- heat is energy
- temperature is a measure of thermal energy

The more heat, the faster the particles move. Cold things have slow-moving molecules, while hot things have fast-moving molecules.

The most common tool for measuring thermal energy (heat) is a thermometer.

• When the colored liquid inside the thermometer heats up, the particles of the liquid move faster and move farther apart. That causes the liquid to take up more space. The colored liquid rises in the tube, and thermometer shows a higher temperature.
• When the air is cooler than the liquid in the thermometer, the particles of the liquid move more slowly and get closer together causing the liquid to take up less space. The colored liquid moves down the tube and shows a lower temperature.

Conduction is when thermal energy is transferred from one solid object to another solid object through direct touching. An example is the heat in a cookie sheet moving up through the pan into the cookies.

 Have FUN learning about
Light, Heat, Electricity, and Magnetism
by clicking here:

http://www.learningscience.org/psc1clightheatelectricitymagnetism.htm

For an electric current to happen, there must be a circuit. A circuit is a closed path or loop around which an electric current flows.

Light travels in straight lines called light rays. Light continues to travel in straight lines until it hits other media or objects. When light hits something, what happens to light depends on the object.

1. Opaque objects block light making a shadow. An example would be a book, a wall, a person, etc.
2. Translucent objects allow some light to pass through. An example would be wax paper.
3. Transparent objects allow all the light to pass through in straight lines. An example would be clear glass windows.

Light can be

1. Absorbed. When a light ray is absorbed by an object, it changes to heat energy. Dark colors absorb more light rays than light colors.
2. Reflected. When a light ray hits an object and bounces off, it is called reflection. Mirrors are a good example of objects that reflect light. Because mirrors reflect all of the light wavelengths, you can see yourself
3. Refracted. When a light ray bends, it is called refraction. Refraction is the change in direction of a wave due to a change in its speed. This happens most often when a ray of light passes from one medium to another, such as air to water, or sunlight through a prism.

Transmission. Sound travels through all sorts of things like water, wood, metal, and air – solids, liquids, and gases. Sound travels fastest through solids because the molecules in solids are closest. Liquids do not transmit sound very well, but gases are the poorest transmitters of sound.

Reflection. In an echo, sound waves travel in one direction, hit something, and bounce back (reflect). That’s why you hear the sound again later

Absorption. When sound waves are trapped or are not able to travel any further, they are absorbed.

Picture shows Bell Laboratories making sound waves visible.

When the vibrations are fast, you hear a high-pitched note. When the vibrations are slow, it creates a low-pitched note.

By filling bottles with various levels of water and tapping the bottles with a metal spoon, different pitches of sound are produced. The more water (the longer the water column), the lower the pitch. This holds true for piano strings, too. The longer the piano strings, the lower the pitch.