Stars, Constellations and Celestial Bodies - Class 3 Notes

Exploring Our Celestial Neighbourhood

1. Stars

a) Stars are celestial objects that shine brightly in the night sky.
b) They emit their heat and light.
c) Although there are millions of stars in the sky, they appear as tiny specks of light because they are located very far away from Earth.
d) Sun is also a star.

2. Planets

a) Planets are heavenly bodies that orbit around a star.
b) Unlike stars, planets do not emit their own light. We can see them because they reflect the light from the Sun.

3. Satellites

a) Satellites are smaller celestial bodies that orbit around planets.
b) They are also referred to as moons.
c) Just like planets, satellites can be seen because they reflect the light of the Sun.
d) Unlike stars, planets and their satellites appear steady in the sky without twinkling.

4. Comets

a) Comets are fascinating objects composed of a large number of rocky particles covered with frozen ice of water and gases.
b) When a comet approaches the Sun, the heat causes the ice to vaporise, creating a glowing coma around the comet.

5. Meteors

a) Meteors, commonly known as "shooting stars," are frequent sights in the night sky.
b) They are celestial bodies that appear as bright streaks of light for a brief moment.
c) Meteor trails, or shooting stars, usually last for less than a second.
d) When meteors enter the Earth's atmosphere and reach the surface, they are called meteorites, which can create craters.

6. Asteroids

a) Asteroids are large chunks of rocks that orbit the Sun, primarily found between the planets Mars and Jupiter.
b) They are often referred to as minor planets or planetoids.
c) Unlike comets, which contain mostly ice, asteroids are composed of rock and metal.

7. Artificial Satellites

a) Some man-made objects orbit around the Earth. We call them artificial satellites.
b) These satellites have some important jobs like helping with communication, predicting the weather, and guiding us during navigation.
c) Examples of a few artificial satellites are Hubble Space Telescope, INSAT 1A, and GPS satellites.

Movement of the Earth

1. Rotation

a) The Earth is shaped like a round ball and it spins around an imaginary tilted line, which we call the Earth's rotation.
b) This rotation makes the Earth turn around itself.
c) When a certain part of the Earth faces the Sun, it receives sunlight, and that's when we have daytime.
d) On the other side of the Earth, where it doesn't face the Sun, it becomes dark, and that's when we have nighttime.
e) It takes approximately 24 hours, which we call a day, for the Earth to complete one full rotation around its axis.
f) As the Earth spins, different parts of the planet experience sunlight or darkness, creating the cycle of day and night that we observe.

2. Revolution

a) The Earth doesn't just spin on its axis, it also moves around the Sun in a particular path called revolution.
b) It takes about 365 and a quarter days, or one year, for the Earth to complete one full revolution around the Sun. This revolution is what brings changes in seasons.
c) The timing of the seasons is different for the two halves of the Earth, which we call hemispheres.
d) When the North Pole leans toward the Sun, the northern hemisphere gets more direct sunlight.
e) So, the northern hemisphere gets warmer, and it becomes summertime there. At the same time, the southern hemisphere experiences winter.

3. Constellations

a) Constellations are groups of stars that form patterns or shapes in the night sky.
b) Constellations have names inspired by creatures and characters from myths and legends.
c) 88 official constellations have been identified and named by astronomers.
d) Some well-known constellations include Cassiopeia, which looks like a "W" shape, Ursa Major, which resembles a big bear, and Orion, which represents a mighty hunter.

4. Moon

a) The moon is Earth's natural satellite that revolves around our planet.
b) The moon follows a special path around the Earth called an orbit.
c) It doesn't have its own light, but it reflects the bright light from the sun.
d) As it moves around the Earth, different parts of the moon get lit up by the sun. We can only see the part of the moon that is getting light. That's why the moon seems to change its shape every day.
e) These different shapes are called phases of the moon.

5. Solar Eclipse

a) A solar eclipse happens when the moon moves between the sun and the Earth. The moon casts a big shadow that covers the sun for a little while.
b) This blocks the sunlight from reaching us on Earth and we can see a glowing halo around the darkened sun.
c) During a solar eclipse, the sky gets darker, almost like nighttime during the daytime.
d) But here's an important thing to remember: never look directly at the sun during a solar eclipse, even if It's partially covered.
e) The sun's rays can harm your eyes, so always use special eclipse glasses or watch the eclipse through a safe viewing device.

6. Lunar Eclipse

a) A lunar eclipse occurs when the Earth comes between the sun and the moon. This means the Earth's shadow falls on the moon, making it look dimmer or even turn reddish-orange.
b) You can safely observe them with your naked eyes.