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CBSESecondary School (English Medium) Class 8
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संकल्पना स्पष्टीकरण आणि व्हिडिओ२६५
अभ्यासक्रम

Constellation

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Topics

  • Celestial Patterns: Constellations, Zodiac Signs, and Nakshatras
  • Key Constellations and their Visibility
  • Activity

Celestial Patterns: Constellations, Zodiac Signs, and Nakshatras

1. Constellation

  • A constellation is a group of stars that seem to form shapes like animals, humans, or objects.
  • Western astronomers have identified 88 constellations. These figures were named based on events or beliefs of ancient times.

2. Zodiac Signs

  • The path of the Sun (ecliptic) is divided into 12 equal parts, each covering 30 degrees.
  • These parts are called zodiac signs or raashis, and they are named Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces.

3. Nakshatra

  • The Moon takes about 27.3 days to orbit the Earth.
  • Each day, the Moon moves through a part of the sky called a nakshatra, covering 13 degrees and 20 minutes.
  • There are 27 nakshatras, and each is named after its brightest star (called the yogatara).
  • Which nakshatra is visible depends on the Earth’s position along its orbit around the Sun.

Key Constellations and their Visibility:

1. Saptarshi (Great Bear) Constellation

The Saptarshi constellation, also known as the Great Bear, consists of seven bright stars arranged in a kite-like shape. This constellation plays a significant role in locating the Pole Star (Polaris). The distinct alignment of its stars makes it an important reference point for navigation and stargazing.

Visibility throughout the year:

  • February: Rises at 8 PM in the northeast.
  • April: Appears on the meridian.
  • October: Sets at 8 PM.

Saptarshi (Great Bear)

2. Sharmishtha (Cassiopeia) Constellation

The Sharmishtha (Cassiopeia) constellation consists of five bright stars arranged in the shape of an "M". It serves as a reference for locating the Pole Star (Polaris), which lies perpendicular to the third and fourth stars in the constellation. Cassiopeia is positioned opposite to the Saptarshi (Great Bear) constellation, meaning when one sets, the other rises. This distinct positioning makes it an important celestial guide for navigation and stargazing.

Sharmishtha (Cassiopeia)

3. Mrug Nakshatra (Orion) Constellation

The Mrug Nakshatra (Orion) constellation consists of 7–8 stars forming a quadrangle, with three central stars pointing towards Vyadh (Sirius), one of the brightest stars in the night sky. It has a distinct and recognisable pattern, making it an important celestial landmark. This constellation plays a significant role in navigation and astronomical observations.

Visibility throughout the year:

  • December: Rises at 8 PM in the east.
  • February: Appears on the meridian.
  • June: Sets at 8 PM.

Mrug Nakshatra (Orion)

4. Vrushchik (Scorpio) Constellation

The Vrushchik (Scorpio) constellation consists of 10–12 stars, with Jyeshtha (Antares) being the brightest star in the constellation. It is located in the southern sky below the celestial equator, making it more visible in the southern hemisphere. During April, it can be seen in the east a few hours after sunset. This constellation is notable for its distinct shape and significance in astronomy.

Vrushchik (Scorpio)

Activity

Understanding the Sun’s Apparent Movement Through Zodiac Signs

  • Draw a large circle on the ground to represent the zodiac path (ecliptic).
  • Assign 12 friends to stand along this circle, each holding a placard with a zodiac sign.
  • Place one person in the center as the Sun.
  • Another person acts as the Earth, walking in a smaller circle around the Sun while always facing it.
  • As the Earth moves, observe which zodiac sign appears behind the Sun from the Earth’s point of view.
  • Allow different friends to take turns as the Earth and discuss what they observe.

Diagram of the experiment

Conclusion:

As the Earth orbits the Sun, the Sun appears to move through different zodiac signs over the year. This is an apparent motion, meaning the Sun doesn’t actually move, but it looks like it does because of Earth’s movement. This explains why on special days like Makar Sankranti, the Sun appears in the Capricorn (Makar) sign. Similarly, the rising and setting of the Sun are also apparent motions caused by Earth’s rotation. Observing which constellation is behind the Sun helps identify Earth’s position in its orbit.

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