In the World of Stars - Standard 7 - General Science - Balbharati

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 In the World of Stars 

Exercise

Q. 1 Write the proper words in the blanks.

(meridian, horizon, twelve, nine, apparent, celestial, ecliptic)

(a) When seen from a great distance, the sky seems to be touching the ground along a circle. This circle is called the horizon.

(b) The ecliptic is used while defining the zodiac signs.

(c) Classified according to seasons, one season will have nine nakshatras.

(d) The rising of the sun in the east and its setting in the west is the motion of the sun apparent.

Q. 2 A star rises at 8 pm tonight. At what time will it rise after a month? Why?

Ans. The star will rise approximately 48 minutes earlier each month. This is because as the Earth orbits the Sun, the night sky appears to shift due to its revolution. This shift causes stars to rise about four minutes earlier each day. In a month, which is roughly 30 days, the star would rise about 30 days x 4 minutes/day = 120 minutes, or 2 hours earlier. Therefore, if the star initially rises at 8 pm tonight, it would rise around 6 pm after a month.

Q. 3 What is meant by The sun enters a nakshatra'? It is said that in the rainy season the sun enters the Mrug nakshatra. What does it mean?

Ans. A "nakshatra" refers to a specific sector of the sky occupied by the Moon during its monthly orbit around Earth. Each nakshatra is associated with certain characteristics and is divided into 27 segments. When it's said that "the sun enters a nakshatra," it means the Sun appears to move into a particular nakshatra from the Earth's perspective.

"The sun enters the Mrug nakshatra" suggests that during the rainy season, the Sun aligns with or appears in the sector of the sky associated with the Mrug nakshatra. This is often used in traditional Indian calendars to mark seasonal changes and is believed to influence weather patterns and agricultural activities.

Q. 4  Answer the following questions.

(a) What is a constellation?

Ans. A group of stars occupying a small potion of the celestial sphere is called a constellation.

(b) What points should be considered before a sky watch?

Ans. Before you go skywatching:

1. Location: Pick a spot away from city lights for better views.

2. Weather: Check the forecast for clear skies. Avoid cloudy or stormy nights.

3. Moon Phase: Choose a night with a smaller or no moon for clearer visibility.

4. Time: Know when specific celestial events, like meteor showers, happen.

5. Equipment: Decide if you'll use binoculars or a telescope and make sure they're clean.

6. Knowledge: Learn about upcoming events and interesting celestial happenings.

7. Dark Adaptation: Let your eyes adjust to darkness. Avoid bright lights.

8. Comfort: Dress for the weather, bring a chair, and use insect repellent.

9. Observation Plan: Focus on specific objects like planets or constellations.

10. Safety: Tell someone about your plans, carry essentials, and be aware of your surroundings.

(c) Is it wrong to say that the planets, stars and nakshatras affect human life? Why?

Ans. Saying that planets, stars, and nakshatras affect human life is not scientifically supported. While celestial bodies like the Sun influence Earth's climate and seasons, there's no credible scientific evidence showing a direct influence on individual human lives. The notion that planetary positions or stars impact personal characteristics or events lacks empirical support and is considered pseudoscience.

Astrology, which often makes such claims, is not recognized as a scientific discipline. Scientific understanding emphasizes natural forces, genetics, and environmental factors in shaping human experiences. Beliefs in celestial influences on individuals are often based on cultural or historical traditions rather than empirical evidence.

Q. 5 Write a paragraph on the birth and lifecycle of stars using figure 20.1

Ans. 
Fig. 20.1

Stars start as clouds called nebulae, full of hydrogen and dust. Gravity pulls particles together, creating a dense sphere that becomes a star. This star transforms over time, going from an ordinary star to a red giant, then a planetary nebula, and finally a white dwarf. Massive stars follow a different path, turning into red super giants, undergoing a supernova, and becoming a neutron star or black hole. These changes take a long time, forming the captivating life cycle of stars.

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