Science and Technology Class 9 Notes Chapter 18 Maharashtra Board

Observing Space : Telescopes

Introduction

• Humans have always been curious about the sky, stars, moon, and sun.
• Early observations helped with agriculture (tracking seasons) and navigation (using constellations).
• Initially, people observed the sky with naked eyes, but they needed tools to see distant objects clearly.
• The invention of the telescope 400 years ago by Galileo revolutionized space observation.
• Today, advanced telescope technology helps us understand the universe and supports daily life (e.g., communication, weather forecasting).

Key Concepts

1. Difference Between Sky and Space

• Sky: The part of space we see from Earth, including stars, planets, and clouds.
• Space: The vast universe beyond Earth’s atmosphere, containing stars, planets, galaxies, and more.

2. Space Observation

• Definition: Studying stars, planets, and other celestial objects using telescopes.
• Importance:
  • Helps understand the universe (e.g., stars, galaxies, black holes).
  • Supports practical applications like weather forecasting, communication, and navigation.

Forms of Light

Light is an electromagnetic wave with different wavelengths.

Visible Light:

• Wavelength: 400 nm to 800 nm (nanometers).
• Only type of light humans can see with their eyes.

Other types of electromagnetic waves (invisible to human eyes):

• Radio waves: Long wavelengths, used in radio telescopes.
• X-rays: Short wavelengths, used in X-ray telescopes.
• Gamma rays: Very short wavelengths, used in gamma-ray telescopes.

Different celestial objects emit various types of radiation, so we need different telescopes to study them.

Telescopes: Definition and Purpose

• A telescope is a device used to observe distant objects in space by collecting and focusing light or other radiations.
• One telescope isn’t enough because different objects emit different types of radiation (e.g., visible light, radio waves, X-rays).

Types of Telescopes

1. Optical Telescopes

Purpose: Detect visible light from stars, planets, and galaxies.

Components:

• Objective Lens/Mirror: Collects light from a distant object.
• Eyepiece: Magnifies the image formed by the objective.

Types:

• Refracting Telescope:
  • Uses lenses to bend (refract) light.
  • Structure: Objective lens collects light, eyepiece magnifies the image.
  • Challenges:
    • Large lenses are hard to make and heavy, causing distortion.
    • Long telescopes are difficult to handle.
    • Images have chromatic aberration (color errors).
• Reflecting Telescope:
  • Uses mirrors to reflect light.
  • Advantages:
    • Easier to make large mirrors than lenses.
    • Mirrors are lighter and don’t cause chromatic aberration.
    • Can be made by combining smaller mirror pieces.
  • Subtypes:
    • Newtonian Telescope:
      • Uses a concave mirror to reflect light.
      • A small plane mirror deflects light to the eyepiece on the side.
    • Cassegrain Telescope:
      • Uses a concave mirror and a small convex mirror.
      • Light is reflected back through a hole in the concave mirror to the eyepiece.

Examples in India:

• Several telescopes with 2 m mirrors are used.
• Largest optical telescope: 3.6 m mirror at Aryabhatt Research Institute of Experimental Sciences, Nainital (largest in Asia).

2. Radio Telescopes

Purpose: Detect radio waves emitted by celestial objects (e.g., stars, planets).

Structure:

• Made of large parabolic dishes that reflect radio waves to a focal point.
• A receiver at the focus collects data, which a computer analyzes to create images.

Example:

• Giant Metrewave Radio Telescope (GMRT):
  • Location: Narayangaon, near Pune.
  • Features: 30 dishes, each 45 m in diameter, arranged to work as a single 25 km-wide dish.
  • Uses: Studies solar system, pulsars, supernovas, and interstellar clouds.
  • Built by Indian scientists, it’s a world-class, cost-effective facility.

3. Telescopes in Space

Why Needed?

• Problems with Ground-Based Telescopes:
  • Atmosphere absorbs some light, reducing image brightness.
  • Atmospheric turbulence shakes images.
  • City lights and clouds interfere with observations.
  • Daytime observations are not possible due to sunlight.
• Solution: Place telescopes on mountains or in space.

Advantages of Space Telescopes:

• • No atmospheric interference, so images are clear and bright.
  • Can observe day and night.
  • Can detect radiations (e.g., X-rays) blocked by the atmosphere.

Examples:

• Hubble Telescope (1990, NASA):
  • Optical telescope with a 94-inch mirror.
  • Orbits Earth at 589 km height.
  • Still active, has made major discoveries.
• Chandra Telescope (1999, NASA):
  • X-ray telescope with special mirrors to reflect X-rays.
  • Named after Indian scientist Subramanian Chandrashekhar.
  • Studies X-rays from stars and galaxies.
• Astrosat (2015, ISRO):
  • India’s first space telescope.
  • Has ultraviolet and X-ray telescopes.
  • Most parts made in India, a unique multi-telescope satellite.

Indian Space Research Organization (ISRO)

Established: 1969, Bengaluru.

Purpose: Develop technology for making and launching satellites.

Achievements:

• Launched many satellites for communication, education, and resource management.
• Supports national and social development.

Key Satellites:

• INSAT and GSAT Series:
  • Support telecommunication, TV broadcasting, and weather services.
  • Enable phone, TV, and internet access across India.
• EDUSAT: Used for education.
• IRS Series: Monitors natural resources and aids disaster management.

Astrosat: Launched in 2015, studies the universe using ultraviolet and X-ray data.

Website: www.isro.gov.in

Key Scientists and Contributions

Hans Lippershey (1608):

• Dutch spectacle maker, invented the first telescope.

Galileo Galilei (1609):

• Made a telescope and used it for space observations.
• Discovered Jupiter’s moons, sunspots, and more stars than visible to the naked eye.

Subramanian Chandrashekhar:

• Indian scientist, honored by naming the Chandra X-ray telescope after him.