Maharashtra Board Class 9 Science Chapter 18 Observing Space Telescopes Solutions

Chapter 18 Observing Space: Telescopes

Question 1. Fill in the blanks with the proper words.
(a) The wavelength of visible light is between …………………..….. and …………………..…. .
(b) GMRT is used for …………………..….. waves.
(c) A certain X-ray telescope is named after scientist …………………..…. .
(d) The first scientist to use a telescope for space observations …………………..…. .
(e) The biggest optical telescope in India is situated at …………………..…. .
Answer:
(a) 400 nm, 800 nm
(b) radio
(c) Subrahmanyan Chandrasekhar
(d) Galileo Galilei
(e) Devasthal, Nainital
In simple words: These answers complete the facts about light wavelengths, radio waves used by GMRT, the Chandra X-ray telescope, Galileo's historic observations, and India's largest optical telescope.

🎯 Exam Tip: Memorize the exact wavelengths of visible light (400 nm to 800 nm) and key scientist names as they are highly scoring and frequently asked in exams.

Question 2. Form pairs

Answer:
(1) – (d) Chandra
(2) – (c) Hubble
(3) – (a) GMRT
(4) – (b) ISRO
In simple words: This matches different space technologies and telescopes with their correct names or organizations, like matching X-ray telescopes with Chandra and Indian radio telescopes with GMRT.

🎯 Exam Tip: Always write the matching pairs side-by-side in your final answer sheet instead of drawing criss-cross lines to keep your presentation neat.

Question 3. What are the difficulties in using ground-based optical telescopes? How are they overcome?
Answer:
Difficulties in using ground-based optical telescopes:
1. The intensity of light reaching the Earth's surface decreases because some of it is absorbed by the atmosphere.
2. Changes in atmospheric pressure and temperature cause the air to move, which makes the images of stars shake and appear blurry.
3. Ground-based telescopes cannot be used during the daytime due to bright sunlight, and their operation is also disrupted by cloudy weather or city light pollution at night.

How these difficulties are overcome:
1. To minimize these atmospheric interferences, optical telescopes are built on high mountain peaks, in dry regions, and far away from city lights.
2. These difficulties can be completely eliminated by placing the telescope in space, outside the Earth's atmosphere, such as the Hubble Space Telescope.
In simple words: Earth's atmosphere blocks and distorts starlight, and city lights or clouds make it hard to see. We solve this by putting telescopes on high, dry mountains or launching them directly into space.

🎯 Exam Tip: Clearly divide your answer into two distinct sections: 'Difficulties' and 'Solutions' using bullet points to make it easy for the examiner to award full marks.

Difficulties in Using Ground-Based Optical Telescopes and Their Solutions

• The intensity of visible light coming from a heavenly body decreases due to absorption as it passes through the Earth’s atmosphere.
• Due to changes in atmospheric temperature and pressure light rays change their path.
• Because of sunlight, we cannot use optical telescopes during the day.
• During the night, city lights and cloudy weather cause difficulties.

Solution:
• To reduce these problems, optical telescopes are situated on top of mountains, in uninhabited places.
• To get rid of all the above problems completely, the telescope is placed above the earth’s atmosphere, in space.

Question 4. Which type of telescopes can be made using a concave mirror, convex mirror, plane mirror, and a lens? Draw diagrams of these telescopes.
Answer:
• A Newtonian telescope can be made using a concave mirror, plane mirror and a lens. This design helps in avoiding chromatic aberration.
Newtonian Telescope Diagram Labels:
• Eyepiece
• Light source
• Plane mirror
• Concave mirror
• Light source
• A Cassegrain telescope can be made using a convex mirror, concave mirror and a lens.
In simple words: A Newtonian telescope uses a curved concave mirror and a flat plane mirror to reflect light to the eyepiece, while a Cassegrain telescope uses a combination of concave and convex mirrors to focus the image.

🎯 Exam Tip: Remember that Newtonian telescopes use a flat plane mirror as the secondary reflector, whereas Cassegrain telescopes use a curved convex mirror.

Question 5. Study the figure and answer the following questions:
(i) Identify the type of telescope shown in the diagram.
(ii) Label the parts marked as (1), (2), (3), (4), and (5).
Answer:
(i) The telescope shown in the diagram is a Newtonian telescope, which is a type of reflecting telescope that uses a curved mirror to gather and focus light.
(ii) The labeled parts of the telescope are:
(1) Concave mirror
(2) Eyepiece
(3) Light source (Incident rays)
(4) Plane mirror
(5) Telescope tube
In simple words: This is a Newtonian telescope. It uses a large curved mirror at the bottom to collect light, which then bounces off a small flat mirror to an eyepiece on the side where you look through.

🎯 Exam Tip: Remember that a Newtonian telescope uses a flat plane mirror as its secondary mirror, whereas a Cassegrain telescope uses a convex secondary mirror.

Question.
a. What type of telescope is shown in the figure?
b. Label the main parts of the telescope.
c. Which type of mirror does the telescope use?
d. What other type of telescope uses a curved mirror?
e. Explain the working of the above telescope.
Answer:
(a) The Newtonian telescope (Reflecting telescope)
(b) The labels of the Newtonian telescope are:
• Concave mirror
• Eyepiece
• Plane mirror
• Light source
(c) Concave mirror
(d) The Cassegrain telescope
(e) Working:
• Light rays coming from space are reflected by the concave mirror.
• Before these reflected rays converge at the focus, they are deflected again by a small plane mirror.
• As a result, they get focused at a point lying on the perpendicular to the axis of the telescope’s cylinder.
• They pass through the eyepiece and we get a magnified image of the source. This setup allows for clear observation of distant celestial bodies.
In simple words: This telescope uses a curved concave mirror to collect light and a flat mirror to bounce it into an eyepiece so we can see a bright, zoomed-in image of space.

🎯 Exam Tip: Remember that a Newtonian telescope uses both a concave mirror and a flat plane mirror to direct light to the eyepiece. Clearly labeling these components will help you secure full marks.

6. Answer the Following Questions

Question a. Explain the construction of Galileo’s telescope.
Answer: The Galileo’s telescope is made up of two or more convex lenses. These lenses work together to refract light and produce a magnified view of distant objects.
In simple words: Galileo's telescope uses simple glass lenses to bend light and make far-away things look much closer and larger.

🎯 Exam Tip: Mention that Galileo's telescope uses convex lenses to refract light, as "convex lenses" and "refraction" are key terms examiners look for.

Question a. Explain the construction of an optical refracting telescope.
Answer:
• The lens facing the object is called the objective lens which is made as large as possible to collect the maximum amount of light coming from a heavenly object.
• The lens closer to the eye is called the eyepiece which uses the light collected by the objective lens and produces a large image of the source.
• Such a telescope is also called a refracting telescope. This design helps astronomers view distant stars and planets with greater clarity.
In simple words: An optical telescope uses a large front lens to collect light from space and a smaller eyepiece lens to magnify the image so we can see it clearly.

🎯 Exam Tip: Remember that refracting telescopes use lenses to bend light, and the objective lens must always be larger than the eyepiece to collect maximum light.

Question b. Explain the construction of a radio telescope.
Answer:
• The radio telescope is made from one or more dishes of a particular parabolic shape.
• As in optical telescope, the incident radio waves are reflected by these dishes and converge at the focus.
• A radio receiver is placed at the focal point.
• The information gathered by this receiver is passed on to a computer which analyses it and constructs an image of the source. These specialized instruments allow astronomers to observe cosmic phenomena that are completely invisible to standard optical telescopes.

The structure of a radio telescope includes:
• Radio waves
• Receiver
• Dish
• Amplifier
• Computer
In simple words: A radio telescope uses a large curved dish to collect radio waves from space, focuses them onto a receiver, and sends the signals to a computer to create an image.

🎯 Exam Tip: When describing a radio telescope, always mention the parabolic dish, the receiver at the focus, and the computer used for processing the signals.

Question c. Why are optical telescopes located in uninhabited places on mountains?
Answer:
• The visible light coming from a heavenly body has to pass through the earth’s atmosphere to reach the earth’s surface.
• During this journey, some of the light is absorbed by the atmosphere and the intensity of the light reaching the earth’s surface decreases. Furthermore, being high up on mountains reduces the interference caused by city lights and atmospheric turbulence.
In simple words: Earth's atmosphere absorbs and scatters light from space, making images blurry. Placing telescopes high on mountains gets them above much of the air and away from city lights for a clearer view.

🎯 Exam Tip: Clearly state the two main reasons: atmospheric absorption of light and the need to avoid light pollution from cities.

Question d. Why can an X-ray telescope not be based on the earth?
Answer:
• X-rays are emitted from distant heavenly bodies.
• The rays coming towards the earth will be absorbed by the earth’s atmosphere and will go undetected. This orbital placement ensures that the high-energy X-rays can be clearly detected without atmospheric interference.
• Hence, X-ray telescopes are placed in an orbit outside the earth’s atmosphere and not on the earth.
In simple words: Earth's atmosphere blocks X-rays from space, so we cannot detect them from the ground. To see them, we must put X-ray telescopes on satellites orbiting high above the atmosphere.

🎯 Exam Tip: Remember to mention that the Earth's atmosphere absorbs X-rays, which is the primary reason these telescopes must be placed in space.

Class 9 Science Chapter 18 Observing Space: Telescopes Intext Questions And Answers

Question 1. What is meant by space observation? Why is it important?
Answer: The observation of distant planets, galaxies and other astronomical objects is called as space observation. It is important for the following reasons:
• Various space based satellites support our telecommunication networks by providing us television broadcasting.
• Meteorology services such as weather forecasting help in disaster management.
• Observation of positions of stars and other heavenly bodies has helped in the study of solar system, solar winds, pulsars, supernova, etc. Additionally, studying these cosmic phenomena allows scientists to understand the fundamental laws of physics governing our universe.
In simple words: Space observation means looking at stars, planets, and galaxies far away. It is important because it helps us with TV signals, weather reports, and understanding how the universe works.

🎯 Exam Tip: Clearly define 'space observation' first, then list at least three practical benefits like telecommunications, weather forecasting, and scientific study to score full marks.

p>Question 2. What is the difference between sky and space?
Answer: Sky: It is a layer of gas that surrounds the earth in which sunlight is scattered making it visible from the surface of the earth. Space: The vast emptiness beyond the sky is called as space. Understanding this boundary helps us study both our atmosphere and the universe beyond.
In simple words: The sky is the air-filled layer we see above us, while space is the completely empty area that lies beyond our atmosphere.

🎯 Exam Tip: Present the definitions of both sky and space clearly to highlight the physical boundary between them.

Choose and Write the Correct Options:

Question 1. The first telescope was invented by
(a) Einstein
(b) Galileo
(c) Newton
(d) Mendel
Answer: (b) Galileo
In simple words: Galileo was the famous scientist who first built a telescope to observe stars and planets in the night sky.

🎯 Exam Tip: Associate Galileo with the invention of the astronomical telescope to quickly answer history-of-science questions.

Question 2. Eight is an wave.
(a) electric
(b) magnetic
(c) electromagnetic
(d) mechanical
Answer: (c) electromagnetic
In simple words: Light is an electromagnetic wave, meaning it can travel through the vacuum of empty space without needing any air or water.

🎯 Exam Tip: Always identify light as an electromagnetic wave since it consists of oscillating electric and magnetic fields.

Question 3. Visible radiation telescopes are also called as
(a) Gamma Ray telescopes
(b) Optical telescopes
(c) X-ray telescopes
(d) Radio telescopes
Answer: (b) Optical telescope
In simple words: Telescopes that help us see regular light, just like our eyes do, are called optical telescopes.

🎯 Exam Tip: Associate 'visible radiation' directly with 'optical' to easily remember this definition.

Question 4. Reflecting telescopes are mainly of two types : ……………….. and ………………. .
(a) Newtonian and Galileoan
(b) Optical and Cassegrain
(c) Newtonian and Cassegrain
(d) Optical and Refracting
Answer: (c) Newtonian and Cassegrain
In simple words: Reflecting telescopes use mirrors to collect light, and the two most common designs are named Newtonian and Cassegrain after their creators.

🎯 Exam Tip: Remember that reflecting telescopes use mirrors instead of lenses, and the two main types are Newtonian and Cassegrain.

Question 5. Giant Meterwave Radio Telescope (GMRT) has been erected at near Pune.
(a) Asangaon
(b) Talegaon
(c) Narayangaon
(d) Bhategaon
Answer: (c) Narayangaon
In simple words: The GMRT is a massive radio telescope located at Narayangaon near Pune, which was chosen because it has very low radio noise interference.

🎯 Exam Tip: GMRT is a world-famous radio telescope located in Maharashtra; memorizing its exact location (Narayangaon, Pune) is highly important for exams.

Question 6. Visible light coming from heavenly bodies have to pass through the to reach the earth surface.
(a) stratosphere
(b) troposphere
(c) atmosphere
(d) biosphere
Answer: (c) atmosphere
In simple words: Light from stars and planets must travel through Earth's thick layer of air, called the atmosphere, before it reaches our eyes or telescopes on the ground.

🎯 Exam Tip: Always remember that the atmosphere causes stars to twinkle and can distort light, which is why we put some telescopes in space.

Question 7. To collect the maximum amount of light coming from an object, the objective lens should be made as as possible.
(a) large
(b) small
(c) circular
(d) None of the options
Answer: (a) large
In simple words: A bigger lens acts like a larger bucket, catching more light from faint, distant stars so we can see them clearly.

🎯 Exam Tip: To see faint space objects, we need to collect more light, which requires a larger objective lens or mirror diameter (aperture).

Question.
(d) flat
Answer: (a) large
In simple words: This is the correct option for the previous question.

🎯 Exam Tip: Always read all options carefully before selecting the correct answer.

Question 8. The images formed by lenses have errors of colours. This is called
(a) chromatic disruption
(b) chromatic aberration
(c) chromatic reflection
(d) chromatic reaction
Answer: (b) chromatic aberration
In simple words: When lenses cannot focus all colors of light to the exact same point, it creates a color distortion called chromatic aberration.

🎯 Exam Tip: Remember that "chromatic" refers to color, and "aberration" means a departure from what is normal or expected.

Question 9. Radio telescope is made up of one or more dishes of shape.
(a) spherical
(b) hyperbolic
(c) parabolic
(d) hexagonal
Answer: (c) parabolic
In simple words: A parabolic shape helps to collect weak radio waves from space and focus them onto a single point.

🎯 Exam Tip: Parabolic dishes are crucial for focusing parallel incoming waves to a single focal point. Keep this geometric property in mind.

Match the Columns

Question 1. Match the items in Column 'A' with Column 'B':

Answer:
(1) X-rays — (d) Chandra
(2) Optical telescope — (c) Hubble
(3) Indian radio telescope — (a) GMRT
(4) Launching artificial satellite — (b) ISRO
(5) Radio waves — (e) telecommunication
These matches connect each scientific instrument or wave type with its corresponding observatory, agency, or application.
In simple words: This table matches different space technologies and waves with their correct names or uses. For example, Chandra is an X-ray telescope, while ISRO is the Indian agency that launches satellites.

🎯 Exam Tip: In match-the-column questions, start with the pairs you are absolutely sure about to easily eliminate other options.

1. Match the following:

Answer:
(1 – d)
(2 – c)
(3 – a)
(4 – b)
(5 – f)
(6 – e)
In simple words: This matches different types of waves or satellites to their corresponding wavelengths or characteristics.

🎯 Exam Tip: Double-check each match by process of elimination to ensure all pairs are correctly aligned.

2. Match the columns:

Answer:
(1 – e)
(2 – a)
(3 – d)
(4 – b)
(5 – c)
In simple words: This matches different electromagnetic waves to their specific wavelength ranges in the spectrum.

🎯 Exam Tip: Memorize the order of the electromagnetic spectrum from longest to shortest wavelength to easily solve matching questions.

Define the Following:

Question 1. Visible radiation
Answer: Light is an electromagnetic wave. Every wave has a characteristic wavelength. Our eyes can see only that light which has wavelengths between 400 nm to 800 nm. Such light is called visible radiation. This range of wavelengths is what makes things visible to us.
In simple words: Visible radiation is the only part of the light spectrum that our eyes can actually see, ranging from red to violet.

🎯 Exam Tip: Always mention the specific wavelength range of 400 nm to 800 nm when defining visible radiation to secure full marks.

Question 2. Reflecting Telescope
Answer: When light falls on the mirror, it gets reflected. Telescopes that use concave mirrors are called reflecting telescope. This reflection allows us to see distant objects clearly.
In simple words: A reflecting telescope uses curved mirrors to bounce light and create an image of far-away objects.

🎯 Exam Tip: Remember that reflecting telescopes use concave mirrors, not convex ones, to gather and focus light.

Question 3. Optical telescopes
Answer: Telescopes which are made from regular lenses and mirrors and used to see visible radiations coming from space are called optical telescopes. They help astronomers study stars and planets using normal light.
In simple words: Optical telescopes are normal telescopes that use lenses and mirrors to let us see the visible light coming from space.

🎯 Exam Tip: Clearly mention "visible radiations" or "visible light" when defining optical telescopes to get full marks.

Question 4. Refracting Telescopes
Answer: Light rays change their direction as they enter a lens from the atmosphere and again when they enter the atmosphere after passing through the lens. This is called refraction. The telescopes that use such lenses are called refracting telescopes. These instruments are highly effective for viewing nearby celestial bodies.
In simple words: Refracting telescopes use lenses to bend (refract) light rays so that distant objects look bigger and closer.

🎯 Exam Tip: Explain the concept of refraction (bending of light as it passes through a lens) to secure full marks for this definition.

Question 5. Radio telescopes
Answer: Many heavenly bodies emit radio waves in addition to visible radiation. A special type of telescope which is used to receive these rays are known as radio telescope. These telescopes often look like giant dish antennas.
In simple words: A radio telescope is a special antenna used to collect radio waves from space instead of visible light.

🎯 Exam Tip: Highlight that radio telescopes detect "radio waves" rather than visible light emitted by celestial bodies.

Question 1. How do refracting telescopes work?
Answer:
• Most refracting telescopes are made with two or more lenses.
• The two lenses are called objective lens and an eyepiece lens.
• The objective lens should be large so that maximum light can be collected from the source. This helps in creating a much brighter and clearer image of the object.
In simple words: A refracting telescope works by using a large front lens to collect lots of light and a smaller eyepiece lens to magnify the image for our eyes.

🎯 Exam Tip: Always name both the "objective lens" and the "eyepiece lens" when explaining how a refracting telescope works.

Question 2. What are the difficulties in using refracting telescopes?
Answer:
• We require a large objective lens which is very difficult to make. Also large lenses are heavy and tend to get distorted.
• As the objective and eyepiece lens are placed on the opposite sides of the telescope, the length of the telescope also increases with increase in the size of the lenses. This makes it difficult to manage a large telescope.
• The images formed by lenses have errors of colours. This is called chromatic aberration. These physical limitations restrict the size and effectiveness of refracting telescopes.
In simple words: Refracting telescopes use lenses, which are hard to make perfect when they are very big. Large lenses are heavy, make the telescope too long, and cause colors to blur around the edges.

🎯 Exam Tip: Remember the term 'chromatic aberration' as it is a key keyword examiners look for when grading difficulties of refracting telescopes.

Question 3. How does a radio telescope work?
Answer:
• A radio telescope is made from one or more dishes of a particular parabolic shape.
• The incident radio waves are reflected by these dishes and converge at a focus.
• A radio receiver is placed at focal point.
• The information gathered by this receiver is then passed onto a computer which analyses and constructs the image of the source. This allows astronomers to study celestial objects that do not emit visible light.
In simple words: A radio telescope uses large curved dishes to collect radio waves from space. These waves are focused onto a receiver, which sends the data to a computer to create a picture.

🎯 Exam Tip: Clearly mention the role of the parabolic dish, receiver, and computer to secure full marks for this process description.

Question 4. What are the two types of reflecting telescopes?
Answer:
• The reflecting telescopes are mainly of two types: Newtonian and Cassegrain.
• The newtonian telescope uses a plane mirror and a concave mirror.
• The Cassegrain telescope uses a convex and a concave mirror. Both designs are highly effective at gathering light from distant stars.
In simple words: Reflecting telescopes use mirrors instead of lenses to collect light. The two main types are Newtonian and Cassegrain, which use different combinations of flat, curved, and convex mirrors.

🎯 Exam Tip: Be sure to specify the exact types of mirrors used in both Newtonian and Cassegrain designs to avoid losing marks.

Question 5. What is the purpose of launching X-Ray telescope Chandra?
Answer: Chandra was launched to study X-rays coming from heavenly objects. Special mirrors which . can reflect X-rays were used in this telescope. This allows scientists to observe high-energy regions of the universe like supernovas and black holes.
In simple words: Chandra is a space telescope designed to look at X-rays from space. It uses special mirrors to help us see hot and energetic things like exploded stars.

🎯 Exam Tip: Remember to mention that Chandra specifically detects X-rays, which cannot be easily observed from the Earth's surface due to atmospheric interference.

Answer the Following:

Question 1. State some of the satellites and their uses.
Answer:
• The INSAT and GSAT series of satellites support our telecommunication network, television broadcasting and meteorological services.
• It is because of them that telephone, television and internet services are available everywhere in the country.
• The EDUSAT satellite is used exclusively for education, helping distance learning reach remote areas.
• The IRS satellite series is used for the monitoring and management of natural resources as well as disaster management.
• Astrosat: It has ultraviolet and X-ray telescopes and detectors. It is a unique system having different kinds of telescopes on a single satellite.
In simple words: Different satellites have different jobs. Some help with TV and internet, some help with school lessons, and others watch over our natural resources.

🎯 Exam Tip: Match the satellite names (like EDUSAT for education and IRS for resource management) with their specific functions to score full marks.

Question 2. What is the specialty of the artificial satellite Astrosat?
Answer:
• This satellite was launched by Indian Space Research Organization (ISRO).
• It has ultraviolet and X-ray telescopes and detectors. Most of the parts used in this satellite are made in India.
• It is an unique system having different kinds of telescopes on a single satellite. Indian scientists are studying various aspects of the Universe using the data obtained with these telescopes, which helps us understand deep space better.
In simple words: Astrosat is India's special space satellite that carries multiple telescopes at once. It helps scientists study space using ultraviolet and X-ray light.

🎯 Exam Tip: Highlight that Astrosat is unique because it carries multiple types of telescopes on a single satellite, and mention ISRO as the launching agency.

Answer in Detail:

Question 1. Explain any two space observation telescope.
Answer: Space-based telescopes provide much clearer images than ground-based ones because they are above the Earth's atmosphere. These space-based instruments avoid atmospheric distortion to capture incredibly clear images of deep space.
Hubble Telescope:

• In 1990, the National Aeronautics and Space Administration launched into space an optical telescope called the Hubble telescope.
• It has a mirror of diameter 94 inches and is orbiting the earth at a height of 589 km from it.
• This telescope is still working and has helped to make important discoveries.

Chandra Telescope:

• In 1999, the National Aeronautics and Space Administration launched an X-ray telescope named Chandra, in space, to study X-rays coming from heavenly objects.
• Special mirrors which can reflect X-rays were used in this telescope.
• Chandra has given us very useful information about stars and galaxies.
• The telescope is named after the famous Indian scientist Subramanian Chandrashekhar.

In simple words: Space telescopes like Hubble and Chandra are sent into space to take clear pictures of stars and galaxies. Hubble uses normal light, while Chandra uses X-rays to study hot and energetic parts of the universe.

🎯 Exam Tip: Clearly mention the launch year, the type of waves detected (optical for Hubble, X-ray for Chandra), and who they are named after to secure full marks.

Question 2. Write short note : GMRT
Answer: Giant Metrewave Radio Telescope (GMRT) is a highly advanced astronomical facility. This unique design makes it one of the most sensitive radio telescopes in the world at low frequencies.

• Giant Meterwave Radio Telescope (GMRT) is a large radio telescope erected at Narayangaon near Pune.
• It uses radio waves having wavelengths of about a metre, coming from heavenly bodies to study those bodies. This telescope is actually a collection of 30 dishes, each having a diameter of 45 m.
• It is called a giant telescope as the arrangement of the 30 dishes over an area which measures up to 25 km across. It works as a single dish having a diameter of 25 km.
• GMRT gives the same data that we would have got from a telescope having a single dish of 25 km diameter.
• Scientists study the solar system, solar winds, pulsars, supernova, interstellar hydrogen clouds, etc. with the help of the GMRT.

In simple words: GMRT is a massive radio telescope near Pune made of 30 smaller dish antennas spread over a large area. Together, they act like one giant dish to study radio waves from space, helping scientists learn about stars and planets.

🎯 Exam Tip: Remember to state the location (Narayangaon near Pune), the number of dishes (30), and their effective combined diameter (25 km) as these are key evaluation points.