Jawahar Navodaya vidhyalaya
Jodhpur
Physics Investigatory Project
Topic :- Astronomical Telescope
Submitted By Submitted To
Yashoda Mrs. Pallavi Mudgal
ASTRONOMICAL
TELESCOPE
Name: Yashoda
Roll Number:
School: J.N.V. Jodhpur
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Index
1. Certificate 3
2. Acknowledgements 4
3. What is an Astronomical Telescope? 5
4. Parts Required 6
5. Working Principle of an Astronomical Telescope 7
6. Uses 10
7. Future Aspects 11
8. Bibliography 12
2
Certificate
This is to certify that Yashoda , student of Class XII,
has completed the project during the academic year
2023-2024 towards partial fulfillment of credit for the
Physics practical evaluation of CBSE board 2024, and
submitted satisfactory report, as compiled in the
following pages, under my supervision.
Mrs. Pallavi Mudgal Examiner
(Physics teacher)
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Acknowledgements
The completion of any project is not complete without
thanking the people behind the venture & this project is
no exception. I take this opportunity to express my
profound gratitude and deep regards to my Physics
teacher Mrs. Pallavi Mudgal or his exemplary guidance,
monitoring and constant encouragement throughout the
course of this thesis. The blessing, help and guidance
given by his time to time shall carry me a long way in the
journey of life on which I am about to embark.
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What is an
Astronomical
Telescope?
An Astronomical Telescope is a simple device based on
optical refraction through spherical lenses, that is used to
view heavenly bodies such as the moon, stars and distant
objects.
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Parts Required
Two Convex Lenses are required:
Objective Lens: This lens is fitted at the front side of
the telescope. It should have a large aperture
(diameter) and a large focal length.
Eyepiece: This lens is fitted at the back side of the
telescope. It should have a smaller aperture (diameter)
and focal length as compared to the objective lens.
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Working Principle of an
Astronomical Telescope
As this telescope uses a lens as an objective, it is called a
refracting telescope or refractor.
The objective lens forms a real, reduced image I of the
object. This image is the object for the eyepiece lens,
which forms an enlarged, virtual image of I. Objects that
are viewed with a telescope are usually so far away from
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the instrument that the first image I is formed very
nearly at the second focal point of the objective lens. If
the final image I’ formed by the eyepiece is at infinity (for
most comfortable viewing by a normal eye), the first
image must also be at the first focal point of the
eyepiece. The distance between objective and eyepiece,
which is the length of the telescope, is therefore the sum
of the focal lengths of objective and eyepiece, ƒ1 +ƒ2.
The angular magnification M of a telescope is defined as
the ratio of the angle subtended at the eye by the final
image I’ to the angle subtended at the eye by the object.
We can express this ratio in terms of the focal lengths of
objective and eyepiece. The object (not shown) subtends
an angle Ө at the objective and would subtend essentially
the same angle at the eye. Also, since the observer’s eye
is placed just to the right of the focal point F2’, the angle
subtended at the eye by the final image is very nearly
equal to the angle Ө’. As bd is parallel to the optic axis,
the distances ab and cd are equal to each other and also
to the height y’ of the real image I. Because the angles Ө
and Ө’ are small, they may be approximated by their
tangents. From the right triangles F1ab and F2cd,
−𝑦′
𝜃=
ƒ1
𝑦′
𝜃′ =
ƒ2
And the angular magnification M is
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𝜃′ 𝑦′ /𝑓1 𝑓1
𝑀= = = −
𝜃 −𝑦′ /𝑓2 𝑓2
The angular magnification M of a telescope is equal to the
ratio of the focal length of the objective to that of the
eyepiece. The negative sign shows that the final image is
inverted. This equation shows that to achieve good
angular magnification, a telescope should have a long
objective focal length ƒ1.
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Uses
Astronomical telescopes are being used worldwide for
scientific as well as educational purposes.
The refracting telescope design was originally used in spy
glasses.
It is also used in long focus camera lenses.
With the addition of another convex lens (inverting lens)
at an appropriate position, this telescope can be modified
into a terrestrial telescope.
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Modified Models & Designs
Galileo’s Telescope
Keplerian Telescope
Achromatic Refractor
Apochromatic Refractor
Image of a refracting telescope from the Cincinnati Observatory in 1848
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Bibliography
Physics (Part I) – Textbook for Class XII; National
Council of Educational Research and Training
Sears and Zemansky’s University Physics by Hugh D.
Young and Roger A. Freedman
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