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Telescopes and Space Probes

How telescopes gather and magnify light, the difference between refractors and reflectors, and how space probes explore the Solar System, from fly-bys to landers.

⏱️ 17 min 🎯 15 activities
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What you'll cover

Two ways to explore space

We explore the Solar System in two ways: by looking out from Earth with telescopes, and by sending robotic space probes to visit other worlds. This module covers how a telescope gathers and magnifies light, the difference between the two main telescope designs, and the kinds of space probe we send and why.

The parts of a telescope

A few key ideas describe how any telescope works:

Match each part

  • Objective
  • Eyepiece
  • Aperture
  • Resolution
  • The main lens or mirror that gathers the light
  • The small lens you look through to view the image
  • The diameter of the objective, setting the light gathered
  • The ability to see fine detail and separate close objects

Refractors and reflectors

There are two main telescope designs, and they gather light in different ways.

Lenses or mirrors?

Which type of telescope uses MIRRORS to gather light?

  • A reflector
  • A refractor
  • A Galilean telescope
  • A Keplerian telescope

Work out the magnification

A telescope has an objective focal length of 900 mm and an eyepiece focal length of 30 mm. Use M = fo / fe to work out the magnification. Give your answer as a number (magnification has no unit).

Why aperture matters

The aperture is the diameter of the objective, and it controls the telescope's light grasp. Light grasp is proportional to the diameter squared, so doubling the aperture gathers four times as much light. A larger aperture also gives better resolution, letting you see finer detail. That is why the biggest research telescopes are built with huge mirrors.

Why choose a reflector?

Select the TWO advantages of a reflector over a refractor.

  • It does not suffer from chromatic aberration
  • It can be made much larger and more cheaply
  • It can only ever be built very small
  • It uses lenses and no mirrors at all

Telescopes in words

The main light-gathering lens or mirror is the _____, and the small lens you look through is the _____. The diameter of the objective is the _____; a bigger one gathers more light. A telescope that uses lenses is a _____, while one that uses mirrors is a _____.

objective eyepiece aperture refractor reflector magnification resolution orbiter lander mirror

Match each space probe

  • Fly-by
  • Orbiter
  • Impactor
  • Lander
  • Passes close to a body once, then flies on, like New Horizons at Pluto
  • Goes into orbit to study a body over time, like Juno at Jupiter
  • Deliberately crashes into a body, like the Deep Impact probe
  • Touches down on the surface, like Philae on a comet

Name that probe

A probe that goes into orbit around a planet to study it over a long time is called what?

  • An orbiter
  • A fly-by
  • A lander
  • An impactor

Why send a robot?

Robotic, unmanned probes have advantages over crewed missions. Tap the TWO advantages of sending an UNMANNED probe.

  • It is cheaper than sending astronauts
  • It can go to dangerous places without risking any lives
  • It can make human judgements on the spot
  • It can carry out repairs by hand
  • It brings a crew safely back home

Through the telescope

Put the path of light through a refracting telescope in order.

  • Light from a distant object enters the telescope
  • The objective gathers and focuses the light
  • A small real image forms inside the telescope
  • The eyepiece magnifies this image
  • The magnified light enters your eye

Plan the exploration

Use what you know about telescopes and probes to answer each question.

  • You want to gather more light from a very faint galaxy. What should you increase?
  • A mission wants to touch down on a comet and study its surface directly. Which type of probe is needed?
  • Why are the largest research telescopes usually reflectors rather than refractors?

Crewed or robotic?

Compare crewed (manned) and robotic (unmanned) space missions. Give advantages and disadvantages of each. Write in clear, full sentences.

  • Give one advantage of a robotic, unmanned probe
  • Give one disadvantage of a robotic probe
  • Give one advantage of a crewed, manned mission
  • Give one disadvantage of a crewed mission