Reflecting telescopes

Draw a ray diagram for an astronomical telescope in normal adjustment.

Include in your diagram:

three non-axial rays

labelled principal foci for the lenses.

An astronomer has two telescopes A and B.

The astronomer uses each telescope to make observations of Mars when Mars is 0.55 AU from the Earth.

Table 1 gives information about A and B.

angular resolution of the eye ≈ 3 × 10⁻⁴ rad

Compare the images formed by A and B.

In your answer, refer to:

the relative brightness of the images

the ability of each telescope to show features on Mars

the effect of any aberrations caused by each type of telescope.

One advantage of using a CCD with a telescope is that the data can be stored and processed on a computer.

Explain two other advantages of using a CCD rather than the eye when making an observation with a telescope.

A student uses a refracting telescope in normal adjustment to make observations of Jupiter. The telescope has an angular magnification of 75

The eyepiece has a focal length of 22 mm.

Determine the distance between the eyepiece and the objective lens.

When viewed through the telescope, the image of Jupiter subtends an angle

Calculate, in km, the distance between the Earth and Jupiter.

mean radius of Jupiter = 7.0 × 10⁴ km

The student places a cap over one end of the telescope. The cap has a circular hole in its centre. Figure 1 shows the end of the telescope, the objective lens and the cap.

State and explain the effect that the addition of the cap has on the chromatic aberration caused by the lens.

Explain two other effects that the addition of the cap has on the image of Jupiter.

Draw a ray diagram to show how a converging lens can cause spherical aberration.

Draw a labelled ray diagram for an astronomical refracting telescope in normal adjustment.

Show three non-axial rays passing through both lenses. Label the principal foci of the lenses.

The James Lick telescope is an astronomical refracting telescope. When in normal adjustment, the distance between the lenses of the telescope is 17.4 m and the angular magnification is 750

Calculate the focal length of the eyepiece lens.

The James Lick telescope can be used to identify binary stars.

Two techniques are available using this telescope:

• using a processed image from a CCD, and

• direct observation using the naked eye.

Compare the use of a CCD with the use of the naked eye to observe binary stars with this telescope.

Draw a ray diagram for a Cassegrain telescope. Your diagram should show the paths of two rays up to the eyepiece lens. The rays should initially be parallel to the principal axis.

A spacecraft passes Pluto at a distance of 12 500 km. The telescope on board has an aperture of diameter 0.21 m and operates at a wavelength of 450 nm.

Discuss whether this telescope is suitable for studying a crater with a diameter of approximately 1 km on Pluto.

The Hubble telescope has an aperture of diameter 2.4 m.

Compare the collecting power of the Hubble telescope with the telescope on the spacecraft in Question 01.2.

An astrophysicist had to decide whether to use a reflecting telescope or a refracting telescope on the spacecraft in Question 01.2.

Discuss which type of telescope to use.

The lenses used in refracting telescopes can cause chromatic aberration.

Complete Figure 1 to show how a lens produces chromatic aberration.

A Cassegrain telescope uses mirrors.

What are the shapes of the primary and secondary mirrors in a Cassegrain

Table 1 contains information about two telescopes, A and B. Each telescope is planned to be the biggest of its type in the world.

Discuss the similarities and differences between optical reflecting telescopes and radio telescopes. Your answer should include references to:

structure

positioning

collecting power.

Go on to discuss which telescope, A or B, will give a more detailed image of an astronomical object that emits both radio waves and visible light.