8/14/2019 Amateur and Professional

1/48

TelescopesAmateur and Professional

8/14/2019 Amateur and Professional

2/48

Galileo 1609

8/14/2019 Amateur and Professional

3/48

The Moon as a World

8/14/2019 Amateur and Professional

4/48

Jupiter has Moons

8/14/2019 Amateur and Professional

5/48

8/14/2019 Amateur and Professional

6/48

Refracting telescopes

8/14/2019 Amateur and Professional

7/48

8/14/2019 Amateur and Professional

8/48

Long focus refractors were awkward but suffered less from

chromatic aberration

8/14/2019 Amateur and Professional

9/48

Isaac Newtons reflecting telescope

Mirrors do not have

chromatic aberration

8/14/2019 Amateur and Professional

10/48

Reflecting telescope

Objective mirrors instead of lenses

8/14/2019 Amateur and Professional

11/48

Three Powers

Magnifying

Resolving

Light Gathering

8/14/2019 Amateur and Professional

12/48

Magnifying Power

Ability to make objects appear larger in

angular size

One can change the magnifying power of

a telescope by changing the eyepiece

used with it

Mag Power = focal length of objective

divided by the focal length of the eyepiece

8/14/2019 Amateur and Professional

13/48

Resolving Power

Ability to see fine detail

Depends on the diameter of the objective

lens or mirror

8/14/2019 Amateur and Professional

14/48

Light Gathering Power

The ability to make faint objects look

brighter

Depends on the area of the objective lens

or mirror

Thus a telescope with an objective lens 2

inches in diameter has 4 times the light

gathering power of a telescope with a lens

1 inch in diameter

8/14/2019 Amateur and Professional

15/48

Herschel & Lord Rosse

8/14/2019 Amateur and Professional

16/48

19th century: epoch of the large

refractors

8/14/2019 Amateur and Professional

17/48

Refracting telescopes

Vienna

Lick

8/14/2019 Amateur and Professional

18/48

Yerkes

Observatory

Largest refracting

telescope with a

one meter objective

8/14/2019 Amateur and Professional

19/48

8/14/2019 Amateur and Professional

20/48

Palomar 5-m

(entered operation in 1948)

8/14/2019 Amateur and Professional

21/48

4 meter

Reflecting

telescope

8/14/2019 Amateur and Professional

22/48

Objective Mirror

8/14/2019 Amateur and Professional

23/48

Dome of 4 meter

Kitt Peak

8/14/2019 Amateur and Professional

24/48

Keck Telescopes

8/14/2019 Amateur and Professional

25/48

SOAR Telescope

4.1 meter

8/14/2019 Amateur and Professional

26/48

SOAR Telescope -- Cerro Pachon

8/14/2019 Amateur and Professional

27/48

8/14/2019 Amateur and Professional

28/48

8/14/2019 Amateur and Professional

29/48

MSU Campus Observatory

8/14/2019 Amateur and Professional

30/48

8/14/2019 Amateur and Professional

31/48

8/14/2019 Amateur and Professional

32/48

A more general expression for the

theoretical resolving power

Imagine that star

images look like Airy

disks

8/14/2019 Amateur and Professional

33/48

Minimum Angle that can be

resolved

R = 1.22 x 206,265 / d

R = resolution in seconds of arc

= wavelength of light

d = diameter of the objective lens or mirror

Note that the wavelength of light and the

diameter of the objective should be in thesame units

8/14/2019 Amateur and Professional

34/48

Examples

For Visible light around 500nm

Our 24-inch telescope

R = 0.20 seconds

This may be compared with the Dawes limit of 0.19

seconds

But with large ground-based telescopes it is difficult

to achieve this

8/14/2019 Amateur and Professional

35/48

Astronomical seeing

Blurring effect of lookingthrough air

Causes stars to twinkleand planetary detail toblur

At the SOAR site: goodseeing means stellarimages better than about0.7 seconds of arc

In Michigan, good seeingmeans better than about 3seconds of arc

Not to be confused withgood transparency

8/14/2019 Amateur and Professional

36/48

Bad seeing on

this sideGood seeing

on this side

8/14/2019 Amateur and Professional

37/48

8/14/2019 Amateur and Professional

38/48

Radio Telescopes

Arecibo

8/14/2019 Amateur and Professional

39/48

8/14/2019 Amateur and Professional

40/48

Radio telescope resolution

= 1m d = 100m

R = 2500 seconds = 42 minutes!

Even though radio telescopes are much

bigger, their resolving power is much

worse than for optical telescopes

Interferometric arrays get around this

8/14/2019 Amateur and Professional

41/48

Very Large Array

8/14/2019 Amateur and Professional

42/48

Interferometry

Size of array = 10 km for a VLA

This becomes the effective d

Now R becomes 25 secsec for a1-m wavelength

For VLBI (very long baseline interfeormetry)

the d = 10,000km and R = 0.025 seconds

8/14/2019 Amateur and Professional

43/48

Observing from space

No clouds

Perfect seeing

Can see wavelengths of light blocked bythe earths atmosphere

8/14/2019 Amateur and Professional

44/48

8/14/2019 Amateur and Professional

45/48

8/14/2019 Amateur and Professional

46/48

8/14/2019 Amateur and Professional

47/48

8/14/2019 Amateur and Professional

48/48

Rooftop telescopes