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ASTRONOMY 161 Introduction to Solar System Astronomy

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Title: ASTRONOMY 161 Introduction to Solar System Astronomy


1
ASTRONOMY 161Introduction to Solar System
Astronomy
Class 11
2
  • If a light source is moving toward you, the
    wavelength is shorter (called a blueshift).
  • If a light source is moving away from you, the
    wavelength is longer (called a redshift).

3
Size of Doppler shift is
proportional to radial velocity.
4
Example
5
Few closing questions
  • 1) What kind of spectrum will be produced by very
    hot, but also very dense hydrogen gas?
  • 2) If you have hot gas in front of a star, what
    kind of spectrum will you see?
  • 3) Which spectrum is more complex that of
    hydrogen or that of helium?
  • 4) What is the maximum blueshift possible?
  • 5) What is the maximum redshift possible?
    (tricky)

6
TelescopesMonday, October 19
7
Telescopes Key Concepts
  • (1) Telescopes use either a lens or a mirror to
    gather light.
  • (2) The main purposes of a telescope are to
    gather light and resolve detail.
  • (3) Radio and microwave telescopes use a
    reflecting dish to focus waves.
  • (4) Telescopes in orbit avoid the distorting
    effects of the atmosphere.
  • (5) Ultraviolet, X-ray, gamma ray, and most
    infrared light is visible only from orbit.

8
(1) Telescopes use either a lens or
a mirror to gather light.
  • Refracting telescopes use a lens to bend (or
    refract) the path of light.

9
  • Light with a short wavelength is bent through a
    larger angle than light with a long wavelength.
  • (This is why prisms spread light into a spectrum.)

10
  • A convex lens (thicker in the middle) focuses
    light to a point
  • Light from a large area is funneled into a small
    area.

11
  • Reflecting telescopes use a mirror to change the
    path of light.
  • Angle of incidence (I) equals angle of reflection
    (R), regardless of wavelength.

12
  • A mirror shaped like a parabola focuses light to
    a point
  • Light from a large area is funneled into a small
    area.
  • Lenses and mirrors (if shaped correctly) produce
    an accurate image of an object.

13
  • Reflecting telescopes use a number of designs

14
(2) The main purposes of a telescope are
to gather light and resolve detail.
  • A telescope is sometimes called a light bucket.
  • Number of photons collected per second is
    proportional to the area of the lens/mirror
  • Area p/4 x D2
  • where D diameter of the lens/mirror.

15
  • A bigger telescope is able to resolve finer
    detail.
  • Two stars are resolved if they are seen as two
    separate points.
  • Smallest angle resolved is proportional to 1/D.

16
  • BIGGER IS
    BETTER
  • Larger diameter for your lens or mirror
    means more light, higher resolution.

17
The worlds biggest telescopes are reflectors
(mirrors), not refractors (lenses).
  • The problem with lenses
  • 1) Lenses absorb light.
  • 2) Lenses sag.
  • 3) Lenses have chromatic aberration colors
    do not focus at same point.

18
The worlds largest refracting telescope
  • Yerkes Observatory, Wisconsin
  • 1 meter diameter
  • Completed 1897

19
Some of the smallest professional refracting
telescopes
  • HATNet, Arizona, Hawaii 0.1 meter diameters.
  • Established 2003

20
Data from HATNet
21
One of the worlds
largest reflecting telescopes (2x8.4 m)
22
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23
LBT First Light ImageNGC 891
NGC 891 LBT First Light 2005 October 12 LBC-B
camera
LBC Blue Image
24
NGC 6946
LBC-B color composite
25
Crab Nebula
LBC-B color composite
26
NGC 2419
LBC-B color composite
27
r 25.13?0.06
28
GRB 070311
LBC-B Data
29
(3) Radio and microwave telescopes use a
reflecting dish to focus waves.
  • Parabolic dish of a radio telescope acts as a
    mirror, reflecting radio waves to the focus.

30
  • Radio telescopes can be huge, because they do not
    have to very smooth.
  • Mirrors must be smooth compared to the wavelength
    of light observed
  • Visible light l 0.0005 mm
  • Microwaves l gt 1 mm
  • Radio waves l gt 100 mm.
  • Resolution of a telescope q l/D

31
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32
(4) Telescopes in orbit avoid the distorting
effects of the atmosphere.
  • Turbulence in the air makes stars twinkle and
    limits resolution (so called seeing).
  • City lights drown out faint stars.
  • Great idea place a telescope in
    orbit, above the atmosphere.

33
Earth at Night
34
  • Hubble Space Telescope (launched 1990)
  • Diameter of mirror 2.4 meters
  • Angular resolution 0.05 arcseconds

35
(5) UV, X-ray, g ray, and most IR is visible only
from above the atmosphere.
  • Infrared (IR) light is absorbed by water vapor in
    the Earths atmosphere.
  • The Spitzer Space Telescope, launched in 2003,
    uses a 0.85 meter mirror.

36
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37
  • Ultraviolet (UV) light is absorbed by ozone in
    the Earths ozone layer, 25 km up.
  • The Hubble Space Telescope could detect UV light
    with l 100 nm.

38
  • X-rays are absorbed by most molecules in the
    Earths atmosphere.
  • Chandra X-ray Observatory, launched in 1999, uses
    grazing incidence mirrors to focus X-ray light.

39
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40
  • Gamma rays are absorbed by just about everything.
  • Making gamma ray mirrors is beyond current
    technology.
  • Compton Gamma Ray Observatory, launched in 1991
    and deorbited in 2000, had several instruments.

41
Sky Radio
42
Sky Microwaves
43
Sky Infrared
44
Sky Optical
45
Sky Optical Again
46
Sky X-ray
47
Sky gamma-ray
48
Telescopes Few closing questions
  • 1) If you double the diameter of a telescope, how
    much more light will it collect?
  • 2) If you double the diameter of a telescope, how
    will its resolution change?
  • 3) Which has better resolution 1 meter diameter
    optical telescope, or 30 meter radio dish?
  • 4) What is the largest X-ray telescope on Earth?
  • 5) How much () is a 10 meter optical
    telescope?
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