Transcript Week_1

ASTR 2020
Space Astronomy
Introduction
ASTR 1200: Why “Space Astronomy” ?
Limitation of Astronomy from the ground:
Earth’s atmosphere is opaque at most wavelengths.
Atmospheric “Windows”:
Visual, near-IR, radio
Turbulence: Limit angular resolution to ~1 arc-second
“Backgrounds”: flux from various sources limits sensitivity.
Visual:
Light pollution
(artificial lighting)
Scattering
(star-light, moon-light, Sun, etc.)
Airglow
(glowing atoms & molecules in upper atmosphere)
Near-IR & radio: thermal emission from atmosphere
Radio: Electronic interference
(RFI = “radio frequency interference”)
Atmosphere is opaque at most wavelengths ….
Diffraction:
Light spreads as
q=l/D
(radians)
In the `far field’ given by
L = D2 / l
D = Diameter of aperture (telescope optical diameter)
L
D
Near field
(shadows)
Far field
(diffraction)
“Airy” pattern
“Seeing”:
The impact of atmospheric turbulence
on images of a star.
Diffraction limited:
q=l/D
Ex: D = 1 m = 100 cm;
l = 0.5 m = 5x10-5 cm
q = [5x10-5]/[100] = 5x10-7 radians ~ 0.1 arc-seconds
(1 radian ~ 206,265 arc-seconds)
Seeing limited:
Seeing-limited
~ 1 to 3 arc-seconds
Diffraction limited
“Backgrounds”:
Airglow as seen from Space
Aurora
Airglow
+ Light pollution
+ scattered star- and moon-light
+ Thermal emission at l > 2 m (VERY BRIGHT!)
+ R.F.I. (Radio Frequency Interference)
at l > 1 cm
ASTR 1200: Syllabus overview
We will meet at MWF 3:00 - 3:50 here (Duane G125)
Homework (30%) to be given roughly every two weeks on Tuesday;
due the following Tuesday, returned on the Tuesday after.
Two Midterms (12.5% each )
Friday, 11 March; Friday, 8 April
Comprehensive Final (25%)
Wednesday, 4 May 7:30 - 10:00 PM
A Class Project (10%): I will ask you to evaluate & design an instrument
to meet “Dan Goldin’s Dream” to image an exo-Earth with 100 km
resolution- more on this later in class.
Participation (10%)
- Clilckers
- Sommers-Bausch Observatory (SBO) observing: (6 sessions)
- Visits to Fiske Planetarium (4 sessions)
See Syllabus for dates/times
SBO dates / times:
Fiske dates / times:
Wed, 3 Feb
Intro to sky, space station, orbits of satellites around Earth, planetary and KBO orbits
Wed, 24 Feb
Exploration of Solar System bodies with robotic spacecraft: Moon, Mars, Jovian system,Saturn, and Pluto
Friday, 18 March
The multi-spectra sky: 3D exploration of the galaxy; Spitzer, Herschel/Hi-GAL, trip to Orion, Carina, etc.
Wednesday, 13 April
Overview of galaxies and cosmology: HST, deep fields, 3D distribution of galaxies, CMB
Course Outline:
Basics of the electromagnetic spectrum
Propertied of EM waves, interaction with matter
Nature of matter & the forces of nature
Limitations of ground-based astronomy
Basics of Gravity & motion
Orbits, velocity, acceleration, propulsion
Navigation in Space
Basics of Optics and Remote sensing
Exploration of the Solar System with robotic spacecraft:
Mercury, Apollo, Voyager, Magellan, Galileo, Cassini, New Horizons
Space Astronomy: Exploring the spectrum
IRAS, Uhuru, HST, CXO, WISE, Spitzer, Herschel, GRO, Fermi, ….
Instructors
• John Bally
D349 Duane 303 492 5786
[email protected]
casa.colorado.edu/~bally/
Office hours: Tuesday
Wednesday
1:00 AM - 2:00 PM
2:00 PM - 3:00 PM
or by appointment
• Aaron Stemo E122 Duane
303 492 5010
Aaron [email protected]
Office Hours: Tuesday
11:30 AM-1:00 PM
or by appointment
Also available in the Astronomy Help Room (AHR)
4:00 PM - 6:00 PM Wednesdays
Duane D220
Web page for Course Material
casa.colorado.edu/~bally/Current_Course/
Syllabus.pdf
Howework/ …
Lecture_ppt_files/ …
Some other interesting Web pages:
http://apod.nasa.gov/apod/
http://heritage.stsci.edu/2015/01/supplemental.html.html
My Background
• Berkeley BS (1972)
• PhD U. Mass. Amherst (1980)
Molecular Clouds, Star Formation, radio astronomy
• AT&T Bell Laboratories (1980 - 1991)
(in group which discovered CMB)
mm-and IR astronomy
star & planet formation
• CU Boulder (1992 - present)
- Hubble Space Telescope, South Pole
- Herschel Space Observatory, ….
Birth of massive stars & clusters
The Galactic Center
“Ecology” of the Interstellar medium
Cosmology
The Golden Age of Astronomy & Physics:
Access to the entire EM spectrum:
Giant ground-based telescopes,
Sensors at visual, near-infrared, radio, UV, X-ray,
& hard gamma-rays
Access to space:
No atmosphere: No attenuation or turbulence
 New phenomena and knowledge
(dark matter, dark energy, nature of matter & energy)
 Understanding of Nature is the driver of the Economy !
Clicker Test:
The number of arc-seconds in a radian is:
1) 1
2) 200
3) 206,265
4) 2x106
The Golden Age:
• Seeing what we can’t see (with our eyes)
- Electronics & silicon technology
=> sensors at all wavelengths
- Large telescopes (Diameters up to 10 meters now;
37 meter in 10 yrs)
- Space telescopes (to 6 meters)
=> No atmosphere
=> Sharp images
=> Access to all wavelengths
Fermi Chandra Hubble
-ray
X-ray UV/visual
Spitzer Herschel ALMA (Chile)
IR
sub-mm
radio
- Powerful computers
=> Model cosmic evolution, stars, atoms, …
NEW DISCOVERIES!
Understanding nature => Enables technology, economy
Hubble Space Telescope
Very Large Array 27 x 25 m (radio)
Green Bank
100 m
(radio)
Kitt Peak (visual)
CXO
(X-ray)
Fermi (-ray)
GRO
(-ray)
Chandra (X-ray)
Hubble
2.4 m
(visual)
James Webb Space Telescope
6.5 - meter diameter
Earth-Sun L2 (~106 km from Earth): 2018
ASTR 2020
Space Astronomy
Friday
The Electromagnetic Spectrum
Electromagnetic Waves
What’s “waving”?
- Electric fields induce Magnetic fields
- Magnetic fields induce Electric fields
What is a “field”?
- the force
experienced
by a charge (+,-)
e.g. electrons
protons
but not neutrons
Star
A large, glowing ball of gas that generates heat and light through
nuclear fusion
Visual wavelength
UV & X-ray wavelengths
The Winter sky ….
Infrared view of winter sky (10 - 120 m)
Electromagnetic (EM) Waves
- Properties of light: it’s a wave … and a particle!
- Wave like properties (EM waves) : frequency, wavelength
[frequency] x [ wavelength] = [speed of light]
f
x
l=
c

x
l=
c
l = f l= c
c = 2.998 x 1010 cm/sec
- Particle like properties (photons) : energy, momentum
[energy] = h f = h 
h = Planck constant
= 6.626 x 10-27 in (c.g.s)
[momentum] = E/c = h f / c = h  / c = h / l
because f = c / l )
How can we know what the
universe was like in the past?
 Light travels at a finite speed
 c = 300,000 km/s = 3 x 1010 cm/sec.
Destination
Light travel time
Moon
1 second
Sun
8 minutes
Sirius
8 years
Andromeda Galaxy 2.5 million years
 Thus, we see objects as they were in the past:
The farther away we look in distance,
the further back we look in time.
No Calculators!
 A photon has
wavelength =1.5x108cm
what is the frequency?
a) 4x10-2 s-1
b) 5x109 s-1
c) 6x1018 s-1
d) 2x102 s-1
e) 6x102 s-1
No Calculators!
 A photon has
wavelength =1.5x108cm
what is the frequency?
a) 4x10-2 s-1
b) 5x109 s-1
c) 6x1018 s-1
d) 2x102 s-1
e) 6x102 s-1