Download Lecture 8 - The Local Group

Space
Observatories,
Airships, &
More
[Oct 20, 2016]
As with all course material (including homework, exams),
these lecture notes are not be reproduced, redistributed,
or sold in any form. Announcements
Exams are being graded…likely completed by Tuesday.
No lecture on Nov 8th.
The James Webb Space Telescope (JWST)
[the successor to the Hubble Space Telescope]
• scheduled
• mirror
to launch in October 2018
= 6.5 meters (21 feet)
• wavelength
range = 0.6μm to 28.5μm (visible to mid-IR)
The James Webb Space Telescope (JWST)
will orbit [the Sun] at the second Lagrange point (L2);
Lagrange points = points in space for a 3-body system
(Sun, Earth, JWST), where objects can orbit each other,
but stay in the same relative positions.
The James Webb Space Telescope (JWST)
JWST Deployment…
please keep your fingers crossed!
Astrophysics Timeline
43
Why put telescopes in space?
Light at certain wavelengths cannot penetrate
the Earth’s atmosphere.
X-ray and gamma-ray telescopes study the hottest and most explosive objects in the Universe.
Infrared telescopes study the places where stars are born and can peer into the centers of galaxies.
The Hubble Space Telescope is able to collect light at UV, visible, and near-infrared wavelengths.
Balloon Experiments
— cheaper than launching into space
— often can recover the payload
Stratoscope I (1957 - 1959)
— 12” telescope to study the Sun’s photosphere
Stratoscope II (1963 - 1971)
— 36” telescope
[Stratoscope I]
Red Bull Stratos
(Felix Baumgartner’s skydive from 128,000 ft)
~39 km
https://www.youtube.com/watch?v=_S5UxmW8FUc
How do balloons work?
Buoyancy!
Buoyancy
If an object is less dense than the
surrounding air (or water), it rises (or floats).
the ideal gas law —
PV = nRT
By heating the air, the volume of the balloon
increases (thus the density of air inside the
balloon decreases relative to the surrounding air).
Buoyancy
If an object is less dense than the
surrounding air (or water), it rises (or floats).
the ideal gas law —
PV = nRT
A helium balloon rises since helium is lighter than
air (primarily nitrogen); the balloon stops rising
when this is no longer the case.
also, as the air pressure decreases,
the helium balloon expands.
While we’re on the subject of Helium…
Why does inhaling helium from a balloon make
your voice sound like Alvin and the Chipmunks?
Often folks think that Helium affects the pitch
(i.e. frequency) of the sound waves. But that is
largely set by the vibration of the vocal cords.
Instead, it impacts the speed of sound and
subsequently the sound quality, making your
voice squeaky and flatter.
—> You sound more like Donald Duck, less like Tweety Bird.
Balloon Experiments
— balloons are often launched from
Antartica and Texas (and monitored
via the Columbia Scientific Balloon
Facility, established in 1961).
— named after Space Shuttle
Columbia, since facility is located
near where the Columbia wreckage
fell to Earth in 2003.
Balloon Experiments
Balloon Experiments
— balloons are made of ~20
micrometer thick polyethylene film.
— reach diameter of ~140 meters in
flight; can carry payloads of ~8000 lbs.
— reach altitudes of ~50 km; flight
durations of < a few days.
— Helium gas is commonly used to fill
the balloon; balloon is partially filled at
launch, with gas expanding as balloon
rises (and atmospheric pressure
decreases).
— parachute for payload recovery.
What brings the
balloon down?
Airplane-based
Observatories
Kuiper Airborne Observatory
(1974 - 1995)
Stratospheric Observatory For Infrared Astronomy (SOFIA)
(2010 - 20??)
Airships
In contrast to balloons, airships are steerable
Airships
A non-rigid airship is better known as a blimp.
Anyone know
why early blimps
(i.e. circa ~1930)
sometimes
exploded?
Airships
While hydrogen is lighter than air, it is also flammable.
The LZ 129
Hindenburg
(1937)
What are those big structures in the distance?
Marine Corps Air Station Tustin
— established 1942 to support airship operations for WWII
— constructed with > 50 parabolic wooden trusses (each)
— plus ~120 ft concrete doors
Marine Corps Air Station Tustin
$35 million, 265-ft long airship that was damaged
(beyond repair) when part of the hangar roof
collapsed in October 2013.
How well do you know
your Solar System?
Question...
One of these objects is just slightly smaller than the
Earth, with a radius that’s about 95% of the Earth’s
radius. Which one?
a) Mercury
b) Venus
c) Mars
d) Neptune
e) Pluto
Answer = B
Question
How many moons does Venus have?
a) 0
b) 1
c) 2
d) 4
e) 7
Answer = A
Question
Which of the following is an observed property of Mars?
a) A cycle of seasons because of Mars’s axis tilt
b) Evidence of past volcanic activity
c) Evidence of erosion by flows of liquid water on its surface
d) Frozen polar caps
e) All of the above
Answer = E
Question
True or false: Saturn is the only one of the giant planets
that has rings.
a) True
b) False
Answer = B
Question
True or false: Jupiter’s mass is larger than the total
combined masses of all of the other planets.
a) true
b) false
Answer = A
Question
True or false: If placed in a (very large) bathtub, Saturn
would float.
a) True
b) False
Answer = A
Question
True or false: As seen from the Earth, Jupiter goes
through a complete cycle of phases, including crescent
and gibbous phases.
a) True
b) False
Answer = B
Solar System
sizes of planets vs. the sun
Solar System
more than just the planets
The Terrestrial Planets
The Terrestrial Planets
Semimajor axis of orbit
(A.U.)
•
Mercury
0.39
Venus
0.72
Earth
1
Mars
1.52
1 AU = 1.5 x 108 km
The Terrestrial Planets
Orbital Period
(years)
Mercury
0.24
Venus
0.62
Earth
1
Mars
1.88
The Terrestrial Planets
Radius
(Earth radii)
•
Mercury
0.38
Venus
0.95
Earth
1
Mars
0.53
Earth’s equatorial radius is 6378 km
The Terrestrial Planets
Mass
(Earth masses)
•
Mercury
0.055
Venus
0.81
Earth
1
Mars
0.11
Note: our Moon has a mass of about 0.012 Earth masses
The Terrestrial Planets
Mean Density
(g/cm3)
Mercury
5.43
Venus
5.24
Earth
5.51
Mars
3.94
The Terrestrial Planets
Rotation Period
(days)
Mercury
59
Venus
243
Earth
1
Mars
1.03
The Terrestrial Planets
Axis Tilt
(degrees)
Mercury
0
Venus
177
Earth
23.5
Mars
25.2
The Terrestrial Planets
Number of Moons
Mercury
0
Venus
0
Earth
1
Mars
2 (both very small)
The Terrestrial Planets:
key properties
Close to the sun
Short orbital periods
Earth is the largest and most massive terrestrial planet
High densities: metallic/rocky composition
Few if any moons
Terrestrial planet atmospheres
Atmospheric composition, in percent
Gas
Earth
Venus
Mars
CO2
Nitrogen
Oxygen
Argon
Neon
0.03
78.1
21
0.93
0.002
96
3.5
0.003
0.006
0.001
95.3
2.7
0.15
1.6
0.0003
Terrestrial planet atmospheres
Atmospheric composition, in percent
Gas
Earth
Venus
Mars
CO2
Nitrogen
Oxygen
Argon
Neon
0.03
78.1
21
0.93
0.002
96
3.5
0.003
0.006
0.001
95.3
2.7
0.15
1.6
0.0003
Differentiation
As planetesimals and planets formed,
large ones became fully molten.
Heavier metallic elements mostly
settled down to the core, and lighter
minerals like silicates rose to the
outer layers.
How do planetary systems form?
How do stars and planets form?
What’s between the stars in the Milky Way?
Gas of varying density, temperature, and composition.
molecular gas
atomic gas
ionized gas
H
H
H
H
p
H
H
H
H
H
H
H
H
H
eH
p
more
dense
temperature (T)
density
p
eep
p
e-
colder
e-
e-
hotter
less
dense
p
Molecular Clouds
Star formation takes place in
molecular clouds, which contain
mostly molecular hydrogen (H2),
and also:
Helium
Volatile compounds: molecules
(H2O, CO, NH3, CH4, etc.) that
can be in a solid (ice) state only
at low temperatures
Refractory materials: Tiny solid
grains of carbon, silicates, and
other metals and minerals
Molecular Clouds
The densest regions
form molecular cloud
cores that can
collapse into starsthese are protostars
Within a cloud,
there are some
denser regions
As the cloud
collapses, the denser
regions collapse
faster and become
more massive
As the cloud core collapses to a
smaller size, it rotates faster.
The protostar forms at the center
of the rotating cloud, and grows
more massive as more gas
accretes onto it.
Surrounding the protostar is an
accretion disk, a rotating disk of gas
that is gradually drifting inward
and adding to the mass of the
protostar.
Protoplanetary
disks
cosmic dust particles
Dust particles collect into
larger aggregations just by
randomly sticking together.
Once a clump reaches about 1
km in size, it starts to exert a
strong enough gravitational pull
to attract more material.
It becomes a planetesimal.
Planetesimals then grow more
quickly, by gravitationally
attracting more matter, and by
merging with other
planetesimals.
cross-section of a
chondritic meteorite
composition of the protoplanetary disk
Terrestrial planets:
Several large planetesimals probably formed within the inner 2 AU:
some merged with other planetesimals, others may have been
ejected from the Solar System through random gravitational
encounters.
The terrestrial planets may have accreted small primary
atmospheres of hydrogen and helium, but these early atmospheres
escaped into space.
Giant planets:
Possibly several rocky planetesimals formed with masses of 5-10
times the Earth’s mass. The largest were able to accrete large
amounts of ices and hydrogen and helium gas.
The giant planets were so massive that miniature accretion disks
formed around them within the protoplanetary disk. Material from
these mini accretion disks coalesced into moons.
See you Tuesday…