Download A Sense of Scale and The Motions of Earth The guitar player

A Sense of Scale and
The Motions of Earth
The guitar player – Pablo Picasso (1910)
Announcements
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Notes from the first lecture are available on the class
web site (www.astro.umass.edu/~calzetti/astro100).
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In-class quiz # 1 will take place Thursday, Sept. 15th
(next week):
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It will include lectures 1 through 3, and the textbook units
1, 2, 3, 5, and 6
It will be distributed towards the end of Thursday s class,
around 10:30 pm;
You can consult notes/textbook
Please, remember to bring a hand-held calculator and a
pencil.
Goals for Today
To get a sense of the scales of the
Universe
n  To work on understanding one particular
way of looking at how the night sky
changes with time.
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Reading Assignments
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Units 3 and 5 of Textbook
Fundamental Astronomical
Assumption:
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Astronomers assume that the laws of
physics and chemistry
are the same throughout the Universe.
A Sense of Time
If we were to compress the time since the Big Bang
into one year, and make the time of the Big Bang
January 1, v  The Earth was formed in mid-September. v  The mammals appeared on December 26. v  All human prehistory (from the first known stone
tools) and history have occurred in the last ½ hour of
New Year's Eve.
All of human history is but a fleeting instant on the
cosmic timescale. Special Astronomical Units
Light-time=Light traveling time=distance
Car-traveling time as distance: Boston is about 1.5 hours away
(assuming the speed of a car is 60 mph)
The speed of light: c = 3x105 km/s.
Destination Distance (km)
London 6,000
Moon
385,000
Sun
1.5 x 108
Jupiter 7.8 x 108
Nearest Star
4 x 1013
Most Distant Galaxy
1.4 x 1023
Light Travel time
0.02 s
1.3 s
500 s (8.3 min)
43 min
4.3 years
14 billion years
Whenever you see "light-(time)” (light-year, light-minute, lightsecond), that means we are talking about distance, not time.
A Sense of Space
1.  The Sun would hold 1.3 million Earths. The radius of the Sun is about 100 times
that of the Earth.
2. There are ~100 billion "Suns" in a galaxy like our
own Milky Way Galaxy. 3.Astronomers can see billions of galaxies. Basic classes of Objects
Planets:
Earth as one
Stars
Sun as one
Galaxies
Milky Way as one
Their sizes:
Earth:
104 km
poppy seed
Sun:
106 km
grape fruit
Milky Way 1018 km
Earth-Sun distance
Universe 1023 km
100,000 Earth-Sun distance
Survey Question:
If the Sun were a grapefruit on one side of the
room, what would be Earth?
1) A poppy seed on the other side.
2) Another grapefruit on the other
side.
3) A poppy seed in my office.
4) An apple on the other side.
(Earth-Sun distance~100x radius of Sun~ 100X100 radius of Earth)
Survey Question:
If the Sun were a grapefruit on one side of the
room, what would be Earth?
1) A poppy seed on the other side.
2) Another grapefruit on the other
side.
3) A poppy seed in my office.
4) An apple on the other side.
Survey question:
What would then the nearest star
be?
1) A poppy seed at the Amherst downtown.
2) A poppy seed on the west coast
3) A grapefruit at the Amherst downtown.
4) A grapefruit on the west coast.
(Nearest star is 4Ly ~ 300,000 AU)
Survey question:
What would then the nearest star
be?
1) A poppy seed at the Amherst downtown.
2) A poppy seed on the west coast
3) A grapefruit at the Amherst downtown.
4) A grapefruit on the west coast.
Another unit astronomers love:
Parsec:
1 parsec = 3.26 lyr
The closest star to us:
Alpha Centauri: 4.2 lyrs = 1.3 pc
Our own Galaxy:
diameter= 75,000 lyrs = 23000 pc = 23 kpc
The closest galaxy:
Andromeda: distance = 700,000 pc = 0.7 Mpc
The Universe:
Size = 1.3 x 1028 cm = 13,500,000,000 lyrs = 4300 Mpc
Now… on to some game of
scales.
52 feet across
1 mile across
160 kilometers across
1 mile = 1.61 kilometers
Infrared photo
Diameter = 12,756 km
1,600,000 km
=1.6 x 106 km
Moon
1AU = 1.5x1011 m
1.6 x 1010 km, or a trillion (1012) times wider than the first picture!
32 AU
100 AU
1,000 AU
10,000 AU
106 AU = 17 ly
1 ly =63,000 AU = 1013 km
1700 ly
170,000 ly
1.7 x 107 ly
1.7 x 109 ly
Your local address:
The Motions of Earth
1. The Earth rotates – this leads to day and night. 2. The Earth revolves around (orbits) the Sun – this
leads to the seasons. 3. The Earth and Sun revolve around (orbit) the
center of the Galaxy. 4. The Galaxy moves through the Universe.
Everything in the Universe is
Moving! … but …
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the further away from us something is, the more
it has to move to be noticeable.
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the motion of the Earth rotating on itself (day/
night) is the easiest to see
Followed by the motion of the Moon around the
Earth (~29 days)
followed by the motion of the Earth around the
Sun
and finally the motion (over tens or hundreds of
years) of other stars
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How Do We Locate Objects on
the Sky?
The Celestial Sphere (C.S.)
Stars, planets, the Sun are at different distances from us, yet for
studying patterns in the sky, we can imagine that all are on the C.S.
The patterns of stars on the
C.S. can suggest shapes of
animals, or cultural objects.
Today, we call them
constellations.
Constellations
The first thing to remember is that the
groupings of stars that most people call
constellations are not actual objects! They are
`maps’ for the sky. In fact, the original
constellations were invented by farmers over
5000 years ago.
There are 88 official
constellations
recognized by the
International
Astronomical Union.
The names of constellations
are in Latin. But most bright
star names derived from
ancient Arabic. The original constellations
were invented over 5000
years ago.
Remember that the
constellations are not real!
Projection
Big Dipper ---- an asterism,
i.e., not an actual constellation,
but a recognizable pattern in the
sky
Orienting Ourselves on the C.S.
There are two
ways to think
about this:
- the C.S. rotates
- or the Earth
rotates while the
sky sits still.
Nadir
Sometimes one
works better than
the other …
Are there stars in the sky during daytime?
Stars, like the Sun and the Moon, appear to rise to the east, and
set to the west.
Only the
Celestial Poles
do not show to
move.
Polaris
The star called
Polaris marks the
position of the
Celestial North
Pole and the
Earth s North
Pole. Often
called the `North
Star .
Latitude and
longitude make a
convenient coordinate
system for locating
objects on the Earth.
In the same way, Right
Ascension (RA, divided
in 24 hrs) and
Declination
(DEC, in degrees) give
us the direction
to look on the celestial
sphere.
Altitude and Azimuth
give us the direction
to look on the celestial
sphere.
The altitude of
Polaris above the
horizon is
approximately the
same as the
observer's latitude
in the Northern
Hemisphere.
Survey Question
In this time-laps photo, the
stars make stripes due to:
1) the Earth rotating.
2) the Earth revolving
around the Sun.
3) the Earth and Sun
revolving around
the Galactic center.
4) the precession of the
Earth s axis.
The Earth orbits around the Sun on a plane
called the Ecliptic (or Ecliptic Plane)
Recall that last time we defined the Constellations as apparent
Associations of stars on the Celestial Sphere
Q: What s the difference between the
constellations and the zodiac?
A: The zodiac is made up of the
constellations which lie in the
ecliptic plane.
As the Earth orbits around the Sun, the Sun appears from the Earth to `cross the
Constellations. It takes 1 year for the Sun to cross all constellations in the zodiac.
Survey Question
What zodiacal constellation is highest in the sky
at midnight in June?
1) Libra
2) Pisces
3) Gemini
4) Capricorn
Libra
Pisces
Gemini
Capricorn
Survey Question
What zodiacal constellation rises at midnight in
June?
1) Libra
2) Pisces
3) Gemini
4) Capricorn
Libra
Pisces
Gemini
Capricorn
Survey Question
One evening at midnight, you observe Leo high
in the southern sky. Virgo is to the east of Leo
and Cancer is to the west. One month earlier,
which of these constellations was high in the
southern sky at midnight?
1) Leo
2) Virgo
3) Cancer
Leo
Virgo
Cancer