Transcript Week 1 Lecture - Department of Physics and Astronomy

PHYS178
Other Worlds
A/Prof. Orsola De Marco
9850 4241
[email protected]
http:/web.science.mq.edu.au/~orsola/
click on PHYS178 teaching
PHYS178 structure
• 7 weeks, 21 hours for the Solar System
(by Orsola De Marco)
• 3 weeks on the details of the Solar System formation
(by Andrei Gilchrist)
• 3 weeks on extrasolar planets
(by Quentin Parker)
Assignments
• For the SS part of the course:
• 5, weekly (short) assignments handed out via web
on Tuesday afternoons.
• Returned in person on following Monday.
• Content of assignments discussed in class on Monday
mornings.
• Grades averaged to form the assignment part
of the course (20% of final grade).
• Class participation also rewarded via additive grades.
Practical
• There is one practical posted on the website.
• You can do it in your own time on any clear night.
There is a minimum requirement of 5 observations
between August 24th and September 11th.
• Due in on September 11.
• You will need to go to the Observatory once and do a
one page write-up.
• This is 10% of the class grade.
Tutorials
• Tutorials start on Monday 10 August (group 1) or
Tuesday 11 August (group 2). Class: C5C 240. (3% points for
showing up).
• Class 1: reading a series of articles on the recent
Jupiter impact. Discussing the article within a group.
• Class 2: Preparing a short presentation electronically
(bring your computer) or on transparencies (provided).
• Class 3: present in front of class (2 minutes each).
This presentation is marked (7% of total mark).
• Class 4: prepare an article of your choice (on the topic
of Solar System science) and present in class.
• Class 5: presentations. The mark is 10% of total.
Office hours
• Office Hours:
• best way to contact me: e-mail
([email protected])
• Second best, make an appointment via e-mail.
• Third best come to my office right after class.
• If you really must, come any time.
Introductions
• Write on a white piece of paper (anonymous):
• Name in capital letters,
• Intended degree,
• Motivation for taking this course,
• Have you taken an Astronomy course before?
If so, what course was it?
• Please write on a separate paper with no name,
the answer to the following questions:
1. What is the name of the equation E = mc2 ?
2. If x+y=3 and xy=2, can you obtain the values
of x and y (just yes or no – and be honest)?
3. Why is the sky blue?
4. What is the Sun?
5. What force makes planets orbit the Sun?
Course Outline
1. The Solar System in context and the celestial sphere
2. Why the sky looks the way it does. Early observers and
the scientific method.
3. The terrestrial planets: Earth
4. The terrestrial planets: Mercury, Venus and Mars.
5. The gas giants: Jupiter, aurorae and tides.
6. The gas giants: Saturn, Uranus and Neptune
and their rings.
This and next week’s outline
• Space and time: sizing up the Universe.
• Orienting yourself in the celestial sphere.
• What do you see when you look up:
• the Sun,
• the Moon,
• the planets …
• … why they look they way they do, why they
are where they are, why they move they way
they move …
• How to impress your girlfriend, boyfriend or
grandmother with your knowledge of the heavens.
• The early observers (Ptolemy, Tycho, Copernicus
and Galileo) and the scientific method.
The Solar System in context
• Powers of Ten
•http://www.youtube.com/watch?v=A2cmlhfdxuY
• Learning Points:
• Powers of ten.
• Log scale
• Size of the Universe
Scales of the Universe
• Units of the Cosmos:
– Solar Radius (Ro)
– The astronomical
unit (AU)
– light years
– parsec (=3.26 ly; pc)
– centimeter (!)
• The Scientific
notation:
–
–
–
–
–
1 = 100
10 = 101
100 = 102
100,000 = 105
When using cm, you see a
lot of, e.g., 1013!
And while we are at it …
• prefix multipliers:
10 = deca
100 = hecto
1000 = kilo (K)
1,000,000 = 106 = million = mega (M)
109 = billion = giga (G)
1012 = triollion = tera (T)
1015 = million trillion (?) = peta (P)
(exa zetta yotta)
And since we are having so
much fun….
• prefix multipliers:
0.1 = deci
0.01 = centi
0.001 = milli (m)
0.000001 = 10-6 = a millionth = micro ()
10-9 = a billionth = nano (n)
10-12 = a triollionth = pico (p)
10-15 = a millionth trillionth (?) = femto (f)
(atto zepto yocto)
Earth
• Radius:
6357 - 6378 km
or 6.4 x 108 cm
(Concept of
approximation)
Sun
• Radius
696,000 km
or 6.96 x 1010 cm
or 1 Ro
• ~100 x Earth
Jupiter
• Radius
69,911 km
or 6.99 x 109 cm
or ~0.1 Ro
• ~10 x Earth
Solar System
• Radius (Pluto)
40 AU
6.0 x 109 km
6.0 x 1014 cm
• 40 x Earth-Sun
Our Galaxy
• Radius
~15,000 pc
or 15 kpc
4.6 x 1022 cm
• 7.7 x 107 x SS
Galaxy – LMC/SMC
•
•
•
•
LMC: 50 kpc
SMC: ~60 kpc
M31: 2.5 Mpc
Virgo Cluster: 18 Mpc
Orienting yourself in the night
• North, South, East and West
• Angular separations
• Constellations and their meaning
The Constellations
• Stars in a constellations are not grouped in space,
they are close because of chance alignment.
Constellations Names
and the Zodiac
• Many constellations were named by the Greeks
(including some southern ones which were more
northern 2000 years ago).
• Constellations names are usually Latin (e.g., Centaurus).
• Stars in a constellation are called with Greek letters
according to their brightness (a being the brightest),
followed by the constellation name in the genitive (e.g.,
a Centauri, also abbreviated a Cen).
• The horoscope…
The day: The spin of Earth
The day: The spin of Earth
• The celestial sphere is an imaginary sphere centered on
the Earth, whose poles are the same as the Earth’s poles
and whose equator is the projection of Earth’s equator.
At the North Pole: how do
stars move during the night?
And at the Equator?
And where is this observer?
The North Celestial Pole
The South Celestial Pole
• To find South at night, look for the South celestial pole
and draw a line down to your horizon. That is South.
Latitude and Longitude
•
•
•
What is the reference frame?
Latitude: equator
Longitude: the Greenwich meridian.
Measuring Latitude
• Your latitude North/South
is the same as the altitude
of the North/South celestial
pole (easy to measure in the
North, where Polaris marks
the spot!)
The seasons
In the Southern hemisphere at noon the Sun is North of the Zenith. You can
find South by tracing a line from the Sun to the horizon or by following your
shadow backwards.
The night sky over the year
The night sky over the year
Celestial coordinates
• Anybody remember
what this picture is
from?
• Anybody remember
what she says when
she hears the
repeating source?
(Woman sitting in car)
“Oh Shit”
music … (Jumps into car, talks on VHF)
“Right ascension, 18 hours, 36 minutes, 56.2 seconds
declination, + 36 degrees, 46 minutes, 56.2 seconds”
(pause)
“CONFIRM?”
A coordinate system
• They are the coordinates of Vega!
• We need coordinates for stars just like we
need coordinates for locations on earth.
• They need to be time and place independent.
Latitude and Longitude
•
•
•
What is the reference frame?
Latitude: equator
Longitude: the Greenwich meridian.
Earth’s orbit around the Sun
Note: Earth’s equator is tilted with respect to the orbital plane
Earth’s orbit around the Sun
“The Sun’s orbit around Earth”
Let’s pretend that the Earth is in the middle
“The Sun’s orbit around Earth”
Let’s tilt our head till Earth’s axis is parallel to the up-down direction
From Earth’s perspective …
The vernal equinox: 
Celestial equator
Ecliptic
Right Ascension and Declination

Right Ascension and Declination

Right Ascension and Declination

Right Ascension and Declination

Right Ascension and Declination

Dec
Right Ascension and Declination

RA
A star’s coordinate are given as two sets of numbers
(measuring angles) called:
Right Ascension
&
Declination
they look like this
13h 12m 13.3s
+60o 45’ 33.2’’
Hours and degrees:
13h 12m 13.3s
+60o 45’ 33.2’’
0o=360o
0h=12h
270o
9h
3h
6h
180o
90o
Precession
Hipparcos lost star catalogue