Transcript Document

Welcome!
PH104 Descriptive Astronomy
MWF 1:00 – 1:50 pm
Weniger 151
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Today’s Slides
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Course Intro
Some Logistics
What IS astronomy?
The Planetary Neighborhood
Some New Units of Measure
The Night Sky
Textbook units covered: 1, 2, and 5
PH104 Descriptive Astronomy
• Instructor Info
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Jim Ketter. Feel free to call me Jim.
Office: WNGR 315
Office Hours: MW 9:00-9:50
You are welcome to stop by at other times or make an
appointment if you need to see me at other times.
– Email: [email protected]
• Lab Instructors: Kristin Dexter, Jake Goodwin,
Jeff Holmes, Tim Surber
Contact information is posted on the PH104 website:
www.physics.oregonstate.edu/ph104
PH104 Descriptive Astronomy
• Most course information will be located at the course
website: www.physics.oregonstate.edu/ph104
• Syllabus and schedule will not be handed out on paper.
• Overview of website info…
• Exam grades (only) will be posted on Blackboard.
• Course counts as a baccalaureate core laboratory course.
• Course Grade (details in syllabus) depends on:
– Labs and Prelabs (Lab Manual online)
– In-class participation (via Qwizdom)
– Exams (2 Midterms and a Comprehensive Final)
PH104 Descriptive Astronomy
• Labs
– All labs are held in WNGR 206.
– You are scheduled in one 2-hour lab per week on either
Tuesday or Thursday.
– Completion of lab is mandatory for passing this course.
• Exams
– There will be two midterm exams, one in week 4 and the
second in week 8. There is also a final, comprehensive
exam (covers whole term).
PH104 Descriptive Astronomy
• Labs and Prelabs
– Prelabs must be turned in at the start of your scheduled
lab (as you enter lab.)
– Both Prelabs and Labs are in the lab manual.
– Lab exercises will be completed and checked off during
the scheduled lab section.
– Do not move around to different labs without discussing
with me and the TA.
– 7 of 8 labs must be completed in order to pass the course.
– There are no make-up labs. Don’t miss lab.
PH104 Descriptive Astronomy
• Labs and Prelabs continued
– You must score 70% or better on a prelab in order for it
to be considered a passing grade.
– You must satisfactorily complete 70% or more of a lab in
order for it to be considered a passing grade. The TA will
make this assessment during the lab.
– You must successfully complete (pass) 7 of the 8 prelabs
and 7 of the 8 labs in order to pass the course, regardless
of your other scores.
PH104 Descriptive Astronomy
• In-class Participation
– Class participation will be augmented via the Qwizdom
“clicker” system.
– Participation requires purchase of Qwizdom unit.
• Night Viewing
– There will be opportunities for some night sky viewing
using telescopes atop beautiful Weniger Hall.
– Attendance is optional but is the one place in the course
where extra credit points are available.
– Depends on weather. Sessions will be announced.
PH104 Descriptive Astronomy
• What Astronomy isn’t.
– It is not astrology. Might have been once but…
– It isn’t memorizing names of stars and constellations.
– It isn’t laying around looking at the sky all night.
• What Astronomy is.
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It’s a start at looking at the amazing universe we live in.
It’s a look at how we know the things we know.
It’s a look at the nature of science.
It’s a look at the historical development of our
understanding of the universe around us.
The Earth
• The Earth is a planet, a body in
orbit around a star (The Sun)
• Radius: 6371 km (3909
miles)
• Mass: around 6 billion
trillion tons
• Actual value:
5,970,000,000,000,000,000,000,000 kg
• Too many zeros!
Use 5.97  1024 kg, instead!
Metric System
•Easier to use (everything is a factor of 10!)
•More in Unit 3…
The Moon
• The Moon is a satellite, a
body orbiting a planet
– Rocky world, littered with
craters
• Bombarded by meteors
• Where are the Earth’s craters?
– Smaller than the Earth
• Less than 1/80 the mass
• ¼ the diameter of Earth
– Small, so cooled quickly!
– Cold, airless and lifeless
The Planets
Why are they so
different?
How did they
get this way?
←Oops! Pluto!
• Wide variety of planets in our Solar System:
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Rocky, hot and airless worlds.
Gas giants and ringed wonders.
Cold planets of blue methane.
Tiny icy bodies.
At relative size (NOT distance)
The Sun
• The Sun is a star, a
huge ball of gas held
together by gravity and
generating light
through thermonuclear
reactions.
• Source of all energy in
the Solar System, on
our planet. (Except…)
• 100x wider than the
Earth, 1,000,000x
larger, and 300,000x
as massive!
• Old, yet still young…
– 4 billion years old.
– Will last another 5 or
6 billion years.
The Solar System
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Planets, asteroids, comets and dust all held together by the Sun’s gravity.
Everything goes around the Sun on elliptical paths called orbits.
All orbits lie in (nearly) the same plane, like peas rolling around on a saucer.
Too big to describe using meters – we need something more convenient.
A convenient measure –
the Astronomical Unit
• It is convenient to measure planetary distances
using the Astronomical Unit, or AU.
• 1 AU = average distance between the Earth
and the Sun.
• 1 AU ~ 150 million km ~ 93 million miles.
Some approximate, average
orbital radii sizes:
• Mercury: 0.4 AU
• Mars: 1.5 AU
• Saturn: 10 AU
• Pluto: 40 AU
A New Measure of Distance
• Stars in our Milky Way
galaxy are very far apart!
– Nearest star is 40 trillion km
away – too large to imagine!
– This is hundreds of thousands
of AU. Whoa! Still too big.
– Light travels 10 trillion km in
one year, so we’ll use the light
year (ly) as a common
measure of distance in space.
– It takes light 4.1 years to travel
from Proxima Centauri to
Earth, so the distance from
here to that star is 4.1 ly.
Getting to Know the Neighborhood
• The Universe is “clumpy” –
galaxies tend to cluster together
because of gravity.
Central region of the Virgo Cluster
– Our immediate neighborhood is
called the Local Group, a cluster of
around 3 dozen galaxies, 3 million
light years across.
– The Local Group is part of the Virgo
Cluster, a collection of smaller
clusters of galaxies.
– Superclusters: still larger collections
of galactic clusters.
– The Universe – simply everything!
Outward to the
Universe!
A hundred years ago,
our galaxy was
believed to be the
entire universe.
50 years ago, they
believe there might be
dozens or hundreds of
galaxies out there.
Today, we know there
are (at least) billions of
galaxies within our
universe!
The Celestial Sphere I
• A useful model of the sky is called the
Celestial Sphere.
• It is not real – it is simply a tool for
understanding and visualizing our sky.
• It was “reality” for the ancients.
• Stars in the universe are located at
various distances from Earth, but can
be imagined as lying on a sphere, with
the Earth at its center.
• This sphere appears to rotate around
the Earth, giving the impression that
stars rise and set.
The Celestial Sphere II
• Important Terms
– Zenith: The point directly overhead on the
celestial sphere (CS).
– Nadir: The point opposite the zenith on the
celestial sphere.
– North or south celestial pole: The point
around which the stars appear to rotate.
– Celestial Equator: An extension of the
Earth’s equator expanded out to the surface of
the CS.
– Horizon: The lower edge of the visible CS.
Constellations and Asterisms
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The human brain is very good at recognizing •
patterns. People thousands of years ago
identified and named patterns of stars on the
celestial sphere.
The names of these patterns have their
origins in mythology from different societies
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from all over the globe.
Sometimes hard/impossible to see. Requires
an active imagination sometimes!
These areas are called constellations.
– 88 internationally recognized
constellations, covering the entire sky.
– Star names frequently include the
name of the constellation in which
they are located.
Just some pattern of stars is not a
constellation – these are called asterisms.
– Big Dipper (of Ursa Major)
– The Teapot (of Sagittarius)
Skywatching
• Under dark skies, you can see
thousands of stars. There are some
stars and constellations, however, that
you can only see from northern or
southern latitudes.
• Constellations that never set (but
simply circle around the Celestial
poles) are called circumpolar
constellations.
• Skywatchers at our latitude in the
southern hemisphere never see our
circumpolar stars (here in the North).
And vice versa…
Finding Our Way Around
• Finding your way around the
celestial sphere is similar to
finding your way around on
Earth.
– The CS is divided by lines of
declination (running East-West)
and lines of right ascension
(running North-South).
– Comparable to lines of latitude and
longitude, respectively.
– Stars can be located on the CS
using their coordinates in this
system, e.g., a star might be found
at 4h RA, 40 degrees declination
(similar again to latitude and
longitude.)