Lecture 11 2/11/2013 12:24:00 PM
Time limit: 1 hour
50 questions, MC
covers chapter 1-3, but a little bit less on chapter 1, more on chapter 1.
Bring a calculator, but only a couple of questions require actual calculations.
Formulas and exact numbers you need will be given—you just need to know
how to use them.
Some questions ask you to remember some of the basics, others ask you to
apply what you know in some of the ways we’ve practiced.
Chapter 1 Highlights:
An overview of our current understanding of the universe.
You should be able to:
o Describe what structures are bigger than what other
structures (example, solar system is part of the milky way
galaxy, galaxies are part of clusters, etc.)
o Describe the approximate relative sized of things (example: is
Jupiter a million times bigger across than earth, or is it more
like 10 times?)
o Know what the following mean: astronomical units, light year.
o Understand how to write a number in scientific notation.
Know how to convert units: for example, if 1 au = 1.5x10^8 km,
then how many km is 5 au?
Know very approximately the sized of things, enough to be able to
pick them out on a multiple choice list
Chapter 1 summary:
We live on a planet, orbiting a star, forming part of a solar system,
inside a galaxy, which is part of a cluster and supercluster.
Superclusters form even bigger structures like walls, filaments,
o Make it easier to write and compare very large or very small
numbers. o Based on powers of 10
o So 3,000,000 = 3 x 10^6
o The exponent tells you how many places the first digit is from
the decimal point.
Astronomical unit (au)
o Defines as the average distance between the earth and the
o Mostly used for distances inside the solar system
o The distance light travels in a year.
o Mostly used for distances between stars or bigger objects like
o If something is for example 4000 light years away, that
means we see it as it was 4000 years ago.
Large planet (Jupiter) is about 10 times as big across as earth.
Sun is about 10 times as big across as Jupiter, so that makes it
about 100 times as big across as earth.
Nearest other star: 4.3 ly away.
Miky way galaxies: about 80,000 ly across, contains about 100
Nearest other galaxies: 1-2 million ly away
Farthest visible objects:
Around 12 billion ly away. The visible part of the universe includes
around 100 bullion galaxies.
In our solar system, earth is a smallish planet, but not the smallest.
The un is a medium sized star—some are smaller but some are
The milky way is fairly large compared to most, but not the largest.
And it is part of bigger structures: clusters, superclusters, etc.
Chapter 2 Highlights:
Locating things in the sky:
o Constellations and asterisms
o Angular distances.
o The celestial sphere.
The main cycles of the sky: o Daily: rising and setting, circles around celestial pole.
o Yearly: seasons, suns apparent motion around the ecliptic,
solstices, equinoxes, etc.
o Monthly: moon phases
Naming of stars
Declination and right ascension (for describing positions on the
Changing your point of view (how does the sky look from different
places on the earth?)
Angular sixe (depends on both actual size and distance away from
Chapter 2 Summary:
o 88 regions in the sky, with well defined boundaries. Every
star is in one constellation. Examples: ursal major, orion,
o Patters or visible groups of stars.
o Example: the big dipper, the winter circle.
o They may include starts from more that one constellations.
Note: stars with the same constellation or asterism appear close to
each other, but they might actually be at very different distances.
o The point directly overhead.
o Is 90˚ away from the zenith.
o A north-south line passing through the zenith.
Celestial north (south) pole:
o The point on the celestial sphere directly above the north
(south) pole of the earth.
Celestial equator: o A circle on the celestial sphere directly above the earths
Defined in elation to a particular observer:
o The basic idea:
Because the earth rotates every 24 hours, the celestial
sphere appears to us to be rotating in the opposite
direction, i.e. east to west.
Whatever your latitude is, that is also the angular distance of the
celestial pole above the horizon.
o Basic idea:
The earths axis is tilted sot that for part of the year, the
northern hemisphere points toward the sun and gets
more direct sunlight.
When the NH is pointing toward the sun and having
summer, the SH is pointing away and having winter. So
it’s the middle of summer in Argentina right now.
Two effects combine to make summer warmer: more
hours of daylight, and sun hits at a more direct angle.
The warts changing distance from the sun makes
almost no difference—its all about the tilt.
Seasons and the ecliptic:
Th apparent path of the sun across the celestial sphere
during a year.
o (the sun appears to over eastward compared to the stars, due
to earths motion around the sun)
o for this reason, some of the constellations visible at a given
time of night (say midnight) will change during the year.
(except that circumpolar constellations are visible all night, all
Moon phases: o The moons orbit a