Download Study Guide for 1ST Astronomy Exam

Study Guide for 2ND Astronomy Exam
Chapters 4 & 5 from AstronomyNotes
The successful student will be able to…
The Lunar Cycles
 Describe the daily and monthly apparent motion of the Moon and its relationship to the Zodiac.
 Draw and interpret lunar phases and the Moon’s relationship to the Sun at each principle phase.
 Name the phase of the Moon from a photograph of the Moon.
 Estimate the number of days between lunar phases.
 Rank images of the Moon in different phases in order of occurrence first to last.
 Characterize the Moon’s apparent motion given its phase and the time of year.
 Explain why the lunar sidereal period is different than the time for a cycle of lunar phases.
Describe the essentials of the geocentric model of the Universe of Aristotle and Ptolemy.
o The position and motion of the Earth
o The nature of terrestrial and celestial matter
o The role of epicycles in the Ptolemaic model of planetary motion.
 Where is a planet on its epicycle when it goes retrograde? Why does it go retrograde only when it is
on that part of its epicycle?
o The role of equants in the Ptolemaic model of planetary motion.
 How was the equant used to explain why there are only 179 days between the Fall Equinox and
Spring Equinox, but 186 days between the Spring Equinox and the Fall Equinox?
 Describe the essentials of the heliocentric model of the Universe of Copernicus.
o The position and motion of the Earth
 List all the motions of the Earth; Rotation on a tilted axis and revolution about the Sun with the time
scales and degree of tilt.
o The calculation of true orbital periods.
 Saturn is in opposition on 2013/04/28 and again on 2014/05/10. There are 378 days between these
two oppositions. Knowing that Earth takes 365.241 days to complete a 360  orbit around the Sun,
estimate the time required for Saturn to complete one 360 orbit around the Sun. (Hint: First find the
number of degrees Earth moves around the Sun in the 378 days between oppositions using a
proportion, then find the number of degrees that Saturn moves through its orbit between oppositions
using subtraction. (See handout from class) and, finally, use a proportion to estimate how long Saturn
takes to complete oe 360 orbit. Ans: The Earth moves 372.6 around its orbit in 378 days. Saturn
moves 12.6 around its orbit in that time. Satrun takes about 10,800 days or 29.6 year.)
o The calculation of distances of the planets from the Sun.
 Identify the right triangles that Copernicus constructed to
determine the relative distances of the planets from the Sun
for inferior and superior planets. See figure to the right.
 Describe how Copernicus could use planetary
configurations to determine the magnitude of the shaded
angles in the figure to the right.
o The true nature of retrograde motion.
 Completely describe the causes of retrograde motion for a
superior planet.
o The reason that superior planets brighten during retrogression.
 Completely describe why superior planets only brighten when in retrograde motion. Include an
illustrative sketch.

 State the flaws of the original heliocentric model of Copernicus.
 Describe Kepler’s three laws of planetary motion and state how the first two laws were contrary to the previously held
ideas of Aristotle and Ptolemy.
 Correctly use the terms ellipse, focus, semi-major axis, perihelion, aphelion, eccentricity in youir
answer to this questions.
 Perform simple mathematical problems using Kepler’s 1 st and 3rd Laws similar to the homework problems.
 See example problems in italics below.
o Calculate the period of an object orbiting the Sun given its semi-major axis in AU.
 1685 Toro is an Apollo asteroid that orbits the Sun. Its semi-major axis is 1.37 AU What is its orbital
period in days? . (Ans: 1.60 years = 585.7 days)
o Calculate the semi-major axis of an object orbiting the Sun given its orbital period in years.

The asteroid 1981 Midas was discovered on March 6, 1973 by Charles T. Kowal at Palomar
Observatory. Its orbital period is 864.541 d. What is its orbital semi-major axis? (Ans: 1.78 AU)
o Calculate the semi-major axis of an object orbiting the Sun given its perihelion and aphelion distances in AU.
 4257 Ubasti (1987 QA) is an Apollo asteroid and Near-Earth object discovered on August 23, 1987 by
Jean Mueller at Palomar Observatory. Its perihelion and aphelion distances are 0.876 AU and 2.42
AU respectively. What is Ubasti’s orbital semi-major axis?
o Calculate the orbital eccentricity of an object orbiting the Sun given its perihelion and aphelion distances in AU.
 6063 Jason (1984 KB) is an Apollo asteroid discovered on May 27, 1984 by Carolyn and Eugene
Shoemaker at Palomar. Its perihelion and aphelion distances are 0.525 AU and 3.91 AU respectively.
What is Jason’s eccentricity? (Ans: 0.763
o Calculate the perihelion distance of an object orbiting the Sun given its semi-major axis and orbital eccentricity.
 4183 Cuno is an Apollo, Mars- and Venus-crosser asteroid. Its semi-major axis and eccentricity are
1.98 AU and 0.636 respectively. What is Cuno’s perihelion distance? (Ans: 0.720 AU)
 Discuss Galileo’s observations of the Sun, Moon, Jupiter and Venus and state how they contradicted the previously held
Aristotelian model of the Universe.
 Describe how each of Galileo’s observations contradicted the Aristotelian geocentric model of the
Universe.
The Universal Law of Gravitation
 Describe the characteristics of gravity in words and in an equation.
 Describe and illustrate by example the nature of the inverse square law as it applies to gravity.
o Just like home work #5 problems #10 & 11.
 State the significance of the low value for G.
Measuring a Body’s Mass using Orbital Motion
 Describe what an astronomer needs to observe to calculate the mass of a distance body using
properties of the distant body’s satellite.
o
A picture of Saturn and its moon Titan appears to the right. What would an
astronomer need to know about Saturn and Titan to calculate Saturn’s mass from
the motion of its satellite Titan?
Orbital and Escape Velocities
 Describe how the orbital velocity of an object in circular orbit depends on the distance from the central object and how
the orbital velocity depends on the mass of the central body.
 Similar to HW #5 Problems #4, 17 & 18.
 Describe how the mass of an orbiting object affects its orbital velocity.
 Remember our class problem of the Moon, spacecraft, astronaut and wrench in orbit around the Earth.
Which went faster to stay in orbit?
 Define escape velocity and state how it depends on the mass and radius of the body that you are escaping from.
 Conceptual questions similar to HW #5 Problems #19 to #21.
Plus…
o
o
Use ratios to compare sizes of astronomical objects.
 See practice problems below
Use a proportion to calculate a scale model of an astronomical object.
 See practice problems below