•Monday 4:00 – 4:55pm
•Sundquist Science Center E-109
•Dr. Spencer Buckner
•www.apsu.edu/astronomy
Office: SSC B – 326
Hours: M – F 12:30 – 2:30pm
or by appointment
Email: buckners@apsu.edu
Phone: 221-6241
Textbook
21st Century Astronomy: Stars
and Galaxies, 4th Edition by Kay,
Palen, Smith & Blumenthal
If you don’t have a book there are older versions in the department
library. Most of the problems are the same but check with me before
using them.
Exams…………45%
Homework…….20%
Projects………..30%
Participation…….5%
90 – 100…A
80 – 89…..B
70 – 79…..C
60 – 69…..D
<60……….F
There will be three one-hour exams during the
semester. The exams will be entirely problems
similar to the homework problems. A formula
sheet will be given out with the exam. Tentative
exam dates are
•Monday February 22
•Monday March 28
•Monday May 2 @ 4:00pm
A scientific calculator will be required for the
exams
Homework will be assigned from the
Applying the Concepts at the back of each
chapter in the 21st Century Astronomy
textbook. Additional problems from other
sources will also be assigned to supplement
the back-of-chapter questions. They will be
due at the beginning of the next class
meeting.
First Homework set is due next week:
Chapter 1 # 41, 42, 45, 49 & 53
There will be two projects assigned
during the semester. The first project
will be due February 29. The second
project will be due at the final exam
period (Monday May 2 @ 4:00pm). In
addition to a written report, you will
make a short (10-15 minute)
presentation on your project.
st
1
Project
Estimate the cost of the wasted energy in
the image below
For high resolution image see
http://www.nasa.gov/mission_pages/NPP/ne
ws/earth-at-night.html#.VMlIqhBdXTp
How to work a problem
•Step 1: What are you trying to solve for?
•Step 2: What information are you given?
•Step 3: What equation(s) do you need to
solve the problem?
•Step 4: Plug in the numbers and solve the
problem
•Step 5: Check for reasonableness
The nearest star is Promixa Centauri,
part of the triple star Alpha Centauri
system. It is 4.243 lightyears from Earth.
If the fastest rocket ever made, the New
Horizons spacecraft, could maintain its
launch speed of 16.26 km/s and it was
launched at this star, how long would it
take to reach Promixa Centauri?
Answer the first two questions
•Step 1: What are you trying to solve for?
Travel time from Earth to Promixa Centauri.
•Step 2: What information are you given?
Speed of spacecraft (16.26 km/s)
and distance from Earth to Promixa
Centauri ( 4.243 ly)
Step 3: what equation(s) do you
need?
Look for example problems in the chapter,
in the appendix, in other textbooks or
online.
For this problem, the average velocity is
the distance divided by the time
Distance traveled d
v

travel time
t
So the time is the distance divided by the
velocity
Distance traveled d
t
Average Velocity

v
Unit Conversions
Distance was given in ly and velocity was in
kilometers per second. Consistent units are
needed throughout. Convert distances to
kilometers (or velocity to ly/sec). Conversion
factors can be found in Appendix 2
13
1 km
4.243 ly  9.46 1015 m ly  1000

4.013878

10
km
m
A word about significant figures: your calculator may spew out 8
or 9 digits but most of them are meaningless. Your answer should
always have the same number of digits as the least number of
significant figures in the given data. You can carry more digits
through the calculations but always round off at the end.
Step 4: Plug in numbers and solve
d = 4.013878 x 1013 km
v = 16.26 km/s
d 4.013878 1013 km
t 
 2.468559656  1012 s  2.469  1012 s
v
16.26 km s
Step 5: check for reasonableness
2.47 1012 s  3.156 107 seconds year  78, 200 years
Is this reasonable? How do I know if is
reasonable?
One for you
Use numbers from Appendix 2 and 4 in the back of the
textbook to answer the following questions.
The New Horizons spacecraft, fastest spacecraft ever
launched, traveled the distance from the Earth to the
Moon in 8.0 hours. If it maintained that speed and it
was pointed in the right direction, how long would it
take to reach
•Pluto?
•Sirius?
New Horizons was launched on January 19, 2006
Step 1 & 2
Step 1: What are you being asked to solve for?
Travel time to Pluto and Sirius
Step 2: What information are you given?
Travel time from Earth to the Moon: 8.0 hours
From Appendix:
distance from Earth to Moon: 384,400 km
distance from Earth to Pluto: 5,756.78 x 106 km
distance from Earth to Sirius: 8.60 lightyears
Step 3
Step 3: What equation(s) will you need to solve the
problem?
d distance
d
v 
 t 
t
time
v
First, find the speed of the spacecraft and they use
that speed to find the travel time to the two objects
d
384, 400km
v 
 13.347 km s
t 8.0hrs  3600 s hr
Step 4: Plug in numbers
For Pluto
d 5, 756.78 106 km
t 
 4.31296  108 s
v
13.347 km s
divide by 3.156 107
s
year
to get a better handle on it
gives 13.67years  14years
That puts it at Pluto in January 2020?!?
Step 4 for Sirius
15 m
m
8.60
ly

9.46

10
d
ly  1000 km
t 
 6.0954  1012 s
v
13.347 km s
divide by 3.156 107
s
year
to get a better handle on it
gives 1.931105 years  193,000 years