Download Define the following terms in the space provided

SCI-103 Introductory Astronomy Exam #1 Fall 2010
Name_____________________
Class Meeting Time_____________
Describe or define the following key terms in the space provided. (1 points each for a total of 7 points)
1) Astronomical Unit (AU)
The AU is the mean distance from the Earth to the Sun, about 150 million kilometers.
2) Right Ascension (RA)
RA is the longitude-like coordinate on the celestial sphere, measured in 0 to 24 hours of RA.
3) Zenith
The zenith is the point directly over the observer’s head at an altitude of 90.
4) Constellation
A constellation is a well-defined area in the sky with boundaries following lines of RA and dec. There
are 88 official constellations that cover the sky. An asterism is an easily recognized pattern of stars that
may be contained within one constellation of spread over several constellations.
5) Circumpolar star
A circumpolar star is a star that is so close to the North Celestial Pole (Polaris, effectively) that during
its daily circle around the NCP it never dips below the horizon at the observer’s latitude.
6) Meridian
The meridian is a conceptual boundary that divides an observer’s sky into eastern and western halves.
The meridian runs from the north point on the northern horizon through the zenith and to the south point
on the southern horizon.
7) Sidereal Day
A sidereal day is the length of time between two successive passes of the fixed stars across the sky. That
time period is 23:56:04, or one sidereal day.
m
Solve the following problems showing your work.
8) Although the Sun contains 99.9 % of the mass of the Solar System, it occupies very little of its volume.
Illustrate how small the Sun is compared to the solar system by calculating how many Sun’s could be set
side-by-side across the Solar system. Use 80 AU for the diameter of the Solar System.
This is a ratio problem.
80 AU 80  1.5  1011 m 

 8,621
2  RSun 2  6.96  108 m 
8,621 Sun’s would fit side-by-side across the diameter of our solar system.
9) The stars in the asterism of Orion’s belt are about 1,600 ly from the Sun. If our solar system with an actual
diameter of 80 AU were shrunk down to 1 meter in diameter, how far away in meters or kilometers would
the stars in Orion’s belt be?
This is a proportion problem.
1m
x

80 AU 1,600 ly
1m
x

80 AU 1,600  63,240AU
1,600  63,240AU
x
 1 m  1.26  106 m  1,260 km
80 AU
If our solar system were shrunk to a size of 1 meter across, the stars in Orion’s belt would be 1,260 km
away.
10) The Helios spacecraft, which holds the record for fastest man-made object, was a series of two spacecraft
launched in the mid-1970s to study the Sun. Both probes were developed through cooperation between the
US and West Germany. Helios 1 was launched in December 1974 and Helios 2 in January 1976, both
reaching the Sun within about three months. The maximum speed of Helios 2 is quoted as about 67,000 m/s
(150,000 mph). How long would this spacecraft, at this maximum quoted speed, take to travel the 2 AU trip
to Mars? Express your answer in seconds and years.
This is a t 
t
d
problem.
v
d
2 AU
3.0  1011 m


 4.48  106 s  0.142 yr  1.7 months
m
v 67,000 m
67,000
s
s
The 2 AU trip to Mars at the speed of the fastest spacecraft ever launched would be about 1.7 months.
11) Imagine that you are observing the stars at an
observatory located outside Miami, Florida (latitude =
26N). You may find the diagram to the right helpful.
S
N
A) At what altitude would Polaris appear above the northern horizon?
Polaris would appear 26 above the northern horizon.
B) Would a star with a declination of +63 be circumpolar? Explain.
The circumpolar boundary is 90 - 26 = 64 dec. A star with declination equal to 63 dec would
be just outside the circumpolar region and would not be circumpolar.
C) What would be the declination of a star that appeared at your zenith?
The declination of the zenith equals the observer’s latitude. So the declination of a star at the
observer’s latitude would be 26 dec.
D) Would you be able to observe stars as far south as -50 declination? Explain.
The southernmost visible star has a declination given by 26 - 90 = -64 dec. So a star with
declination of -50 would appear to rise and set. It, in fact, would appear 14 degrees above the
southern horizon at transit.
E) What would be the altitude of a star with a declination of -35?
The celestial equator will appear 64 above the southern horizon. A star of declination -35
would then appear 35 closer to the horizon or at an altitude of 29 above the southern horizon.
Answer the following Multiple Choice Questions by circling the correct response.
12) Imagine you are taking a leisurely sail up the inter-coastal waterway from Miami to Boston. Each night on
your journey of a few weeks, you spend some time observing the stars. Which of the statements below
would represent one of your observations?
A) The northern stars were above the horizon less time each succeeding night.
B) The region of the sky that was circumpolar increased each night.
C) Polaris was seen farther from the zenith on each succeeding night.
D) Stars near the celestial equator were above the horizon for about 15 hours.
E) None of the above were observed
Use the drawing below showing the Sun and several constellations to answer the next question.
Sun
Gemini
Taurus
Cancer
Leo
Pisces
 East
South
West 
13) If you could see stars during the day, the drawing above shows what the sky would look like at noon on a
given day. Which of the constellations shown would be highest in the sky six hours later than the time
pictured above?
A) Leo
D) Taurus
B) Cancer
E) Pisces
C) Gemini
14) If you could see stars during the day, the drawing above shows what the sky would look like at noon on a
given day. In which of the constellations shown would the Sun be found six hours later than the time
pictured above?
A) Leo
D) Taurus
B) Cancer
E) Pisces
C) Gemini
15) Imagine that you are visiting OCC’s sister University of Namibia located next to the country of South
Africa. You step outside at night to see the stars. Where would you look to see Polaris?
A) North, near the horizon (0 altitude)
B) Near the zenith (90altitude)
C) North, near 43 altitude
D) Northwest, in the direction towards the U.S.A.
E) Polaris cannot be seen from this location.
16) The long exposure image of star trails shown below was taken
while looking toward the east. From which of the locations listed
below was the image obtained?
A) Fairbanks, Alaska (Latitude 65 N)
B) Syracuse, New York (Latitude 43 N)
C) Miami, Florida (Latitude 26 N)
D) Phitsanulok, Thailand (Latitude 0 N)
E) Sydney, Australia (Latitude 34 S)
EASTERN HORIZON
17) From Kiruna, Sweden at a latitude of 67.5 N, the star Betelgeuse
with a declination of 7 is
A) Circumpolar
B) Rises and Sets (Southernmost visible star has a dec of 67.5 - 90 = -22.5 and the circumpolar boundary is 90 - 67.5 = 22.5. Everything in
between -22.5 dec and 22.5 dec rises and sets)
C) Never Rises
18) Which of the following locations is closest to the celestial equator?
A) RA = 14 h
dec = +85
D) RA = 0 h
B) RA = 14 h
dec = -85
E) RA = 8 h
C) RA = 23 h
dec = +43
dec = -43
dec = -2
19) Which of the following coordinates in your local horizon system (in Syracuse, NY at 43 N) is closest to the
North Celestial pole?
A) Az. = 90,
Al. = 90
D) Az. = 180, Al. =43
B) Az. = 35,
Al. = 2
E) Az. = 273, Al. =52
C) Az. = 3,
Al. = 48
20) The star Capella has a declination of 46. If you are at
latitude of 15 N, what is its maximum (meridional) altitude?
A) 59
B) 39
C) 31
D) 29
E) 21
CE
Capella
46
59
44
S
75
15
N
The pictures and questions below pertain to the apparent motion of the stars as seen by an observer in Yuma,
Arizona. A map of the United States below indicates the location of this city.
Santa Barbara,
CA
Yuma, AZ
21) Which of the labeled stars represents
Polaris? B
22) Which of the labeled stars is NOT a circumpolar star? E
40 Altitude
23) In which direction would star A be apparently moving at
the instant pictured.
A) It would not be moving at all.
B) It would be moving straight up.
C) It would be moving straight down.
D) It would be moving to the left.
E) It would be moving to the right.
30 Altitude
24) The stars as seen toward the East
would be following paths parallel to
which of the indicated rays.
A) 57 ray
B) 33 ray
C) 25 ray
D) Stars do not parallel any of these rays.
A
B
C
D
20 Altitude
E
10 Altitude
North
57
33
25
East
25) Stars seen looking South appear above the horizon for approximately how long?
A) 24 hours
B) Greater 12 hours but not 24 hours
C) About 12 hours
D) Less than 12 hours
26) Looking south the stars would follow which of the paths indicated below?
South
South
A
South
B
C
South
D
South
E
27) Madrid, Spain and New York City, U.S.A. have the same latitude. The longitude of Madrid is 3E and the
longitude of New York City is 74W. If the bright star Vega passes through the zenith in Madrid, at some
moment, how many hours later will that same star pass through the zenith in New York City? Explain your
reasoning briefly.
If you could see both the Sun and the other stars during the day, this is what the sky would look like looking
south at noon on January 1 for an observer in the northern hemisphere. The Sun would appear in the sky next to
the more distant stars in the constellation Sagittarius, (labeled constellation C). Also shown are other
constellations (named and labeled A, B, D, and E) that will be visible above the horizon at this time when facing
south.
28) Rank the constellations (A - E) in the order that they would first appear to rise above the horizon on this day.
First to rise 1 __E__ 2 __D___ 3 __C___ 4 __B___ 5 __A___ Last to rise
The figure below shows the evening sky as it would appear while looking north at 9PM tonight for an observer in
the northern hemisphere. Notice Polaris, the North Star, appears fairly high in the sky – while other stars (labeled A
- D) appear to slowly move in circles around the North Star.
29) Rank the stars (A – D) in order of the number of hours (from greatest to least) that each star is above the horizon
during each 24 hour day.
Greatest number of hours above horizon 1 __D__ 2 __B___ 3 __C___ 4 __A___ Least number of hours
above horizon.
Answer the following five questions referring to the Whole Sky Map below.
All Sky Map
B
C
East
A
Celestial Equator
West
Ecliptic
D
12 Hr RA
6 Hr RA
0 Hr RA
18 Hr RA
12 Hr RA
30) What is the name of the path connecting the points A through D and represents the apparent path of the Sun
through the stars.
_____Ecliptic___________________
31) What is the name of the point labeled A?
____Fall Equinox_______________
32) When the Sun is at point B where will it rise along the local observer’s horizon? (Assume a northern
hemisphere observer.)
____The Sun will rise north of due east___
33) At which of the labeled points A through D will the Sun be above the horizon for the shortest time for an
observer at Syracuse, NY?
________D_______________________
34) What is the declination of the Sun at the point labeled C?
_____0 dec (on the celestial equator___
35) At which of the labeled points A through D will the Sun be above the horizon for the longest time for an
observer located on the equator?
__All stars, including the Sun are above the horizon for 12
hours as seen from the Equator. So the Sun will be above the
horizon for 12 hours for all points on the ecliptic_____
36) It is a common belief that the Sun is overhead at noon. Demonstrate that this is not true by calculating,
using a simplified celestial sphere drawing what the maximum altitude of the Sun is on Mar 22 as seen from
Syracuse, NY.
The latitude of Syracuse, NY is 43. The declination of the Sun on Mar 22 (the Spring Equinox) is 0
dec which is on the celestial equator. Since the altitude of the celestial equator is 90 - 43 = 47, the
Sun will have an altitude of only 47 on Mar 22 as seen from Syracuse, NY.
37) In a few sentences, explain why the mean solar day (24 hours) is different from the sidereal day (23h 56m
4.09s)
A solar day is the length of time between two successive passes of the sun across the same spot in the
sky (e.g. crossing the meridian, overhead). That time period is, on average, 24:00:00, hours, or one mean
solar day.
A sidereal day is the length of time between two successive passes of the fixed stars across the sky. That
time period is 23:56:04, or one sidereal day.
The difference occurs because during one sidereal day the Earth, besides rotating completely once, has
revolved slightly (about 1) around its orbit. For the Sun to return to the same spot in the sky, the Earth
must rotate further on its axis about 1 degree or equivalently about 4 minutes to make up for the angular
shift due to its revolution during the sidereal day.
Astronomy Formula and Constants Sheet for Exams
Conversions
Formulas
A
L

2D
360 
Main Sequence Lifetime t 
M
1010 yr
L