ASTRONOMY 130
CELESTIAL SPHERE
PURPOSE: To compare the horizon and equatorial coordinate systems and to learn how to determine sidereal time. To make use of a celestial globe in understanding the basic coordinate systems.
PROCEDURE: Making use of the celestial globe, answer the questions in this lab pertaining to the horizon and equatorial coordinate systems as well as sidereal time.
The celestial globe is a small model of the celestial sphere, or, in other words, a spherical star chart mounted in such a fashion that it can be oriented to represent the true aspect of the sky as seen by an observer at any point on the earth at any time. Since the surface is spherical, the distortion inherent in flat star maps is avoided. On the other hand, it forces you to view the constellations from the outside inward rather than from the inside outward.
Several hundred stars have been plotted on the globe as well as the great circles representing the hour circles for every hour from 0 to 23 hours. The celestial equator, ecliptic, and parallels of declination for every tenth degree are represented. The celestial equator is marked off every 5 minutes and every sixth hour circle is marked off in degrees. The boundaries for each constellation are also shown. The boundaries are lines that are either parallel or perpendicular to the celestial equator. The base that holds the globe is marked off in degrees of azimuth, every 5 degrees. To determine altitude, you will need a calibrated measuring tape, which is marked off in degrees.
The globe will turn about the north and south celestial poles which are mounted to a meridian ring. When using the globe for some measurements it must be set for the proper latitude of the observer. Other measurements do not require the globe to be set for a specific location.
Part I - Problems not involving the proper orientation of the globe.
Part II - Problems involving the proper orientation of the globe.
The problems will be answered on separate sheets.
PART INAME ;
When you use the globe be sure you understand the orientation of the constellations before you start to work.
1. The stars on the globe are shown in yellow with the largest dot representing the brightest star. Give two names for the brightest star in Auriga. and .
2. What is the proper name for the star () gamma in Orion? .
What is the magnitude (brightness) of this star? .
3. Look at the constellation of Capricornus, does it have any first or second magnitude stars? If yes, give their names . Repeat for the constellation of Gemini. .
4.Look at the constellation of Cancer and locate its boundaries. What is the range in size of this constellation in right ascension and declination? (R.A.) (Dec.)
5.Locate the constellation of Aries. Can you say that the sun passes through the constellation of Aries? Explain your answer. .
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6. Determine for the following objects:
StarConstellation R.A. Dec.
Betelgeuse . . _.
Antares . . .
Merak . . .
Canopus . . .
7. Determine for the following objects:
Object NameConstellation R.A. Dec.
double star . . . .
star cluster . . . .
nova . . . .
8. Determine for the following:
R.A. Dec.ConstellationName
05h 30m -17.5o . .
22h 30m 58.5o . .
09h 55m 69o . .
21h 28m 12o . .
Part II
The globe now must be set for the proper latitude. The latitude of DVC is 38oN, so the altitude of the celestial pole must be set at 38o. Be sure that the north celestial pole is located above the north cardinal point (that is, make sure the NCP is closer to the north cardinal point than the south cardinal point).
1. Determine for the following:
ObjectRising AzimuthMeridian Altitude Azimuth Setting Azimuth
Deneb . . . .
Arcturus . . . .
Fomalhaut . . . .
M 31 . . . .
2.When Sirius is observed rising, what is the altitude and azimuth of () alpha Aquila?
Alt. Az. .
3.When the Pleiades are observed setting, what is the altitude and azimuth of () alpha Virgo?
Alt. Az. .
4.When Arcturus transits, what is the altitude and azimuth of Antares?
Alt. Az. .
5. What is the meridian altitude of () beta Cassiopeia?
and why are there two answers to this question?
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6.Set the Globe for 60oN latitude. Determine the following.
ObjectRising AzimuthMeridian Altitude Azimuth Setting Azimuth
Fomalhaut . . . .
M 31 . . . .
7. Why do the values of rising azimuth, meridian altitude, and setting azimuth change when you change latitude? .
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8. Sidereal time is defined as the right ascension of an object that is on the celestial meridian. When the following stars are on the celestial meridian determine the proper sidereal time.
ObjectSidereal Time
Vega .
Aldebaran .
Regulus .
Sun (3/31) .
9. How will the results of question 8 depend upon the latitude of the observer?
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10. Set the Globe once again for the latitude of DVC.
Hour angle is defined as the distance (in hours, min’s, and sec’s) from the celestial meridian to the object’s hour circle. The value is (+) if west of the celestial meridian and (-) if east of the celestial meridian. Set the Globe so that () alpha Ophiuchus is on the celestial meridian. Determine the following:
ObjectHour Angle .
Leo .
Hercules .
Cygnus .
Sun (10/14) .
11. To determine the amount of time an object is above the horizon, you need to determine the hour angle it has when it rises and the hour angle is has when it sets. If you add the absolute values of these two hour angles you will get the amount of time the object is above the horizon. Determine for the following:
ObjectRising H.A.Setting H.A. Hours Above
Capella . . .
Sun (6/21) . . .
Sun (12/21) . . .
12. The star () beta Aries is to be observed when the sidereal time is 21h 30m. Determine the following for this star.
R.A. . Dec. . Hour Angle .
Altitude . Azimuth .
13. The star () beta Cetus is to be observed when the sidereal time is 03h 50m. Determine the following for this star.
R.A. . Dec. . Hour Angle .
Altitude . Azimuth .
14. The star () beta Gemini is to be observed when it has an hour angle of 2h 20m. Determine the following for this star.
R.A. . Dec. . Sidereal Time .
Altitude . Azimuth .
Part III
With the use of the Globe answer the following questions, assume you are at DVC unless otherwise stated.
1. What is the altitude of Polaris? .
2.What would be the altitude and azimuth of a star if it were seen in the southeast on the horizon? Alt. Az. .
3.What would be the altitude and azimuth of a star seen at the zenith?
Alt. Az. .
4. If a star rises at 45o azimuth, where will it set? .
5. What is the azimuth of the vernal equinox when it is just rising? .
just setting? .
6. If a star is seen at the zenith at your location, what is the dec. of the star? .
7. What is the declination of the north celestial pole? .
8. What is the declination of a star that sets due west? .
9. What is the right ascension of a full moon on September 22? .
10. What is the least declination of a circumpolar star as seen from New Orleans, Louisiana (latitude 30oN)? .
11. The end star on the handle of the Big Dipper will be seen at the zenith at what latitude? .
12. What is Sirius’ highest altitude at our location? .
13. The declination of the sun is -10o. At what latitude will the sun be just circumpolar?
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14. The star Vega is observed to have a meridian altitude = 71o with an azimuth = 0o. At what latitude will this be observed? .
15. The right ascension of a star = 5h 00m, the sidereal time = 2h 00m. What is the star’s hour angle? .
16. What is the hour angle of an object with a right ascension = 16h at 10:00 p.m. on June 21st?
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