Celestial Sphere Lab
Introduction
The purpose of this activity is for you to gain a clearer understanding of the celestial sphere, the Sun, the Moon, and the Earth by making virtual observations of a simulated sky. You will be using a computer program called ÒStellariumÓ which will chart and display the stars, planets, comets, Moon, Sun, galaxies, nebulae, etc. as they would appear from any spot on the Earth – north, south, east, or west, at any point in time – past, present, or future. This is a complicated and extensive program that has lots of menus and options – so please only make the changes to the program that are described below.
Start Stellarium by double clicking its icon. The program automatically will start in Òfull screen modeÓ. This program is a little unusual in its controls and menu system. This section of the lab is simply intended to familiarize you with the controls and teach you how to use Stellarium. Complete the following checklist – marking off each item as you go.
q Use the mouse to click and drag and notice that you can change the direction in which you are viewing the sky.
q Try left clicking on an object in the sky to ÒselectÓ it. Information about that object will appear and remain on the screen as long as that object is selected. Right click anywhere on the screen in order to ÒreleaseÓ or ÒdeselectÓ the object.
q Use the scroll wheel on the mouse to zoom in or out.
q Notice the information displayed at the bottom of the screen (which describes the simulated view) showing your location, field of view (which changes as you zoom in or out), simulation frame rate, and date and time.
q When you move the mouse over this information it reveals a Òpop-upÓ menu. There is another pop-up menu that appears when you move the mouse to the left of the screen. Notice that when you pass over items in either menu a brief description appears and a corresponding keyboard shortcut.
q In the bottom pop-up menu find the time controls. Experiment with going fast-forward or backward in time. Then return to normal time rate and set time to now. Also notice that the triangular ÒplayÓ button can also serve to pause the simulation and freeze the view at a particular date and time. (The triangle turns into the ÒpauseÓ symbol when time is frozen.)
q In the left pop-up menu find the Date/time window and use it to select any particular time. This can be done by clicking the up and down arrows, but also by typing in a particular number. Try typing in the year 3 – this will instantly change the simulated view to the year 3 AD. Try clicking on the down arrow and notice that the years will go negative for BC. Return the time to present day – can be done most quickly by the Set time to now control in the bottom pop-up (even while the date time window is visible).
q In the left pop-up menu find the Location window and notice an extensive list of sites that can be simulated. You can also enter latitude, longitude, and elevation to create a custom location. Try changing the simulated location and observe the results. Before continuing set the location to Knoxville.
q In the bottom pop-up menu try clicking on the following controls to turn certain aspects of the simulation on and off: Constellation lines, Constellation labels, Equatorial grid, Azimuthal grid, Ground, Cardinal points, and Atmosphere. Note: turning the atmosphere ÒoffÓ makes it possible to see stars during daylight hours when the sun is in the sky.
q There are other optional things to view that can be accessed using the Sky and viewing options window found in the left pop-up menu. Open this window and go to the Markings tab and try turning on and off Constellations, Show boundaries.
q Now go the left pop-up menu and open the Help window. Notice an extensive list of keyboard shortcuts. For example you will see that one of the shortcuts is to turn constellation boundaries on/off by simply pressing the letter B on the keyboard. Keyboard shortcuts can be extremely handy and helpful! (IMPORTANT NOTE: keyboard shortcuts do not work whenever a window (like Date/time, Location, etc) is active. The window must be closed or deactivated (dimmed) before the shortcuts will operate – this can be frustrating!)
For this set of questions you will be observing simulations of the sky as it appears from Knoxville. Make sure the location is set to Knoxville and the date/time are set to now. Record all observations and answers on the given data sheet.
1. Set the time to go fast forward at a comfortable rate so that days pass by in a few seconds (click the fast forward button four times). Now Òlook aroundÓ at the celestial sphere in motion. Use your imagination – visualize a huge sphere rotating around the Earth. Also imagine you are on the spinning Earth simply looking Òout thereÓ almost like being on a merry-go-round. Observe the east horizon, west horizon and north horizon. Record the direction in which the stars rise and set. Record the direction (clockwise or counterclockwise) of the apparent rotation about Polaris.
2. Now stop time (pause the animation) and set the date to December 25 of this or last year. Arrange your view toward the south zoomed out to a field of view around 100¡. Turn off the atmosphere. Turn on the meridian line (keyboard shortcut Ò;Ó). Open the Date/time window and adjust the time of day to find the precise time (to the nearest minute) at which the Sun crosses the meridian. This is noon apparent solar time in Knoxville.
3. Now go forward in time by increments of one solar day (keyboard shortcut Ò=Ó). Move forward in time one day at a time for a whole year, simulating what you would see if you went out and faced south at midday every day. Describe the apparent motion of the Sun relative to your horizon over the course of the year. Describe the apparent motion of the Sun relative to the celestial sphere over the course of the year.
4. Use the date and time controls to find the date on this year when the vernal equinox occurs. This will be the date on which the Sun is located closest to the celestial equator (right ascension 0h) at midday (12:36 EST or 13:36 EDT). You may wish to turn on the celestial equator (keyboard shortcut Ò.Ó) and the ecliptic (keyboard shortcut Ò,Ó) and turn off the meridian (keyboard shortcut Ò;Ó). Use the same setup to find the date of the summer solstice, when the Sun is farthest north of the equator at midday (right ascension 6h). Repeat the process for the years 2096 and 2103.
5. Change the date to the year 7400. Try different views and time skips, and repeat some of the previous observations. Describe the ways in which the sky is similar to todayÕs sky. Describe the ways in which the sky is different from todayÕs sky.
6. Determine the constellation and date of the vernal equinox in the year 7400.
7. Determine which bright star is fairly close to the celestial north pole and could be called the Ònorth starÓ in the year 7400. Before proceeding you should reset the date to the current year!!!!
In this section of the lab you will perform each of the following observations as simulated from different locations on Earth. Set the site of observation to the given location and then make each observation in order to fill in the table. Note: the time of day shown by Stellarium is always equal to the time it would be here in Knoxville (or whatever time zone is set on the computerÕs clock and operating system). So if you change the location to, say, Los Angeles, which should be Pacific Time, then the time of day shown by the program is still Eastern Time, which is three hours ahead of clocks in Los Angeles.
q In the program you can specify a city or you can specify a latitude and longitude. This is done from the left pop-up menu in the Location window. Just pick a city from the list.
q Make the date is set to the current year.
q From the bottom pop-up menu the Azimuthal grid can be useful for these observations.
q At each location on Earth I invite you to try different views of the sky and different time skip intervals in order to get a real feel for the appearance of the celestial sphere from that site.
q You only need to determine coordinates in the table to the nearest one degree. One way to do this is to simply use the gridlines. If you zoom in you should be able to simply read off the nearest degree from the gridlines. You may want BOTH sets of gridlines turned on.
q The row in the table for Knoxville is already filled in with examples of these observations. You may want to confirm these values with the program.
1. Stop the animation and turn to the north or south horizon so that you are viewing the celestial pole(s). Record which pole(s), CNP and/or CSP, and its altitude above the horizon.
2. Center your view on the observerÕs zenith. Then search through time for a prominent star that passes through or near to the zenith. Record the name of the star and its constellation.
3. Find the altaz coordinates of the ÒbeginningÓ ÒmiddleÓ and ÒendÓ of the celestial equator. In other words where does it rise, how high does it transit the meridian, and where does it set.
4. Determine the maximum and minimum altitude that the Sun will attain as it crosses the observerÕs meridian at this location. Hint: go fast forward in time until Sun is on the meridian (keyboard shortcut Ò;Ó). Then set the date to each solstice and each equinox and check the SunÕs altitude. Record altitude max and min and the dates on which these occur.
In this section of the lab you will investigate the occurrence of eclipses. For these exercises you will remove the simulated horizon and atmosphere so that you can continuously observe the Moon, Sun, and stars.
q In the Location window return the viewing location to Knoxville.
q Set the date to the year January 1, 2153.
q From the bottom pop-up menu choose Switch between azimuthal and equatorial mount (Ctrl M) and Òlight upÓ this icon. Turn on the Equatorial grid and you should see that your view is now aligned not with the ground and horizon but rather with celestial east and west being left and right and with the celestial north pole being up.
q From the bottom pop-up menu choose to turn off the Ground, the Cardinal points, and the Atmosphere. From the left pop-up menu use the Sky and viewing options window, and under the Markings tab turn on the Ecliptic (of date) (or use keyboard shortcut Ò,Ó).
q Find the Moon and select it. One way to do this is to use the Search window from the left pop-up menu. Type Moon and hit enter. Or you can simply Òlook aroundÓ for the Moon and click on it.
q Now track the Moon. You can track the object that is currently selected by keyboard shortcut ÒTÓ or tapping the keyboard space bar. You should see the Moon move to the center of your view and stay there as time and/or date is changed.
1. While tracking the Sun in the year 2153 find the date and time in January when the Moon is nearest to the New phase. You can judge the extent of the MoonÕs ÒnewnessÓ by the percent illuminated value, which is shown at the bottom of the list of information for the Moon whenever it is selected. You should find that the new phase of the Moon in January does not cover the Sun but instead makes a near pass by it, so there would be no eclipse.
2. Check each new Moon of 2153 to find the two closest passes by the Sun. It is convenient to use the Date/time window to move forward a synodic month 29.5 days (click the month up by one and the day back by one or two. Again find the time when the Moon is nearest the Sun. Check for an eclipse. You should find these two times to be six months apart.
3. For each of these close passes zoom in and adjust time to see if the Moon actually covers part or all of the Sun. Turn the ground and atmosphere back on and see if the eclipse is visible above the horizon. Observe the eclipse from beginning to end and determine the date and which type it is, as seen from Knoxville. Record anything notable in the comments section.
4. Now search for a lunar eclipse during the same year. Advance the days to find a full Moon (should be about two weeks before or after a new Moon). You can judge the extent of the MoonÕs ÒfullnessÓ by the percent illuminated value. Similar to the way you found the solar eclipse look for a lunar eclipse that is visible from Knoxville that year and record the date and type. Helpful hints: a solar eclipse is always preceded by a lunar eclipse two weeks earlier or followed by a lunar eclipse two weeks later, and the Moon must be full and located near or on the ecliptic for a lunar eclipse to occur. You will have to move back and forth in time and look for the EarthÕs shadow passing over the full Moon.
5. Time permitting, repeat the process to look for eclipses during the year 1865 and 2024 viewing from Knoxville.
The Sky from Knoxville
1.
Every night stars rise in the
__________ and set in the ___________.
Circumpolar stars revolve about polaris in a _____________________ direction.
2.
Local standard time on December 25
at which the Sun crosses the meridian: ____________.
(This is Ònoon apparent solar timeÓ for Knoxville.)
3.
Describe SunÕs motion relative to
the observerÕs horizon over the course of one year:
Describe SunÕs motion relative to the celestial sphere over the course of one
year:
4.
Dates of equinoxes
and solstices
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2017 |
2096 |
2103 |
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Vernal Equinox |
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Summer Solstice |
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5.
Year 7400
Similarities to todayÕs sky:
Differences from todayÕs sky:
6.
Year 7400
Constellation of Vernal Equinox:
Date of Vernal Equinox:
7.
Year 7400
Pole Star:
The Sky from Other Places
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Site Information |
Celestial Pole(s) & Altitude |
ObserverÕs Zenith: Example Star and Constellation |
Celestial Equator:
Begins |
SunÕs Appearance at Transit (midday) |
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Location |
Longitude |
Latitude |
Max. Alt. |
Min. Alt. |
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Knoxville, Tennessee |
84¡ W |
36¡ N |
CNP: 36¡ |
Vega, Lyra |
(0¡, 90¡) |
77¡ |
31¡ |
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Fairbanks, Alaska |
148¡ W |
65¡ N |
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Quito, Ecuador |
79¡ W |
0¡ |
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Sydney, Australia |
151¡ E |
34¡ S |
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Eclipses
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Viewing from Knoxville, TN |
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Year |
Date & Time |
Type |
Comments |
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2153 |
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2153 |
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1865 |
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1865 |
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2029 |
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2029 |
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2029 |
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