Name:
Name:
TG
Unit 1 – Astronomy – The Sidereal Day
Aim
The aim of this experiment is to use the apparent motion of the stars in order to measure how long it takes
for the Earth to complete one 360o rotation about its axis – a sidereal day.
Equipment
• Sidereal scope
• Tripod
• 24-hour stopwatch
• Planisphere
Caution:
At no time should the sidereal scope be used to look
at the Sun!
Discussion
From your previous observations of the night sky answer the following questions.
Question 1
In which direction do the stars in the southern half of the sky appear to rotate about the South Celestial
Pole (SCP)?
Question 2
If you are facing north, in what direction do the stars appear to move?
Question 3
In what part of the sky will you need to look to find the stars that have the fastest angular motion?
Method
Step 1
Use the planisphere to choose a suitably bright star in the appropriate part of the sky and at a time you
want to make your observations.
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Step 2
Set up your sidereal scope on its tripod*, as shown in Figure 1a. Rotate the cap with the Perspex square
so that the engraved line is as near to vertical as you can get it. Adjust the position of the scope so that
your chosen star appears to the right of the engraved line, as shown in Figure 2a, when viewed through
the eyehole.
Figure 1a
Figure 1b
* If you don’t have a tripod you can tape your scope to a pole or another suitable object. Figure 1b.
However, you will probably need someone to help you attach the scope whilst you are spotting the star!
Figure 2a
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Figure 2b
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Question 4
Why does your chosen star appear to be fainter when you are looking at it through your sidereal scope
than with the naked eye?
Step 3
Once you scope is set up with your chosen star in view turn the LED on. At the moment the illuminated
line occludes the star, as shown in Figure 2b, start the stopwatch. It is crucial to the success of the
experiment that the sidereal scope is not knocked or moved whilst the experiment is running. So be
careful not to put your eye against the scope while you are viewing the star.
Step 4
On the following night come out 10 to 15 minutes earlier than the previous night and start watching for
your star to appear in your scope. Remember not to knock or touch your scope! Once the star appears in
your scope turn the LED on. When the illuminated line occludes the star stop your stopwatch and record
the time.
If the sky is overcast and your cannot record the passage of your chosen star, leave the stopwatch
running, and try again the next night. You will need to start viewing an extra five minutes earlier for each
successive night that you cannot view the star.
Enter your results in the appropriate spaces in the results table.
Results
Start Date:
Finish Date:
(approximate)
(approximate)
Start Time:
Finish Time:
Elapsed Stopwatch Time:
Calculations
Sidereal Day Length:
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Question 5
Comment on how your result compared to those obtained by your classmates?
Question 6
Use the class results to calculate an average value for the length of the sidereal day?
Average Sidereal Day Length:
Question 7
How does your result and the class average compare to a 24-hour clock day? Try and explain what you
have discovered?
Conclusion
Summarise your findings from this experiment.
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The Siderealscope can also be readily adapted to observe the Sun – a Solarscope!
To convert the siderealscope to a solarscope you will need to remove the end cap that has the Perspex
square and LED. Replace it with a sheet of tracing paper and reverse the scope as shown in Figures 1a
and 1b.
Figure 1a
Figure 1b
During the year the Sun’s angular size varies between 0.52o and 0.54o with an average angular size of
0.53o.
Based on this and some simple geometry and trigonometry a set of concentric circles with a separation
equal to the Sun’s average angular size can be drawn and printed onto tracing paper. Figures 2 and 3. (To
print without jamming your printer at home you will need to cellotape the tracing paper to a normal sheet
of A4 – bottom, top and sides)
Figure 2
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From these rings the Sun’s passage across the
sky can be observed and timed.
Figure 3
Constructing A Sidereal Day Scope
Materials
Qty.
Materials
Part Number
1
60/600 mm Mailing Tube
1
Battery Holder Snap 9V (purchased as a pkt of 5)
S6100
1
Battery Holder 2 x “AA” Cell
S6112
1
LED 5 mm Circular Green
Z4087
1
Mini Toggle Switch 250V AC & 2A
P7654
1
Header Pin & Plug 2-Way
P2731
1
2.0 metre Wire Hook-Up 10 x 0.12 mm Red
W2220
1
2.0 metre Wire Hook-Up 10 x 0.12 mm Black
W2221
1
Heat shrink Tube 1.2 m x 1.5 mm Black
W4100
2
AA Alkaline Batteries
1
Perspex Square 3 mm x 60 mm x 60 mm
Equipment
• Hot-glue gun
• Soldering iron
• Craft knife
• 7/32” Rat Tail File (Used for sharpening chain saw blades)
• Steel ruler
• Scribing tool / Compass
• Packing tape
• Black paint
• Wire cutting pliers
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Safety
When using a soldering iron:
• Work in a well-ventilated area to avoid any fumes.
• Ensure that the hot tip of the iron is kept well away from the iron’s electrical cord.
• Take care not to burn your fingers.
When using a craft knife try to make small repeated rather than one large forceful cut. This
reduces the risk of the knife slipping and cutting your finger(s). When you are not using the knife
put its cap back on.
Never use your sidereal scope to look at the Sun.
Method – Constructing The Sidereal Scope
Step 1
Without removing the masks from the Perspex that protect it use a pair of soft jaws to clamp the Perspex
square into a vice. Use the rat-trail file to file a groove into the middle of one side of the square. The
groove needs to be deep enough for the LED to fit into as shown in Figure 1a.
Step 2
Remove one side of the mask from the Perspex. With the aid of a steel ruler and the scribing tool
carefully etch a thin horizontal line across the Perspex square as shown in Figure 1b.
The best results will be achieved by making several firm passes along the same line rather than one heavy
pass.
Figure 1b
Figure 1a
Step 3
Remove the second mask from the Perspex. Use the hot-glue gun to glue the LED into position as shown
in Figure 2a.
Step 4
Once the glue has cooled use some black paint to paint over the side of the LED that will face into the
tube as shown in Figure 2b. The side that will face into the tube is the one that has the etched line on it.
Figure 2b
Figure 2a
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Step 5
Use the craft knife to carefully cut out the inner circle from one of the Mailing Tube’s end caps as shown
in Figures 3a and 3b. You will also need to clip out a 1.0 cm gap from the lip of the cap as shown in
Figure 3b. This is where the LED will sit.
Figure 3b
Figure 3a
Step 6
Use the hot-glue gun to fix the Perspex square to the end cap as shown in Figure 4a. Remember that the
side of the Perspex with the etched line needs to face into the tube. Trim the LED leads so that they are
1.5 cm in length. Remember to keep the long lead as the longest after trimming.
Figure 4b
Figure 4a
Step 7
Using a pin or compass point carefully pierce an eyehole into the centre of the other end cap as shown in
Figure 4b. To avoid any errors due to parallax whilst you are using the scope make sure that the hole is
no larger than 1.5 mm in diameter.
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Method – Making The LED’s Electronic Circuit
Figure 5 shows the circuit that needs to be constructed in order to power the Sidereal Scope’s LED.
Figure 5
Step 8
Solder one end of the 9V battery holder snap to a 100 cm length of wire hook-up. Remember to use some
heat shrink to cover the exposed join.
Step 9
Solder the other end of the 100 cm wire hook-up to one of the pins for the 2-way header plug as shown in
Figure 6a. Now solder one end of a 135 cm length of wire hook up to the other pin that will clip into the
2-way header plug. The pins of the LED will then slide into the header plug as shown in Figure 6b.
Figure 6a
Figure 6b
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Step 10
Solder the other end of the 135 cm wire hook-up to the middle pin of the mini toggle switch. Remember
to put some heat shrink onto the wire before you solder then use it to cover the exposed join. Take a 55
cm length of wire hook up and solder one end to one of the end pins of the mini toggle switch. It doesn’t
matter which one. Cover the join with heat shrink. See Figure 7a.
Step 11
Solder the remaining end to the other end of the 9V battery holder snap. Remember to put some heat
shrink onto the wire before you solder then use it to cover the exposed join. See Figure 7b.
Figure 7a
Figure 7b
Method – Assembling The Sidereal Scope
Step 12
Insert 2 x 1.5 Volt batteries into the battery holder and then clip it to the rest of the circuit. Attach the
completed circuit to the Sidereal Scope’s cardboard tube with packing tape. The battery pack should be
placed so that it is close to the middle of the tube. See Figures 8a and 8b.
Figure 8a
Figure 8b
Figure 8a shows a sidereal scope that has been set up by taping it to a pole. The tape has been applied
somewhat enthusiastically!
Figure 8b shows a sidereal scope that has been mounted to a tripod.
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For teachers
Materials, parts and costing list – all electronic parts were purchased at Dick Smith.
Qty.
Materials
Part Number
Cost
1
60/600 mm Mailing Tube
1
Battery Holder Snap 9V (purchased as a pkt of 5)
S6100
$2.28 ($0.47)
1
Battery Holder 2 x “AA” Cell
S6112
$1.67
1
LED 5 mm Circular Green
Z4087
$0.25
1
Mini Toggle Switch 250V AC & 2A
P7654
$2.29
1
Header Pin & Plug 2-Way
P2731
$0.58
1
2.0 metre Wire Hook-Up 10 x 0.12 mm Red
W2220
$0.50
1
2.0 metre Wire Hook-Up 10 x 0.12 mm Black
W2221
$0.50
1
Heatshrink Tube 1.2 m x 1.5 mm Black
W4100
$3.77
2
AA Alkaline Batteries*
$1.60
1
Perspex Square 3 x 60 x 60 mm**
$0.22
$2.45
The heatshrink tube is used to cover the soldered joins between wires.
*The cost for the batteries will depend on the quantities in which you buy them. The listed price was
based on $15.99 for a pack of 20 from Coles on January 17th 2008.
**Perspex sheet can be purchased from Bunnings Hardware in the following sizes:
600 x 1200 x 3 mm for $43.12 or
900 x 1200 x 3 mm for $69.49
You should be able to get 200 squares from a 600 x 1200 x 3 mm sheet!
This gives a unit cost of $0.22. The listed prices were obtained on January 17 th 2008.
An approximate cost for making 1 sidereal scope would be: $10.60.
Equipment
• Hot-glue gun
• Soldering iron
• Craft knife
• 7/32” Rat Tail File (Used for sharpening chain saw blades)
• Steel ruler
• Scribing tool / Compass
• Packing tape
• Black paint
• Wire cutting pliers
• Small paintbrush
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Balloon Helicopter
Professor Bunsen (A local source for purchasing Balloon Helicopters)
http://www.profbunsen.com.au/index.php
http://www.profbunsen.com.au/proddetail.php?prod=G19&PHPSESSID=314cf8ab060fe32e2537d2e347
2e51ac
AU$1.91 ($2.10 including GST) each
Balloon Helicopter Assembly Video
http://www.youtube.com/watch?v=UI7FUKbKU-E&NR=1
Arborscientific – Newton’s Laws & Balloon Helicopter Flight
http://www.youtube.com/watch?v=m6NnMQGQYDc
Lift Force - NASA
http://www.grc.nasa.gov/WWW/K-12/airplane/short.html
http://www.grc.nasa.gov/WWW/K-12/airplane/bga.html
Lift from flow turning (Newton’s 2nd and 3rd Law)
http://www.grc.nasa.gov/WWW/K-12/airplane/right2.html
You Tube Demonstrations
http://www.youtube.com/watch?v=AvLwqRCbGKY
http://www.youtube.com/watch?v=S-SAQtODAQw&feature=related
Incorrect Theories of Lift
http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html
http://www.grc.nasa.gov/WWW/K-12/airplane/wrong2.html
http://www.grc.nasa.gov/WWW/K-12/airplane/wrong3.html
A Physical Description of Flight
http://www.aviation-history.com/theory/lift.htm
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Nuclear Marbles
https://sites.google.com/site/culverphysics/Home/conceptual-physics
Originally from Conceptual Physics, Prentice-Hall 2002
The Physics Teacher (Top 10 Most Downloaded Articles)
http://tpt.aapt.org/most_downloaded?month=2&year=2010
Radioactivity Applets
http://www.lon-capa.org/~mmp/applist/decay/decay.htm
Shows a square of pixels decaying over time and a graph representing the decay process. The half-life is
adjustable.
http://www.nuclides.net/applets/radioactive_decay.htm
A comprehensive applet that shows the decay chains for a large number of different radioisotopes via
their positions in the periodic table.
http://newnet.lanl.gov/main.htm
Although US based this applet allows you to estimate your yearly exposure to radiation in units of mrem.
http://www.nih.gov/od/ors/ds/rsb/raddkcalc/calcframe.htm
This applet has Radioactive Decay/Activity Calculators for a large number of radioisotopes.
http://www.ndt-ed.org/EducationResources/CommunityCollege/Radiography/Physics/nature.htm
This website and its applets pretty much cover our course.
Thermistor & LDR
Dick Smith Electronics
Thermistor
http://www.dse.co.nz/dse.filereader?4d40d3f90073fcde2742c0a87f3b071c+EN/catalogs/SUP1000077
Light Dependent Resistor LDR
http://www.dse.co.nz/dse.shop/4d40d3f90073fcde2742c0a87f3b071c/Export/catalogs/SUP1000072
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