Module 2
Observing the Universe
LCOGT Activity Form
Title: How to Build an Astrolabe
Credit (template): Master and Fellows of St John's College, Cambridge
(http://www.joh.cam.ac.uk/library/library_exhibitions/schoolresources/astrolabe/)
Keywords:
Astrolabe, map, time, location, date, model, altitude, zodiac
Age: Level: Secondary School
Time: 1hr
Group: Individual
Supervised: Supervised
Cost: Low (< ~5 EUR)
Location: Outdoors
Language: EN
Brief description:
Astrolabes are ancient astronomical instruments that allowed astronomers to measure the
positions of objects in the night sky and calculate their own position in time and space. In this
activity you will create your own astrolabe and learn how to use it to collect information about
the position of the Sun, the time of events including sunrise and sunset, and the location of
other astronomical objects in the sky.
List of Materials:
Per student:
• Astrolabe template (three pages printed onto thin card and one page printed onto an
acetate sheet)
• Piece of medium-thick card
• Scissors
• String
• Split pin
• Glue
•
Drawing pin or other sharp tool
Goals: After carrying out this activity, students will have successfully built and used an
astrolabe. They will be familiar with how to use the astrolabe to find the current location of
objects on the sky using the time and date, to find the position of the Sun using the zodiac and
to calculate the time of sunrise and sunset.
Learning Objectives:
•
•
•
Learn about the history of the astrolabe as an important ancient astronomical instrument.
Build an astrolabe
Learn how to use an astrolabe to read the date and time, and locate a number of
astronomical objects in the sky at any time by altitude and direction.
Background Information:
Astrolabes are an ancient astronomical instrument. They were first used in ancient Greece,
before being developed further in the medieval Islamic world and becoming the key
astronomical instrument of the western Middle Ages.
Looking at a map of the skies it appears that the stars are all at an equal distance from the
Earth, fixed on the inside of an enormous sphere that has the Earth at its centre. The twodimensional representation of the sky seen on star charts and astrolabes is the starry equivalent
of a map of the earth.
The front of the medieval astrolabe shows a map of the night sky on the rotating rete. Its name
is taken from the Latin word for ‘net’, because of the appearance of the spikes that indicated the
positions of individual stars. The rete also shows the path of the Sun against the background
stars; this path is known as the ecliptic, and the constellations through which the sun passes on
the ecliptic are the well-known constellations of the Zodiac.
The astrolabe in this picture was made in Iran in 984
AD. It currently resides in the Museum of Islamic Art, Doha (Qatar).
The modern astrolabe in this kit uses a sheet of transparent acetate for the rete, with the
position of stars indicated by dots. The brightness of the star is shown by the size of the dot: the
larger the dot, the brighter the star.
Beneath the rete of the medieval astrolabe sits a plate inscribed with a projection of sky above
an observer at a given latitude: the plate could be removed and replaced with others calibrated
for different latitudes if necessary.
The plate and the rete nest inside the body of the astrolabe, called the mater or Mother on this
template, which is inscribed on its outer edge, or limb, with scales of degrees (back) and hours
(front).
On this template the plate is integrated into the mother (front) and calibrated for latitude 52 N.
Fixed to the centre of the astrolabe is the rotating rule used for taking readings.
On the front of the mother you will see that the compass points and their divisions are marked
with letters. These letters label lines that extend from the horizon line up to the zenith (the point
in the sky directly above you). These lines tell you in which direction an object will appear. If a
star on the rete is on, or close to, the line labeled ‘SE’, you simply look towards the south-east to
locate it. The altitude lines explained previously will tell you where to look (e.g. near to the
horizon or above your head).
On the back of the astrolabe is a rotating bar called the alidade or label, which is used to
measure the altitude of objects above the horizon. This is divided into 5 degree sections for
taking altitude measurements, and is also engraved with a calendar and divisions of the zodiac.
By using the data from both sides of the instrument and the measured positions of objects in the
sky, the user can calculate several facts about their position in time and space, including the
hour of the day, the date, and their position on the Earth’s surface.
Skills: Visual Interpretation
Enquiry-Based Learning model:
● Level 2 Guided enquiry
Full Description:
Building your Astrolabe
1. Print out the Astrolabe template provided. Once you are finished, you should have 3
pages printed onto thin white card, and a fourth printed onto an acetate sheet.
2. Carefully cut out each part of the astrolabe template. You should have the following five
pieces when you have finished:
a. Mother, back
b. Mother, front
c. Rete
d. Label
e. Rule
3. Glue together the two sides of the Mother (front and back), placing the sheet of thicker
card between them and cutting it to size when done. Write your name on the front of the
Mother in the space indicated.
4. Continue assembling the astrolabe, placing the Label on the back of the Mother.
5. Place the Rete on the front of the Mother then line up the Rule on top.
6. Use you pin to make a hole through the circle at the centre of the rule that goes through
all the layers. Place split pin through the hole to hold the astrolabe together.
7. You should be able to rotate each of the following layers independently: the Rule, Label
and Rete.
8. Make a small hole in the top of the Mother, thread a small piece of string through the
hole and tie the ends to make a loop. Thread another small piece of string through this
loop and tie up again into another loop.
9. Read the Background Information provided for more information about your model.
10. Now your astrolabe is ready to be used!
Using your Astrolabe
An astrolabe can provide all sorts of information about the night sky. In this activity you will learn
how the astrolabe can be used to calculate the date and time, find out where along the ecliptic
the Sun is located, measure the altitude of stars and navigate by finding directions.
i. Calculating the date and the zodiac
There are twelve zodiacal constellations in the sky these are the constellations through which
the Sun appears to move throughout the year. Each constellation has then been divided into 30
smaller sections. When using the astrolabe, each of the twelve sections represents a month and
each of the 30 smaller segments is a day.
On the back of your mother you can read the date using the constellations of the zodiac.
1. Line up the label with the part of the sky the Sun is currently travelling through on the
zodiac scale.
2. Read off the date using the label on the calendar scale.
3. Note that the zodiac is divided into 360 parts and a year is divided into 365 (or 366)
days, so the match will not always be exact.
Alternatively, if you know the date you can work out which constellation the Sun is currently in.
4. On the back of the mother, line up the label with the current date using the calendar
scale.
5. The position of the Zodiac that the Sun is in on this date can be read using the label and
the zodiac scale.
6. You can now turn over your astrolabe and line up the rule against the rete at the point in
the Zodiac for the date.
7. Rotate the rete and rule together until the rule points to the current time of day on the
time scale. The position in the Zodiac that you just found will now be in the position of
the Sun at the current time and date.
8. Use the altitude and direction lines on the front of the mother to see where in the sky the
Sun is.
iii. Measuring altitude
The astrolabe can be used to measure the altitude of an object above the horizon. This
information can then be used to work out other things, such as the time and date if you are
looking at the Sun or stars.
9. Hang the astrolabe from your thumb using the string loops at the top.
10. Hold the astrolabe sideways in front of your face and line up your eye with the middle of
the astrolabe.
11. Slide the label around until it lines up with the object you want to measure.
12. Now read the altitude from the position of the label on the elevation scale running along
the edge of the Mother. If you do not know which is the elevation scale, see Background
Information.
13. On the front of the mother you can set the height of your object by lining up the rete with
the series of concentric ovals marked with their height in degrees. (For example, 10° is
just above the horizon and 80° is almost directly above you.)
iv. Finding directions
The astrolabe can also be used to work out which direction an object is in.
14. Look at the front of the mother, you will see that the compass points and their divisions
are marked with letters. These letters label lines that extend from the horizon line up to
the zenith (the point in the sky directly above you). These lines tell you in which direction
an object will appear.
15. Choose a star, if the rete is on, or close to, the line labeled ‘SE’, you simply look towards
the south-east to locate it. The altitude lines explained previously will tell you where to
look (e.g. near to the horizon or above your head).
16. Note: This astrolabe is a 24-hour clock using UTC.
v. Calculating the time of Sunrise and Sunset
The astrolabe also allows you to calculate the time of sunrise and sunset throughout the year.
17. Begin by lining up the label with the date. Read off the Zodiac Scale (e.g. Leo 29).
18. Turn your astrolabe over and line your zodiac scale number along the horizon (Eastern
horizon for sunrise, Western horizon for sunset).
19. Next, line your rule up with your zodiac scale number on the rete.
20. You can now use the rule to read off the time for sunrise or sunset along the time scale.
Now answer the questions below:
•
•
•
•
•
•
•
•
•
What is the zodiac scale for the Sun on December 31st?
On what date will the Sun be at Taurus 23 on the zodiac scale?
Where on the zodiac scale is the Sun at it’s highest midday altitude? What date is this?
Where on the zodiac scale is the Sun at it’s lowest midday altitude? What date is this?
What time does the sun set on 1st January?
What time does the sun rise on 5th July?
How long is the day on 7th October?
What direction does the Sun set on 4th February?
Using the astrolabe, what are the dates for the equinoxes and solstices? (Remember.
The solstices are the longest/shortest days and the equinoxes occur when day and night
are equally long.)
Answers:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Capricorn 9
14th May
Gemini 30
Sagittarius 30
4pm (16:00)
3:55am
9 hours
3 degrees South of West
Spring Equinox: Pisces 1 (20 March); Autumn Equinox: Libra 28 (22 October); Winter
Solstice: Sagittarius 30 (21 December); Summer Solstice: Gemini 30 (22 June)
Evaluation:
Q. What might stop you seeing the stars as shown on the astrolabe?
A. cloud cover, hazy skies, buildings, trees, hills, light pollution
Q. How accurate do you think the astrolabe is? What will affect its accuracy?
A. accuracy of assembly, the level of accuracy of the various parts (e.g. nearest 5 degrees of
altitiude), shape of the Earth (not a perfect sphere), movements of the Earth are no perfectly
regular, leap years not allowed for.
Q. Are there any astronomical objects the astrolabe cannot account for? Why not?
A. The Moons and planets. Both change their positions relative to the stars all the time.
How to Build an Astrolabe
Astrolabe template page 1: Mother, back
Print this page on thin card.
http://www.joh.cam.ac.uk/library/library_exhibitions/schoolresources/astrolabe/
How to Build an Astrolabe
Astrolabe template page 2: Mother, front
Print this page on thin card
http://www.joh.cam.ac.uk/library/library_exhibitions/schoolresources/astrolabe/
How to Build an Astrolabe
Astrolabe template page 3: Rete
Print this page on acetate
http://www.joh.cam.ac.uk/library/library_exhibitions/schoolresources/astrolabe/
How to Build an Astrolabe
Astrolabe template: Rule and Label
Print this page on thin card
http://www.joh.cam.ac.uk/library/library_exhibitions/schoolresources/astrolabe/
How-to Guides
How to Use the Robotic Telescopes
To use the robotic telescopes, you will need an LCOGT On Sky account. If you do no yet
have access to the network, or if you have any issues accessing your account, contact
your LCOGT project coordinator
Before beginning, you must decide whether you want to submit your observation requests
to a queue or whether you want to carry out your observations in real time. For the second
option you will need to contact the project coordinator at least a couple of days in advance
and they will reserve the telescope for the time and duration you require. Please do not
feel hesitant to request a slot, just send the time, date and duration to your project
coordinator.
Instructions
1. Begin by opening your browser and going to http://lcogt.net/observe/
2. Enter your login details as requested to access the observing platform.
The first page you are directed to upon logging in to On Sky is your Observation
Homepage. On this page you will see a your project and your available telescope time
(quote) in minutes.
Note: If you run out of observing credit, just contact your project coordinator to
request more.
3. Select ‘Book a Slot’ or ‘Request Observations’. The ‘Book a Slot’ option is only relevant
if you have contacted your Project Coordinator to reserve a specific time for your
observing slot. If you have not booked a slot, skip to step 6.
Note: You must submit your observation requests at least one hour before your slot
is due to begin.
4. To schedule observations during your slow, return to your Homepage and scroll down to
the section ‘Upcoming Slots’. Simply click the relevant slot and skip to step 7.
LCOGT Scheduler
All eleven telescopes in the LCOGT network can be scheduled as a single global entity. Although
requests are made for a specific telescope class, you won’t be able to identify specific sites or
telescopes. (Don’t worry, all 1-meter telescopes are identical). Instead, each observation will be
scheduled on the best telescope available, and in the event or a failure due to weather or technical
problems, your observation will be rebooked on the next available telescope.
The scheduler automatically considers all observing constraints -- such as when your target object
can be observed and from which sites, to brightness of the Moon -- so you don’t have to worry
about anything!
5. To request observations without a scheduled slot, begin by selecting the time period
within which you need your observations from the options on the left-hand; side of the
page: ‘24-hours’, ‘1 week’ or ‘2 weeks’.
Time Windows
The Time Window is the amount of time during which the target is eligible for
observation. For example, if you select a Time Window of
one week your observation will be scheduled within the next week, or not at all.
7. On the next page enter a request title at the top of the page and select the option ‘Add
an Observation’. You will see a pop up box as shown on the image below.
Don’t be intimidated by the
number of parameters on this
page, if you don’t have a
specific observational target in
mind or would like to avoid
having to choose filters and
exposure times, you can simply
select an object from the list on
the right.
The list includes a number of
stunning astronomical targets,
categorised by object type. For
more information about the
various types of deep-sky
object refer to the Glossary at
the back of this handbook.
8. Select the object you would like to observe, click its name on the list and press ‘Add’.
Skip to step 14.
9. If you would like to be adventurous and try to observe a known target that is not listed,
type the name or coordinates into the relevant field.
10. The next step is to select which filters you would like to use (like on a camera). The
system is automatically set to capture three images, one with a red filter (R), one with a
green filter (V) and one with a blue filter (B). But you can select from a list of other filters.
11. Now select an exposure time, this is how long the shutters will stay open. The dimmer
the object, the longer the exposure time needed to capture a decent image.
12. The last field asks how many of each image you would like (remember that you have
limited observing time!).
Las Cumbres Observatory Global Telescope Network
The Las Cumbres Observatory Global Telescope (LCOGT) Network is made up of eleven
telescopes located at some of the best observing sites around the world. The telescopes can be
controlled robotically from inside your classroom; all you need to get started is a computer
connected to the Internet and your login details.
13. Once you have completed the form, click ‘Add’.
14. To observe more than one object, select ‘Add Extra Target’ and complete the previous
steps for your new target. Note that one observation request should take no longer than 30
minutes. You can see the duration of your request at the top of the page.
15. Once you have added all the targets you wish to observe, check there are no problems
with your observations. If you targets each have a green tick on them, you are good to go.
If there is a red symbol this means there is a problem. Hover over it to find out what the
problem is and resolve it. You may need to choose a new target.
16. You’re finally ready to submit your observation request. It’s as easy as clicking ‘Submit’
at the top of the page.
You will then be taken to your Submitted page, where you will find a list of all your
observation requests and the status of each observation, including whether the request
was cancelled or completed, and if the
observation is pending or was for some
reason unschedulable.
Blue = Submitted but pending.
Green = Successful. Your images
are waiting.
Red = Observations failed.
Black = Observations were
cancelled by you or an
administrator.
13. After submitting observation requests using a pre-booked time slot, you can watch all
of your observations happening in real-time. Just click on the your request from the
"Submitted" page prior to or during the time window of your slot.
Unfortunately, you won’t be able to see through the eyepiece of the telescope, but you can
watch as the telescope slews to your object via an on-site webcam while watching the
progress of your observations.This page also provides a virtual view of the night sky
showing the location of your target object(s)!
14. When your observations are completed you can access the images by clicking on your
Observation Homepage. Then, just scroll down to ‘Your Recent Observations’ and click on
the image you want to see.
Well done on completing an
astronomical observing session!