Activity 5 Under the Milky Way
- Activities 1 to 4 in this strand developed the skills
needed for stargazing. In this Activity you go stargazing
and put those skills to work.
Specific Learning Outcomes
- You will experience the night sky on a clear night, and
be able to identify the brightest stars and constellations
for yourself. Depending on light conditions, you will also
see the Milky Way.
- When you are planning a stargazing session, you should
consider the following factors.
Sunset Time and Season
Planets and Satellites
Binoculars and Telescopes
- Each of these factors is
discussed in detail under its own heading, below.
- Activities 1 to 4 in this strand cover
direction-finding as well as Star Wheel making. It is best
to work through these before trying a serious stargazing
session. All stargazers at a session should have their own
Star Wheel and know how to use it.
- Beginners should start with the City Wheel even at a
dark sky location where the Milky Way is clearly visible.
This is because the City Wheel is simplified and is by far
the easiest way to get started using a Star Wheel. But make
sure you have copies of the Milky Way Wheel available to
answer the inevitable question: What star is
- The human eye has two types of light receptors: rods
and cones. The cones are specialised for colour vision
while the rods are specialised for faint light. The rods
cannot even detect colour, but they can see much fainter
light. This is why things look black-and-white by moonlight
there is not enough light for colour vision.
- The light from very bright stars is just bright enough
for colour vision. That is why some bright stars look red,
orange or blue. Most stars, however, are too dim for colour
vision. We see them with our rods only, and they appear
- Over a period of 20 minutes in the dark, the rods
become more and more sensitive to dim light. This is called
dark adaptation. It means that after about 20 minutes of
stargazing you can usually see a lot more stars than you
could when you started.
- As soon as you look at a bright light this extra
sensitivity goes away. It takes another 20 minutes for it
to come back. This means you do not want to flash a torch
around when you are stargazing, but you do want to see your
Star Wheel. The solution is quite simple.
- Rods have a low sensitivity to red light. You can use a
dim red light without losing your dark adaptation. You can
look at you Star Wheel with a dim red light, and still see
the faintest stars when you look up at the sky.
- Making a red torch is simple. Attach a sheet of red
paper or cellophane to your torch with a rubber band. Use
as many layers as needed to make the light dim. You should
be only just able to read by it. One or two layers of red
paper is often enough, but with red cellophane you might
need four or more layers.
- If you are stargazing in the city surrounded by
streetlights then a red torch is not much use the
streetlights will prevent you from dark adapting anyway.
But even in the city it is worth making the effort to find
a stargazing place where you are shaded from streetlights
and house lights. This will allow your eyes to dark adapt
and you will be surprised how much more you can see. If you
find such a spot you will definitely benefit from using a
- If you are away from city lights altogether then a red
torch is essential equipment.
- If you are taking a group
of students you should
facilitate a discussion of dark adaptation and get them to
make their own red torches.
- During the day the sun lights up the sky. The sky glows
blue and overwhelms the other stars, which are all fainter
than the blue of the sky.
- At night streetlights light up the sky. The sky glows
white and this overwhelms the fainter stars and the Milky
Way. Only the brighter stars shine through. This effect is
called light pollution.
- Unlike the sun, streetlights do not illuminate the
entire atmosphere. Their effect is limited to a dome-shaped
region of air over each city. If you are in the city you
see less stars and often cannot see the Milky Way at all.
If you are out of the city, look back and you will see the
effects of the streetlights as a dim white dome hovering
over the city. This is called a light dome. Apart from the
light dome, the rest of the sky will be almost totally dark
and the number of stars visible will take your breath
- Oddly enough, a dark sky does not always look any
blacker than a light polluted sky. The difference with a
dark sky is that you can see the Milky Way with exquisite
clarity, and you can see thousands of faint stars.
- How far do you have to get away before you can see a
truly dark sky? That depends on atmospheric conditions, but
you should notice a significant improvement in the sky by
the time you are about five to ten miles (eight to fifteen
kilometres) away from the edge of the city. By the time you
are 20 miles (30 kilometres) away you should be able to
look back and see the light dome. This is a sign that you
are reasonably clear of the light dome the Milky Way
will look fantastic at this distance.
- Although it is best to start stargazing in the city,
consider making a trip to a dark skies location if you
- You could also lobby your local city authorities to
take steps to reduce light pollution in your city. See the
Skies Association web site for more information about
- Moonlight lights up the sky at night, and if it is
bright enough it has a similar effect to light pollution
it stops you seeing the Milky Way and the faint
stars. If you are planning a dark-sky session and hoping to
see the Milky Way at its best, you need to go between last
quarter and first quarter a week either side of new
Check phases of the moon here.
- When selecting a star gazing site the ideal is to have
a low horizon (no mountains or tall buildings) in all
directions. On the top of a hill is often good for this.
Unfortunately it is not always possible to find such an
ideal site. Look at your Star Wheel to see which part of
the sky contains the most interesting stars on the night
you plan to go stargazing. Try to have a low horizon in at
least that direction.
- When assessing different sites you can visit them in
daylight to look at the horizon.
Sunset Time and Season
- If you live at latitude 45 or above you will find that
it does not get properly dark until maybe 11pm in the
summer. This may make it impractical to organise a group
stargazing trip, especially for children.
- In the winter you will find it is dark early enough,
but is bitterly cold for stargazing.
- In these latitudes the best time for stargazing is
likely to be in spring before daylight saving has started
and autumn (fall) after daylight saving has finished.
- Of course, you can stargaze all year round.
sunset times here. The brightest stars appear about 30
minutes after sunset, and it is usually sufficiently dark
about one hour after sunset.
- In some parts of the world you cannot guarantee a clear
sky when you plan a stargazing session. How you manage this
factor depends on your local climate. How many clear nights
do you usually have?
- In Dunedin, NZ, perfectly clear skies are comparatively
rare. We get a lot of coastal cloud. If I want to plan a
guaranteed clear dark-sky session I plan at least 16
postponement nights. I select only nights with the moon
below the horizon during the stargazing session. I postpone
the session at 9am in the morning unless the sky is
perfectly clear at the stargazing place, and the forecast
is for clear skies until at least noon the following day.
Details of postponements are posted on the Internet so that
all participants can check them during the day. If the sky
and forecast are both still okay at sunset, then we travel
for one hour by bus to get away from the Dunedin light
dome. (Dunedin has a population of 100,000. Travel times
may be longer from larger cities.) The result is a
guaranteed jaw-dropping spectacle. Given the Dunedin
microclimate, I can only be sure of delivering this
wonderful experience by making these elaborate
- I hope you are blessed with a climate that delivers
more clear nights so that your stargazing arrangements can
be simpler. Depending on your climate, it may be just a
matter of choosing a time of year when clear skies
- When you are stargazing, you do not move around very
much. Unless conditions are genuinely tropical, you must
make sure that all stargazers are well wrapped up in warm
clothes. The need for gloves, hats, jackets, several pairs
of trousers, and very warm socks cannot be
Planets and Satellites
- In Activity 6 Planet Hit List
you will learn how to predict
which planets will be visible. It is valuable to
know where the bright planets will be, and which of them
will be visible during your stargazing session.
- Just after dark is the best time for spotting
satellites. It is a good idea to visit
Heavens Above and
find out which (if any) of the high-interest satellites
like the International Space Station will be passing
overhead during your stargazing session.
Binoculars and Telescopes
- If you are organising a stargazing session for a group
it is desirable to have as many pairs of binoculars
available as possible. Some of the best targets for
binoculars are described in
Activity 8 Jewels of the Sky.
- If you have a telescope available, all the better,
provided you have an experienced operator. With one or two
telescopes a stargazing session can easily consist of
standing in a queue most of the night. The solution to this
is to turn queuing into an educational experience. Get
those in the queue to locate stars and constellations with
their Star Wheels. You can also pass a pair of binoculars
up and down the queue.
What You Need
- Working from the City Wheel, make a list of all the
stars and constellations that will be visible during your
stargazing session. You might also include some targets
from the Milky Way Wheel, or, if you have binoculars
available, some targets from Activity
8 Jewels of the Sky.
- Make this list into a kind of scavenger hunt as a way
of keeping students focussed. You can also get students to
work in pairs and sign one another off when they have
demonstrated that they have found the target.
- A sketching activity is a useful challenge that helps
develop the skill of making drawings from observations.
Give students extra copies of the City Wheel and get them
to sketch the Milky Way on it, or some of the
constellations that are not already shown on it.
- Every stargazing session is different so we cannot give
specific instructions. If you have considered all of the
above factors, then you are on your way to having a
successful stargazing session.
- Wishing you Clear skies!
Publication date 30 Nov 2002
Copyright © C J Hilder, 2002. All rights reserved.