Birmingham is the UK's second largest city, with
an immediate population of over one million, and a catchment area of
some 7 million people. Observing from this massive metropolitan area
can be difficult, with it being impossible to escape the localised and
general light pollution present. Even driving into the country doesn't
help, as the glows from the massive industrial area of the Midlands are
always present on the horizon.
The images shown here reveal just how bad light pollution in Birmingham and the
surrounding area is, and the problems experienced with localised light pollution
caused by street and security lighting.
In this section - Birmingham's Night Sky - Coping with Light Pollution
- Seeing Faint (Drift method & Averted Vision)
This is Birmingham at night - or at least the part which
is 3 miles east of my home. The city centre, which lies just 5 miles
to the south of my location, produces far more light pollution than this
A view of Birmingham from the South of the city. This
photograph was taken some 12 miles distant at the Clent Hills, a
"darkish" site where I have made many Meteor watches
over the years. This short exposure was made under very transparent
skies, with no haze present!
This is the view of the street-lighting in my road,
and directly outside my house. These Sodium lights replaced old fashioned
Mercury lamps in 2003. The road is now well illuminated after dark-
as is the night sky!
This image taken from my back garden shows the problem I have with local
light pollution. Each light is on a passive IR sensor, and remain on for
several minutes when activated. The two lights in the foreground present
the biggest problem, as they shine directly into my garden. Both remain on
for 5 minutes each time they become activated, whereas the others stay on
for around three minutes. Although my observatory protects me to a certain
degree from the direct glare of these lights, the sky becomes saturated with
stray light whenever they are triggered. This is the view looking North.
Houses to the South are similarly equipped, as are the houses to the East.
To the West is street lighting as shown in the images above.
The best way to illustrate the problems that light pollution cause to the visual
observer is through photographs of the night sky. These two images were taken
in September 2005. Left we see Mars near to the Pleiades, whilst right is Orion
rising in the South Eastern sky. Both images were taken with a digital camera
set at ISO 200, and 10 seconds unguided exposure. The sky was very transparent
on the night, with no haze present at all. You can just make out the tree being
illuminated from a security light on the left. The orange sky is from general
light pollution of the
The vast majority of us who want to enjoy and observe
the night sky have to do so from area's where there is light pollution to
various degrees of severity. You should not let this discourage you from
going outside with a telescope or binoculars and making those observations.
There is very little we can do about the problem if we live in a town
or city, so learn to live with it and try to adapt to your local conditions.
Never make light pollution an excuse for not observing!
It is possible to do certain things which will help
you see those faint variables (or tricky nebulae if the Deep Sky is your
thing) visually from even the brightest of skies. It is absolutely
untrue to say that visual observations of faint stars cannot be carried out
in light polluted skies - as I hope the light curves within these
pages will show! Here are a few ideas which I have employed to
help me observe from bright skies for over forty years...
To counteract the problem of security lighting, bedroom
lights etc. shining directly into the observatory, I have placed matt black
screening in strategic positions around the garden. Although this does
little in preventing the light from polluting the sky, it does help to keep
the observatory and observer reasonably dark. These are very simple
timber constructions which have lasted for many years, and require very little
Occasionally stray light will still get to you, despite
the precautions you take. This is especially true if you use a
moderate/large reflector and have to stand on a ladder to get to the eyepiece,
placing your line of vision above that of your screens. A good tip
is to add a screen to your telescope (left).
This is a piece of heavy duty black card (purchased
from any art & craft shop) attached to the side of the telescope with
velcro pads opposite the eyepiece. It does not need to go completely
around the telescope. It stops stray light from entering the draw
tube hole (which brightens the field when viewed through the eyepiece) and
protects the observer's eye whilst observing. It also allows the observer
to get closer to the Moon to observe, without Moonlight falling into the
light path reflected from the secondary. The velcro pads allow the
shield to be easily removed in windy conditions. It's light in weight,
and won't cause balancing problems if you use a Dobsonian. Very cheap
and very effective!
One final solution is to use an observing hood. This
goes over the head of the observer as well as
over the eyepiece, thus keeping out all stray light. It does cause
problems in the winter, as it tends to cause the eyepiece to dew up very
easily. You can buy these from various astro-suppliers for silly money,
but why bother? Use a black bin-liner (or two if they are very thin
like Birmingham City Council provide). They work just as well, and
cost next to nothing. Be prepared for some strange looks if your
neighbour looks out of the window and spies you wearing a black bin bag on
your head, and always remember that your wearing it if you have surprise
visitors. It can be embarrassing!
It never ceases to amaze me that some people spend several thousand pounds on a
telescope, and a very small fraction of that cost on an eyepiece. A good
eyepiece will make an average telescope perform well, but a poor quality
eyepiece will surely make a good (and expensive) telescope perform badly.
Good quality eyepieces are expensive, but you
only need to buy them once! Give lots of thought to the eyepieces you
are going to buy. You only get what you pay for!
Apart from protecting ourselves from stray light and
treating our telescopes like a much loved pet
, what can we do as an observer
to help in seeing faint objects in bright urban skies? Well there are
two methods which I use (and many others use too I should add) that I can
absolutely recommend in trying to capture every photon of light collected
by the telescope. The drift
method, and averted vision.
The eye is very sensitive to movement. Place the object (or where you think
the object is if it's invisible) on the eastern side of the eyepiece field,
switch off the drive and let the stars drift slowly. Whilst staring at the
centre of the field, the object under observation will become visible as it
reaches this central point. It will be obvious that this method employs the
use of averted vision (see below) as well as the movement of the star in
helping to detect faint objects. With practice you will be able to make
estimates of very faint stars using this method, but remember that you must
always note it as a glimpse if you only see it for a second or two. Gently
tapping the side of the telescope can also help in detecting faint objects.
As the telescope dampens the shake, the eye can and will pick up faint -
previously unseen - stars. Practice, practice, practice..
As astronomers we know that by glancing to the side
of an object and letting photons fall on the more sensitive parts of our
eye, we can see things that are not normally visible. This is termed
'Averted Vision', as the most optically sensitive part of the retina is off
set from the centre of the eye. By allowing light to fall upon these sensitive
area's, we improve our chances of seeing faint stars, structure in Nebulae
and fine Planetary detail. However merely averting the eye away from the
object under observation is not enough. There is a right and wrong
way to use averted vision. The retina has two well defined area's which
we will call for arguments sake the sweet spot and blind spot. To use
averted vision correctly, the light from the object under observation must
fall upon the sweet spot of the retina. For right eyed observers, this
means averting the eye to the right and slightly upwards - left eyed observers
would do the opposite - so that the object lies to the nose side of vision.
Obviously we are all different in our physiological makeup, so you
will have to decide just how far to the left or right & upwards you need
to avert your eyes to get maximum effect. The drawing to the right shows a
general area where this should fall, but all it takes is practice to find
your best averted
The blind spot of the eye refers to the area where
the optic nerve actually connects to the retina.
This lies opposite the sweet spot, so that a
right eyed observer who averts his eye to the left will actually see less
than if averted vision was not used at all! It therefore becomes obvious
that a casual gaze around an eyepiece field with your eye in search of something
faint is counterproductive and will only result in frustration!
What about the use of binoculars or binocular viewers?
It seems that by using two eyes averted vision cannot be used at all,
as both sweet spot & blind spot will be used at the same time. Well
the trick is to simply look upwards. This allows the light to fall
on a slightly less sensitive part of the retina, but miss the blind spot
of both eyes completely. The benefits of using both eyes to observe
will far outweigh the disadvantage of finding the perfect averted sweet spot
to make your observation.
As a final word on this subject I can only repeat that for
those of us who live in a city environment Light Pollution will not go away.
Never let a bright sky, street lamp or a security light stop you from
observing the heavens - and never let anyone tell you that casual or serious
observing can't be done from an urban location. Don't take their word
for it. Go out and look for yourselves...