3.2i
plan the equipment needed for a naked-eye observation session
(red torch, clipboard, pencil/rubber, warm clothes)
3.2j
demonstrate an awareness of naked-eye observing techniques
(dark-adapted eye, ‘relaxed’ eye and averted vision)
The single factor that puts people off Astronomy the most when they are invited out
of a warm home on a cold winter night to look at some astronomical object is the
cold. Wrapping up warm is important as Astronomy sessions may last a long time.
Even in the summer, night temperatures can drop and it pays to wear warm clothing.
As well as coat and gloves, a hat is important and an extra pair of socks helps to
keep your feet warm.
When a telescope is set up ready for use, it may take about 20 minutes before it has
cooled to the temperature of the surroundings. Waiting this length of time helps to
stop ‘wobble’ in the air around the telescope caused by different temperatures of air
and telescope. Images through the telescope will be steadier as a result.
A pair of binoculars is useful to have with you, even if you are using a telescope.
Sometimes it is quicker to scan a wider region of the night sky and locate an object
with binoculars. Once found, the telescope can be pointed in the right direction.
Recording what you see is a good reminder of what has been viewed over the years.
In order to do this, you need to be able to write down details and times as you go
through an observation session. If a white light is switched on, your night vision is
lost immediately. A red torch is very important as this can be switched on and your
night vision is not affected. There will then be enough light for you to record details
and also to draw diagrams. Nights can get quite damp and so a map cover or other
type of plastic cover for paper and clipboard is useful to have. Biros and ink pens
will not function in the damp conditions, so a sharp pencil – or better still a
propelling pencil (a new lead can be quickly clicked into place) should be available.
A rubber to correct mistakes is helpful to have.
Long sessions outside are more comfortable with a garden chair – or a recliner if you
are looking for ‘shooting stars’. The back of the chair can be a helpful support for
binoculars if a tripod is not available. A small table is also useful to put equipment
on.
One of the most difficult objects that I have viewed is Pluto. Viewing conditions had
to be perfect – dark skies (no light pollution or Moon shining). A crisp, clear night
with no haze above was also important. I was using my 10” Newtonian reflector
(below 8” size would not gather enough light to see Pluto). Having checked accurate
star charts, so that I knew where to hunt for the dwarf planet, all this would have
been a waste of time if I had not prepared my eyes and used a few ‘tricks of the
trade’.
Dark-adapted eyes are able to detect much fainter night sky objects. Allow 20
minutes before you attempt to look for fainter objects. Placing your hands over your
eyes whilst your eyes are open ‘relaxes’ the eyes and if left for 30 seconds can help
speed up the ability of your eyes to see objects. When looking through the eyepiece
of a telescope, try not to squeeze your other eye shut. A ‘relaxed’ eye covered by a
hand but still open beneath aids your viewing eye.
Once the stars had been located where Pluto was to be found, I looked straight down
the eyepiece to see the dwarf planet. The high magnitude of the object put it at the
very limit of viewing. I knew that the dwarf planet should be in the centre of the
view. Then I was told by a friend to look slightly to the side of where the dwarf
planet should be. By looking directly at Pluto, I was allowing the light from Pluto to
fall on the cones of my retina – the colour sensing receptors. These need a brighter
light to function and so they did not detect Pluto. By using averted vision, looking
slightly to one side of the object, light from Pluto was now falling on to the rods in
my retina. These are for black and white vision and are much more sensitive when
low light intensity is involved. Almost immediately I detected a hazy object – Pluto.
Trying to look slightly to one side of where you want to find an object is a little
difficult to get used to. Your brain tries to take over and make your eyes look
directly at the object. As you practice averted vision more often, this technique
becomes more straightforward.
My record of the night viewing when Pluto was seen – the heading relates to
the fact that Pluto was still one of the planets in the Solar System at the
time and having viewed Pluto, it meant that I had seen all 9 planets at that time.