Donors &
Southern Colorado Astronomical Society
Southern Colorado Astronomical Society
We've put together this page to help our visitors and guests when attending a Southern you
should know, and yes even proper etiquette to follow.  We want for you to experience the
best possible time with us, looking at the stars is surprisingly a little more involved than
We've put together this page to help our visitors and guests when attending a Southern
simply looking at the stars.  Armed with a little foreknowledge will make your time with us a
wonderful experience.

Answer: The short answer is that it helps to preserve your night adapted vision…not really
said let’s do take a closer look at why astronomers use red lighting when conducting night

The eye is such a wonderful part of your body, it allows you to see your world in full color,
track motion, detect distances.  In the presence of bright light your iris becomes narrow,
basically limiting the amount of light entering your eye and thus striking your retina.  In the
dark your iris opens wide to allow as much light as possible into your eye.  That part of the
process is nearly immediate.  For astronomers and star gazers alike it is important that
first their eyes allow as much light as possible to get to the retina so they can see the dim
stars and objects above.  Think of when you have had an eye examination, when the
optometrist shines their pen light into your eye, your iris narrows quickly to reduce the
amount of light striking the retina.  That’s were the second part of the process takes place,
and this is a slower process.  

Cones and Rods.  The retina is comprised of 2 very important types of cells with regard to
your night vision, cones and rods.  Cones are that which allow you to see in full color and
respond best in lit environments, rods on the other hand perform best in very low light
conditions giving you night adaptive vision.  Cones are clustered towards the center of the
retina while rods are loosely gathered away from the center of the retina.  Cones “see” or
process color while rods do not.  Thinking about the location of your cones and rods
consider this, your eye doctor shines the little white light into your eye and your iris narrows,
this limits the area of exposure on the back of the retina to only the area of cones.  When
the light is removed your iris starts to open allowing light to strike a larger surface area on
the retina and depending on how light the examination room is bringing your rods into
play.  Okay so you are now outside to do some star gazing, it’s dark and your iris has
opened about as wide as it is going to get, your rods are being brought into play now.  
Remember rods do not process or “see” color, they do however register the quantity or
intensity of light getting into your eye.  In an environment where there is a lack of light your
rods become active or excited, again this is a slow process, taking anywhere from 15
minutes to ½ hour for them to reach their maximum potential for receiving light.

Your rods respond differently to different color light.  Wait a minute, I thought you said rods
do not process color?! Yes that is true, rods only “see” in shades of gray.  Rods do however
process intensity of light and wavelength of light but do not pass along the color
information to your brain. Whoa!  That’s deep.  Light is frequency which means it has a
wavelength.  In the case of red that wavelength is around 700 nm (nanometers).  This
wavelength has the least amount of effect on the rods in your eyes.  You do see the red
light however, that is because your cones are still working, your cones see red, your rods
detect the amount of light helping to form the overall picture.  Because your rods are  blind
to the color red this allows your rods to remain active, any other color will over stimulate
your rods, causing your eyes to covert back to using the cones for your primary vision.  
Achieving that balance is the goal.  As mentioned above it takes anywhere from 15 to 30
minutes for your eyes to adjust to the dark environment.  During this adjustment time if you
see bright light this causes the process to start all over again.

So why do astronomers and star gazers use red light, this allows their eyes to be as
sensitive as they can possibly get, the red light does not affect their night adapted vision.

Question:  I’ve seen some star gazers using a green light, is it the same as using a red

No actually.  Remember the rods in your eyes cannot detect or see the red light wavelength
which is about 700 nm.  Green on the other hand is at a wavelength of 530 nm, meaning
yes green will affect your night adaptive vision.  The trick here is to not view any bright light
sources what so ever while you are allowing your eyes to adjust and of course once they
have made the adjustment.  If a bright light is shined at you close your eyes quickly to
reduce the amount of adjustment time your eyes will need to go through.

In the end we at SCAS Pueblo want you to have the best viewing experience possible when
you’re at one of our star gazing events.  It’s going to be dark so do bring a flashlight along
with you however once you arrive at the event site please turn off your regular flashlight and
give yourself a little time to allow your eyes to adjust to the darkness.  You’ll be surprised
how after even 10 minutes of adjustment how well you can see. And don’t worry, we’ll have
red flashlights there so you will know right where we are at.  We are looking forward to
seeing you at one of our events.
Laser pointers at SCAS Pueblo events

What exactly does Laser mean?
 Light Amplification by the Stimulated Emission of ordinary
light bulb. Many lasers deliver light in an almost-perfectly parallel beam (collimated) that is
very pure, approaching a single wavelength. Laser light can be focused down to a tiny spot as
So to address the topic, if you have a laser pointer that you wish to use at a SCAS Pueblo
event, please by all means go right ahead.  Many of our members have laser points that we
use to help us point out targets in the night sky, very useful when trying to point to a star or
area to a group of people.  We do however have a few rules regarding laser usage.

Never Point a laser at another person.  While most lasers are of a low power class, not
capable of burning it’s not a chance we wish anyone to take.

Never Point a laser at a telescope.  This is a very scary situation.  Remember our telescopes
are nothing more than big photon buckets, light collectors with a powerful lens, or magnifier at
the end, at this point even low wattage laser beams can permanently damage the eye of
someone looking through a telescope should a laser beam be aimed at or sweep across the
front glass of the telescope.

Never Point a laser beam at an aircraft.  While this may seem harmless consider that there is
a change your laser beam could hit a reflective surface on the aircraft and bounce that beam
into the eyes of a passenger or the pilot. Sure the chances are slim of this happening but
there is still a chance, why run the risk of hurting someone.

Color of laser.  We are okay with any color laser you bring, red, green, violet, or blue.

If anyone is conducting astroimagery at that event please do not shine your laser pointer into
the sky as this will ruin the imagery.

Remember we are here to enjoy the night sky not a laser show so use your laser only when
needed.  The beam of light as it is pointed up to the night sky can be seen by anyone looking
through their telescope, be courteous of your fellow star gazer.

We do this because we want people to learn about the night sky, and
because we enjoy the opportunity to show the wonders of the Universe
payment enough for us.

Allow your night vision to work.  We have 2 different types of viewing
events, one where we are set up inside of the city where the lights are
bright, the other is under dark skies.  When we are set up under bright
lighting conditions allowing your night vision to come in is not critical as
it is probably not going to happen.  We conduct events under the bright
lights of the city to encourage people to try astronomy, to become
energized by the sights found in a telescope.  Under dark sky conditions
you really begin to see the wonders above.  This is when it becomes
important to allow your night vision to develop.  Night vision typically
reaches its maximum effectiveness after ½ hour of being in the dark
however as a general rule even after 15 minutes your night vision has
already begun working and you will find star gazing much more
pleasurable.  We would recommend that should you plan on attending a
Dark Sky event arrive 15 to 30 minutes early to allow your eyes to adjust,
you will get so much more from the experience.

It’s dark and naturally your vision has been reduced.  We do select
locations that are safe and free from hazards however the one hazard
we cannot eliminate is the legs of tripods of which our telescopes are
mounted to.  When you approach a telescope take a moment to become
aware of the location of its legs and anything else in the immediate area
the owner of the telescope might have set up to support star gazing.

Try not to touch the body of the telescope.  When viewing distant planets,
stars, or other objects making contact with the telescope will cause
vibration.  This in turn will distort the view in eye piece until the telescope
stops moving.  When looking through the eye piece it is natural to want
to grab the lens, especially when it is dark as this helps you to judge the
distance from your eye to the eye piece.  This will cause vibration in the
telescope and obscuring your view.  Once you have placed your eye to
the lens try moving closer and farther away from it to bring the image
into view.  You may need to focus the telescope, simply ask the owner
how that is done, they will be more than willing to show you how their
telescope operates.  Remember you are looking at objects that are
millions of miles away, disturbing the rest of the scope, even in the
slightest, will cause the object to shake in the eye piece.

During those warm summer months we do have visitors that show up
with no intension of looking through a telescope, typically they fly in and
become a general pest, yup, bugs.  We would recommend you spray
yourself with some kind of insect repellent or bring a personal repellent
device that clips to your belt.  When you're trying to enjoy the night sky it's
extremely bothersome to fight off mosquitoes.

event is to look through a telescope however we do want you to
understand something about the object you are looking at.  Ask us what
it is you are looking at, how far away is it, does it have a name, or any
other question you might think of.  Looking is only part of the event,
understanding what you are looking at rounds out the experience.

Pack out your trash.  If you bring snacks, bottled water, or anything else
that generates trash please take the empty wrappers and containers
with you.  We like to leave the area we are viewing in just as we found it,
clean.  As we try to select locations that benefit everyone we want to
ensure the owner of the proper is please with us, leaving trash about
discourages a return visit so help us to keep our events going by taking
your trash with you.

daytime.  For the most part you would be correct except when we want to look at
the star closest to us, the Sun.  It is very important that you understand when we
are looking at our Sun our telescopes are equipped with some highly specialized
filters.  These filters allow us to point our telescopes directly at the Sun without
worry or fear of damaging our eyes.  These filters block 99.9% of the energy being
emitted by the Sun.  Without these filters looking through our telescopes would
blind you in a fraction of a second, so this becomes a “DO NOT try this at Home”