OBSERVING AND WEATHER
Reading weather maps can tell you a lot about what your local conditions
will be. If the jet stream is overhead, you will not be able to expect
good Seeing. Likewise, if the isobars (lines of equal barometric pressure)
are close together, this implies high winds and lots of turbulence. But
if the isobars are far apart, and nowhere near a front, Seeing conditions
can be superb. High pressure centers are noted for clear, dry, air, especially
soon after the passage of a front. Look for the area behind a high pressure
front that has a large distance between isobars, and you may have both
good Seeing and good Transparency.
For the upcoming 48 hours, though, someone has already put this together
for you in an easily-read format. It is called the Clear Sky Clock and
can be found at http://www.cleardarksky.com
Choose your state, and a site near your home, and you will be able to
tell a lot about the upcoming weather as well as get information on the
light pollution at the site, and driving directions on how to get there.
This is a wonderful asset to the amateur astronomer.
There are many things that are too large, or too fast, to be observed
with optical aid. These are best observed with the naked eye. These include:
Aurorae: The outflow of charged particles from the Sun impacting the
magnetic field of the Earth and causing a glow where the magnetic field
contacts the Earth at the poles causes wonderful red and green glows in
the upper atmosphere that we see on the ground as aurorae. When they are
visible, they occupy a large portion of the sky, and are best seen with
Satellites: They move too quickly to be tracked by telescopes. Either
a handheld pair of binoculars, or simply the naked eye, should be used
to watch these man-made objects.
Meteors and meteor showers: Because they are so fast, and can be anywhere
in a large area of the sky, the naked eye is best for these. These are
small pieces of rock and dust that enter the atmosphere at high speeds.
The Milky Way: Nothing beats the naked eye for viewing this at a dark
site. At its best, it appears like clouds broken up by dark lanes and
rifts. The camera may show more, but this is most spectacular to the naked
The Constellations: Our "connect-the-dots" brains have ever come up with
ways to make figures in the stars by connecting the dots in various patterns.
The patterns, though, are too large to be enjoyed any other way than with
the naked eye.
AUGMENTATION OF VISION
Our eyes are the weakest link in the optical chain that allows us to
view objects in the Universe. We have known how, for hundreds of years,
to correct our vision's weakness by using glasses. But daytime vision
is different than nighttime vision. First, the color to which our eye
is most sensitive shifts from the green to the blue as we dark adapt and
begin to use only the rods in our eyes. This is called the Scotopic Shift
and is well documented in the literature. This further reduces our sensitivity
to red light, making red light even more useful at night, but it reduces
the acuity of our eyes from their daylight best. Myopes (near-sighted
people) benefit from having a pair of night glasses with about 0.75 diopters
additional negative correction, while hyperopes (far-sighted people) benefit
from an equivalent increase in positive correction (as do presbyopes,
the older folks who wear reading glasses). Buying a pair of glasses with
this strengthened prescription will usually improve the quality of one's
night vision, where focusing on the sky is concerned. Stars will appear
sharper and smaller. Because of this, fainter stars will be seen and more
stars will appear, making the night sky even more impressive than it already
It should be noted, here, that these glasses are not for driving, or
for looking through the scope¡ªmerely for improved naked-eye observing.
Where the use of glasses in the telescope is concerned, unless you have
more than 2.0 diopters of astigmatism, you are probably better off viewing
without glasses. You can refocus the telescope to compensate for the necessary
correction. This will enable your eye to get closer to the eyepiece, making
it easier to see the whole field of view, and it will eliminate the light
scatter and reflection issues that all glasses have. If you have more
than 2.0 diopters of astigmatism, or are unable to accommodate for somewhat
less, then you have to use glasses at the scope, and you should look for
eyepieces with long eye-relief to provide room for your glasses behind
the eyepiece when you are viewing.
Other ways to augment our night vision:
- never drink alcohol for 6 hours before or during observing. Alcohol,
when metabolized, destroys the chemical that improves our night vision.
- always keep blood sugar levels up. This assures alertness in the brain
and reduces fatigue. Cookies, fruit, or simply some carbohydrates will
work just fine.
- drink coffee or colas to get caffeine if you must. You can't see much
through closed (asleep) eyes.
- always use dark glasses if you are outside during the day. These help
reduce the incidence of cataracts (opaque areas in the lens of the eye)
and brunification (the yellowing of the lens in the eye that occurs
as we age). It's especially important to keep the eyes shielded for
48 hours before an observing session, but it's a good idea any time.
- make sure there's beta-carotene in your diet. There's no evidence
that mega-doses improve vision, but if your diet is deficient in this
vitamin important to vision, a simple vitamin pill with it will assure
you that you get enough. Don't go above 100% of the RDA, though.
- stay warm. Being too cold causes reduction of blood flow in the eye.
- keep your eyes moist. Remember to blink, even when staring for a long
period of time. If you suffer from dry eyes, an eye drop may help. Use
the tear-replacement type only. The other types take too long for the
eye to clear after using.