Seeing - backyard vs country

Just wondering what others' opinions are. Do you find seeing conditions
improve significantly when observing at a more remote location? I'm not
referring to light pollution but image quality on planets for example.

Thanks,
Dan

Dan:
Just wondering what others' opinions are. Do you find seeing conditions
improve significantly when observing at a more remote location? I'm not
referring to light pollution but image quality on planets for example.

Not so much with planets. I have observed the moon and planets with my
Questar from Bangkok (very good, with still, humid air, albeit
gray-yellow with pollution), Cairo (so-so, with dry air and dust), and
other large cities, and gotten very acceptable results. The bright and
well defined star clusters such as M45 and many globulars are also
reasonable urban targets.

It's in observing the dim, diffuse deep-sky objects--galaxies and
nebulae--that the difference is seen. And light pollution (and air
pollution to scatter the light and reduce sky contrast) /are/ the
issues in urban areas in my experience.

Davoud

--
usenet *at* davidillig dawt com

Hi Dan,

Seeing or the total effect on image quality due to optically significant
turbulence from the ground up has usually emphasized the upper layers
like the jet stream. If all the seeing was up there then the backyard /
country effect would be small.

Seeing is due to the temperature gradients that translate to speed of
light gradients that are driven by the wind. It would be like changing
your mirror figure with the wind.

It seems that most seeing is near the ground layer so the details of the
lower atmosphere is important. At one site we measured 0.5 or so arc
second seeing, quite good, and find that 80% or more is near the ground.

Think of air as water and at night the radiation of the ground to space
cools the ground below the temperature of the air. This in turn cools
the air near the ground. The details are important as a slope over 0.5
degrees or so will cause the denser air to flow (drainage flow) like a
river.

City structures interact with the flow of air elevating the boundary
layer where mixing takes place.

People,telescopes,buildings,hills, mountains, continents all contribute
to the modification of air flow and temperature structure and thus
effect the propagation of light.

In the back yard environment I have measured cooling of the night air by
the roof of a house or the heating if it is cold any they have the heat
on. The driveway if paved can also be in the beginning of the night
hotter than the night time air and a source of seeing. Height is every
thing as the layer near the ground is the most intense and grows with
time. Every foot of elevation helps in some location and others you need
to be 100's of feet above the ground to get a good improvement.

Getting away from complex structures helps make the air have a smoother
temperature structure (isothermal--same temperature) and thats why
observers find better seeing next to the ocean and on mountain peaks.

Another interesting effect is the time when the heating of the day is
balanced with the cooling of the night and the temperature gradient with
height in the lower layers disappears for a few minutes. This happens
near sunset and sun rise and has been used by solar and planet observers
to obtain higher resolution.

Finally the telescope structure can produce "tube seeing" if it is not
isothermal with the air.

Dan


Dan wrote:
Just wondering what others' opinions are. Do you find seeing conditions
improve significantly when observing at a more remote location? I'm not
referring to light pollution but image quality on planets for example.

Thanks,
Dan

I'm living in the countryside surrounded by fields with only thinly
scattered houses and farms. The seeing is usually awful regardless of
time of year or crop or snow cover. Only rarely does it settle down.

Moving around my available area to avoid observing over the top of the
house or over hedges or trees has made no obvious difference to my
seeing at all.

I even drove a few miles down to a south-facing seashore to check the
seeing there. Again no difference in seeing from back at home
immediately before or after the trip.

Over the years I have discovered that anything below 35-40 degrees
altitude is nearly always hiding behind a seeing "brick wall" and
hardly worth looking at.

There is no tarmac locally.

My home site does at least have very dark skies. (in winter) Though I
always prefer lunar and planetary observing if there's anything up
there to look at.

Chris.B

Chris,

What kind of scope do you have ?
What is the best seeing you have observed and what is typical ?

d.

Chris.B wrote:
I'm living in the countryside surrounded by fields with only thinly
scattered houses and farms. The seeing is usually awful regardless of
time of year or crop or snow cover. Only rarely does it settle down.

Moving around my available area to avoid observing over the top of the
house or over hedges or trees has made no obvious difference to my
seeing at all.

I even drove a few miles down to a south-facing seashore to check the
seeing there. Again no difference in seeing from back at home
immediately before or after the trip.

Over the years I have discovered that anything below 35-40 degrees
altitude is nearly always hiding behind a seeing "brick wall" and
hardly worth looking at.

There is no tarmac locally.

My home site does at least have very dark skies. (in winter) Though I
always prefer lunar and planetary observing if there's anything up
there to look at.

Chris.B

I have various achromatic refractors. Most used is a Celestron CR150HD
6" f/8 on a massive old Fullerscopes mounting. My smaller Vixen 90/11
only gets used when an object is hidden from the 6". (the latter can't
easily be moved)

It is rare that I can use much more than about 120x on the planets.
Which is my favorite power by force of seeing conditions. 150x is
occasionaly possible.

The best seeing was one night in mid winter with shallow snow cover.
When I convinced myself that I could see detail on Saturn at 120x that
defied explanation. I was limited to that low power at the time by an
aging eyepiece collection more suited to my old (entirely home-made) 5"
f/15. Having now obtained a range of higher powers and a Barlow I
haven't had remotely similar conditions since that night. I remember "a
discussion" at the time with David Knisely about a certain Saturn ring
division (Encke) that is not supposed to be visible at such low power
in a 6". But which was seen perfectly clearly as a razor-thin line. I
can usually see all the regular details (Cassini, shadow on the belts,
polar shading etc) on Saturn at 45x though I make no claims for great
visual accuity. :-)

The moon will occasionally take much higher magnifications. I have used
240x on Plato with the 6". Only rarely are craterlets visible because
of the visible thermal agitation. But sometimes a transparent ripple
will slowly creep across the Moon and the detail will literally jump
out at me.

I had similarly poor seeing conditions in the UK on the west coast
despite being rural and much nearer the sea. I'm presently living in
rural Denmark.

I now add digital "snaps" to my usually-fruitless visual observations
of the planets and Moon. One day stacking software may allow my snaps
to become worth sharing. But small camera rotations between exposures
makes it impossible to stack at the moment. The handheld camera
captures almost exactly what I can see visually.

Regards
Chris.B

Here's my old Fullerscopes website. NOw long overdue for an update.

http://mysite.wanadoo-members.co.uk/...k4/index.jhtml

"Dan" wrote in message news
Just wondering what others' opinions are. Do you find seeing conditions
improve significantly when observing at a more remote location? I'm not
referring to light pollution but image quality on planets for example.

I have not found this and have often found the opposite depending
on your location. My consistently best seeing experience was from
the patio of a sixth floor apartment in the Soundview area of the
Bronx in the 1970s. Near 11PM my view of planets and the moon would
improve dramatically apparently due to the uniform cooling of the NYC
heat dome and sea breezes off of the LI Sound/East River. I now live
in a town south of Boston and lunar/planetary seeing is usually
mediocre.

--

Hilton Evans
---------------------------------------------------------------
Lon -71° 04' 35.3"
Lat +42° 11' 06.7"
---------------------------------------------------------------
Webcam Astroimaging
http://home.earthlink.net/~hiltoneva...troimaging.htm
---------------------------------------------------------------
ChemPen Chemical Structure Software
http://www.chempensoftware.com

"Dan" wrote in message
news
Just wondering what others' opinions are. Do you find seeing conditions
improve significantly when observing at a more remote location? I'm not
referring to light pollution but image quality on planets for example.

Thanks,
Dan



In terms of seeing conditions, absolutely. I don't know how you can
separate out the light pollution factor, though, at least not at my home
site. I live directly across from I480, five miles from Cleveland-Hopkins
airport, and have about 8 billion trees around my immediate home, all
obscuring about 20 degrees of the sky, making observing low-to-the horizon
objects all but impossible. For me, moonrise, Marsrise, et al are all about
two hours later than their actual appearance. I can only see the very
brightest objects.

When I go to a remote location, the skies are much darker, there's more
that's apparent even to my naked eye, the horizon isn't obscured by trees
(at least not much), and I can see things like M4, which are invisible at
home. And no neighbors turning on useless backyard and frontyard lights
that screw with what little dark adaptation I've got at home.

I think every location has its pluses and minuses and it is quite
difficult to generalize "seeing" by whether it is rural or urban.

My backyard is in San Diego and about 4 miles from the ocean. It is
most often relatively calm and the astmosphere is stable with a lack of
high winds. If the target is quite high so that it is free from the
effects the trees and building then I will commonly have quite decent
views. Even when low on the horizon, first clearing the trees, the
double-double will cleanly split at under 100x. Most often I get a
clean separation at 67x. However sometimes there is an easterly wind
known as a Santa Ana condition, this means seeing will be bad.

Going to the country, I have two sites, one on the west side of the
mountains, one on the east. In general the one on the west side is not
as dark but seems to consistently have better seeing.

I think I am pretty lucky compared to many folks because the seeing is
quite decent most of the time and reasonably dark skies within less
than an hours drive.

jon

I think every location has its pluses and minuses and it is quite
difficult to generalize "seeing" by whether it is rural or urban.

My backyard is in San Diego and about 4 miles from the ocean. It is
most often relatively calm and the astmosphere is stable with a lack of
high winds. If the target is quite high so that it is free from the
effects the trees and building then I will commonly have quite decent
views. Even when low on the horizon, first clearing the trees, the
double-double will cleanly split at under 100x. Most often I get a
clean separation at 67x. However sometimes there is an easterly wind
known as a Santa Ana condition, this means seeing will be bad.

Going to the country, I have two sites, one on the west side of the
mountains, one on the east. In general the one on the west side is not
as dark but seems to consistently have better seeing.

I think I am pretty lucky compared to many folks because the seeing is
quite decent most of the time and reasonably dark skies within less
than an hours drive.

jon