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# How High a Fence?

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### #1 Ennis

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Posted 17 March 2013 - 11:59 PM

I am probably going to have a house built for me later this year. Unfortunately, about a half-mile from the lot I'm considering is a high school, complete with a stadium and its attendant lights. I'm thinking, though, that a wooden privacy fence will block the stadium lights on the nights when they are turned on, so that they will not interfere too much with my observing. If my backyard is medium in size, how high should I make the fence? Six feet? Six and a half? Seven feet? Local ordinance prohibits fences higher than seven feet. Also, I'm concerned that if I make the fence too high, it will block my view of the sky near the horizon.

Thank you.

Ennis

### #2 herrointment

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Posted 18 March 2013 - 01:29 AM

Honestly, if it REALLY matters to you I'd pass on that location. That's a big bunch of light bulbs you'll be up against. I have enough trouble with one!

Best of luck!

### #3 Hilmi

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Posted 18 March 2013 - 02:26 AM

I understand that sometimes you have no choice about where you buy the plot, for example budget restrictions or the need to be near your work place etc....

So, in order to help you out. you need to know how far from the fence you will be observing, then you need to estimate the angle from horizontal that you need to point the scope to be above the light. Lets call this angle A. The distance from your observing point to the fence is B and the height of your mount from the ground is C and the height of the fence needed is D

D = C + (B/tan(A))

Its been a while since I did basic trigonometry, so it would be good if somebody was to validate this calculation.

### #4 Midnight Dan

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Posted 18 March 2013 - 06:13 AM

Hi Ennis:

You really have two concerns with light pollution. The first is direct glare from nearby lights and that's what you're trying to avoid with the fence. That will definitely help with your observing, but it won't overcome the second issue, skyglow.

Stadium lights are extremely bright and the light will scatter around them in the air causing the sky to glow, even if the direct source of the light is blocked. This is why, from dark sites in the country, you can see light domes on the horizon over cities, even when the city lights themselves are not visible. On nights when the stadium is in use, it will significantly reduce what you can see due to skyglow.

There's always competing needs in life, so it's understandable if this is a good location for other reasons. But if astronomy is a top priority, you may want to consider other locations.

As for the fence, Hilmi has given you good advice. You can't say how tall the fence needs to be without knowing how far your observing spot is from it, how high the lights are, how far away the lights are, and how high your scope will be off the ground. Then it becomes a trigonometry problem.

Probably easier to just go outside and stand at your viewing spot looking at the lights. Have a friend hold up a 2x4 at the fence location and raise it till it appears to block the lights.

-Dan

### #5 Ennis

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Posted 18 March 2013 - 09:25 AM

You have all made good comments, and I understand exactly what each of you is saying. I *would* prefer to simply find another lot -- but so far I have been unable to find one, unless I go outside the city altogether to a rural area, and there are rattlesnakes out there! Inside the city, bright lights are almost everywhere. At least at the location I have found, it is pretty darn dark when the stadium lights are turned off, and it doesn't seem too bad when the lights are on as long as the lights are out of direct view. The lights are north of the lot I'm considering, too, and almost at the horizon, so they would not hinder most of the objects I would be observing.

Amateur astronomy is not very compatible with urbanization! Everywhere one turns, there is a shopping center, a mega-church, a high school, a big box store, or a huge car dealer, all with bright lights!

Anyway, my guess, from using my trusty tape measure, is that a 6.5-foot fence will be more than adequate to block a direct view of the lights. As I wrote, the backyard will be moderate in size, and so I would be observing about 25 feet or so from the fence.

E.

### #6 csa/montana

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Posted 18 March 2013 - 09:31 AM

There's always competing needs in life, so it's understandable if this is a good location for other reasons. But if astronomy is a top priority, you may want to consider other locations.

Agreed; the light spill from this stadium will definitely diminish good viewing.

### #7 CharlesW

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Posted 18 March 2013 - 09:48 AM

You might consider a portable screen instead of raising the fence to 7'.
7' fence boards are going to be expensive and maybe difficult to find, and the fence might look out of proportion to the yard.
Or just figure out the football schedule and work around it.

### #8 rdandrea

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Posted 18 March 2013 - 10:52 AM

I'd suggest that you check with the local building department and the homeowners association (if any). Local building codes or subdivision covenants might limit the height of a fence.

### #9 Spaced

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Posted 18 March 2013 - 11:02 AM

Rattlesnakes will avoid you if they can. The fact that they live in that part of the country seems like a relatively insignificant factor to drive major life decisions.

### #10 Kfrank

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Posted 18 March 2013 - 11:14 AM

Rattlesnakes will avoid you if they can. The fact that they live in that part of the country seems like a relatively insignificant factor to drive major life decisions.

Agreed, and, if it gets cool at night, the snakes won't be active.

### #11 FirstSight

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Posted 18 March 2013 - 12:23 PM

I am probably going to have a house built for me later this year. Unfortunately, about a half-mile from the lot I'm considering is a high school, complete with a stadium and its attendant lights. I'm thinking, though, that a wooden privacy fence will block the stadium lights on the nights when they are turned on...

NOPE. I am regularly around high school stadium lights at night, since I referee HS soccer games (a bit of an ironic conflict of interest, financing my astronomy hobby via the income produced in part under stadium lights). Often, when going to a rural or smaller-town school I haven't been to before in the darker months, I'm able to confirm that I'm on the right track toward the site by the bright indirect skyglow of the stadium lights becoming easily visible by the time I'm within a mile or so of the site, well before I sight them directly. If you're going to be a half-mile away from turned-on stadium lights, it's relatively easy to block their direct glare, impossible to reduce the huge amount of diffused light pollution from scatter, especially if the air is more moist than bone-dry. In other words, the fence will probably do you less good than you might hopefully anticipate.

THE UPSIDE is that high schools generally schedule athletic contests to end much earlier than professional or collegiate contests, and the lights are usually off by not later than around 10pm. But you'll still have to consider what extent of dusk-to-dawn lighting the school is going to implement around the building and parking lots, especially areas where they park the school buses.

### #12 mich_al

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Posted 18 March 2013 - 12:44 PM

If you already own or have access to the lot then go out and observe for a few nights and see what the experience is. If it comes to building a fence then go with the max. Rattlesnales and the like can be dealt with, lights and sky glow not so much. Now is a much easier time to change directions than later!

### #13 DeanS

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Posted 18 March 2013 - 01:55 PM

I also have to deal with a high school stadium, and a couple of softball fields nearby. Good news is they don't stay on too late so are not a huge problem. And luckily the high school has some of the best shielded parking lot lights available, just wish the city would use them every where, and make car lots do the same.

### #14 tomcody

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Posted 18 March 2013 - 01:57 PM

I live about a half mile from a high school and NO fencing will help with the outdoor lights when an evening event is happening. I also have a 6.5 ft privacy fence that helps with neighbor window lights but thats all!
My advice DON"T buy there if astronomy is your interest, move a few miles outside of town and get as dark a site as you can. Drive around with a small scope or binoculars at night and try some locations first.
If you do end up there, put up a 7ft fence to help with neighbor's lights and do not make a big investment in astro gear for the back yard as you may be disappointed by the results that your city backyard yields.
As for snakes, in the city with a privacy fence I still got a 6ft cotton mouth (very deadly snake according to the animal control person that removed it) in the back yard, mating season migration, I was told.
Rex

### #15 okieav8r

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Posted 18 March 2013 - 04:11 PM

Ennis, I have to echo what everyone else is saying here. I live about a quarter mile from a high school stadium, and when those lights are on, there is no escaping it. It lights up the whole neighborhood, and no privacy fence is going to help. I'm lucky because I don't generally do astronomy at home, unless it's a quick look at something. But at the worst, it will probably cheat you out of maybe 3 hours of observing every once in a while.

### #16 TL2101

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Posted 18 March 2013 - 04:32 PM

I built a simple light shield to block my neighbors porch lights. Being portable I can move it around the yard with the scope.

### #17 Rich_W

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Posted 18 March 2013 - 04:51 PM

I love that light shield! I've been envisioning stringing up a tarp somehow to block my neighbor's parking lot style lights which completely illuminate the back of my house -- but something small like this looks like it would help a lot.

### #18 Ennis

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Posted 18 March 2013 - 09:46 PM

"But at the worst, it will probably cheat you out of maybe 3 hours of observing every once in a while."

That's what I'm thinking, too. I'm going to try to determine how often the stadium lights are turned on, and for how long.

Thank you, everyone! All of you made excellent comments, and I am grateful. I still have a lot of looking to do -- both during the day and at night -- before I buy a lot, and I will be careful about any decision I make. Finding a decent-sized lot -- most lots nowadays are really small -- in a dark location is proving much more difficult than I had thought. The lots in the rural areas are generally larger but more expensive, and they have rattlesnakes, which gives me deep concern. I'm not sure I could ever observe calmly knowing that a rattlesnake could slither by at any moment. From what I have read, they are quite unpredictable.

### #19 Midnight Dan

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Posted 19 March 2013 - 06:16 AM

This from Wikipedia on rattlesnakes:

"Rattlesnakes tend to avoid wide open spaces where they cannot hide from predators and will generally avoid humans if they are aware of their approach.[64] Rattlesnakes rarely bite unless they feel threatened or provoked."

The lot you buy may have rattlesnakes, but once it's cleared for your home and kept open by normal mowing, you should have no problems. The snake is interested in rodents and other small prey, and is interested in having lots of weeds and brush to hide in. The last thing it wants is a confrontation with a large "predator" like yourself in an open area.

-Dan

### #20 star drop

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Posted 19 March 2013 - 07:20 AM

This from Wikipedia on rattlesnakes:

"Rattlesnakes tend to avoid wide open spaces where they cannot hide from predators and will generally avoid humans if they are aware of their approach.[64] Rattlesnakes rarely bite unless they feel threatened or provoked."

The lot you buy may have rattlesnakes, but once it's cleared for your home and kept open by normal mowing, you should have no problems. The snake is interested in rodents and other small prey, and is interested in having lots of weeds a brush to hide in. The last thing it wants is a confrontation with a large "predator" like yourself in an open area.

-Dan

I agree, don't worry about the snakes. Could it be that someone else in your family doesn't want to be near the snakes?
I used to live two miles away from the Buffalo Bills stadium. When events were held observing with a 25" telescope (and anything smaller) was impossible in the stadium's direction.

### #21 planet earth

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Posted 19 March 2013 - 07:23 AM

Probably easier to just go outside and stand at your viewing spot looking at the lights. Have a friend hold up a 2x4 at the fence location and raise it till it appears to block the lights.

-Dan

Actually that's probably the easiset way.
Then there are online trig calculators for height of tree etc. for when one is rusty on trig!
http://www.carbidede...s-trigright.asp
http://www.forestryf...treehgtclcs.htm

Sam

### #22 csa/montana

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Posted 19 March 2013 - 10:28 AM

This from Wikipedia on rattlesnakes:

"Rattlesnakes tend to avoid wide open spaces where they cannot hide from predators and will generally avoid humans if they are aware of their approach.[64] Rattlesnakes rarely bite unless they feel threatened or provoked."

The lot you buy may have rattlesnakes, but once it's cleared for your home and kept open by normal mowing, you should have no problems. The snake is interested in rodents and other small prey, and is interested in having lots of weeds and brush to hide in. The last thing it wants is a confrontation with a large "predator" like yourself in an open area.

-Dan

Not always! My area is mowed down for quite a distance all around; yet, many years ago, a 4' rattler was comfy on my back doorstep!

Also, in August, they shed their skins, and are "blind", as the skin covers their head, and will strike without warning.

It pays to be vigilant at all times, in rattler country.

### #23 Darenwh

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Posted 19 March 2013 - 10:45 AM

If you build a fence for this purpose just make it the normal 6' privacy fence. If it's not tall enough (which it likely won't be) then just put a couple galvanized fence rings on the surface and use two pieces of PVC tall enough to go to the ground and up as high as you need to block with a black fabric light blocking material between them from 5.5' up to the top. Place one pole in a set of rings, unroll the lightblock material and place the other pole in a set of rings. You have a temporary light block that won't detract from property values or bother neighbors/hoa's. Simple and effective solution to the problem of light tresspass from the highschool. If you are too close you may need to make a couple blocking sections to cover the distance without too much sagging between supports. This will be cheaper than building a taller fence and just as, or more, effective.

### #24 JayinUT

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Posted 19 March 2013 - 11:05 AM

I've build light shields, I've used light shields. I rarely use them in the backyard anymore since I have a relative dark suburban backyard. Having said that the benefit for a light shield is to increase the contrast I saw from nearby lights. What they don't do is to improve the sky brightness that exists in the sky above. The brightness above will trend to go down after about 12:00a.m. to 1:00a.m. so that can help, but to get the best of conditions for visual observing, get thee to a dark site or buy in a dark site. I wish you the best of luck on balancing your needs and finding a site that is best for you. If you have a family that can further complicate the matter. I found a home I loved, wanted that was in the country yet close enough to get the kids to school and my wife and I to work. My wife wanted to be on the outer rim of suburbia and we know who won that one, it was a compromise. We have a nice home, in a decent location for suburban observing but I will head out to a dark site whenever I want to really observe, be it public land or my own land.

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