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Field of View needed to see most Celestial objects

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#1 Rumbleripper

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Posted 11 February 2013 - 07:38 AM

Hello:

This is my first post here and I am interested in getting into night viewing and photography of the sky. I am going to be purchasing a telescope in the next few months and probably setting up an observatory to do my astrophotography from.
My situation is that I live out in the country and have about 10 acres of land, but it is mostly covered with trees. My home has trees very close which provide nice shade in the summer. There are some areas in my property where I can see a section of the sky (say 30 degree field of view).
I know I need to cut down some more trees to get a better view, but I don't really want to cut down more than I need to as I would like to not alter the vegetation more than I have to. The trees I have are about 60 to 70 feet tall.
Since the sky does rotate overhead(or the earth rotate) how large a FOV do I really need if I wanted to photograph most objects in the Northern hemisphere? I know that I would only have access to many objects when they were in my "window" of view, and could only access them at certain times of the year, but I would be willing to wait to capture certain objects for the sake of not cutting down a huge swath of trees.

Thanks for any input.

#2 droid

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Posted 11 February 2013 - 08:15 AM

At first blush , my instinct is to say slow down, lol.

But on second thought , we dont know enough about your level of knowledge in the night sky to make any sort of educated statement here.

As fro fov, that will vary greatly depending on the object.

#3 Tony Flanders

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Posted 11 February 2013 - 09:08 AM

This is my first post here and I am interested in getting into night viewing and photography of the sky. I am going to be purchasing a telescope in the next few months and probably setting up an observatory to do my astrophotography from.


You have very ambitious plans; if I were you, I would try out the waters before making any commitments. Astrophotography takes years to learn; there's no point in hurrying the starting point by a few months.

I would recommend starting out with strictly visual observing. Once you can answer from first-hand experience the question you just asked here, you can start thinking about the bigger picture.

My situation is that I live out in the country and have about 10 acres of land, but it is mostly covered with trees ...

How large a FOV do I really need if I wanted to photograph most objects in the Northern hemisphere?


Do you literally mean the northern celestial hemisphere, or do you mean most of the objects potentially visible from your location? Those are two very different things! For what it's worth, the southern celestial hemisphere happens to have far more interesting objects than the northern -- and many of those are readily visible from the U.S.

Basically, what you need is a broad strip to the south, perhaps 45 degrees wide, cleared just as far out as you possibly can. And also a shorter strip to the north. You'll want that anyway, so that you can align on Polaris. Everything in the sky crosses that strip, called the meridian.

I would estimate you could get away with cutting no more than 2 or 3 acres and still have a pretty decent view of the sky.

#4 careysub

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Posted 11 February 2013 - 09:12 AM

One consideration is that you will probably want access to the full sky available at your latitude - i.e. from close to the horizon to the North Pole.

If you have a clear view of a "slice" of the sky from (near) the horizon to the pole by timing your observations by clock and calendar you can see anything (weather permitting).

#5 Dennis_S253

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Posted 11 February 2013 - 09:42 AM

I would agree with Tony on the North-South view. There would not be any objects you couldn't see, unless they where to close to the horizon and something beyond your land obstructed the view. You can download Stellarium (for free) and start doing some research on the objects in the north-South directions. As Tony said, the Meridian runs North-South and all objects cross it. There also at there highest when the do. Which usually means the best view, because your looking through less atmosphere. Welcome to CN and clear skies to you.

#6 csrlice12

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Posted 11 February 2013 - 10:09 AM

While I don't have 10 acres in dark skies (I have 10 sq ft with 3 street lights with skyscrapers across the street); I do share your tree flocked view (nothing below 30* in any direction). There is still plenty to see though, and, to be truthful, as a "general" rule, anything below 30* from the horizon gets fuzzier due to all the atmosphere you're looking through). You probably will want to clear some of the trees out (just advertise free firewood, around here, people would be lining up) down the road. +1 on holding off on AP for now, get used to the scope and the sky first...

#7 Tony Flanders

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Posted 11 February 2013 - 10:42 AM

As a "general" rule, anything below 30* from the horizon gets fuzzier due to all the atmosphere you're looking through).


That is absolutely true. It's possible to image things less than 30 degrees above the horizon, but not desirable.

But for visual observing, it's often desirable to go lower. The reason, in a word, is that a very large fraction of all the great stuff in the sky never gets any higher than 20 or 30 degrees from mid-northern latitudes. That's because the center of our galaxy is far south, in Sagittarius.

In practice, 20 degrees is good enough. If the trees are 70 feet tall, that means cutting a bit over 200 feet deep, and perhaps 100-150 feet wide so that objects stay in the gap long enough to observe and/or photograph them. But remember that a tree that's 70 feet tall today will be 71 feet tall next year. Pesky things, trees ...

Of course, there are also all the beautiful twilight phenomena, like the recent conjunction of Mercury and Mars. But that's really not possible in an area that's predominantly forest. Need to go somewhere else for those.

#8 csrlice12

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Posted 11 February 2013 - 11:02 AM

"But remember that a tree that's 70 feet tall today will be 71 feet tall next year...."

...bigger trees call for bigger scopes...... :lol:

#9 Tony Flanders

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Posted 11 February 2013 - 11:34 AM

"But remember that a tree that's 70 feet tall today will be 71 feet tall next year...."

...bigger trees call for bigger scopes......


Actually, perfectly seriously, one approach that's often adopted by suburbanites in particular is to build their observatories high off the ground. It's a very effective way to increase the amount of sky you can see. Unfortunately, it's also very costly, since it requires building a massive pier from the ground to the observatory floor.

Going up to 70 feet isn't likely to happen, but 20 feet is eminently feasible.

#10 Dennis_S253

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Posted 11 February 2013 - 11:45 AM

Being that the OP didn't say where he or she was from, it's hard to say what is possible. I know for me here in FLorida I'd miss a lot of the Messier's and other stuff if I only went to 30 degree's above the horizon. Heck, I couldn't even see Polaris if I only could see to 30* above the horizon.

#11 Rumbleripper

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Posted 11 February 2013 - 11:55 AM

Hey everyone, thanks for all the input.

It is pretty much what I thought, I need a good strip going north to south. On the North side don't need to go too low towards the horizon as the objects will rotate back to the meridian. The southern objects are where I have to decide how far towards the Horizon I want to go.
The figure I was looking for was the 30 degrees or so above the horizon on the southern horizon and towards the east and west, I feel if i had about 4-6 hours of "window" watch time, which at the celestial equator would mean about 90 degrees FOV (45degrees from either side of the meridian). As I track objects further north of the Celestial equator my FOV would need to gradually diminish as the object will traverse slower, so for a 4-6 hour tracking would need less than 90 degrees. At the pole region as long as I could see say 10 to 15 degrees around Polaris, I imagine I would be good.

FYI I am at 45 degrees latitude.

#12 jg3

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Posted 11 February 2013 - 12:27 PM

You seem to appreciate the forest where you've located, so you'd do well to make some very reversible commitments on acquiring equipment, before any long-term commitment on clear-cutting parts of your land.

I'm in forested country, and have a clear viewing swath that bears just a little off from north-south. So I can see everything that can be seen (for my latitude) for 1 to 4 hours if I wait for the right times of year and night (except low planets, of course). Didn't cut anything down for it, just lucky.

I'd suggest you take a slow walk all over your property and look for some candidate viewing spots having the most of a clear view on a straight or curved swath from Polaris to approximately due south. (Learn how to find those directions by day, with compass or GPS if needed.) Also find candidate spots that would have such views if not for one tree, or maybe just some overhanging limbs, or overhead utilities.

Get to know the night view from your candidate spots, including the partly-obstructed ones. Go out at night to a spot and observe with whatever you have, as you acquire equipment (even if binoculars or just a planisphere). Don't worry about what's too far east or west - these will come in their time. You might, like me, find two or three spots each best for different parts of the sky, and set up at one for a night based on what you plan to observe.

As you gain observing experience and acquaintance with your land and its views, you will be able to narrow the candidate list and make better-considered tree-cutting decisions.

Welcome, and good luck. - John

#13 Tony Flanders

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Posted 11 February 2013 - 01:31 PM

Being that the OP didn't say where he or she was from, it's hard to say what is possible. I know for me here in FLorida I'd miss a lot of the Messier's and other stuff if I only went to 30 degree's above the horizon.


Actually, the closer to the equator you are, the better.

The southernmost Messier, M7, is at declination -35. And M82, the northernmost, is at declination 70. That means that M82 rises 30 degrees above the horizon as far south as latitude 10N, in Venezuela. And M7 rises 30 degrees above the horizon as far north as latitude 25N, in the Florida Keys.

#14 Rumbleripper

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Posted 11 February 2013 - 03:32 PM

Again thanks everyone for input. I am going to go out in the next few days and scope out due North-South line and see what I can arrange without removing too many trees.

Clear skies everyone.

Gaetano

#15 Dennis_S253

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Posted 11 February 2013 - 04:07 PM

Sounds like a plan Gaetano. Tony, I never thought to much about that. I guess I am in a good location. I can see all 110 Messier's. I guess you guys up north have a hard time with objects in the southern sky. Clear skies all...






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