Need some help with geometry

[Gavin1234]

So looks like my primary school geometry teachers were right along when they said one day I might need to use a protractor.

I’ve had to move my scope further from my house a few meters to get a better view of objects early in the morning. I had previously marked out the spots for my tripod legs and got really good alignment very easily by using those. It was point straight at true south.

Trying to setup the same way in my new spot and I’ve run into a problem. I’ve got an iPhone 7, 8 and iPhone X, a galaxy s6 and a brand new iPad Pro and all of the compasses don’t work. They all give me different lines and none match the original line that works.

I’ve drawn out a line for the original spot and basically I want to draw another line about two meters away that is exactly parallel to it so they are both pointing to true south.

How do I make sure they are both parallel? Too big for a compas and if I just measure the difference between the two at regular intervals how do I make sure the tape measure is at the right angle. Do I have to go get a protractor?

[raymo]

Forget geometry, just plonk the tripod down in the new location, with the legs
in approximately the same orientation as before [ in other words with the counterweights pointing approximately South], mark the feet positions,
and then do an accurate DARV polar alignment, and all done. The feet
almost certainly won't be pointing accurately due South, but the mount will be, which is all that matters. If you are new to DARV, just google it; it is easy to do, and you will probably need 30 mins to do it the first time, and 10-15 mins at
any later time. All you need is a camera with a screen. Of course if you
put a different mount/scope down on the leg marks it wouldn't be properly aligned, but probably well enough for visual use.
raymo

[Lee]

Originally Posted by Gavin1234

So looks like my primary school geometry teachers were right along when they said one day I might need to use a protractor.

I’ve had to move my scope further from my house a few meters to get a better view of objects early in the morning. I had previously marked out the spots for my tripod legs and got really good alignment very easily by using those. It was point straight at true south.

Trying to setup the same way in my new spot and I’ve run into a problem. I’ve got an iPhone 7, 8 and iPhone X, a galaxy s6 and a brand new iPad Pro and all of the compasses don’t work. They all give me different lines and none match the original line that works.

I’ve drawn out a line for the original spot and basically I want to draw another line about two meters away that is exactly parallel to it so they are both pointing to true south.

How do I make sure they are both parallel? Too big for a compas and if I just measure the difference between the two at regular intervals how do I make sure the tape measure is at the right angle. Do I have to go get a protractor?

I've been thinking the same in preparation for installing new wheels on the underside of my observatory roof..... Pythagoras is your friend.

Take the line you have. Measure it. Call this x.
If you want another line 2m away, exactly parallel, draw out two right angle triangles from the ends of the line, using your line as one side, and the 2m spacing as the other. The length of the diagonal (hypotenuse) will be the square root of (x^2 + 4). Ie if your current line (x) is 4m long, the diagonal distance will be 4.47m. Find the point from each end of your line where arcs of length 2m and 4.47m meet (for a 4m line) - this is the ends of your new parallel line.
Remember the 3-4-5 triangle.... that's one special case you can use too.....

[JA]

Originally Posted by Gavin1234

I’ve drawn out a line for the original spot and basically I want to draw another line about two meters away that is exactly parallel to it so they are both pointing to true south.

How do I make sure they are both parallel? Too big for a compas and if I just measure the difference between the two at regular intervals how do I make sure the tape measure is at the right angle. Do I have to go get a protractor?

If you want another line parallel to the first you could use a few methods. Here a three possible methods:

1. Use a corner of a large sheet of ply, particle board/MDF perhaps in conjunction with a straight edge as your reference to help you draw a perpendicular at both ends of your line. Measure along both these 2 perpendiculars an equal amount (the 2 metres you require) and then make a mark on both perpendiculars. Join these 2 marks with a straight line and hey presto you have a parallel line 2 metres away from your original line. Even if the corner of the sheet you use is not perfectly square it doesn't matter, provided you use the same corner of the sheet to draw your perpendiculars.

2. Make a compass from a steel pin (like a large screwdriver) attached to a cord or rope with some sort of marking device (maybe chalk or texta) at the other end. Then use the compass to help you draw an equilateral triangle at either end of the line, whose bases lie along the line. Then bisect the base of the equilateral triangles and draw a line from this bisection point up through the apex of the triangles. These lines are perpendicular to your main line, and then as above measure along these perpendiculars and markout the 2 metres. Join these 2 marks with a straight line and hey presto you have a parallel line 2 metres away from your original line.

3. Use a Pythagorean Triad to "draw" a large 3-4-5 triangle at each end of your line, to help you set up a right angle at both ends of your line, then proceed to draw perpendiculars to your line and mark out 2 metres along each perpendicular. Join these 2 marks with a straight line and hey presto you have a parallel line 2 metres away from your original line.

Have fun

Best
JA

[Gavin1234]

Thanks a bunch once again guys. I think I’ve got it sorted.
The line on the left is the original tested as good north/south line. The one on the right is the new one. Just ignore the red line

I’ll try and do an alignment shortly so I know for sure.