Telrad reticule size...

[Llamanaut]

Can anyone tell me the radius/ diameter of a DIY telrad reticule based on tirion's skyatlas 2000.0 please? My heads gone all fuzzy and i cant work it out, nor can i guesstimate myself due to cloud

Is the fov 4 degrees? Will that equate to 4 minutes of ra in tirions book?

[Doc]

I think they are 4°, 2°, and 0.5°

[Llamanaut]

what size would that be in tirions skyatlas?

[Bizibilder]

One hour of Right Ascension is 15° and as Doc says the outer ring of a telrad is 4°. However - there is a complication! The Telrad gives a field of view of 4° FROM THE OBSERVERS POINT OF VIEW which is NOT 4° on the celestial sphere (except at the equator). Look at an atlas and you will see that lines of Right Ascension get closer together as you get nearer the poles - so the Telrad will show its 4° as covering a progressivly larger value of right ascension as it is pointed at objects nearer the poles.

You are comparing two unlike things. The Telrad shows 4° PROJECTED onto the celestial sphere. Right Ascension is a measure of an angle of rotation. All a bit apples and oranges - or is that chalk and cheese!!

I hope this makes some sense!!

[Llamanaut]

thats why my head was so fuzzy! getting my head round it now though thanks, wanted to make a rough telrad finder for star-hopping using tirions skyatlas, i got it to work roughly and thats close enough for me...

[Bizibilder]

Do you have Cartes du Ciel? - (Free download star atlas/planetarium) - You can put as many Telrad circles on a chart as you like!! Very useful!! You can also print off your own "finder charts" with as many, or as few, Telrad circles as you need. Sorry I forgot to mention this in my last post!

[Llamanaut]

think someone mentioned that to me, i downloaded it but i didnt like it much, maybe i need to dig it out again and have a play with it... im hooked by double stars at the moment which are a tad more difficult to find than galaxies and nebulae but for me offer far more satisfaction when u do find them

[TopHouse]

You do know that the latest stellarium has telrad built in don't you? You have to enable the ocular plugin, restart stellarium and when you hold ctrl and press 'B' it turns it on and off.

As an estimate i reckon you could zoom stellarium in till it matches the scale in your book and turn on the telrad option and it should show on screen the size you need. I don't have that book but have a look in the inside covers etc as a couple of atlas books have a telrad template that you can trace.

EDIT

Just done a 'look inside' the atlas 2000 and on about 2nd page there's a telrad template, i looked inside the deluxe edition, dunno if thats what you have

[Llamanaut]

No i have the bog standard edition which has an acetate sheet with the grid squares but without the telrad finder or magnification chart. Ive made a rough diy telrad guide which seems to work. Its only so i can roughly measure how many telrad hops it'll take me to reach target in some of the more remote spots. As im concentrating more on doubles nowadays. Just for curiosity sake whats the diameter/ radius of the skyatlas deluxe telrad?

[TopHouse]

I don't know, I don't have it lol, I used the look inside feature at Amazon and it doesn't show actual size i don't think. BUT, if you bring up a selection of one of it's pages in stellarium, zoom it till it's the same size as the book page, then turn on the stellarium telrad ring, you can hold your one against the screen and see if it's around the right size.