Hi Terry - I wasn't going to respond to this subject again untill they'd undone the straps on the special jacket they've got me in and let me out of solitary confinement: but I now understand the blank post Outbackmanyep sent me with the little "teleporting man " icon - it really was a cryptic message!
Ignoring the (more obvious) possibility that it was a rude response based on a poor opinion of my DX3-bred faculties: I must now conclude Outbackmanyep was secretly telling me that some other (weird?) person would soon be teleported along to enable us to expand our various perspectives.
Terry, one of the understandings I evolved as I debunked (with Gary's erudite assistance) my "nonsensical" RA circles (you got that didn't you Outbackmanyep - I called them "nonsensical") was that even if I levelled the baseboard, drew a line on the revolving (azimuth) board of the dob that was aligned with the scope's optical axis and aligned that geo North-South and marked off my RA circle from this - it would be meaningless and afford no benefit because the altitude (declination) axis of a dob is directly above and moving in a manner such that it (the declination/altitude movement) can NOT slew along any particular Hour Angle but merely bisect it at a very arbitrary (for the purpose of targetting) point in the sky. An EQ mount has a polar aligned azimuth/RA axis and an altitude/dec axis set at 90 degrees to it, allowing movement in a plane parallel to the polar axis (ie describing Hour Angles.)
I'm not in agreement re the stars presenting elliptical paths across the sky: setting the Declination on an EQ allows the Polar aligned azimuth axis to define/track any night object's circular passage from East to West via that axis' single revolving movement - but what I think is important for me to recognize in your own (ie Terry's) mental imagery is that, like mine, some points are rather abstruse to express (without modelling) and we may mangle parts of the logic but we do arrive at a somewhat intuitive appreciation of the interacting mechanics of the sky and any mounts we use to observe. Far more interesting from my perspective than just accepting rote-like what this or that represents or facilitates. (Getting into the mental gymnastics as Gary said!)
To this end I can only say to Netwolf that I suggest you obtain a model of my world (they are plentiful this time of year in Oz - there is a ritual about to start called "The Australian Open" where - from an inhabitant of DX3 point of view - disrespectfull things are done to representations of our homeland.)
Netwolf, mark a North and a South pole onto your acquired model of DX3, run, say 4 longitudinal lines from pole to pole with texta to represent the Hour Angles (mark the 0,6,12,18) and then anywhere along the Equator pin another little disk you have scissored out and marked with 4 Hour angles similarly gradated: and give it a little twirl - one of 2 things will most likely happen: (a) you will find yourself sharing a padded cell with yours truly or (b) you may have to revise your prior assertion that 6 will not "align" with 6 and etc etc.
I leave you all for the time being (they want to put this strange jacket back on me) confident that I leave all our readers that much more unenlightened/antagonistic/confused or simply downright stunned by my latest contribution to this delightfull topic.
I hope I don't screw-up adding my lil' diagram..but here goes
lets use terminology that reflects what is goin on... are we not actually aligning with the earth's polar axis? ("pole-stars" whatever, are merely a convenient indicator).... we create the angle of 'tilt' to get our base parallel with a base as it would be if we were on the equator.
this then allows us to pivot the base, around that axis, in 'equal and opposite' rotation to the earth's rotation, thus staying fixed on the same point over time.... as opposed to "pointing to the pole" we are pointing parallel...
think of it like a conrod always pointing at the piston...the gudgeon-pin is parallel to the crank...
as for "declination"..is that to do with the tilt of the earth's axis relative to our orbital-plain?? jargon annoys me
cheers
Russ
Last edited by omnivorr; 20-01-2008 at 02:33 AM.
Reason: sorry for bitmap.. i HATE 'Paint'
Greetings omnivorr - good to hear from you: I wasn't going to encourage this thread anymore (it was a promise I made to get me out of "high security") but since I've been let out and have "gone back to my own planet" they won't be able to restrain me anymore - so here goes.....
I actually started all this to ascertain the merit of putting setting circles on a dob mounted scope: ie was there any merit in it?
I wasn't getting into debating any value in declination indicators (I've triggered enough confusion!) - just Right Ascension scales; concluding that if you used them, they only give one (possibly two) correct positions/points in the sky that are correct RA points (both of these are meaningless from the point of useability because you can't slew/move your scope along these longitudinal positions to get the necessary Declination required to fix/pin-point/locate objects because moving the dob mount's altitude axis will instantly change the RA setting you have supposedly set with your RA indicator - even though you have set this scale from a zero or reference point of geographical north south.)
You're right, jargon can be really annoying, but in specific subjects it helps for people who are interested in the same pursuits. (eg your use of mechanical analogies is fine with me, but half of today's mob wouldn't know what the crank is, let alone the gudgeon pin!) It has also become evident to me during the life of this "thread" that many people really have no real innate/intimate understanding of RA (what Gary called "the mental gymnastics in how lines of RA and Dec are mapped out....." but are happily functional accepting the "it is so" viewpoint - and good on them!
However, if we align with the Earth's polar axis (which is an EQ set-up) we aren't aligning our mount base parallel with what it would be at the equator - rather we're aligning it with how it would be at the north or south poles, off-setting it to these positions with respect to our latitude, to arrive at an analogous positioning - which is why a dob mount sitting on the poles instantly becomes an EQ mount.
Having said all this, I will be putting setting circles on my dob-mounted GSO 10" Newt - but only because I'm waiting for my Round Table equatorial platform to arrive; and in that set-up they will have some relevance - especially as this purchase postpones the likelihood or me getting an Argo Navis system for some time!
Hi Darryl, ...I'd better explain myself before I go causin' any worse confusion or bother to anyone by it. As I'm only just startin to peck at this roast-chicken called stargazing, I'm nowhere near the bones of it yet!
so this is my approach ( no Dob yet, still counting pennies for it)...
base on ground.. compass beside it... line on base parallel to axis thru the tube (i.e. "lightpath" of tube, not pivot-axis) inline with compass n-s. Now, chart to tell me correction from magnetic N to true N,
.. put compass-ring on Dob base , align it with compass, then shift base x degrees according to correction chart for my location......
my base is now aligned true north-south, but still not parallel with the earth-axis.... for this the eq-platform , with correct angle of tilt for my location, goes under base...north aligned with base, thin end north (for southern hemisphere) now the base is aligned with n-s axis and parallel with it... and can rotate on the eq-platform to follow the east to west apparent motion of the sky..... all the above is taken as if there is no turntable, just the base of the dob, or a fixed dob.... there is in fact no need for a turntable that I can see..... tube swings n-s , platform swings e-w... entire hemisphere of sky covered... somebody correct me if I've missed something please!!
so.. to the next step of the path to Go-To, I'd assume some scale applied to each axis....( but whether degrees ,minutes , or mm&inches ..I don't care.. whatever is the convention...) ..some scale or other, in whatever language the direction-sensing apparatus and motors can use to work with the controlling software... a scale on the arc of the tube, and a scale on the arc of the eq-platform.... { keeping the turntable on the base might be a matter for manual-pointing convenience but I could only see it unnecessarily confusing the tube-arc calculations.... therefore, no turntable..and no ring of any scale on the base, but for the simple compass-correction at setup.}
well, that's my plan of approach.. I hope.. (if)when I've had my Dob a while and ready to start "chasing"
I had in fact thought of a motorised design.. and later strayed across a photo of same/similar someone has made, but now can't find it , that demonstrates my approach, completely doing-away with the turntable....
(a member of BAS, I think it was)... I'll enquire soon, when I join
Hi again omnivorr - removing or dispensing the ability to rotate the dob base of your scope (ie the azimuth motion) and taking into account all your other steps (which is how I first postulated this subject in my first post that started this thread) and sitting it on an EQ platform will prevent you from looking at any objects that are not on the meridian line you have set by where you've plonked the mount on the EQ platform. That is, you will only be able to move the scope along the north south line parallel with the scope's light-path axis (as you refer to it) directly above this scope-tube position.
This is because an EQ platform is fixed to the ground and cannot rotate, it only describes the apparent path of an object's motion for a limited arc-movement (approx 1 hour usually.)
Keeping the mounts ability to revolve in the horizontal plane as well as the vertical allows you to point at almost anything in the sky before you then activate the EQ platform's tracking drive. Otherwise you'd have to physically drag the proposed fixed/static baseboard of your "crippled" dob mount around on the fixed platform/base of the EQ platform to sight up objects not on the meridian you've plonked it on! Analogue setting circles will function as a rough setting fix/go to with the unfettered dob mount on an EQ platform.
Dear Vinnie - I'm sorry if you find my thread offensive or off-putting (though you could of course ignore it) but omnivorr replied to me and brought up the issue of EQ platforms.
Many dob mount people use them and find them of great merit: and for the life of me I can't see how this thread could possibly interfere with you (or anyone else's) ability to view responses to "replies from a couple of blokes who have asked for reasonable advice re mounts" (sic) - your quote.
Perhaps you have taken unintended offence (or do not/cannot appreciate) attempts by me to inject a little humour into subjects which we are all passionately interested in. Perhaps you are unable to understand that the content actually is quite serious, and that like yourself, many of us are really quite experienced/knowledgable about areas pertaining to these interests. I myself can call on over 50 years of experience/involvement in skywatching and AA.
One thing I totally disagree with is your confused perception of this thread as containing "slanging" or "bunfighting" - it has not and never will contain such from my part, and I don't believe any other contributor to the thread has done such.
At any rate Vinnie, I wish you the best and (belated) New Season's Greetings and the capacity to surf and view or interact as you wish, regards, Darryl.
ps - back in 1956 I started with my old man's binoculars, the star atlas (mainly northern hemisphere) and The Big Golden Book of Astronomy; with a burning desire and head full of questions and wonder: however, I would never attempt to tell others how they should get started in anything - but perhaps that's because I'm a bit of an anomoly amongst Australian Aboriginal people, a mad astronut and (proud) Kokatha (Western Desert) man!
To Vinnie: sorry u feel that way. ...if u stuck around u might yet learn something, despite your 45yrs of "experience".
I myself have exactly zero experience..or as near to make no nevermind!!
My Mudda has near 70 years of experience ..in cooking. She still can't cook beyond over-boiled veg and dry-cooked meat....... so forgive me if I flippantly disregard your dramatic coat-fling exit stage left.....
To Darryl, and any other observers...
....if the tube rotates on axis x (parallel to earth-axis), starting from E horizon... while at the same time pointing at any point from the S horizon to the N horizon ( pivot-axis of tube now verticle, at end of fork pivotted from the x axis) ....whatever the tube is pointed at will remain aligned sofar as the scope tracks it by following in rotation on the x axis..... is this not correct????
Hi again omnivorr - our mothers must have used the same cookbook!
All this is very hard just using words: if we could on-line make continuous sketches and point etc it'd be solved in a flash!?!
Reading your last paragraph I understand the x axis as being "polar aligned" (ie parallel to the Earth's axis of rotation) but am not 100% about the "pivot axis of tube now verticle, at end of fork pivotted from the x axis"
From my perspective, if saying the above you are saying "pivot axis of tube which is at the end of fork pivotted from the x axis is perpendicular (at right angles) to this x axis (ie it rotates or spins around a projection or imaginary extension of this x axis) then you have your EQ set-up and the object pointed at will be able to be tracked as it moves from east to west.
Will leave you to ponder my (imagined) re-phrasing of your statement - I'll sign off for the night in case The Thought Police come knocking.....have no idea who would possibly sick 'em onto me though!?!
Oh! Darryl ...yes it would be so much easier if together we could point to the east and raise our arm to follow the stars in the sky... I'd bend my arm at the elbow to point north/south... you'd see it in front of your own eyes... not just my vague words!! you'd see immediately what I mean, and immediately show me if/where I'm wrong, by demonstration in front of my eyes.. ( something like "Netmeeting" setup on our puta's, and drawing on graphics -tablets would help, but sofar at my end I'm not yet "on top" all that )
..but let's say, together side by side we're facing east... I hold my arm out pointed at the horizon, straight, ..my fist at the end is the open end of the telescope tube..... my shoulder is the pivot-point for my arm.. let's say I'm leaned against a stump beside me , on my left, so my shoulders are parallel with the earth-N/S-axis...... now my straight arm moved at the shoulder will follow the movement of the sky.. my shoulder is doing the job of the EQ-platform.
..now I bend my elbow to point my fist N-S...parallel to my shoulder-line, (it will point down to the ground!--my right arm to point north) or my left arm to point south....it will point up to the sky! ) I don't have an elbow that can swing both ways... but a Dob does) ... so my fist can point E-W from shoulder movement. and anywhere N-S from elbow movement, along the parallel-to-earth-axis N-S horizon...
doesn't this leave a gap between the "real" N-S horizon and the "polar-aligned" one? ( on the south end)
...well, there's nothing to stop the shoulder axis pointing below its horizon!!, (my shoulder can't swing behind my back, but the EQ-platform mounted arm can!!) and the (left arm) elbow can range in that field too! ...it'll just mean a short duration of track until that object rises above the polar-aligned-horizon of the shoulder (to the East) ....all this is if the object goes behind the earth....
but imagine an object very close to the south polar point (of the sky, not the Earth).. at some convenient distance from earth. In the southern hemisphere. .. that point will not go behind the earth ..... at a certain point from the equator that "object" could be observed without any tracking, it would remain centre-scope, ..only revolving.. like an old EP on a platter
....your EQ-mount "crippled" scope could lie flat on either side or be flagpole erect... no difference between'em! ...every point on your latitude focused on the same point purely by the 'alt' angle...
I've concluded from all this : "Azimuth" is a flat-earth concept!!!
What can I say - that you deigned to imagine some sort of choreographed "pas de deux" as we swung our arms and pivotted our elbows every-which-way, doing a Monty Python version of "The Right Ascension Waltz" - but you told me you were leaning against an old stump: not a monster scope!?! Those instruments you're surrounded by quite rattled my gudgeon pins!
Please tell me that you only own a pair of K-Mart binoculars with one lens broken, if only to alleviate my jealousy!
And to think that I was contemplating one day ammending my profile to boast of my own puny gear: to become what my mate calls a "blowhard." (no offence fellas, I actually enjoy drooling over other people's equipment lists!)
No wonder you wanted to talk about crankshafts and gudgeons!!! Those babies in the photo look like they pillaged a D9 or two!
But even if you do only have the K-Mart nocs, I'll still look forward to seeing your posts on IIS.....
Regards, Darryl.
Hi
was looking for threads explaining Dec and RA gradations for EQ mount setting circles and found this thread.
I'm kind of getting my head around the Equatorial co-ordinate system and can understand how RA is divided into 24hrs, but can someone explain the How the Dec co-ordinates work.
I'm using an equatorial fork mount, and the RA axis is set to 38deg for Melbourne. That said, if I align my RA axis to point to the SCP, and the tube is parallel to the RA axis, my understanding is that the Dec is 90Deg. But I read that the Dec is divided into 4 quadrants of 90 deg.
So if I move my OTA on the Dec axis by 90 deg toward azimuth (alt/az) or overhead, would that be 0 deg Dec? what happens if I move further up?
to clarify, I'm starting Dec at 90 deg pointing to the SCP when RA is aligned to SCP, I then move only along Dec by 90 towards North, then Dec becomes 0, and how does the Dec axis increment or decrement? to -10deg, -20 deg and so on?
secondly, in the eq co-ordinate system, if all objects have constand RA and Dec co-ordinates, what actually changes depending on time of day? is it the hour angle? I'm using stellarium to visualize.
Hi
was looking for threads explaining Dec and RA gradations for EQ mount setting circles and found this thread.
I'm kind of getting my head around the Equatorial co-ordinate system and can understand how RA is divided into 24hrs, but can someone explain the How the Dec co-ordinates work.
I'm using an equatorial fork mount, and the RA axis is set to 38deg for Melbourne. That said, if I align my RA axis to point to the SCP, and the tube is parallel to the RA axis, my understanding is that the Dec is 90Deg. But I read that the Dec is divided into 4 quadrants of 90 deg.
So if I move my OTA on the Dec axis by 90 deg toward azimuth (alt/az) or overhead, would that be 0 deg Dec? what happens if I move further up?
to clarify, I'm starting Dec at 90 deg pointing to the SCP when RA is aligned to SCP, I then move only along Dec by 90 towards North, then Dec becomes 0, and how does the Dec axis increment or decrement? to -10deg, -20 deg and so on?
secondly, in the eq co-ordinate system, if all objects have constand RA and Dec co-ordinates, what actually changes depending on time of day? is it the hour angle? I'm using stellarium to visualize.
Whe the scope is aimed at the SCP it is actually pointed at -90deg dec. As you point it away from the SCp towards the celestial equator you approach 0deg. If you go furter north you are then aiming into the +ve Dec area. the N celestial pole is+90 deg.
Whe the scope is aimed at the SCP it is actually pointed at -90deg dec. As you point it away from the SCp towards the celestial equator you approach 0deg. If you go furter north you are then aiming into the +ve Dec area. the N celestial pole is+90 deg.
Thanks. what happens if you go below the SCP? does it go from -90 to zero again? so SCP is -90, below that say -80, -70 and so on?
Thanks. what happens if you go below the SCP? does it go from -90 to zero again? so SCP is -90, below that say -80, -70 and so on?
Yes
If you are standing on the south pole and look at the zenith you are looking at the SCP. Going any direction away from that is moving to less negative declination.
For me at latitude 29deg south, the SCP is 29 deg above the horizon. From that point (at -90 dec), if I move my scope say 10deg down it will be pointing at -80deg dec. The stars at that spot will move around the SCP with time and 12 hours later they will be 10deg above the SCP. As this shows it doesn't matter which direction you move away from the SCP it will still be moving to less negative dec.
thanks. as the position of the objects in the equatorial co-ordinate system don't change significantly (we're rotating and not the stars), do we use the Hour angle to find an object?
eg, position of sirius from stellarium at 0011hrs at Melbourne is
and at 0311hrs is
RA/DE(j2000): 6h 4m 8.8s / -16d 43' 1.1"
HA/DE : 21h 56m 22s / -16d 43' 44"
so if I were to have a list of objects with their RA/DE values and I use just the gradations on my equatorial mount, after polar aligning, how do i find out what the RA angle would be or where the object would be?
I'm guessing it would be based on an offset of the RA angle from the observing time and position
thanks. as the position of the objects in the equatorial co-ordinate system don't change significantly (we're rotating and not the stars), do we use the Hour angle to find an object?
eg, position of sirius from stellarium at 0011hrs at Melbourne is
and at 0311hrs is
RA/DE(j2000): 6h 4m 8.8s / -16d 43' 1.1"
HA/DE : 21h 56m 22s / -16d 43' 44"
so if I were to have a list of objects with their RA/DE values and I use just the gradations on my equatorial mount, after polar aligning, how do i find out what the RA angle would be or where the object would be?
I'm guessing it would be based on an offset of the RA angle from the observing time and position
I have never used the hour angle just the RA and DEC.
Yes you are correct. You set the RA by offsetting against a known RA.
Even for a goto scope it has to be originally aligned to a known point but the computer will then compensate for the rotation of the sky with time.
If you start at a known star and set the RA setting circle on your scope it will only be correct at that time without tracking. If the scope tracks then the RA will remain correct until you turn off the scope.
I hope I don't screw-up adding my lil' diagram..but here goes
jargon annoys me 
, that demonstrates my approach, completely doing-away with the turntable....
so forgive me if I flippantly disregard your dramatic coat-fling exit stage left.....
