Finding Skyobjects using Alt/Az and Ra/Dec and learning Constellation Navigation
Hi guys,
Im trying to get my head around locating objects in the sky for viewing and wondering if theres any simple guides to learn from.
I have a Dobsonian scope, so Im limited(I think) to Alt/Az for lcoating objects in the sky.
However it seems that RA/Dec coordinates is how every star/object is located.
What is the most common way that Dob owners to their viewing?
Is it more so starhopping, or do we use coordinates prior to starhopping using starcharts.
In light of all that, is their a common beginners guide to learning the night sky and objects/stars/constellations that assist the learner.
I just picked up two books'; Collin Stars & Planets and Atlas of the Southern Night Sky. I also have Starry Night Pro 6, which I've been going through the tutorials but it seems to focus more on the northern hemisphere.
As a Newbie as well with an 8 inch Dob, if found that star hopping to limit the search size for faint of high mag objets has worked pretty well for me. There are heaps of threads on making your own altzumith circles for a Dob base, and I thnik the Alt function is taken care of by an object commonly known as a Inclinometer, which I belive you can get from trade/hardware suppliers.
I've asked around my local hardware places though and no-one seems to have any idea of what I'm talking about. Try getting to know how to use the various star maps and planisperes and be like the proverbial kangaroo and hop to it!
One other thing that Im still getting use to is the finderscope showing the view backwards. This is a little bit of a pain when starhopping, but Im slowly getting use to this.
Is this just a matter of 'getting use to', or is this where a ''Red dot finder'' or ''Telrad'', or even Refractor guidescope is the better investment for replacing a finder scope. Is the finderscope always the most common tool for object finding? What are the prefered finderscopes better than this and more use friendly, or is it just a habit of getting use to?
You may find it useful to read the finderscope article in the latest Australian Sky & Telescope that came out in the last few weeks.
Yes, many people are very happy using the "red dot" type finder which are non-magnifying or "unit power". Problems are:- 1) because they are non-magnifying, you may not be seeing the object of interest and having to put the dot on a "blank" part of the sky where you expect it to be, relative to adjacent stars (of course, you often don't see the fainter/smaller objects in an 8x or 9x finderscope also), and 2) when your scope is pointed to a high elevation, it's a bit of effort to twist and turn to get your eye in the right location to use the finder.
Practice using the finderscope with both eyes open. The eye on the sky also "sees" the cross hairs and therefore you can fairly quickly move the scope until the object you can see in the sky (bright star/planet usually) comes into the finderscope field of view in the other eye.
Remember to always start the search with a wide field of view - eyepiece of, say 26mm focal length or longer.
Another option is to use a green laser pointer as a finder. There is a lot to be said about this - laser safety, relevant State laws/permits, performance in cold weather, interference if there are other nearby observers/astroimagers (search for threads on IIS). I've found it to be the quickest way to point my scope to the required part of the sky.
I have a sense that its a bit like terrestrial maps and directions - some people have a very good sense of direction and some people don't. The sky is easier because you can usually see most of it at once, but you often cannot see everything on land at once. What is most disconcerting is when there is a lot of moving cloud cover. One gets glimpses of stars through the holes and wonders - which star is that, which constellation? Very confusing!
But when you can see the whole sky, I find it very easy to consult a chart and say to myself - OK, the object I want is about 40% of the way from that star to that one over there, and then up "a bit" towards that star. Then it is easy to move the scope until the laser is pointing to that area, then go to the 30mm eyepiece and compare what I see, with a good chart or planetarium program. It's much the same using a unit power finder. A bit more complicated using a straight-through finderscope with both eyes open and much more difficult using a right-angle finderscope where you are not looking at the sky naked-eye at the same time. I would recommend that a right-angle finderscope always needs to be used in combination with a unit-power finder or laser finder. (Unless, of course, you become an expert at getting behind your scope and sighting along it to the part of the sky you want. This is harder than it sounds! Eg. first time binocular users are inevitably looking too low in elevation when they look at an object in the sky, then lift the binoculars to their eyes.)
Of course, one day I'll buy an Argo Navis and have computerised "push-to" on my dob and I'll be laughing and spending more time observing than searching. I do the opposite at the moment, but treat it as part of the apprenticeship - I still enjoy the thrill of the "hunt" and the exultation of the "find"!
I have a Dobsonian scope, so Im limited(I think) to Alt/Az for lcoating objects in the sky.
However it seems that RA/Dec coordinates is how every star/object is located.
What is the most common way that Dob owners to their viewing?
Is it more so starhopping, or do we use coordinates prior to starhopping using starcharts.
Hi Leinad,
Looks like you made a good start with the Collins Guide and the Atlas of the Southern Night Sky.
The important thing to understand is that RA/Dec coordinates are a (more or less) absolute reference grid, independent of the position of the observer, whereas Alt/Az coords are relative to the position of the observer in the universe as well as to time - so they change continuously.
In order to locate things, RA/Dec is only of use if you have instruments that can measure them from a fixed reference point (i.e. alignment of the scope with the Celestial South Pole). In parallel with Eric's comparison above ("I have a sense that its a bit like terrestrial maps and directions") no one goes around his neigbourhood navigating by latitude and longitude (the terrestrial equivalent of RA/Dec), and even if you would want to you would need a GPS or something.
Most entry-level dobs do not come with setting circles or the like, so measuring RA/Dec is not possible - and not necessary in the beginning.
In star hopping you will learn to recognise familiar patterns in the sky, like constellations or parts of them, asterisms - just like you recognise the streets in your neighbourhood by all sorts of clues like buidlings, trees, traffic signs and the like. A good way to get started is to take seasonal sky maps for each cardinal direction (as found in most astro-magazines and Astronomy Australia 2008 for example), and match the maps with what you see in the sky, naked eye - to learn how to recognise the patterns. I'm sure Starry Night can print them for you too, exactly for your location and time.
Many people recognise Orion's Belt, and you will learn for example that M42 is just a few degrees 'above' it - likewise you can locate the Southern Cross as an 'anchor-point' and find eta Car from there (which except in inner cities is a naked eye object anyway), as well as the Jewel Box Cluster and much more...
On p18 of the ASNS is a handy tip on how to use your hands to roughly estimate distances in the sky - use it! For now I suggest you don't worry too much about RA/Dec etc... try to recognise the patterns first...
First things first, I'd be pretty much listening to what Erick and Karlsson have to say as I've learnt alot from reading their posts and especially Erick's observation reports.
I'm afriad (getting used to the finder) is pretty much the way to go. However I have just fitted a Telrad, $79.00 from Bintel which I use to easily find bright stars/obects, then use my right angle finder scope to fine tune and then I use a 32mm wide angle polssl to move from object to object.
If I get lost, a quick look through the Telrad generally shows me if I'm still in the right area.
I'm not favouring any products by the way, I've just found out Rigel, produces a device that appears to do pretty much the same as a Telrad, but I've never seen or used one so can't really comment.
If your anything like me, just being out there is half the fun. If you read some of the observation reports, you'll see people seem to be able o look at heaps of objects in a really short time frame. I don't think we're up to that level, to just pick two or three objects and concentrate on finding them and as out skill improves, so will the observing. That's my thought for the day anyway.
..... especially Erick's observation reports.
....
Darren, you are too kind, with an emphasis on the TOO! Of recent times, the reports to read are those from ngcles, SAB, goober, glenc and Rob_K and others earlier (eg. look for Sentinel). I'm still an exuberant newbie, excited when I find a PN that everyone else cut their teeth on years ago and forget to record all the details (magnification etc.)
These other guys speak of seeing, transparency, magnitude, size, position angle, NSEW directions, structure, filaments, colour..... One day I hope I'll understand, and maybe be able to say these things myself and not make too many blunders!
One other thing that Im still getting use to is the finderscope showing the view backwards. This is a little bit of a pain when starhopping, but Im slowly getting use to this.
Yes, this is what I'm currently fighting and it can be a pain when star hopping somewhere new. Sends me a bit loopy
I take it you have a right angle finderscope with the left/right reversed? If so, you may find it easier to replace it with a straight through, and simply flip the atlas upside down.
If you've got lots of naked eye stars then a 1x finder would be useful.
Once you've bagged a target for the first time, it's amazing how easily you can get back there... the memory kicks in and you hop down the stepping stones to the target.
When first starting the best accessories are a pair of binocs and a planisphere. While your scope is cooling just cruize about mapping the constellations and getting familiar with the layout of the sky.
Don't try to do too much each session. Try picking one or two constellations and have a good dig around in them with the bincos and scope and repeat this a few times (good themes can be sourced from Sky and Telescope or a basic star atlas). Quickly you will become very familiar with surprisingly large parts of the sky which will make starhopping easier.
Try to make haste slowly. Bite off too much and its all too confusing.
My first scope was a tasco on an eq mount and I have to say I never succeeded in using the setting circles to reliably find stars. I now have a dob and love to star hop.The thing that I found most useful was some leftover knowledge of some constellations from a star camp years before. If you've got someone who can point out a few salient constellations it makes a huge difference. I've found that I can work out others from there. I find dark skies help, as a lot of constellations (like Fornax) consist of fairly faint stars. I've been finding my way around for about a year and am still discovering constellations.
My joy in finding things was greatly enhanced by a telrad. It made things so much quicker to just be able to point the scope reliably at the patch of sky that I'm interested in. I still use the finder to hone in on fainter things, but these days I seem to be more able to just pop onto something with the teltrad.
I also find the Atlas of the Southern Night sky very helpful, but I use it in conjunction with current star charts from AS&T or Sky and Space. These reflect the sky as it is currently oriented, whereas the Atlas requires a bit of spatial gymnastics to reflect what you see as you look up.
Hope this helps and I hope that you come to enjoy star hopping as much as I do - I find it evokes quite a sense of accomplishment!
Probably you have to wait until around midnight this time of year when Corvus and Virgo have some elevation - and another couple of weeks for that Moon to slip away. I've attached two screen shots showing how I get there.
Probably you have to wait until around midnight this time of year when Corvus and Virgo have some elevation - and another couple of weeks for that Moon to slip away. I've attached two screen shots showing how I get there.
Excellent post for the star hop to M104, although only having found it a couple of nights ago, I premise this with the fact that from light polluted area's it is very faint and you may need to use averted vision.
Excellent post for the star hop to M104, although only having found it a couple of nights ago, I premise this with the fact that from light polluted area's it is very faint and you may need to use averted vision.
In another thread a while ago I suggested to pull a dark cloth over one's head and eyepiece whilst looking at faint fuzzies - it improves your dark adaptation a bit. With M104 in particular this method has proven to work well: cover your head, give it ten minutes or so, and M104 will start to 'grow on you' = literally... Your 15mm and 9mm EP's will probably give you the best shot, but learn by experimenting!
Hey goober, yes its a straight-through. Flipping the starchart upside down makes sense. I'll give this a try next viewing session.
Thanks
Quote:
Originally Posted by goober
Yes, this is what I'm currently fighting and it can be a pain when star hopping somewhere new. Sends me a bit loopy
I take it you have a right angle finderscope with the left/right reversed? If so, you may find it easier to replace it with a straight through, and simply flip the atlas upside down.
If you've got lots of naked eye stars then a 1x finder would be useful.
Once you've bagged a target for the first time, it's amazing how easily you can get back there... the memory kicks in and you hop down the stepping stones to the target.
It's been said before the only stupid question is the one that's not asked!
Starting out, I'd use the 40mm eyepiece. I got one for my 8" and found it useful because the field of view was big enough to avoid getting lost. (I actually got it because it gave 30 magnification, the same as my highest magnification binoculars. Well it seemed like a good idea!) In time, you may find the 26mm is sufficient field of view for you starhops?
In this starhop to M104, those asterisms - the isosceles triangle arrowhead pointing the direction to "Stargate", then on in the same direction to "Jaws", then follow where Jaws is pointing to M104 - are so distinctive that you will quickly find yourself centred on M104 or its location. I take the point made that city light pollution may be a problem, but M104 is a bright little fellow, I expect you'll see it in your 40mm, unless your observing location is lit up too much and your eyes poorly dark adapted.
Now I didn't quite understand your question, but swapping eyepieces to observe at higher magnification should not cause any problem. You need:-
1. The OTA stable as you swap eyepieces - so have sufficient friction on the Alt bearings in particular, so that that pulling eyepieces in and out and the change of weight doesn't cause the OTA to swing - up mostly, given you are going to lighter eyepiece through an empty focusser intermediate step. But don't worry if it does - Alt is the easiest adjustment on a dob. Just swing the OTA back down when you have the eyepiece in place and focussed roughly. You'll probably pass over the object easily. (In fact, when I'm on a faint object with faint stars around, and I want to check focus, I often swing the OTA up or down until I find a brighter star, focus on it, then swing back to the target.) You'll also learn to hold the OTA stable with the left hand while you change eyepieces with the right hand (and in complete darkness! )
2. A rapid change of eyepieces. In this warmer weather eyepieces can stay on the eyepiece rack. I've added a few more racks to my 8" to hold everything I want, within reach. Bottom caps off, top caps on. If I have a 2" in the focusser, I have the 1.25" I want to use next already fitted into the 2"-->1.25" adapter. Let me visualise what I do:- left hand resting on OTA to stop it moving. Object of interest centred in the lower mag eyepiece field of view. Eyepiece cap comes out of right hand pocket to cap the eyepiece - softly so as not to move the OTA. Loosen focusser screw with right hand and lift out eyepiece. If I don't have a spare 2" hole in rack (and I do now ) place eyepiece in left fingers while still preventing OTA from moving with the left hand. Reach down and pick up the adapter holding the 1.25" eyepiece. Fit it into focusser and tighten the screw. Place eyepiece from left hand into rack. Remove cap from 1.25" eyepiece and place in pocket. Done!
3. Rapid focus to quickly see the object. If you have parfocal eyepieces (all are focused at same point on the focusser) - great! But not these GSO ones. So already have memorised how you have to change the focusser for this particular eyepiece swap and quickly adjust to get rough focus. Sometimes the focus point is so different that you wonder what has gone wrong - where has everything gone! But you cannot muck around moving the scope to try and see something. Rack the focusser to where it should be - half a turn in or whatever. Once you can see the object, re-centre it, if the scope has moved or earth rotated too far (you were too slow!), then spend time focussing on it, or the nearest bright enough star, then study and enjoy.
Not sure if that answers your question
Eric
Edit: Oooh? Your question has gone! Here's an answer - we'll let everyone guess the question
Hey goober, yes its a straight-through. Flipping the starchart upside down makes sense. I'll give this a try next viewing session.
Thanks
It does depend if you are looking to the east or to the west. You just have to "suck it and see". Fiddle until the chart is the orientation you are seeing. This is what having a live planetarium program running on a laptop beside you can be the best. (Except turning the laptop screen upside down??)
I think the biggest fear of having the laptop outside as a reference guide will be killing my vision. I believe the best way to go for me I think is to start small, print out the star sheet, plan my starhop, and find that target!
Im so exited to findg M104, Im slightly disappointed of the moon as its directly north of where I'll be searching.
I'll have to save this one for a week when the moon goes away. Oh well, no big loss as it allows me to research further into navigating and plotting my targets in the meantime.
Quote:
Originally Posted by erick
It does depend if you are looking to the east or to the west. You just have to "suck it and see". Fiddle until the chart is the orientation you are seeing. This is what having a live planetarium program running on a laptop beside you can be the best. (Except turning the laptop screen upside down??)
and forget to record all the details (magnification etc.)
)
) place eyepiece in left fingers while still preventing OTA from moving with the left hand. Reach down and pick up the adapter holding the 1.25" eyepiece. Fit it into focusser and tighten the screw. Place eyepiece from left hand into rack. Remove cap from 1.25" eyepiece and place in pocket. Done!
