Night sky navigation

[JOC]

Is there a primer in SGL (there are dozens listed and not always by useful thread names) about how to make sense of the navigation data.  Various lists that I have give things like RA in a time format, Declination in degrees, minutes and seconds, PA in degrees.  All this data is currently like a foreign language to me.  I send the goto off after all sorts of objects only to be told they are below the horizon or not visible for some reason.  OK, I can use Stellarium and make life easier, but it must be possible to tell from these numbers in the tables what will be useful to me at any time and what I discount.  Can these values tell me what will be above the horizon where I am and roughly what direction something is likely to be in?  i.e. can I sweep the tables and find things that are in the region NNE to SSW and above the horizon for viewing or is this not what the values show.  Sorry if this is a daft question, but I'm quite baffled by what it all means.   

[popeye85]

I've wondered about this myself but since I have a dob I just look at a sky chart, look up at the sky and if it's visable I view it simple! Never had much need to lean about RA and declination. Would be handy to know though.  

[Cosmic Geoff]

It would be too tedious to explain all the terms here, but If you have a copy of Norton's Star Atlas or equivalent, you can see the RA and Dec on the chart, and by checking with the night sky outside, get an idea of which bits of the evening's sky are accessible.  In the southern UK, anything south of  -38 deg S in declination (in practice more like -25 deg) will be permanently inaccessible.  The further North the declination, the more likely it is that you can see it anytime.   What RA is due south at the time of observation? Any object with a similar RA will be at its best position for observation.

Tonight RA of 5hrs is due south in early evening.

Pleiades: 3h47 +24 07'  = well placed

M68: 12h 40 -26 45 =  no good.

A plastic planisphere (q.v) will show you what's visible at a particular time, when set for the appropriate time and date. This is probably the best answer. 

[cloudsweeper]

+1 for the Planisphere - really handy.  It shows (for your location) what you can see throughout the year and throughout the night.

Doug.

[cloudsweeper]

.......also, I'm purely alt-az and visual, so don't really bother much with RA and Dec.  One simple thing: if you look at a chart with RA given in hours, one hour corresponds to 15 degrees.  (24 hours - full circle - 360 degrees - so one hour corr. to 15 deg).

Doug.

[Gazabone]

Cornwall Astronomy Society have s couple publications you might find helpful but please bear in mind what you can see will depend on your latitude (how far north or south you are). These links work well if you are anywhere near 50degrees north (the latitude of Cornwall). 

http://www.cornwallas.org.uk/Freds 2017 Astronomy Challenge.pdf

 

this link is to the home page of CAS where you'll find a link to "Gareth's viewing challenge" which gets updated each month;

http://www.cornwallas.org.uk/

the February one is here;

http://www.cornwallas.org.uk/2017-02.pdf

Hope you enjoy it, starting to find your way around the sky can be frustrating but extremely rewarding when you start finding the objects you're looking for. Keep persevering, you will do it. 

[Nyctimene]

Rectascension and declination of heavenly bodies values are fixed numbers - compare them to longitude and latitude on earth; all star maps show just these coordinates.

Whether you can actually see a celestial object at a given time and place, depends of the two motions of our planet, the daily rotation around it's axis, and the annual revolution around the sun.

Computer programs, as in star map apps, but also a planisphere,  transform the static RA and dec values according to time and location. This will lead to the terms of azimuth (North 0°, East 90°, South 180°, West 270°, and again North 360°=0°) and height (above horizon) from 0° to 90°. If an object is below 0°, it's not visible. Each star chart program will give you the azimuth and height values, as will a planisphere; so you can see, what is above the horizon, and in which direction it can be found.

Hope that helps.

Stephan

 

 

[JOC]

Thanks for all the info folks

Gazabone, I've taken a look at those links - your Gareth in Cornwall seems a great chap for sorting all that information out for folks.  I think it's quite useable for me 51"41' N over here in Essex :-D

[RT65CB-SWL]

1 hour ago, cloudsweeper said:

+1 for the Planisphere - really handy.  It shows (for your location) what you can see throughout the year and throughout the night.

Doug.

...and it needs no power source to operate; (unless you have one on a smartphone).

[Gazabone]

On 01/03/2017 at 11:13, JOC said:

Thanks for all the info folks

Gazabone, I've taken a look at those links - your Gareth in Cornwall seems a great chap for sorting all that information out for folks.  I think it's quite useable for me 51"41' N over here in Essex :-D

Thanks, yes, at your latitude you should find the "challenges" will work for you.  Just be mindful that the higher the number in the magnitude column, the fainter the object is.  At the moment M42 is well placed but a couple of my favourites is M81 Andy M82.

happy viewing ??

[JOC]

The higher the magnitude number the fainter the object - got it!  That sounds a bit like toxicity the higher the LC50 number the less toxic sonething is!

[LukeSkywatcher]

I have to agree that a planisphere is about the easiest piece of gear to use outside. 37 yrs of observing and i have no clue about RA/DEC/hours/mins/seconds. Ive never had a reson to learn about them. OK,i understand what RA and DEC are (up/down/left/right). 

I started off @ age 6 using 10x50 bins and a planisphere. Now happy enough to navigate the night sky without using anything but my eyes. Ive never planned my sessions, so strictly speaking i dont need to know much about the night sky and finding my way around. I just point the scope and see what i find. Move on if nothing jumps out at me.

[cloudsweeper]

Nice one Paul.  I only bother with RA and Dec and the Ecliptic just to be aware of the science!  It does help with knowing what can be seen and where.

Doug.

[LukeSkywatcher]

Obviously it helps if you know your way around. You dont need to know every single star,constellation in the night sky. This is why TLAO is such a great book. It assumes (correctly or incorrectly), that most observers know Orion and acts like a road map for the night sky. I still think a planisphere is about the best way to learn.

I have a 12" Philips planisphere pinned on my wall to remind me where i started at all those yrs ago. Its not my original one. Its a newer glow in the dark one,which i have to say is pretty useless for reading in the dark unless your eyes are about 3" away from it.

[JOC]

I'm trying to do it all at once, maybe was a little bad for not doing the formative stuff with binoculars.  The thing is we've rather rushed at this.  My son's school got a telescope and they promised the students an astonomy club on a Friday night - the trouble was all during Autumn term they didn't get a clear Friday night and it kind of all fell apart.  In an effort to avoid mass disappointment on my son's behalf, I reasoned the only way to get him a view of the night sky with any degree of reliability was to get a telescope ourselves - that way when it was dark and clear we could take advantage and not be limited to school hours either.  As it turns out he doesn't seem overly enthusiastic - perhaps there was a caveat of excitement to doing it as school, with mates and not with 'fuddy duddy' parent in tow.  So the telescope has kind of fallen in my lap - it's a nice thing and I think I may as well put it to use and perhaps see some things I wouldn't otherwise see.  However, I kind of like knowing what I'm looking at and am going down the route of picking interesting sounding objects off of lists.  If I find something interesting the Goto will help me find it, but I'm spending ages finding objects on the Goto (which takes me a while esp. if I press the wrong button) only to be told X,Y and Z are below the horizon - it happened about 8 times on the trot the other night - red light on, look in my book, type what I want in, object below horizon, damn, red light on etc.  I just wondered if I knew what all the figures meant whether I could automatically rule out those below the horizon from the numbers. 

[LukeSkywatcher]

JOC, from your last post, you are doing nothing wrong. Getting to grips with astronomy is a huge learning experience no matter which direction you approach it from. Should you use a scope or bins when starting?. There is no right or wrong answer. Whatever helps you, is the right way. Go-To systems are not as easy to use as you would first think (or as suggested by scope makers), you do need to know a little to be able to align the scope (at least 1 single bright star in the night sky).

Regarding your son.......

It probably did sound like a good idea to him and something which he was interested in,especially seen as he would be with mates. Sad that the whole thing fell apart. I think its great that you bought a scope for him to use at home. I'm sure he will once again show an interest, when you yourself get your head round it and can start showing him things. When you do (and you will soon), maybe ask him if he wants to invite some friends around to look through the scope. Make a night of it and maybe even order in pizza?.

[rockystar]

sounds like some kind of list generator may be of help to you, so that it will produce a list of things that are visible on any given night for your location and telescope.

I use Sky Tools for this, It's a paid Windows app, but I believe there are free ones out there, check out http://dso-browser.com/ for instance

 

[LukeSkywatcher]

4 minutes ago, rockystar said:

sounds like some kind of list generator may be of help to you, so that it will produce a list of things that are visible on any given night for your location and telescope.

I use Sky Tools for this, It's a paid Windows app, but I believe there are free ones out there, check out http://dso-browser.com/ for instance

 

Go-To supplies that list for you when you enter in your location (by any means). Obviously for Go-To to work at its best you need to do a 3 star alignment so the satellites can triangulate your exact location. I rarely do anything more then a single star alignment or a solar system alignment.

[rockystar]

10 minutes ago, LukeSkywatcher said:

fairGo-To supplies that list for you when you enter in your location (by any means). Obviously for Go-To to work at its best you need to do a 3 star alignment so the satellites can triangulate your exact location. I rarely do anything more then a single star alignment or a solar system alignment.

fair enough. It sounded like she was entering objects into her goto that were not visible to her though; I just thought if she had a plan, she wouldn't be frustrated with constantly entering those objects.

[LukeSkywatcher]

35 minutes ago, rockystar said:

fair enough. It sounded like she was entering objects into her goto that were not visible to her though; I just thought if she had a plan, she wouldn't be frustrated with constantly entering those objects.

Trial and error. If you are not that familiar with the night sky from your location, you may indeed enter objects which are not visible. If the Go-To is correctly aligned/triangulated to your location, it shouldnt really be throwing up objects which are not visible.

LOL, i remember a few yrs ago i got a Celestron Skyscout as a Christmas present. I was in Lanzarote at the time and instructed it to show me the Moon. It had me pointing the thing towards the ground/my feet...........even though the Moon was high above me.

Best thing i ever did was sell that Skyscout (at a big loss). Useless piece of kit.

600 quid new...........a year later, i think i got 80 quid for it.

Ouch!!!!!!!!!

[Paul M]

RA is somewhat archaic but once upon a time when people routinely navigated by the stars it all made sense. It relates to Sidereal Time which is actually a better time keeper than Solar time but the Sun rules our circadian clocks so we stick with that one! 

It's a complex subject but I'm sure there are plenty of references out there in cyberspace. I just had a quick look at the Wikipedia entry for RA and I don't think it's very useful. The Wiki on Sidereal Time probably helps explain why RA is tabulated in Hrs, Mins and Seconds.

Perhaps the best way to treat RA is as an oddly numbered grid similar in nature to longitude on Earth. The lines converge at the poles yet the two grids constantly shift relative to each other, whereas declination is similar to latitude the lines quite sensibly remain parallel and fixed. I really, really struggled with RA as a boy. I was always trying to reconcile RA with local time and never managed until I'd developed an understanding of how Earth rotated relative to the stars and how that differs from where we see the Sun in the sky on any given day.

 

[JOC]

LukeSkywatcher I guess if I let the goto do Skytour mode it would probably limit itself to things I could see on a given night, I haven't tried that mode yet'  However, it will still let you type in any Messier number for instance.  So if I sit there with a Messier list and think to myself that globular clusters sound interesting targets; then, until I type them into the goto system, I don't know that I won't be able see them until the system says 'Below the horizon'.  I also don't know roughly what direction they are in - I have a preference for the section of sky between NE and SW (L-R).  Or if they will be that close to the horizon that the hedges will stop me viewing them even uf they are miraculously Above the horizon!  Can you tell everything I had fun and games with!!!  I just assumed that knowledge of those numbers might help with all that.  

As rockystar suggests a target list on a given night would probably help - someone has shown me one on the Cornwall astronomers site, but that suggested app. might also be useful.

I like the idea of invite son's mates around too!

[domstar]

Hi, do you use stellarium. If it looks like it's going to be clear I check out my part of sky for the evening and click on a few dsos to check the magnitude and if I'm clever, write them down. I have a limited view if I stay at home,which at least helps me focus on a particular area.

[JOC]

domstar - I like stellarium a lot, but tend to run it most on a mobile.  I'm still at a stage of not really knowing what something is likely to look like after I click on it and I am not sure I can say to the mobile app. show me all Messier objects, or all double or coloured stars, or all nebulas - the thing is that at the moment I am still relying on the goto so what I find to look at really needs to be in its lists.  I am not yet at the finding things manually by star hopping route.  I'm still at the hold my hand point.  I want things:  in my favourite bit of sky, easy to find, interesting to view once I get there, findable in the goto unit, above the horizon before about 11pm, -  Yup I want it all!!  LOL  I was so annoyed that all the Messier globulars were below the horizon - they sounded really stunning to find!!

[cloudsweeper]

I use the Pocket Sky Atlas or  Stellarium out there with me (in the shed, anyway).  That way, I know what I am able to view, and when it's in the EP (manually or GoTo), I check it against the reference source.  Stellarium is particularly useful here, as you can zoom in and compare closely the star patterns there and as you see them.  (Reverse the view in Stellarium as necessary to make it easier.)

Doug.