North, south, east and west

[craigfoot]

Ok, so I'm a little confused. . .been reading and I think I'm right in saying that in the sky east and west are reversed?!

Usually, when stood on earth and facing north, I have east to my left, south behind me and west to my left. . .but if I'm looking up at polaris and have Ursa major to my left is this in the west??

I'm sure this isn't as confusing as it sounds?

Thanks

Craig

[craigfoot]

Oh. . so I'm confusing myself unnecessarily. . through my skywatcher 130 will I be seeing a reversed east/west? I know north/south are upside down

[Dark Knight Gazer]

Hi Craig,

In Hull, If you face North, the East is to your right, West is to your left and the South behind you. As we are currently in August, Ursa Major will appear below Polaris. At the beginning of December Ursa Major will be to the right (East) of Polaris. In March it will be above Polaris. At the start of June it will be left (West) of Polaris.

I was kindly given a plastic Philips Planisphere recently. Worth getting a hold of one.

Hope this helps.

Clear skies!

[craigfoot]

I confused myself there, obviously east is to my right. . thanks

But in the sky is it the same??

[Dark Knight Gazer]

Yes, it's still the same. The objects in the sky move as the seasons/month go by. A good book to get started (suggested by most here) is Turn Left At Orion. This will tell which objects are visible during the year and where to find them in the sky.

[craigfoot]

Yeah I've got that book, and I get most the basics of things moving around. . think I'm just confusing myself with something I read about east and west being reversed in the sky.

Thanks

[oldpink]

I still always manage to get it wrong when I'm adjusting the scope using EQMod esp when it median flips

I normally guess and watch which way the stars move on the screen

[Northern Soul man]

HI Craig and a very warm welcome the the SGL Mate!! - not sure if you mean that when looking through the scope that East and West are reversed - think that's what your getting at - welcome to the world of Astronomy - I think nearly every scope you get - has a different way that the sky is orientated through it and to make matters worse - the views through your low power finder are also different ??? - I've been observing for many years and STILL get mixed up.

The sky through different scopes is portrayed differently - the Newt gives you both an upside down and right and left reversed, the view through an SCT scope (with a star diagonal in place) gives you the right way up, but left and right are reversed I THINK???

You can buy a better finder scope to put on your scope to help finding things - its called a RACI (Right Angled Correct Image) finder - so looking at a star map - the location of the objects will be as you see them on paper, making it easier to find your way around (this is what I used when I first started star hopping).

Even easier is using a scope with GOTO - they are quite accurate and take the whole frustration of finding objects in the night sky easier - some people like using GOTO's and others find not using GOTO's - you have the 130 - think its a newt - and yes - you have it correct - so looking through the EP - starting at the top and working clockwise "around" the EP - you have South (at the top), West (round to the right), North (at the bottom) and East (to the left).

Keep at it Craig - it gets easier - I THINK!!!

Paul.

[craigfoot]

Hi Paul, thanks for your comments. . it all sorta makes sense. . think I really just need to find time and clear sky's to play around more. . I've been taking it slowly for 18 months and read lots and used the scope and binoculars to try and learn as much as I can.

I'm looking at the raci and telrad options and have another thread running on that subject.

The GOTO sounds good, but also expensive. . and I think some of the fun must be finding things yourself, easy isn't always fun

[Paul M]

The principle is the same on the sky as it is on the ground.

If you are looking at the southern half of the night sky, moving left towards the eastern horizon is simply "moving east"

If you are looking at an object low on the SW horizon and move your telescope to the left you have moved it "east" even though it's just got closer to the south cardinal point!

If you are looking at the same object and move the telescope to the south you actually lower it towards the horizon not towards the south cardinal point because that is actually moving to the east!

Near the zenith it can  get very confusing.

It's all a bit academic anyway. On my SynScan hand controller I have 4 direction keys. What, with inverted images, having the eyepiece at all kinds of crazy angles and being stood with my back facing every contorted direction conceivable it's a trial and error which key need pressing.

I usually find the right one on the fourth attempt.

[craigfoot]

Yeah, sounds like I should concentrate on other things. . east is east (I think!)

[acey]

Ok, so I'm a little confused. . .been reading and I think I'm right in saying that in the sky east and west are reversed?!

Usually, when stood on earth and facing north, I have east to my left, south behind me and west to my left. . .but if I'm looking up at polaris and have Ursa major to my left is this in the west??

I'm sure this isn't as confusing as it sounds?

Thanks

Craig

You are right: cardinal directions on the sky are different from on the ground. On a star map, if north is at the top then west is on the right. This is because when you look at the ground you're looking at the outside of a sphere (the Earth) but when we look at the sky we are, in effect, looking at the inside of a "celestial sphere".

A telescope introduces further potential confusion, because it inverts the image (i.e. rotates it through 180 degrees). Moreover, every mirror in the system introduces a left-right inversion. A Newtonian (e.g. dob) has two mirrors, so these cancel and we only have inversion to deal with, which we do by turning the map round. But a refractor with a mirror diagonal gives an image that is inverted and reversed, so turning the map is not enough - you'd also need to look at the map in a mirror.

In practice it's not hard to find your directions when looking through a telescope (let's stick to the Newtonian/dob example). Look at high power with any drive switched off, so stars drift across the field of view. Where they enter is east, where they leave is west (easy to remember: the sun rises in the east and sets in the west, which is what the stars do too). Once you've established the east-west line in your field of view, north-south is of course at ninety degrees to that, with north being ninety degrees clockwise from east (or ninety anticlockwise from west). If you're aiming your telescope due south (which is generally the best place in the sky to aim for, since it's where objects rise to their highest in the sky) then east-west will be horizontal (stars will move right to left) and north will be "down" in your field of view.

When you look at the sky with the naked eye you have a much bigger field of view, so the curvature of the celestial sphere becomes much more apparent. Watch for a while and you'll see that all the stars are slowly circling Polaris (which stays still). Polaris marks celestial north, and the stars are all moving westwards on the celestial sphere - though this of course does not mean they're all moving towards terrestrial west. It means they're moving anticlockwise, with Polaris at the centre.

Let's take your example of Ursa Major. This constellation rotates anticlockwise round Polaris, completing every revolution in a smidgeon under 24 hours (the smidgeon is why we see different constellations over the course of a year). If you're looking at Polaris and Ursa Major is on your left, this means it is gradually setting towards your northern horizon (though won't actually go below the horizon). At its lowest, Ursa Major will lie over the northern terrestrial horizon, and be seen to be underneath Polaris. As it continues its rotation, the constellation is seen to the right, and then eventually above Polaris (overhead), which is the highest it reaches in the sky. At that time, Ursa Major is on the meridian (the north-south line) and offers the best views, since we see it through least atmosphere. But to see it there at night you need to wait until Spring - right now, Ursa Major reaches that highest point every day during daylight.

If you read something like "Saturn is low in the western sky during early evening" then this means you should look towards the terrestrial western horizon. But if you read that star X lies a few degrees west of star Y, then this refers to celestial co-ordinates. It means that if you point your telescope at X and leave it pointing at that bit of sky with no drive, then after a while star Y will drift into your field of view.

Just spend some time watching the stars (and not relying too much on technology to do all the thinking for you) and you will very soon get the hang of it all.

[stevend]

Lie on your back and look up at the sky with your head North and feet South, East is to your left and West is to your right. A traditional compass is based on looking downwards at the Earth whereas in astronomy we are looking upwards hence the reversal of East and West and why planispheres, which are held over your head, are the same.

Edit: what acey said above. I had left my computer in the middle of composing and therefore did not see his response before mine.

[craigfoot]

Thanks

[RichM63]

Yeah, and clouds are always directly above.

[Northern Soul man]

Yeah, and clouds are always directly above.

Yeah - White, grey, thick, thin, no Stars, Planets DSO's, Nebulae - thanks for that !!!! (OK - who's bought some new gear!!!)- just looking up, out of the window - can you guess what I can see??

Paul.

[Charic]

Ok, so I'm a little confused. . .been reading and I think I'm right in saying that in the sky east and west are reversed?!

Usually, when stood on earth and facing north, I have east to my left, south behind me and west to my left. . .but if I'm looking up at polaris and have Ursa major to my left is this in the west??

I'm sure this isn't as confusing as it sounds?

Thanks

Craig

craigfoot........Not quite......... Imagine, or Lay flat on the ground face down? with your head orientated to North. keeping your body straight. North is your Head, South is your toes, East is to your right, and West is to your left. This is what we have grown up to know and learn. These are the 'normal' cardinal compass points. 

Now roll over onto your back. North, South, East and West are still there. They haven't moved!  but East is now apparently on your Left! whereas just a minute ago it was on your Right? It hasn't moved, but you have!  Its because now your looking up to the Sphere, instead of the normal, looking down,  this is why Star maps have their East/West reversed to make alignment correct for observations. 

Now if you take a PLANISPHERE and look at the Cardinal points it goes N, W, S, E  whereas were used to the familiar N,E,S,W but holding the Planisphere whilst lying on the ground, face up, the Planisphere now makes sense, and will now show East to the left and West to the right if Head to toe are still aligned North-South. Lying down is also more comfortable (on a recliner)  than just trying to hold the Planisphere over your head at arms length. Your arms will soon get tired, but a Planisphere is designed to be held aloft, with the sky behind it!

You just have to ensure that you set the time (GMT -  Greenwich Mean Time) and date correctly, and have the direction you wish to look at, indicated at the bottom position of the Planisphere.  So for this moment in time its 2300 Hrs, so 2200Hrs GMT is aligned with the 28th August, and I'm facing North, so 'N' should be at the bottom of my Planisphere, and I either hold aloft or lay down (Toes facing the direction you want to view?), and What is on the Planisphere now should match the night sky.  What you see in the Inner display (the Star map) indicates the stars from  directly overhead and down to the horizon. Polaris should be in the centre hole! There is also a small 'x' on the rotating section of the Planisphere. That 'X' marks your Zenith, your 'Directly Overhead' but this 'x' is hard to see at night, and sometimes just as hard  to see with any light, as its so small.

Only use the Pole Star, Polaris if you want to navigate your way through the night, in the Northern hemisphere. The other Stars appear to rotate around Polaris, due to the fact that Planet Earth is spinning at 1000 Mph, Anti-clockwise, viewed from the equator, looking North.

*EDIT* How on Earth did I miss #13 by stevend? Sorry matey    Well said, and in only two lines? Oh! well. Still something to learn about the Planisphere maybe?

[craigfoot]

Lol thanks. . who thought the compass was so complicated! Off to buy a planisphere now!

[Charic]

WHSmith have Planisphere's. The Philips version at £14.99 'Glow in the Dark' feature is not brilliant, and the centre of the Planisphere won't have a hole, instead it has a button? You'll destroy your night vision, trying to charge the Star map?  I have four Planisphere's, two came in a bundle with my first telescope, one I've had for Years, Runs out this Year, the Planetary data? and the 'Glow in the Dark version. There is a standard version at £6.99. PM me your address and you can have this one for FREE, but  the Planetary data  on the back of the Planisphere runs out this Year!

[craigfoot]

Thanks

[craigfoot]

Hi, been thinking about this too much again. . think I've got east and west sorted, but. .

If I'm facing south and move the scope upwards is it heading north

And if I'm facing north and move upwards is this heading south or is it heading north until I pass polaris (or another point) when it then becomes heading south?

[acey]

Stand at the Earth's north pole. Walk in any direction and you're heading south. Aim your telescope at the north celestial pole (Polaris, for present purposes). Move it in any direction and you're going south on the celestial sphere.

All the confusion that arises in this topic comes from mixing up terrestrial cardinal points and celestial ones. By "facing north" you mean facing terrestrial north. Celestial north is  a point directly above your terrestrial north horizon. Your terrestrial southern horizon is on the meridian line that joins celestial north and south.

If your scope is aimed at terrestrial south (i.e. is aimed at the meridian) and you move it upwards, then it is going towards celestial north, and also in fact towards terrestrial north (if you sweep it right round).

If you're facing terrestrial north and move the scope upwards then it is going towards celestial north until you reach the north celestial pole (Polaris), then it is going towards celestial south. It is also in fact going towards terrestrial south, if you continue to sweep right round to the opposite horizon.