Confusing orientation for star maps and atlas of constellations

[Mountain_Wanderer]

G'day,

I'm a beginner and am getting pretty confused about which way up I need to read star maps, maps of constellations etc. I bought a set of star maps (by Wil Tirion) which are great and market themselves as having a southern orientation, which I gather means that they are printed the correct way up if you are viewing from the southern hemisphere.

So I've had a look at the star map sheet containing the southern cross (Crux constellation) which is best viewed facing south. The confusing thing is that, from my point of view, the map sheet is actually upside down! I actually need to turn it upside down to see it all make sense, but at the expense of having to read all the star labels upside down. However, if viewing objects facing north, the star maps are the "correct" way up as I see them from the southern hemisphere and the labels on the star maps are also the correct way up to read.

I also manage to have a constellation atlas written by a northern hemisphere author, and everything is in reverse. Crux is actually printed in the book up the correct way as I'd see it, and all the constellations viewable from the northern hemisphere facing north are actually printed upside down in the book. What the?

Confusing! And I know there must be a sensible explanation for this out there which I can't seem to make sense of. Perhaps someone could offer some wisdom?

The key reason for my question is this... Wil Tirions star maps include a CD that contains all the maps in electronic format, a set each from a southern orientation and a northern orientation. So in theory you can also print off the same maps rather with a northern orientation.

To make the sky more understandable for a beginner like myself, would it be better to split the set of star sheets into 2 halves and print the map sheets facing north using the southern oriented version, and print the map sheets facing south using the northern oriented version. In theory this means that, from a southern hemisphere orientation, you could face north or face south and see the stars correspond exactly to what is on the star map, and have all the star labels the right way up so as to be readable?

Just a question. Hope one can provide answers to this mystery...

cheers

Jowel.

[michaellxv]

Star charts can be a bit confusing like that. You will find different charts with different orientations depending on their intended use. e.g. some are reversed left to right to suit the view through a telescope.

In the case of the charts you have imagine yourself at the south pole. Now you face north all the time and the charts are correct.

Easiest way to line them up is to lie on your back with your head south and hold the chart up against the sky, this is the view the chart gives you. Roll the chart from east to west to follow the 'movement of the stars'.

Once you get used to it you can do it standing up.

[Brian W]

Yup my problem exactly which is why I downloaded Stellarium a free software which when configured to your location shows you what you are looking at and is designed to be used with a mid sized scope. Give it a try!
Brian

[Alchemy]

I had some star chrts... But found a computer, much handier as it showed the whole sky and you can then zoom in to an appropriate level.

I have now got an iPad and a couple of programs , some free....too easy.

The trouble with charts they show everything at once, you're trying to find something in the corner, everything is getting damp and soggy, it sounded good when you bought them, but given modern technology is leaps ahead.... I didn't bother with them

I have , desktop universe, star atlas pro, starry night, star map pro and goskywatch.... Last 2 are iPad apps, the voyager one is also highly recommended, and all are useful on those cold rainy nights

[Screwdriverone]

Hey Jowel,

Try these (http://sites.google.com/site/southernastronomer/), made by Rob Horvat from my astro club WSAAG

They are written specifically for southern observers.

Cheers

Chris

[Mountain_Wanderer]

G'day. Yeah I downloaded Rob's charts. Very nice :)

I also have Stellarium but I actually want to stay away from computers. Charts are nice to use in the field.

What I want to do it have set of star charts that show the sky exactly as I'd see it, like what Stellarium does.

[astro744]

The charts are all the same whether north, south, east or west since the stars will remain fixed for the current epoch. The only thing that a printed chart cannot not offer you that a computer can is the abilitry to rotate the labels to match the orientation of your head as you view the sky. eg. facing north Leo the Lion is 'upsidedown' but you as a southern hemisphere observer want the labels at least to be rightside up. If you were to face south and tilt your head over your shoulders you would see Leo rightside up and you would want the labels to be the same. another eg. is Orion. When it rises in the east it is upside down, north to the lower left for southern hemisphere observers. When it sets in the west it is rightside up with north on the lower right. For northern hemisphere observers it is the opposite but which charts does either observer use since both are correct (as far as lables go) at some point just depending on how you look at them.

Note too that Crux is circumpolar for southern Australia and is down low and upside down in the evening in summer and up high and rightside up in the evening in winter and the reverse is ture for the pre dawn hours. A printed chart cannot rotate its labes to match Crux as it circles the SCP.

It's all a question of orientation and how easily you can remove the horizon as your main reference point from your mind. Same thing happens when viewing through a telescope. eg. When viewing Saturn for the first time I've had many people say to me that it's on it's side and I say tilt your head and it wont be. It just happens to be on it's side because of the geometry of the planets position in the sky, the horizon, the observers position when viewing, the position of the eyepiece with respect to the horizon. ie. many factors affect the view.

I prefer charts and don't use computers at the telescope either as I find the screens too bright even in 'red' mode.

Keep at it and you will eventually be able to read star charts from any angle and that includes road maps when driving.

[Mountain_Wanderer]

G'day again. Just wondering if I was facing north, looking from a Sydney location, what would be the limit of view? I've had a look in the Astronomy 2010 star maps and they seem to show that Sydney people can see no further than +55 degrees. Does this ever change with the seasons or is it pretty much the same all year round?

[michaellxv]

This is true. Google Celestial Sphere for diagrams and explanations.

[Screwdriverone]

Hi Jowel,

Nope. Doesnt change, just the constellations visible change during the year. The tilt of the earth and the latitude of Sydney and the Earth getting in the way means that you can only see as far north as the horizon.

Most of the time you can only see as far north as the trees, houses or hills dictate from where you are viewing. For example, there is only about 1-2 weeks a year where I can see Andromeda Galaxy from my front step (which faces north) when it is between the two storey houses across the street and even then, its pretty low down. Go out west where the land is flat and the view to the horizon is unobstructed and you will see it higher and also more stars which are further north.

The "higher" you go up Australia in latitude (Brisbane, Townsville, Darwin etc) the more of the Northern sky you can see, but inversely, the less of the Southern sky you can see. Thems the breaks....

Sydney has a pretty good mix of the ecliptic (zodiac constellations and the path of the moon and planets) as well as an almost complete view of the southern gems around the South Celestial Pole. The time of the year dictates what orientation these take and what is visible during the night time hours.

Cheers

Chris

[stephenb]

Hi Jowel,

No it doesn't change with the seasons. The maximum declination in the sky you can see (in both directions, north and south), is determined by your latitude on the Earth.

For example... if you stand on the Equator at night, and look south you will be able to see to -90 degrees south declination (South Celestial Pole) in the sky. And if you look north, you will be able to see to +90 degrees north declination (North Celestial Pole) in the sky.

If you start travelling south, to say, Sydney, you will see less of the north sky.

An very, very simple equation to work out your northern declination limit is to subtract your current terrestrial latitude from 90: thus: 90 - 35 (Sydney's latitude) = 55. +55 is you most northern declination limit.

I hope this makes sense.

Also, try playing around with your home latitude on Stellarium and see what the effects are (http://stellarium.org/).

Regards,
Stephen