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geeek
2002-Feb-06, 01:05 AM
this is going to sound horribly dumb. oh well. are there stars that someone who stays on the north pole will never see? also, can someone in the southern hemisphere view stars that those in the northern hemisphere see? thanks if you can help.

ljbrs
2002-Feb-06, 02:10 AM
Yes. If you want to view everything visible from Earth, you need to do a lot of traveling. Also, there are constellations which are not visible at certain times of the year, while others are circumpolar and are in our night sky throughout the year. The same is true for the Southern Hemisphere's inhabitants.

The folks in the Southern Hemisphere get a good view of the Galactic Center. They can view the two Magellanic Clouds (which are two of our neighboring galaxies). We cannot view these up here in the Northern Hemisphere.

Therefore, one needs to become a World traveler if one wants to view everything. You must be a World traveler during different seasons of the year. The same is true for those "Down Under" -- except the sky which is unavailable to them would easily be viewed by us.

I suppose the best place to drag a telescope would be high on a mountain in Chile, far from any brightly-lit cities, so you could get a glimpse of both hemispheres.

I did not answer everything you asked (because I forgot to copy and paste your question), but this is a start...

ljbrs /phpBB/images/smiles/icon_smile.gif /phpBB/images/smiles/icon_biggrin.gif

Peter B
2002-Feb-06, 04:23 AM
Gíday geeek, and welcome to the BABB.

The answer to your questions are, generally, yes and yes.

To give you a bit more detail, itís worth imagining how the Earth moves through space in relation to the stars, and to imagine yourself standing at various points on the Earthís surface. This sort of stuff works much better at a planetarium, so if thereís one near you, itíll be well worth a visit.

The first thing to remember is that when the Earth rotates on its axis, the direction the axis points doesnít change (well, over thousands of years it does, but we donít really need to bother about this at the moment).

So imagine youíre standing at the North Pole during the northern winter (so itís dark all the time). As you watch the stars hour by hour, youíll find that they move around the sky in a circle. The centre of that circle will be directly overhead, and is known as the North Celestial Pole. The starsí movement is simply caused by the Earth rotating on its axis, and the stars will be where they were 24 hours ago. Now have a look at stars right on the horizon. Those stars will move around the horizon, never rising, never setting. But any stars below the horizon will never become visible to you, because the Earth gets in the way. All the stars visible to you at the North Pole are in the Northern Celestial Hemisphere, and all the stars not visible to you are in the Southern Celestial Hemisphere.

Now imagine you travel down to the South Pole. The effect will be the same, but reversed. All the stars previously invisible will now be visible, and those previously visible will now be invisible.

The reason this effect occurs is because the Earthís poles donít shift, except over the very long periods of time I mentioned earlier. There are parts of the sky which arenít ever visible from the polar regions because the Earthís poles are always pointing in the same direction.

Now imagine youíve travelled to somewhere on the Equator. At night time, all the stars will rise in the east and set in the west, again, simply because the Earth is turning on its axis. The North Celestial Pole will be on the horizon in the north, and the South Celestial Pole will be on the horizon in the south. Now while youíll be able to see lots of stars, some stars will be invisible because theyíll only be in the sky during daylight. However, six months later, the Earth will be on the opposite side of the Sun, so those stars will now be visible at night time, and other stars will be invisible.

For me in Australia, the Southern Cross is visible throughout the year, low down in the sky in summer, higher in the sky in winter. However, if I was to move a little way north, the Southern Cross would be below the horizon in summer, and only low in the sky in winter. If I continue to move north, thereíll come a point where I can never see it (though I donít know how far north Iíd have to be).

I hope this helps, but if it doesnít, please ask. Thereís nothing wrong with asking Ė it shows youíre interested in finding out.

GrapesOfWrath
2002-Feb-06, 09:27 AM
On 2002-02-05 23:23, Peter B wrote:
For me in Australia, the Southern Cross is visible throughout the year, low down in the sky in summer, higher in the sky in winter. However, if I was to move a little way north, the Southern Cross would be below the horizon in summer, and only low in the sky in winter. If I continue to move north, thereíll come a point where I can never see it (though I donít know how far north Iíd have to be).
I tried to look it up. This website (http://www.windows.ucar.edu/the_universe/crux.html) says you have to be below 30 degrees north latitude to see some of the Southern Cross. The southern most part of the sky that is considered part of the constellation Crux (which contains the four stars known as the Southern Cross) seems to be a line at about 65 degrees south. 90 degrees north of that would be 25. Acrux (alpha crucis) is at 63 degrees south, so you'd have to be below 27 degrees north to see the cross. To see the whole constellation at some time, you'd pretty much have to be in the tropics or farther south.

<font size=-1>[Fixed arithmetic, sheesh]</font>

<font size=-1>[ This Message was edited by: GrapesOfWrath on 2002-02-06 07:29 ]</font>

Argos
2002-Feb-06, 11:44 AM
On 2002-02-05 21:10, ljbrs wrote:


The folks in the Southern Hemisphere get a good view of the Galactic Center. They can view the two Magellanic Clouds (which are two of our neighboring galaxies).


You bet it is an awsome view!



I suppose the best place to drag a telescope would be high on a mountain in Chile,


Brazil is better, atop the mountains near the Atlantic coastal line, over the Capricorn tropic (only when it is not raining)./phpBB/images/smiles/icon_biggrin.gif

Another Phobos
2002-Feb-06, 04:40 PM
Brazil is better, atop the mountains near the Atlantic coastal line, over the Capricorn tropic (only when it is not raining)./phpBB/images/smiles/icon_biggrin.gif


Why Brazil? Chile's mountains seem better due to the drier air and the smoother air flows off the Pacific (air turbulence generated from air moving across the land of South America). Probably less smoke from the constant slash & burning across the rain forests of South America too. Of course, the mountains of Chile are the location of the ESO's new VLT.

ljbrs
2002-Feb-07, 01:11 AM
Quote:
--------------------------------------------------------------------------------


Brazil is better, atop the mountains near the Atlantic coastal line, over the Capricorn tropic (only when it is not raining).


--------------------------------------------------------------------------------



Why Brazil? Chile's mountains seem better due to the drier air and the smoother air flows off the Pacific (air turbulence generated from air moving across the land of South America). Probably less smoke from the constant slash & burning across the rain forests of South America too. Of course, the mountains of Chile are the location of the ESO's new VLT.


That is exactly why I selected Chile. Astronomers need clear skies and would need to be near the equater so as to avail themselves of both hemispheres (which would still depend upon Right Accension (R.A.) which changes the view gradually during the year only to repeat the following year.

However, I personally do not like high places (oxygen deprivation). Therefore, my viewing would be limited to lower elevations and more clouds. Perhaps a desert would solve that problem for me. Comfort at all costs...

ljbrs /phpBB/images/smiles/icon_smile.gif /phpBB/images/smiles/icon_biggrin.gif /phpBB/images/smiles/icon_wink.gif

Argos
2002-Feb-07, 03:18 PM
On 2002-02-06 20:11, ljbrs wrote:



Why Brazil? Chile's mountains seem better due to the drier air

The topic is about the position of the celestial sphere. As to see both halves of the sphere the location I suggest presents some advantages./phpBB/images/smiles/icon_wink.gif





That is exactly why I selected Chile. Astronomers need clear skies and would need to be near the equater


In the region I suggest the elevations reach 2800 m above the sea level. A pretty dry environment, specially in the (chilly, even there) winter nights. The Capricorn Observatory is located there, and its cameras yeld images of rare beauty. Of course Chile is the best, since you don't mind losing some interesting pieces of the Northern sky./phpBB/images/smiles/icon_biggrin.gif



<font size=-1>[ This Message was edited by: Argos on 2002-02-07 10:23 ]</font>

Argos
2002-Feb-07, 03:59 PM
On 2002-02-06 11:40, Another Phobos wrote:

Why Brazil? Chile's mountains seem better due to the (...) Probably less smoke from the constant slash & burning across the rain forests of South America too



The region I placed my hypotethical tropical Bossa-nova telescope belongs to the subtropical eco-system, a quite different scenario from the Amazon Forest, way up north. It's something more like Florida, or Georgia. It is not directly related to the the burning of the Rain forest. South America in general, and particularly Brazil, are vast geographic spaces, and there you can find nice places for a scope. Not to mention the most advanced infra-structure you can find in a place located 1 hour drive from Rio and S„o Paulo, which are international-class centers. And there is all that Samba and Mulatas and Bossa Nova...(Oh, Lord! Fly me down to Rio, again)

<font size=-1>[ This Message was edited by: argos on 2002-02-07 15:17 ]</font>