What declinations will I be visible to see from my latitude?

[Arion]

I was just assembling a list of interesting stars that I should try to find and that of course raised the question which of these stars would never be visible because they are just too far south.

Now my latitude is 53°52'N and if basic geometry isn't failing me this means that hypothetically at midsummer, I could see the sky down to -43°52'. But even with me living in a really flat area, that's not going to be realistic, isn't it? Peeking at the horizon will get me way too much air in the view. How much should I realistically subtract to get the maximum practical declination south at which I can still see something worthwhile?

I think I once heard the number "30° above the horizon", but would you agree with that? And do light conditions factor into this or is that a separate issue?

[lenscap]

If you download planetarium software like;

http://stellarium.org/

you can put in your location & display all the celestial objects that are visible at any time. (free download)

You can see down to about -30 DEC at the moment.

Anything within about 15 degrees of your horizon will be difficult to see clearly because of the thickness of atmosphere & perhaps pollution & light pollution. Sadly the bright planets are all low at the moment but still well worth a look.

[Arion]

Somehow I am not surprised this is available for Linux. ^^

[kirkster501]

90 degrees minus your latitude.  So if you're 50 degrees North you can theoretically see to -40.  If you're 20 degrees North you can see down to -70 degrees.  You won't see that low because of atmospheric effects so add another 3-5 degrees.

[ollypenrice]

1 minute ago, kirkster501 said:

90 degrees minus your latitude.  So if you're 50 degrees North you can theoretically see to -40.  If you're 20 degrees North you can see down to -70 degrees.  You won't see that low because of atmospheric effects so add another 3-5 degrees.

Agreed, though I think 3 to 5 degrees is very optimistic! Sky quality, light pollution and horizon altitude govern the real limit. Here we have slightly raised horizons, which have the advantage of blocking LP, and then the limiting factor becomes the dryness of the sky. Humidity lifts the LP higher. Dry nights have lower limiting altitudes. I'd say that if you can usefully go below 15 degrees you're doing darned well.

Olly

[Arion]

Light isn't great here (though I am surprised how much you can see with just your eyes) and humidity is always high. So I guess something like 20° as a cutoff point would sound realistic?

[Stub Mandrel]

1 hour ago, ollypenrice said:

I'd say that if you can usefully go below 15 degrees you're doing darned well.

Us planetary imagers say go for it! I've got down to 2.5 degrees this year, this image was at 3.5 degrees. Ok, it might not be showing much, well barely any, detail but that's partly the dust storm ... I've got some details from Mars last night when it was at 10 degrees.

3.5 degrees...

10 degrees:

 

[ollypenrice]

11 hours ago, Stub Mandrel said:

Us planetary imagers say go for it! I've got down to 2.5 degrees this year, this image was at 3.5 degrees. Ok, it might not be showing much, well barely any, detail but that's partly the dust storm ... I've got some details from Mars last night when it was at 10 degrees.

3.5 degrees...

10 degrees:

 

I'm impressed!

Olly

[kirkster501]

I read an article that says when you're looking at about 10 degrees above the horizon you're looking through about ten times as much atmosphere as when looking straight up to the zenith.

[ollypenrice]

22 minutes ago, kirkster501 said:

I read an article that says when you're looking at about 10 degrees above the horizon you're looking through about ten times as much atmosphere as when looking straight up to the zenith.

That makes sense if you imagine the layer of atmosphere around the globe then put two lines of sight through it for the same observer, one to his/her zenith and the other to his/her horizon.

The same geometrical effect explains why roughly spherical 'bubbles' like the Rosette and the Veil (or, indeed, the 'Bubble' itself) look like circular objects. A line of sight to their centre passes through relatively little glowing gas whereas lines of sight towards their outer edges passes through many times as much, making the gas visible.

Olly

[Stub Mandrel]

The impact of azimuth is immediately apparent if you think of how much the sun's light is attenuated as it approaches setting.

[kirkster501]

it amazes me that when the ISS is at about 30 degrees above the horizon from where I am n Nottingham, the ISS is actually over Germamy at that time!  

[Arion]

The ISS is freaky in so many ways. Is there a good site that shows the current position of the ISS above the ground?

[Stub Mandrel]

ISSTracker.com