Stellarium Snapshots (III)
Unexpectedly, this one will be in English (booo hooo, pity! 🙂 if you want a translation (well… the language type of…), comment and I’ll translate to Spanish, or Italian).
(Bueno, os lo diré en español… si queréis una traducción comentar | Va bene, vi lo dirò in italiano… se volete una traduzione commentare).
Although I left aside the Stellarium posts series for some days (while programming a game in a new IDE that I am both configuring and understanding how it works, and writing ‘Logic Gates’ series also), I must write this one as a full User’s Guide with some clarifying concepts (remember: I haven’t read the TOC yet… [Table Of Contents…]).
I’ll start back in.. say… six hundred years ago…
Believe it or not (you never know how disbelieving people can be…), hundreds of years ago people thought the Earth was flat as a pizza. This resulted in cartography and astronomy developing as if the Earth was really flat, so most people do not have in their minds some (basic spherical) concepts…
For instance, when we go through a flat landscape, such as that which can be observed in the Spanish wide regions of Castilla León and Castilla la Mancha, or other flat landscapes, such as most of Poland (talking about Poland, I remember while walking on its streets in a journey I made years ago, I noticed the road was soft (the kind of feeling you would have if you were walking on a pizza medium tough dough layer, besides there were footprints on the asphalt because they use a different type of asphalt which literally melts and gets soft above some ambiance temperatures much lower than those which can be reached here in Spain, they use other range of temperatures values due to the difference in climate between Spain and Poland. I am (not) ‘sure’ (, but) they may be having trouble with their roads, because of the increase in temperature worldwide, … what was its name?… oh, yes! global warming…), we don’t usually think of those flat surfaces as being part of a fully spherical surface (with a very big radius) that is the surface of our planet. So we don’t think in spherical terms, because we do not perceive ourselves as living onto a planetary scaled type of spherical bolard.
In the image above you can see some spherical bolards onto a flat surface, but believe it or not, that surface is NOT flat, but also spherical, look at this image below.
I will give you a link to read directly and then I will comment this text.
‘The Altitude [slight edition: and] Azimuth [Altitude, Azimuth] coordinate system can be used to describe a direction of view (the azimuth angle) and a height in the sky (the altitude angle). The azimuth angle is measured clockwise round from due North. Hence North itself is [zero]°, East 90°, Southwest is 225° [IMPORTANT NOTE (1)], ->>> [ 180º for South + 90º for West, – 45º, because Southwest is in the middle of those two coordinate values, that’s 270º – 45º = 225º, according to the Stellarium page for Astronomical Concepts for which I put a link above, this 225º does not make sense when though in trigonometry terms, because in geometry North is not 0º degrees, it is 90º degrees, and the increasing sense for angle values is counter-clock wise, and not clock wise as is the case for Astronomy], and so on. The altitude angle is measured up from the horizon [it is called Right Ascension, RA]. Looking directly up (at the zenith, just above our heads) would be 90°, half way between the zenith and the horizon [horizontal pizza surface where the man in the image is standing on] is 45°, and so on. The point opposite the zenith is called the nadir [right below our feet, vertically opposite to our heads along the direction of our standing up bodies].
IMPORTANT NOTE 1: In geometry, and their physics world implementations, we usually take angle values from 0º degrees respect the horizontal positive value which increase counter-clock wise, this is why the cosine value for 0º degrees is 1, positive, and 180º cosine is -1, negative, both of them |1| in absolute value, or base vector modulus. This is not the case here, note ‘here’ is for astronomy and astronomers.
The Altitude and Azimuth coordinate system is attractive in that it is intuitive – most people are familiar with azimuth angles [really? 🙂 ] from bearings in the context of navigation, and the altitude angle is something most people can visualise pretty easily.
However, the altitude and azimuth coordinate system is not suitable for describing the general position of stars and other objects in the sky – the altitude and azimuth values for an object in the sky change with time and the location of the observer [because the coordinate system, in this case, is centered on the observer and not on the object being observed].
Stellarium can draw grid lines for altitude and azimuth coordinates. Use the button on the main tool-bar to activate this grid, or press the z key.’
The above image man, who is standing on a pizza like surface, in the center of a sphere, is not in the center at all, but on the (spherical) surface of this sphere of despicable mass in kinematics analysis, which is our planet…
(? … Earth [for short] 🙂 ).
And once this ordinate (?) system has been introduced, let me show you some snapshots I took with the program some moments ago.
Here you can see the ground [Ground [Ctrl + G]] button highlighted in the toolbar on the bottom left part of the image, it corresponds to the shadow area below the horizon, onto with the N, for North, and E for East, are. The bright dotted N (for ‘name’) is for constellation’s names which appear in blue. The symmetrical horizontally dotted N next to that button is for constellation’s lines, also in blue. Click on those and you’ll toggle the view from with/without. Which I did for the next image on the ‘Ground’ button [sort of… floating out there].
This other image is the same as the previous one, but without ground (nor toolbar). You can see the Sun here. Its position is scarcely LESS than MINUS fifty degrees from the horizon [in absolute values is the other way around: |-52| is greater than |-50|].
50º are swirled in three hours and twenty minutes, so according to this image, the Sun would have to rise upon the horizon’s line (the surface of the pizza) at 03:16:20 PLUS 3 and a half hours (more or less), that’s 06:46:20 (the more or less error is because the Sun is not exactly at -50º in this snapshot) PLUS the UTC hour lapse according to your longitude, that’s 08:46:20 (more or less). The astronomical calendar for Oviedo, Spain for today says it will be day at 831 (they must have been in a hurry, I should have written it like this: 08:31).
The next image is the same, with the ground visible and the other grid divisions.
There are two types of grids, one in orange, the other in blue. The one in orange gives positions respect to the ecliptic, that’s the plane into which the Earth orbit is contained (hmmm… say.. the room where the table onto which the pizza is). The blue grid is the other and it is set according to the rotation axis, that is why grid lines pass through the Ursa Minor constellation (the other grid centers itself near Perseus).
IMPORTANT NOTE: The [M] key toggles the mount of the image, in these images, the horizon line appears to have zero arc degrees of difference with the horizontal plane, the bottom or top of your monitors), but it is not so, it is a representation. The real inclination of the horizon (the pizza onto the man in the drawing above is standing, which I foretold is a tile of a sphere), can be seen by pressing Ctrl key together with M key, if the horizon in the other mode was a horizontal line then the inclination has the same degrees as your latitudes.
In the next image I leave only the blue grid.
Next one is the same view without the ground.
In this I zoomed out a little and made the two grids visible, so you can see the Northern coordinate centers for the two of them, one on Ursa Minor, and the other slightly above Perseus.
Besides the flat like hundreds of years ago referred to, astronomical and geometry concepts, there is another important thing to consider: inclination.
In the top part of the above image there is a representation of the Earth swirling around the Sun through the ecliptic plane (hmmmm… sort of taking the Circular metro line in Madrid and having a pizza laid flat on a table… more or less).
You can see in that scheme, the rotation axis inclined, not perpendicular to the plane, and for this much more like really it is set I made some screen snapshots changing the mount from equatorial to azimuthal, this is why you will see the horizon, and the ground inclined in the next images.
Both grids visible (above image).
Same without ground (above image).
Same with only the blue grid (says azimuthal, but I don’t think so, might be a bug.. I told you, I haven’t read the TOC yet…) (above image).
Same with ground (above image).
Same with the two grids (above image).
Same with only the orange grid (image above).
Same without ground (above image). You can see here the Southern orange grid center below the Sun slightly on its left.
Same zoomed a little (image above).
If you go back to ‘October-Precession’ image you can see the scheme and read the explanation on how precession makes the Earth not to rotate EXACTLY around the Ursa Minor-South Cross axis. It is sort of… pointing towards the ceiling with a lantern while swiveling it around, the light on the ceiling is not pointing on the same spot all the while, but is changing its position constantly.
And talking (once more) about precession, ‘THIS’ is an image I uploaded here in my blog some months ago. In that image you can directly see the alpha angular acceleration value, generally considered as a scalar for calculations in physics, and its implementations, represented as what it really is: A VECTOR.
And I’ll tell you once more: some constellations appear symetrycally reflected from what should be their disposition according to their neighbor constellations in the same near area (Casiopea appears as if reflected in a mirror pane, viewed from here at that moment, checked visually with my eyes, Orion appeared right oriented, but Casiopea appeared horizontally flipped).