Martin Timothy
Well-Known Member
http://apod.nasa.gov/apod/image/0911/NGC253_SSRO.jpg
Pythagoras told us the square on the hypotenuse, which is the straight line opposite the right angle provided by Microsoft Picture Manager, is the sum of the square of the other two sides.
1359 squared is 1846881, 1037 squared is 1075369, add the upper and lower to get 2922250, find the square root is 1709, thus the Galaxy subtends an angle of 1709 pixels rounded out to 1700.
We want to know because there are two more distant spiral galaxies located below right center in the same shot, the lower and smaller of the two fits into a box 14 X 14 pixels, the other is around 16 long, for the sake of simplicity we add another pixel to make it 17.
Divide that by the angle of 1700 pixels subtended by the much closer NGC 253, and find the more distant galaxy is one hundred times smaller, we are gonna say that it is similarly one hundred times more distant.
Sky Catalogue 2000.0 tells us NGC 253 subtends an angle of 25.1 arc minutes or .4163 of one degree, we divide that by the one thirty degrees of the Milky Way to get 310.78, which means NGC 253 is that many times further away than the center of the Milky Way galaxy.
Radio data from Sagittarius A* recognized as the heart of the MW galaxy, has returned a distance of 24,250 light years, NGC 253 is 310.78 times further away, multiply the distance to A* by 310.78, and get 7,536,415 LY as the distance to NGC 253!
The smaller of the two is somewhere around fourteen pixels across, however since it was less than that we do some more calculus, as each pixel is taken away so does the distance increase, should it become eight and one half pixels the distance would be 1578.83 million light years.
Since it was not that small, we will say half way between seventeen and eight and a half, so add four and a quarter pixels for an image half as wide again of twelve and three quarter pixels .. a fair total, then for a place that is similarly halfway between the upper and lower limits, go to a distance half way between at 1130.46 million light years.
FAQ's: How can you say all spiral galaxies are the same size??
Reply: The MW galaxy has the same overall profile as many similar disc galaxies, including NGC 253, ie an active center and emission nebulae spaced similar distances apart, less active and smaller galaxies have less active profiles, while spherical galaxies fall into a different category altogether, neither classes of object should be mistaken for anything else.
Where each pixel in image width corresponds to 188.2 million ly .. which is why we say galaxies are at a given mean, using the best estimate of the MW at one hundred thousand light years across as a yard stick.
We would be speaking in terms of millionths of a pixel in image width, were we to locate the true size of distant galaxies .. there is a critter called a Dwarf Spiral can trip you up, however all calculations should be accompanied by redshift data, which will expose any of those trying to sneak onto the main list.
This pic shows the relationships in the Milky Way family.
The MW is surrounded by star clouds which formed in emission nebulae at the tidal boundary of the galaxy .. the gravity source can not keep the disc stable outwardly for ever, and bits will spin off and go their own way at that place, this is the physical force that makes all similar disc galaxies roughly the same size, give or take.
The arms in spiral galaxies are a density wave, down which Hole Matter travels from the center trailing expanding emission nebula in its wake, whence form globular clusters and stars, see file material and very rare photos.
Clusters of stars resembling bunches of grapes form, and as expansion continues the individual grapes become stars, see the Pleiades, the Magellanic Clouds formed when a particularly virulent particles of Hole Matter arrived at the tidal boundary, then spun off into intergalactic space, maybe to keep expanding to form other major spirals, which will keep expanding from infinity - like a Mandelbrot Set - to spawn similar galaxies!
Q: How likely is it that globular clusters are juvenile galaxies?
Reply: Probably unlikely, in this model the compressed matter in the spiral arms expands in emission nebulae, to form stars and globular clusters, that drift to stations above and below the disc as the spiral evolves into an ellipse .. the globular clusters form a placenta that effectively shields the galaxy from radiation, and a buffer zone against collisions and impacts with other galaxies.
Q: So galaxies calve?
Reply: Sure they do, look for rare shots of spidery looking juvenile galaxies drifting away from parent bodies!
At left above galaxy M31 the closest major galaxy in the constellation Andromeda, not counting Dwingeloo 1 located directly opposite the nucleus of the MW, which thus remains invisible from Earth, the fuzzy blob below right center of M31 is satellite galaxy M32, the large blob in the disc slightly below left center is M110, both are embryo galaxies that could expand as a child galaxies of M31!
LSB galaxies are numerous and collisions between them are frequent, they do not show up at all on most conventional photo’s, and are thought to produce an abundance of silver which absorbs their light, their presence was revealed after large numbers of blue arcs centered on super massive elliptical galaxies, turned up in deep field shots at right.
Astronomers started looking for more and found millions near and far, during the collision phase if two colliding members are compatible, they combine then rapidly evolve into an active disc, as the nascent black holes lurking at the heart of both respond then reproduce.
