The Structure and Proportions of the Known Universe
Submitted: Friday, 13th January 2006 by Graeme Clement
The extremely minuscule proportions of the diameters of celestial objects to their distances apart are a little known fact. This is because of their misleading, but quite necessary, gross exaggeration in all diagrams of astronomical systems, as I explain below. From this unavoidable mis-impression arise misconceptions such as, among “New Age” people, that alignments of planets exert not only a measurable gravitational influence on the Earth and its inhabitants but also a significant one. When astronomers make advance announcements of such phenomena, such persons issue dire warnings of global disasters, but of course these never materialise (though they seem never to learn from those non-eventualities). Another common fallacy of similar basis is that, as astrologers teach their clients and the public and invoke science in support, the planets at the time of one’s birth exert sufficient gravitational force to influence one’s personality.
Following are approximate diameters and distances of Solar System objects and of some neighbours inside and outside of the Galaxy in which the Sun orbits, the “Milky Way”:-
The nearest star (apart from the Sun, of course) is Alpha Centauri, 4.3 lightyears away. (One lightyear is the distance light travels in one year, approximately 95 million million [95,000,000,000,000] kilometres.)
The Milky Way Galaxy is 100,000 lightyears across.
Our nearest independent galactic neighbour, the Andromeda galaxy, is 2.3 million lightyears distant.
To comprehend the foregoing figures is a challenge to the human mind. To bring them down to a meaningful scale, consider the Solar System reduced in size so that the Sun’s diameter (1.5 million kilometres) becomes 330 millimetres (or 33 centimetres). On the same scale, the planets would range as follows:-
In view of the foregoing, it is clear that any attempt to draw the Solar System to scale, on any surface of practical size, would render the planets invisible because of their tiny proportions.
As within the Solar System, interstellar space (the voids between the stars of a galaxy) is similarly very empty, with the exception of more or less tenuous bodies of gas and dust. For this reason, mergers of galaxies, which are common on astronomical time scales, rarely if ever produce stellar collisions.
For reasons similar to those I described above, to comprehensibly range beyond the Solar System, it is necessary to further greatly reduce the scale. For this purpose, consider the reduced scale of the Solar System, as described above, further reduced by a divisor of one million.
On that scale, Neptune’s orbit around the Sun becomes one millimetre in radius instead of one kilometre.
The nearest star, Alpha Centauri, would then be 10 metres away; the Milky Way would be 215 kilometres across; and the Andromeda galaxy would be 4,800 kilometres away. (On the reduced scale of the Solar System as formerly described above, Alpha Centauri would be 9,500 kilometres away, the Milky Way would be 215,000,000 kilometres across, and the Andromeda Galaxy would be 4,800,000,000 kilometres away.)
The nearest galaxies, along with the great one in Andromeda (visible to the unaided eye from the Northern Hemisphere) and the Milky Way, form what is known as the Local Group of galaxies.