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 Sun:-
• 1.5 million kilometres in diameter;
• Mercury:-
• 60 million kilometres from the Sun, and 5,000 kilometres in diameter;
• Venus:-
• 110 million kilometres from the Sun, and 12,000 kilometres in diameter;
• Earth:-
• 150 million kilometres from the Sun, and 12,750 kilometres in diameter;
• The Moon:-
• 385,000 kilometres from Earth, and 3,500 kilometres in diameter;
• Mars:-
• 230 million kilometres from the Sun, and 6,750 kilometres in diameter;
• Jupiter:-
• 780 million kilometres from the Sun, and 143,000 kilometres in diameter;
• Saturn:-
• 1,430 million kilometres from the Sun, and 120,000 kilometres in diameter;
• Uranus:-
• 2,900 million kilometres from the Sun, and 50,000 kilometres in diameter;
• Neptune:-
• 4,500 million kilometres from the Sun, and 50,000 kilometres in diameter.

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:-

• Mercury would be 1 millimetre in diameter and 13 metres from the Sun.
• Venus would be 2.5 millimetres in diameter and 24 metres from the Sun.
• Earth would be 3 millimetres in diameter and 33 metres from the Sun.  The Moon would be 1 millimetre in diameter and 8.5 centimetres from Earth.
• Mars would be 1.5 millimetres in diameter and 51 metres from the Sun.
• Jupiter would be 3.2 centimetres in diameter and 175 meters from the Sun.
• Saturn would be 2.7 centimetres in diameter and 320 metres from the Sun.
• Uranus would be 11 millimetres in diameter and 645 metres from the Sun.
• Neptune’s diameter would be 11 millimetres and its distance from the Sun would be one kilometre.

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.

What lies beyond the Local Group?

There are many thousands of millions of galaxies, forming clusters of galaxies and superclusters of clusters.  Superclusters are known to form the largest structures in the Universe; these form walls around vast voids, which resemble bubbles.

The Local Group is an outlying part of the Virgo cluster, which in turn is a member of the Hydra-Centaurus supercluster.

Far beyond the Virgo cluster lies the Great Wall, a relatively thin but substantial sheet of galaxies which extends across the part of the sky visible from the Northern Hemisphere, into the part seen from the Southern Hemisphere, and vanishes from our view behind the body of the Milky Way.

The Milky Way and many other galaxies nearby are drawn toward a Great Attractor, which lies hidden from our view by the Milky Way.  Here the expansion of space is distorted, so that all the local part of the Universe is drawn toward a point 150 million lightyears away, and which is believed to be a mass of more than 10,000 galaxies.

Article by Graeme Clement (The Cosmic Sentinel). Discuss This Article at the IceInSpace Forums.