Our first understanding of the solar system was an Earth-centered system orbited by the sun and moon, a handful of planets, and a sphere of fixed stars. Today, we know of thousands of objects in our sun-centered solar system, with new discoveries occurring all the time.
From our perspective, we could say that the solar system grew over the centuries. And yet, the vast majority of the objects that we know of today did exist way back when. So really, it is our understanding of our solar system and new discoveries that make it appear that our solar system is expanding.
Early Models of the Solar System
The first models of our solar system, also known as the geocentric or Ptolemaic model, had Earth at its heart. This system was based on what could be viewed in the sky with our naked eyes.
Earth was surrounded by eight spheres, which contained the moon on the innermost sphere and followed by Mercury, Venus, the Sun, Mars, Jupiter, Saturn, and the fixed stars. The model was ordered taking into account the various orbital periods of the objects and was calculated to be approximately 1.2×108 kilometers (7.3×107 miles, 1.2×10-5 light years, or 0.8 AU) in radius. Keep in mind, this model was assumed to be the size of the entire universe, not just our home planet and intermediate family.
Between the mid 1500s and early 1600s, with Nicolas Copernicus’ publication, On the Revolutions of the Heavenly Spheres, and with the invention of the telescope and Galileo Galilei’s observations of solar system bodies, it was concluded that:
- the Earth was not the center of our solar system after all.
- that some bodies in our solar system, such as Jupiter and Saturn, had moons of their own
These two ideas increased not only the tally of objects in our solar system, but also the overall understanding of it.
Current Models of the Solar System
Each new discovery, from the moons of Jupiter in 1610 to the discovery of Uranus in 1781 to the initial concept of the Oort cloud in 1950, drastically increased the size of our little area in the galaxy.
The current model of our solar system begins with the Sun at the center surrounded by eight planets, a handful of dwarf planets, hundreds of moons, and thousands of asteroids, comets, and other small bodies. We call this the heliocentric model. Our solar system is currently believed to be nearly 1.8×1013 kilometers (1.1×1013 miles, 1.87 light years, or 1.2×105 AU) in radius, about 150,000 times larger than originally believed.
And since the originally believed size of the universe was mentioned above, the currently accepted size of the universe has gone from about 1.2×108 km (1.2×10-5 light years) to at least 8.6×1023 kilometers (9.1×1010 light years), more than 7 quadrillion (7 followed by fifteen zeroes) times.
New discoveries = Bigger Solar System
New discoveries are what drive the expansion of the solar system. Of course, the solar system is evolving and changing on its own time scales, but for the most part, the time scales are much too long for our short human time frames.
With each new discovery of a moon, dwarf planet, asteroid, comet, etc., the solar system is growing. And while a new asteroid found orbiting the Sun between Mars and Jupiter doesn’t exactly change the known diameter of the solar system, our knowledge and understanding of our solar system does. And that counts too.
How do we keep discovering new things?
The invention of the telescope in the early 1600s was a game changer in astronomy and new astronomical discoveries came immediately. Telescope improvements are continuing even to this day: more reflective mirror surfaces, larger diameters of mirrors and lenses, and the ability to put telescopes into space are just a few. And not just telescopes, but the ability to take photographs of outer space as well.
The first identifiable image of an astronomical object was of the Moon in 1840 and amateur astronomers did much of the astrophotography that took place over the next few decades. Astrophotography for research purposes became popular in the late 1800s with the introduction of dry plate photography that use a glass plate coated with a gelatin substance containing silver bromide. Film became popular in the early to mid 20th century with the use of large telescopes including the 5 metre Hale telescope. The introduction of CCDs in the 1970s revolutionized astrophotography with greater sensitivity to be able to see dimmer objects.
The majority of new astronomical discoveries are found by professional astronomers. They typically have access to largest telescopes in prime locations with the best technologies.
Survey telescopes can map entire sections of the sky in just a few days and can quickly catch any new or moving objects (such as SDSS and the upcoming LSST). Other telescopes respond quickly to these new or moving objects studying them in greater detail (such as PanStarrs, which is both a survey and rapid response telescope, or LCOGT).
Some telescopes stare at the same patch of sky for extended periods of time to search for slower moving or longer period objects (such as the Kepler space telescope). And there are a few telescopes that are even in space in orbit around Earth (such as Hubble), at Lagrange points (such as SOHO and the upcoming JWST), or even traveling to distant worlds (such as Cassini and New Horizons).
There have even been missions that are traveling towards interstellar space (such as Voyagers 1 and 2).
Many of these telescopes have some of the best imaging devices, spectrographs, and other equipment available, which makes it possible for astronomers to not only see further into our universe, but take a closer look at objects within our own solar system.
Professional astronomers, however, are not the only ones who are making new discoveries. The amateur community is gaining traction and greatly contributing to both the object tally and our understanding of the solar system. Many of them have modest equipment but their contributions to astronomy are invaluable.
As mentioned above, amateurs were among the first to experiment with astrophotography. Now, nearly all astronomers and amateurs participate use various astrophotography techniques in their research.
There have been a number of asteroids (such as asteroid 2011 SF108 and many more by this amateur astronomer) and comets (a few are found here and here) discovered by the amateur community, new details about the planets (such as Jupiter’s scar), as well as telescope innovations (such as those by John Dobson).
Our Growing Solar System
From a handful of bodies to hundreds of thousands, and from an Earth-centered to Sun-centered system, and even discoveries of new bodies or new features on known ones, our solar system has grown and changed in size, shape, structure, and understanding. And with telescope and imaging technology improving, as well as growing numbers of amateur astronomers contributing to the discovery list, who knows if we will ever discover all there is to know in our constantly expanding and fascinating solar system.