A montage of the planets and the Earth's Moon. These images were taken by a variety of spacecraft. Source: Courtesy NASA/JPL-Caltech
The Sun and the planets formed around 5 billion years ago, from a cloud of gas and dust left behind by dying stars. This was mostly Hydrogen and Helium, but there were traces of the heavier elements which would allow the formation of solid planets and, eventually, life.
The cloud collapsed into a rotating disk, with almost all of the material concentrated in a central bulge, where the Sun would form. At certain distances out from the centre, mass started to accumulate and gravity pulled in more and more material. The planets were beginning to form. They swept the area around them clear of small pieces of dust and rock as they orbited. They also frequently collided with larger rocks, growing in the process. Eventually they reached their current size. The material left became the comets and asteroids.
For another billion years or so stray comets and asteroids continued to bombard the planets. Many planets and moons, such as Mercury and our Moon, still show the scars from this period in the form of craters.
Today we can see the same process taking place around other stars, such as several young stars within the Orion Nebula.
The Solar System today consists of the Sun, 8 planets, at least 3 dwarf planets, at least 63 moons and countless other small bodies including asteroids, comets and Kuiper Belt objects. At the centre is the Sun, its gravity dominating the system and locking the others into their particular orbits.
The Solar System TodaySource: IAU/Martin Kornmesser.
The area around the Sun can be divided into several distinct regions:
As well as the Sun and the Moon, five of the planets (Mercury, Venus, Mars, Jupiter and Saturn) are visible to the unaided eye and have been known since ancient times. The remainder (Uranus and Neptune) and the dwarf planets have only been discovered since the invention of the telescope.
Hi Lauren, we ran this past our Planetarium experts, who have prepared the following reply:
Planets in our solar system all vary in their composition. The inner ones like Mercury, Venus, Earth and Mars have a great deal of silicon, oxygen, nitrogen, sulphur, magnesium, and iron. The outer planets Jupiter, Saturn, Uranus and Neptune have lots of hydrogen and helium, The cold worlds beyond Neptune, like Pluto , are different too. But the chemical elements in planets is only part of the story. How they have combined as chemical compounds is more important. For example, Earth has lots of oxygen and hydrogen, but together they make water. Or Neptune has carbon, nitrogen, oxygen and hydrogen in the form of methane and ammonia. See these links to follow up...
Earth history, composition and atmosphere
Neptune - Wikipedia
Earth composition - Wikipedia
Hi Nikki - we checked with our experts at the Planetarium, and they've responded as follows:
Planets can have rings for several reasons. By meteor impact with moons of the planet that throws material around it. By material from a moon being ejected by an internal process. By material being too close to the early planet which couldn’t form into a moon. By a moon being broken up by tidal/gravity stresses. By violent collision which another moon. Some planets have experienced one or more of these events in their history giving rise to rings of different types and sizes, while other planets have not. In our solar system the ring systems are around only the gas giants which have larger gravity and many moons giving more opportunity for one or more of these to occur but the exact process is still not fully understood.
When Planets align when viewed from the Earth we call it a planetary conjunction, and these are not too infrequent. On the morning of the 3rd December, just before sunrise, Mercury will be low in the sky, then Venus and higher in the sky will be Saturn. These will be visible no matter where you are on the Earth.
The planets of our solar system frequently “line up” in one way or another as they orbit the Sun at different speeds and distances from the Sun (inner planets more quickly than outer planets slower). The alignments as seen from Earth, or from an imaginary viewpoint above the solar system looking down, are interesting but have no effect on us in any observable sense. Gravity of the Sun and of the planets, and the speed of the planets around the Sun, hold the solar system together but the vast distances between the planets means this force is very weak.
An interesting site can be seen at : http://www.solarsystemscope.com/ (not a Museum Victoria site).
You've raised one of the hottest and controversial topics in cosmology; the multi-verse, branes, the big bang, repeated or cycling of the universe etc.. etc.. The short answer is that astronomers, cosmologists, physicists, and philosophers just don’t know for certain although they are using the best mathematics, rigorous modelling and extensive measurements. As far as travelling between supposed universes is concerned, there are no answers either as we have no certainty whether “borders” exist, how objects might cross over if they do, what mechanism might be involved. It is all very much hypothetical and speculative but grounded in the strongest research possible. It really is “cutting edge” but that’s what makes science and inquiry so exciting!
There is an excellent BBC Horizon documentary from 2010 called “What Happened Before the Big Bang” it really covers everything you are asking about.
The first animal in space was a dog named Laika - she was launched into orbit around the Earth in 1957 in the Russian satellite Sputnik II.
Hey JB & Connor, complex question! Basically, it's always hard to predict what will happen in the future. There are so many factors and variables that influence social and technological development. These sites should give a idea of current ideas and plans in space colonisation ...
There are frequently stories about the end of the world. The next date making its rounds on the internet is 21st December 2012 Taken from the NASA web site http://www.nasa.gov/topics/earth/features/2012.html is the following:
There is no credible evidence for any of the assertions made in support of unusual events taking place in December 2012.
Another common misconception is that when there is a planetary alignment, calamities occur. Planetary alignments actually occur about every 50 or 60 years so over the last 4.3 billion years since the Earth formed we are still here. The next big planetary alignment is on September 8th 2040 when most of the planets will cluster together, this should give spectacular viewing (if you are still around.!)
If the star was twenty light years away, we would see the explosion in twenty years time! We will see the light of the explosion but not feel the shock waves as it too far away. Light waves travel faster and further than any other form of waves. So no, you would not die.
Peter - according to the information provided by NASA at http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sun&Display=Facts, the Effective Temperature of the Sun is 5504 °C
Riley - Mercury can't 'burn to ashes' as the surface is essentially rock, and rock doesn't behave this way when it is hot - althought the surface of Mercury is made of exceptionally hot and inhospitable rock dotted with impact craters, it is essentially similar to the moon in many ways. You can learn more at http://museumvictoria.com.au/discoverycentre/infosheets/planets/mercury/
Benn - Pluto wasn't really 'demoted', just reclassified; it probably shouldn't have been classified as a planet in the first place. You can read the full story at http://museumvictoria.com.au/about/mv-news/2006/problem-of-pluto/
Isaac - scientifically there's no direct evidence of life inhabiting any other planets yet, but given the size of the universe and the liklihood of habitable planets, it seems like a reasonable guess that there is life elsewhere in the universe. NASA has its own research department dedicated to searching for evidence of life elsewhere in the universe, called the NASA Astrobiology Institute; you can learn about their research at http://astrobiology.nasa.gov/about-astrobiology/
Hi Connor, great question! Although it does sound a bit frightening, the earth is constantly being bombarded by meteorites - because the earth's surface is mostly sea, we don't have many of the records of these impacts, but rest assured, they happen costantly. Thankfully, these are all pretty small and pose a low threat, nothing large enough to trigger an extinction.
There is a research unit of NASA that examines 'Near Earth Objects', asteroids,comets and meteorites that have potential to strike the earth. The website is at http://neo.jpl.nasa.gov/; we mention this to assure you that there are many experts monitoring this, and that doesn't appear to be a significant threat from an extinction caused by a large meteorite strike any time soon.
We love receiving comments, but can’t always respond.
The Moon appears inverted, or upside down, when viewed from one hemisphere compared to the other. It’s the result of the different angle viewers have from locations south or north or the equator. The effect is to make the sunlit portion appear to increase from the left side of the Moon during the month as seen from Australia (southern hemisphere) while from the right side as seen from America (northern hemisphere).
Hi Vanessa, all employment positions at the Museum are listed on our website. Good Luck.
We have two separate factors in this excellent question but they are not connected. Jupiter’s spin or speed of rotation is simply how fast it turns on its axis (its “day”), and orbital speed is how long it takes to travel around the Sun (its “year”).
Gracie, as indicated above the Solar System developed from elements that later made life possible. But there of course may have been forms of life in other solar systems. You can read more about this on the website for NASA’s Exobiology and Evolutionary Biology Program.
Lollypop, you can find out how to research your question by reading our reply to Maddie on 20 November.
Tegan, the Lunar & Planetary Institute has some great ideas for making model solar systems that would be great for demonstrations.
Hi Sophie, check out this page for information about why Pluto is no longer considered a planet: http://museumvictoria.com.au/planetarium/discoverycentre/faqs/why-pluto-is-not-a-planet/
Hi Rhys, we are in the process of updating the information on the Melbourne Planetarium webpage’s, some information about the Dwarf planets can be found here:http://museumvictoria.com.au/about/mv-news/2008/new-dwarf-planets/ Keep checking the websites for updates.
Earth’s gravity is a direct result of its mass and volume, so even if its orbit changed, its mass would not. So, no, the gravity would not change.
Hope this helps!
Hi Graeme, this is a hoax that's been around for a few years and comes around every July/August. You can find further information about it at the Sydney Observatory blog and the Astronomical Society of South Australia site. For reliable information about the night sky you can go to the Planetarium's monthly Skynotes, the August edition of which should be out soon. You can find further information about Mars on this infosheet.
Hi Margaret, the Scienceworks Shop has lots of merchandise that may be of interest to you. You can contact them on 03 9392 4806.
Hi Marleen, the Planetarium staff believe the star referred to is Canopus, the second brightest star in the night sky. Sirius, the brightest star in the night sky rises just before dawn, but unlikely to be seen, being too low to the horizon. The brightest object to be seen in the morning night sky is in fact Jupiter. This can still be seen high in the northern sky even as the sky lightens and turns blue.
Hi Pasquale, the planets do indeed rotate around the sun as it says in the article above. The apparent 'movement' of the sun across the sky is actually caused by the rotation of the earth - one rotation equals one earth day. You can find further information and links on our website here and here.
Yes, Emma, Mercury is often visible in the night sky. For up-to-date information about where and when to catch a glimpse of the planet, check out Melbourne Planetarium's monthly Skynotes newsletter.
Hi Alan - our Planetarium staff think that the bright star you are seeing is the second brightest star in the night sky - Canopus. It is low in the south west in the early morning, just before sunrise.
Achim, the mass of Jupiter is an incredible 318 times that of earth, and is generally calculated to be, in kilograms, 1.9 times 10 to the power of 27! More info here.
Hi Skye - Whilst we are not affiliated with any Queensland astronomy site in particular, there are several astronomy groups with websites that may interest you! Try the Astronomical Association of Queensland, and the South East Queensland Astronomical Society to begin with.
The declassification of Pluto apparently produced heated debate among astrologers particularly on blogs. It seems that just because it's not a planet anymore doesn't mean that it is not considered significant by the astrological community. Just like for astronomers, Pluto's re/declassification does not detract from its interest and, possibly, only increases that interest.
Hi Milka! It's great that you've got such an interest in astronomy. We'd suggest that you have a look at the other infosheets available on this site (lots of your questions are answered there), and if you'd like to learn more, have a look at Australian Astronomy's "Learning More" page for some fun and useful links!
Space is a pretty big topic but this website is a good place to learn about it. We have lots of great information including sky maps, moon phases, Skynotes and infosheets. You might also want to visit the Planetarium to see one of our shows. The NASA website also has a vast amount of information on space and should keep you busy for ages!
That does sound confusing - perhaps if you combine the information provided in the three Infosheets on the Solar System, the Sun and Jupiter, the answer might present itself.
If a solution is still not forthcoming, you can log an enquiry with the Discovery Centre and we can check with the museum astronomer.
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