The diagram below shows the path of the Sun across the sky in Melbourne for four important dates:
The outer circle on the diagram represents the horizon and the inner circles are lines of constant elevation, drawn at 15° intervals. The radial lines are lines of constant azimuth drawn at 15° intervals also.
The position of the Sun at each hour of the day is marked and the time indicated. All times are Australian Eastern Standard Time. Add one hour for daylight savings.
Hi Ellie -if you're asking about how fast the Earth moves then three concepts can be involved: rotation speed, orbital speed, and time measured against longitude.
The Earth’s rotation speed on its axis does NOT change daily so there is no faster or slower rate during the day. The Earth is very stable in its rotation.
The Earth’s orbital speed (how fast is travels round the Sun) does change slightly during the year as its orbit is not a circle but an slight ellipse. The Earth is a little faster in its path when closer to the Sun and a little slower when further, however the actual difference in speed is extremely small.
The Earth’s rotation can mark time by observing how many degrees of longitude it turns each hour. With 24 hours to one complete rotation west to east being equal to 360 degrees (a full circle), then each hour would match 15 degrees of longitude (15 x24 = 360). This rate does NOT change during the day.
Here are some websites to follow up…
Yes, this was an illusion. Have a look at our response to John Jones’ enquiry (above; 14th April 2010), which addresses this. Also, you might find the explanation in the following link helpful: http://www.astronomynotes.com/nakedeye/s5.htm.
The Sun does not travel the same path throughout the year, but follows the path shown in the following diagram: Path of the Sun
As far as what is the difference between ‘real time’ and ‘clock time’, the following extract taken from this UK web-Sundials should explain the differences quite clearly.
Sundials tell "sun time". Clocks and watches tell "clock time". Neither kind of time is intrinsically "better" than the other - they are both useful and interesting for their separate purposes.
"Sun time" is anchored around the idea that when the sun reaches its highest point (when it crosses the meridian), it is noon and, next day, when the sun again crosses the meridian, it will be noon again. The time which has elapsed between successive noons is sometimes more and sometimes less than 24 hours of clock time. In the middle months of the year, the length of the day is quite close to 24 hours, but around 1 September the days are only some 23 hours, 59 minutes and 41 seconds long while around Christmas, the days are 24 hours and 31 seconds long.
"Clock time" is anchored around the idea that each day is exactly 24 hours long. This is not actually true, but it is obviously much more convenient to have a "mean sun" which takes exactly 24 hours for each day, since it means that mechanical clocks and watches, and, more recently, electronic ones can be made to measure these exactly equal time intervals.
For more detailed information, the above web site should be looked up.
The Earth does orbit the Sun, taking 1 year to do so. The Sun also rotates about the centre of the galaxy, where there is a super massive black hole. It takes the Solar System about 240 million years to complete one orbit of the Galaxy , so the Sun is thought to have completed 18–20 orbits during its lifetime. So, yes, the Earth orbits both the Sun and a black hole.
Hi Lloyd - there's no need to be baffled; the short answer is that there are no 'new stars behind the sun' because unlike earth, the stars do don't orbit the sun; this is explained in our responses to STEVE above.
The only time that the Sun rises due east and sets due west is at the Spring and Autumn Equinoxes, 21st March and 21st September. After the Spring equinox the Sun gradually rises and sets further south until the solstice on 21st December, then starts moving northwards. So for your house to have the Sun shining on the south facing side, it needs to be between these two equinoxes. After the Autumn equinox the Sun rises and sets northwards of east and west, so no Sun on your south wall.
For more information, please see the following link: http://museumvictoria.com.au/discoverycentre/infosheets/planets/the-path-of-the-sun/
Hello Cool - we ran this past our experts in the Planetarium, and their response is as follows:
In Australia, seasons begin on the first day of a particular calendar month – March for autumn, June for winter, September for spring and December for summer. This is also the convention followed internationally by meteorologists. One idea for Australia following this rule, is that during the early years of Australia’s white settlement soldiers would change from their summer to winter uniforms on the first of the month.
Indigenous Australians have a more tactile view of the seasons. They link the seasons to the local conditions and environment, and also to the activities of the birds, plants and animals around them. With such a diverse climate across Australia, it’s no surprise that the seasons vary greatly across Indigenous groups. Some regions have five seasons and others only three as the Bureau of Meteorology explains.
In other countries, such as Britain and the USA, the seasons are said to begin on the equinoxes and solstices – Spring Equinox, Summer Solstice, Autumn Equinox and Winter Solstice. These are the times when Earth reaches a particular point along its orbit around the Sun.
I hope this helps
Hi again Steve - The sun is not at any point directly 'between' earth and the Southern Cross. An important point to consider here is that unlike Earth, the Sothern Cross does not revolve around our Sun.
If you look at the diagram at the top of this page, you can see the path of the sun as it appears to us here in Melbourne throughout the year. If we were to factor into this diagram the relatively static position of the Southern Cross, it would be close to the southern horizon. Notice that the southern most path of the sun (in the Summer Solstice) does not intersect with the position of the Southern Cross.
This means the Sun does not obstruct our view of the Southern Cross - so, we are never on 'the other side of the sun' to the Southern Cross. As we've explained previously, the Sothern Cross may not be visible during the day due to brightness of the Sun, but it is still there.
Hi Jim, if you were at one of the poles during a summer equinox the Sun continues to make a circle in the sky, but now it would dip below the horizon for a while. It may appear to be an ellipse, but in actual fact it is still a circle. This YouTube clip, http://www.youtube.com/watch?v=ZZcafg-meJA shows what it would look like a little further away from the pole. This web link may also be helpful.
Hi John,There are two websites that may help you determine the angle of the sun at your house on a particular date. The Rise and Set Times on the Planetarium website provides a calendar for the visibility of the sun in Melbourne. There is also an online resource about how to make your own Sun Angle Calculator.
Hi Casper, the Sun’s path is at its lowest in the sky on the Winter Solstice – 21st June, see here for more information.
Try to think of it this way - If you were “on” the Southern Cross and looked towards Earth with a theoretical, highly powerful telescope, then Melbourne would always be visible, because the bottom of the Earth is pointing towards the Southern Cross. As the Earth spins on its axis, Melbourne would appear to rotate around the globe. As go further north from Melbourne, say to Sydney, then as the Earth spins, an observer on the Southern Cross would see Sydney disappear briefly on each rotation. The further you travel north the less time you will be able to see the Southern Cross, until you can never see the Southern Cross.
It is like that the Sun is at the centre of a globe of stars, and the Earth always points to one spot in the sky which is close to the Southern Cross. In reality this is not so, but the concept is true.
I hope this may clarify it a bit more for you.
Hi Steve - The Sun is at the centre of our Solar System, and all planets revolve about the Sun. The Sun at the centre of our Solar System, is in our galaxy called the Milky Way Galaxy amongst about 400 billion other stars. All the stars that can be seen with the naked eye are in our galaxy. It's important to remember at this point that our sun is not at the centre of the galaxy.
Because we revolve about the Sun, which is very close to us, all the other stars which are much further away, do not appear to move as we move around the Sun. So the constellations, such as The Southern Cross, look the same wherever we are. As the axis of the Earth is tilted, the south pole axis points towards the Southern Cross, so that constellation is always visible in the lower latitudes such as Victoria.
Hope that helps
We love receiving comments, but can’t always respond.
The link to this section of the NASA website gives a brief insight to the history of the evolution of the theory of the planets movement around the sun.
Hi Georgina - Several factors effect sunrise and set times, such as surrounding buildings or mountains, elevation above sea level, etc; however the main reason in this case is because Sydney is much further east than Melbourne, by approximately 700 km.
For advice about seating, you would probably be best to check with MCG staff directly - MCG contact details can be found here.
Hi, Fernando. The "Time and Date" website gives information about the length of days for several locations in regional Victoria, including Ballarat. Hope this helps!
Hi Mel, the Tropic of Capricorn is technically an infinitesimally thin line, although the uncertainty in the measurement of the Earth's obliquity corresponds to an error in positioning of the Tropic of about 3cm. We can't locate the Tropic any better than this, so this is a kind of width. At the moment the Tropic is at 23°26'16.7" S. But the obliquity of the Earth varies and is decreasing around a half a second of arc per year, so the Tropic is moving slowly northwards at the same rate. This corresponds to something like 13m per year. So depending on what kind a timeframe you want to look at this also puts limits on how precisely you can locate the tropic. Within a decade, for example, we can't locate the Tropic more precisely than a 133m band.
Hi there John. As in the Northern Hemisphere the Sun rises in the East and sets in West (due to Earth’s rotation from west to east), but its path as seen from the Southern Hemisphere is across the northern sky. You might find this link and this one useful.
Hi there Suradi - thanks for your question. According to the Museum's Planetarium Presenters, these days a Sun Path can be got using any good astronomy program or planetarium software such as Starry Night or Stellarium. Please note, if you would like to use our diagram for anything other than private use then MV copyright acknowledgement would be expected.
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