(Thanks to Graeme Houghton for this great photograph taken from the grassy knoll just to the side of Rye pier)
Rye is sixty three kilometers due south of the central business district of Melbourne. Between the two there is just water; Port Phillip Bay. Just occasionally one can see the Melbourne Central Business District from the Rye foreshore.
This is very odd because you should only be able to see the tips of the two tallest buildings in Melbourne. The rest are over the horizon. (see the calculation below).
What you are seeing is something really quite fascinating. You are seeing an atmospheric phenomenon, refractive looming and possibly a Superior Mirage.
Let me explain.
Firstly, there is nothing superior about a superior mirage. It just means it is up there rather than down here.
We are all familiar with inferior mirages. These are the ones that occur on hot days. One sees what, to all intents and purposes, looks like a puddle of water in the road ahead. However, it stays ahead. Just like the end of the rainbow, it cannot be reached. The effect is caused by the bending of light rays. The air near the road is hot and therefore has a lower refractive index than the air above. The layers of differing refractive index behave rather like an optical fiber; the image in the higher, cool, denser, air being reflected at the boundary with the lower, hot, less dense air.
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An image of the palm tree is seen reflected in a pool of light from the sky. Diagram from: What is a mirage? How is it formed? |
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A superior mirage is a rarer event. It requires there to be a temperature inversion. This is when the air near the ground is colder than the air above. In the case of Port Phillip Bay it occurs when the water, and hence the adjacent air, is colder than the air above. In this instance the layers of differing refractive index cause the rays of light to be bent, and sometimes reflected, downwards. Under these conditions you can actually see over the horizon.
The literature tells us that superior mirages can take the form of towering, looming, and inversion, depending on the particular density structure of the air column.
However, being pedantic - and what scientist isn't - the title Superior Mirage should only be applied to the latter case. That is the case of the inverted image. Mirage is a French word meaning reflected image. Towering and looming involve the refraction of light. The inverted image involves the (internal) reflection of light. Strictly speaking, that alone is the Superior Mirage.
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The image appears to be elongated Diagram from: The Superior Mirage: Seeing Beyond |
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The Vikings see over the horizon.. Diagram from: The Superior Mirage: Seeing Beyond |
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An inverted phantom image in the sky. Diagram from: The Superior Mirage: Seeing Beyond |
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And there is yet another type of superior mirage, the fata morgana : a complex mirage in which distant objects are distorted as well as elongated vertically. For example, a relatively flat shoreline may appear to have tall cliffs, columns, and pedestals. The phenomenon occurs under much the same meteorological conditions as the superior mirage with inversion, and contains features of both towering and inversion.
Let us do a simple calculation.
Straight line distance between Rye and Melbourne = 63 km.
Assume the Earth to be a sphere of diameter= 12742 km.
It can be shown that (See link).
D = 3.856 √ h
Where D is the distance to the horizon in km. seen by an eye h metres above the ground (or sea).
A pedant will notice that the above formula is not dimensionally correct. It gives, however, a very good approximation to the correct answer.
Thus for a person of average height standing at the edge of the sea with toes in the water (h= 1.67 m)
the horizon is a mere 4.6 km. away, ie. approximately 3 miles in the old numbers.
For a person of the same height standing on the observation deck of the Eureka Building in Melbourne h = 285 + 1.67. Their horizon is some 65 km away.
These people can just see each other, since 65 + 4.6 = 69.6 km is just greater than the physical distance, 63 km.
Working the other way. A person with toes in the water in Rye should only be able to see a building in Melbourne provided it is taller than 234 metres.
There are only two buildings in Melbourne taller than this. The Rialto Tower (285 m) and the Eureka Tower. (300 m). Only the top of these two buildings should be visible from the Rye waterline.
So if you ever see the Melbourne Central Business District from the sea front at Rye you are seeing a Superior Mirage of the refractive looming type.
Note: The hill on the Mornington Peninsula, Arthur's Seat , is 314 m above sea level and 60 km from Melbourne. Using the above formula it is straightforward to show that seeing the Melbourne CBD from Arthur's Seat requires good visibility but does not require the unusual meteorological conditions.
Superior Mirages (know as the hillingar in Icelandic) are common in the Arctic and the Antarctic. They have played an important role in Arctic and Antarctic exploration. In other parts of the world they are less common. They occur most frequently after dark. Could car headlights seen over the horizon be interpreted as UFOs?
Some well known examples of seeing beyond the horizon are:
Seeing the Isle of Man from the Lancashire coast. (Seeing this in August 2005 inspired me to write this page)
Seeing the Norwegian mountains from the top of the Cairngorms in Scotland.
Seeing the mountains of Greenland from the mountains of Iceland.
If you can add to my list or report any interesting related phenomenon please write to me:
tony.heyes@physics.org
Note: I wrote this page and then asked the experts to comment. In this context I am very grateful for stimulating input from Andy Young of the Department of Astronomy at San Diego University.
Seeing Melbourne from the foreshore at Rye is an interesting Atmospheric phenomena. I have seen looming. I have not, as yet, seen an inverted image.
Andy writes (September, 2005):
Finally, I'd like to urge you to show actual photographs of the looming of Melbourne as seen from Rye. With a telephoto lens, you just might discover there are some zones of the image that are inverted (i.e., miraged) after all. Usually the late spring and early summer are the best seasons for superior mirages, so you have some good opportunities coming up in the next few months.
Andy Young is also an expert on the related phenomena: Green Flashes
For further reading see:
Atmospheric Optical Mirages
Atmospheric Refraction
Refraction and Mirages
Arctic Climatology and Meteorology
Earth curvature and atmospheric refraction across Monterey Bay
Walker 'stunned' to see ship hovering high above sea off Cornwall
If you liked this page please do not fail to visit the page describing The Night Sky at Rye.
NOTE:
It seems it is some of the followers of the Flat Earth Guru, Pastor Dean Odle , of the Fire & Grace Church in Opelika, Alabama have taken an interest in this page and consider me to be part of - and I quote......"a Luciferian conspiracy, initiated by Copernicus, to deceive people into believing that we live on a spherical moving planet"Clearly a badge I will wear with honour!Here is Pastor Dean Odle putting us straight!
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