Logging Requirements: When you visit the posted coordinates you will find a plaque with information about the Toronto Magnetic Observatory. Please use the Message Centre link at the top of this cache page to answer the following questions based on the plaque and the information on this cache page:
- When was the plaque affixed to the Transit Pillar? (from the plaque)
- How was Longitude established by the observatory in 1883? (from the plaque)
- Are the magnetic and true north poles in the same location?
- Where is the the agonic line in North America?
- In what country was the magnetic north pole located in 2001?
- What can be the effect of magnetic storms on the sun on the local magnetic declination?
The Earth's magnetic field is believed to be generated by electric currents in the conductive material of its core, created by convection currents due to heat escaping from the core.
Compasses tended to "wander" from north when measurements were taken at different locations or even at a single location over a period of time. The astronomer Edmund Halley noted this and the problems it would cause for navigation in 1701. This is magnetic declination and is a feature of the Earth's magnetic field and local magnetic disturbances in the earth's crust. The Toronto Magnetic Observatory was established to conduct experiments to determine what causes the changes in declination.
Magnetic declination or variation is the angle on the horizontal plane between magnetic north (the direction the north end of a compass needle points, corresponding to the direction of the Earth's magnetic field lines) and true north (the direction along a meridian towards the geographic North Pole). This angle varies depending on position on the Earth's surface, and changes over time.
Changes in declination can be quite large. At Yellowknife, NWT, for example, the declination is changing by more than one degree every three years. On the other hand, at Ottawa, the yearly change in declination is almost zero.
Magnetic declination also undergoes changes that are much more rapid than secular variation and are a result of magnetic activity. These variations can be smooth and cyclic, with amplitudes of several minutes of arc in southern Canada, or, during magnetic storms, large and erratic. Changes in declination become increasingly irregular in both amplitude and frequency as one approaches the North Magnetic Pole, a result of the weak horizontal component of the magnetic field. The number of times per year that a compass user will be affected by changes in declination caused by magnetic storms will depend both on the user's application and location.
It is important to remember that the annual change does not remain constant with time. Therefore, using the annual change to update the declination on an old map is likely to result in an error in the updated declination.
The North Magnetic Pole moves over time due to magnetic changes in the Earth's core. In 2001, it was determined by the Geological Survey of Canada to lie near Ellesmere Island in northern Canada at 81.3°N 110.8°W. It was situated at 83.1°N 117.8°W in 2005. In 2009, while still situated within the Canadian Arctic territorial claim at 84.9°N 131.0°W, it was moving toward Russia at between 34 and 37 miles (55 and 60 km) per year. As of 2015, the pole is projected to have moved beyond the Canadian Arctic territorial claim to 86.3°N 160.0°W.
The direction in which a compass needle points is known as magnetic north. In general, this is not exactly the direction of the North Magnetic Pole (or of any other consistent location). Instead, the compass aligns itself to the local geomagnetic field, which varies in a complex manner over the Earth's surface, as well as over time. The local angular difference between magnetic north and true north is called the magnetic declination. Most map coordinate systems are based on true north, and magnetic declination is often shown on map legends so that the direction of true north can be determined from north as indicated by a compass.
Magnetic declination has been measured in many countries, including the U.S. The line of zero declination (the agonic line) in North America runs from the North Magnetic Pole through Lake Superior and southward into the Gulf of Mexico. Along this line, true north is the same as magnetic north. West of the line of zero declination, a compass will give a reading that is east of true north. Conversely, east of the line of zero declination, a compass reading will be west of true north.
Magnetic declination is still very important for certain types of navigation that have traditionally made much use of magnetic compasses.
This EarthCache is located at an historic point - the only point in Toronto that had its longtitude fixed in 1854.
In 1837, the British Government funded the installation of a magnetic observatory at Greenwich. The Association continued to press for the construction of similar observatories around the world, and in 1838 their suggestions were accepted by the Government and funds were provided. In 1839 the British Government and the Royal Society prepared four expeditions to build magnetic observation stations in Cape Town; St. Helena; Hobart, Tasmania and (eventually) Toronto. Teams of Royal Artillery officers were sent out to take the measurements. The team assigned to Canada originally planned to build their observatory on Saint Helen's Island off Montreal, but the local rocks proved to have a high magnetic influence, and the decision was made to move to Toronto instead. The team arrived in 1839, and set up camp at Fort York in a disused barracks while construction started on new buildings. The observatory was given 10 acres (4.0 ha) of land to the west of King's College; the Ontario Legislature now occupies the area on which the college was located.
The observatory, officially "Her Majesty's Magnetical and Meteorological Observatory at Toronto", was completed the following year. It consisted of two log buildings, one for the magnetic instruments and the other a smaller semi-buried building nearby for "experimental determinations". The north end of the main building was connected to a small conical dome which contained a theodolite used to make astronomical measurements for the accurate determination of the local time (based on an accurate determination of the precise Longtitude.)
Using the measurements from the Toronto and Hobart sites, Sabine noticed both short-term fluctuations in magnetic declination over a period of hours, and longer-term variations over months. He quickly concluded that the short term variations were due to the day/night cycle, while the longer term ones were due to the number of visible sunspots. He published two introductory papers on the topic in the Philosophical Transactions of the Royal Society. The first, in 1851, was a collection of early measurements; the second in 1852 correlated with Heinrich Schwabe's sunspot measurements, which had been made widely available in Alexander von Humboldt's Cosmos, also published in 1851. With further data collected from the Toronto site, Sabine was able to demonstrate conclusively that the eleven-year sunspot cycle caused a similarly periodic variation in the Earth's magnetic field. He presented a third and conclusive paper on the topic in 1856, "On Periodical Laws Discoverable in the Mean Effects of the Larger Magnetic Disturbances", in which he singled out the Toronto site for particular praise.