Question: When one is at a high latitude, it is well known that a magnetic compass is, at best (unless one is intimately familiar with local idiosyncrasies), nearly useless. What is another type of simple early navigation device which can in fact be used to find direction at any time during the day, even at the poles?
- aside from your Mark I eyeballs, there is none
- two magnetic compasses, several miles apart, can be used to infer location based on known lines of magnetic flux
- the sun compass
- a cross staff, or mariner’s astrolabe
Answer: C. The Sun Compass draws on the fact that the sun´s shadow from a point (like a sundial’s gnomon) in the middle of a disk describes different hyperbolas at different times of the year. You don´t have to know the time of the day in order to get general directions within a few degrees. It is believed that the Vikings may have used a similar ‘bearing dial’ instrument. (At high latitudes, as elsewhere, the direction of the sun is towards east in the morning and towards the west in the evening, but during the middle of the day of course, its location in the Southern sky is much less ambiguous than at lower latitudes.)
Subject: Another Angle On Fronts
Question: Approximately what are the actual slopes of cold and warm fronts?
- Warm fronts slope up (in the direction of movement) at about a 30 degree angle. Cold fronts slope more, although down (in the direction of movement) and more steeply, at about a 45 degree angle.
- A warm front slopes up only at a ratio of about 20 to one, while a cold front is a wedge of air about twice as steep, or 10 to one (again in the opposite direction).
- Actually, fronts are really quite shallow. It’s more like 1:40 for cold fronts, and 1:80 for warm fronts.
- still too steep: cold fronts average roughly 1:100, warm fronts 1:200
Answer: D. That makes sense when you think about the sucessively lower and lower cloud types that one might see over a period of two days, for example as a warm front moves eastward over a given point in the US. (So fronts really aren’t nearly as narrow as one would think, when looking at them on Surface Analysis, Weather Depiction, or any other type of weather chart.) I hasten to add that these are averages. Cold fronts can have slopes as steep as one in 50, though the average is 1:100; and warm fronts can be as shallow as one in 400.
Subject: Reaching Up To Grab You
Question: What is the tallest man-made object that you might have to watch out for while flying over the North American continent?
- Including the TV antennas, the top of the Sears Tower is about 1730 feet AGL (above ground level). It’s MSL (above mean sea level) height is 2325 feet.
- Canada’s CN tower in Toronto, Ontario is the tallest self-supporting structure, at 1815.5 feet above the ground.
- The KTHI-TV transmitting tower in Blanchard, ND (northwest of Fargo, ND) is the tallest standing structure at 2,063 feet AGL (3058 MSL).
- There are actually tethered aerostats along the southern US border which can rise to 15,000 feet.
Answer: D. (If you consider structures only, then it’s C.) The tethered aerostat radar system is used for drug interdiction, and has (or has had) active sites at Yuma and Ft Huachuca, AZ, Deming NM, Marfa, Eagle Pass, Matagorda and Rio Grande TX, Morgan City LA, Cross City and Cudjoe Key FL, and Lajas, Puerto Rico.