Figure 1. The picture to the left shows the North Star is located directly over the Earth’s axis of spin. Now that you’ve made a sextant, you can take that sextant and measure the angle of objects relative to the horizon. If you examine the diagrams below, you can see that measuring the angle of elevation of the North Star is the same as your latitude on the Earth. So, using your sextant and the stars, you can figure out your latitude on the map. To calculate your latitude use this formula: Latitude = 90 Degrees – Protractor Angle Figure 2: As you move from the equator to the North Pole, the angle of elevation of the North Star relative to the horizon changes. Figure 2 Figure 3 Homework: On the next clear night, try to find the North Star and measure your latitude according to your homemade sextant. At the North Pole, your protractor should read 0 degrees. Your latitude is (90-0) degrees. At 45 degrees latitude, your protractor should read 45 degrees. Your latitude is degrees. At the equator, your protractor should read 90 degrees. Your latitude is (90-90) degrees.
Contents [] [] Example An example illustrating the concept behind the for determining one’s position is shown to the right. (Two other common methods for determining one’s position using celestial navigation are the and methods.) In the image to the right, the two circles on the map represent lines of position for the Sun and Moon at 1200 on October 29, 2005. At this time, a navigator on a ship at sea measured the Moon to be 56 degrees above the horizon using a . Ten minutes later, the Sun was observed to be 40 degrees above the horizon. Lines of position were then calculated and plotted for each of these observations. Since both the Sun and Moon were observed at their respective angles from the same location, the navigator would have to be located at one of the two locations where the circles cross. In this case the navigator is either located on the Atlantic Ocean, about 350 nautical miles (650 km) west of Madeira, or in South America, about 90 nautical miles (170 km) southwest of Asunción, Paraguay. In most cases, determining which of the two intersections is the correct one is obvious to the observer because they are often thousands of miles apart. As it is unlikely that the ship is sailing across the Chaco, the position in the Atlantic is the correct one. Note that the lines of position in the figure are distorted because of the map’s projection; they would be circular if plotted on a globe. Note also that an observer in the point would see the Moon at the left of the Sun, and an observer in the Madeira point would see the Moon at the right of the Sun, and that whoever measured the two heights was likely to observe also this one bit of information. Angular measurement
Using multiple methods helps the navigator detect errors, and simplifies procedures. When used this way, a navigator will from time to time measure the sun's altitude with a sextant, then compare that with a precalculated altitude based on the exact time and estimated position of the observation. On the chart, one will use the straight edge of a plotter to mark each position line. If the position line shows one to be more than a few miles from the estimated position, one may take more observations to restart the track. In the event of equipment or electrical failure, one can get to a port by simply taking sun lines a few times a day and advancing them by dead reckoning to get a crude running fix. Latitude was measured in the past either at noon (the "noon or from , the north star (assuming it is sufficiently visible above the horizon, which it may not be in the Southern Hemisphere). Polaris always stays within 1 degree of the celestial north pole. If a navigator measures the angle to Polaris and finds it to be 10 degrees from the horizon, then he is about 10 degrees north of the equator. Angles are measured from the horizon because locating the point directly overhead, the , is difficult. When haze obscures the horizon, navigators use artificial horizons, which are reflected into a . Latitude can also be determined by the direction in which the stars travel over time. If the stars rise out of the east and travel straight up you are at the equator, but if they drift south you are to the north of the equator. The same is true of the day-to-day drift of the stars due to the movement of the Earth in orbit around the Sun; each day a star will drift approximately one degree. In either case if the drift can be measured accurately, simple will reveal the latitude. Latitude = 90 Degrees – Protractor Angle Longitude can be measured in the same way. If one can accurately measure the angle to Polaris, a similar measurement to a star near the eastern or western horizons will provide the longitude. The problem is that the Earth turns about 15 degrees per hour, making such measurements dependent on time. A measure only a few minutes before or after the same measure the day before creates serious navigation errors. Before good chronometers were available, longitude measurements were based on the transit of the moon, or the positions of the moons of Jupiter. For the most part, these were too difficult to be used by anyone except professional astronomers.
After having transmitted the DSC distress alert on appropriate DSC distress channels (HF, MF and/or VHF), prepare for the subsequent distress traffic by tuning the radiocommunication set(s) (HF, MF and/or VHF as appropriate) to the corresponding distress traffic channel(s). If method b) described above has been used for transmission of DSC distress alert on a number of HF bands: take into account in which HF band(s) acknowledgment has been successfully received from a coast station; if acknowledgments have been received on more than one HF band, commence the transmission of distress traffic on one of bands, but if no response is received from a coast station then the other bands should be used in turn. The distress traffic frequencies are: HF (kHz): Telephony 4125 6215 8291 12290 16420 Telex 4177.5 6268 8376.5 12520 16695 MF (kHz): Telephony 2182 2174.5 VHF: Channel 16 (156.800 MHZ). Distress traffic The procedures described earlier are used when the distress traffic on MF/HF is carried out by radiotelephony. The following procedures shall be used in cases where" the distress traffic on MF/HF is carried out by radiotelex: The forward error correcting (FEC) mode shall be used unless specifically requested to do otherwise; all messages shall be preceded by: at least one carriage return, line feed, one letter the distress signal "MAYDAY"; The ship in distress should commence the distress telex traffic on the appropriate distress telex traffic channel as follows: carriage return, line feed, letter shift, the distress signal "MAYDAY",
L6 Clouds: Stratus (St) L6 Stratus in a more or less continuous later, or in ragged shreds, or both but no stratus fractus of bad weather (no precipitation). Notes: Stratus most commonly occurs as a grey, fairly uniform, featureless, single layer of low cloud. Occasionally it can be dark or threatening, although at most it can only produce weak precipitation This feature makes it fairly easy to distinguish it from nimbostratus, which nearly always produces rain, snow or ice pellets. When occurring alone, stratus shreds (fractus) appear grey when viewed towards the sun and white when viewed away from the sun. Fog will often lift into a layer of stratus by an increase in wind or a rise in temperature. . Stratus is sometimes comparatively thin and the disc of the sun or moon may be seen with a clear outline. Source: National Weather Service JetStream - Online School for Weather Stratus Clouds of a Continuous Layer. L6 Clouds – Symbol = Gray days from a continuous cloud layer are usually of the stratus Type 6 Cloud. These clouds often look like fog high off the ground An overcast day is a day full of stratus clouds in the atmosphere. The clouds are virtually indistinct covering the sky in a fairly uniform and grayish manner. While the dreary day will look as if precipitation is going to develop, it often does not. If rain or snow is produced in measurable amounts, the clouds are likely to be nimbostratus clouds. Often, the sun will "burn off" a foggy layer seemingly lifting the stratus clouds from the ground. However, the presence of these clouds often indicates colder weather is on the way. Source:
L6 Clouds - Nimbostratus Nimbostratus clouds are layered, uniform, rain clouds. A cloud can quickly change to or from nimbostratus; that is, it can quickly start or stop raining during your observations. In a situation like that, you can pick a cloud type and make a note in the comments about intermittent rain. These clouds are generally very dark, and are associated with large areas of continuous rain during the warmer months. Nimbostratus can also produce snow or sleet during the colder months. Synopsis Nimbostratus clouds (1). These Nimbostratus clouds developed as a result of a stationary front stretching from Michigan southwestward to Oklahoma. Source: University of Missouri, Department of Soil, Environmental and Atmospheric Sciences On-line Atlas: Nimbostratus Synopsis Nimbostratus cloud layer at (1) with lower fractostratus elements (2) present beneath the main cloud body. Viewer is looking southeast. Photograph taken just north of a weak stationary frontal zone draped southwest-to-northeast across Missouri. Source: University of Missouri, Department of Soil, Environmental and Atmospheric Sciences On-line Cloud Atlas:
L8 Clouds: Cumulus (Cu) and Stratocumulus (Sc) at different heights L8 Cumulus and stratocumulus other than that formed from the spreading out of cumulus; the base of the cumulus is at a different level from that of the stratocumulus. Notes: Typically, cumulus forms beneath patches or a sheet of stratocumulus. The cumulus may even rise into or through the Stratocumulus. Source: National Weather Service JetStream - Online School for Weather Multi-level Cumulus and Stratocumulus Not From the Spreading of Cumulus Clouds L8 Clouds- Symbol = . A mixed sky of varying cloud types can occur when a new layer of cumulus or stratocumulus form underneath other clouds. Typically, cumulus clouds form beneath existing stratocumulus clouds. The cumulus may even rise into or through the Stratocumulus. A noticeable difference in height can be seen in this mixed sky. Source:
combinations. This altocumulus is a single level, the greater part of which is sufficiently transparent to reveal the position of the sun and moon. The clouds do not progressively invade the sky, and the individual elements change very little. These thin altocumulus clouds usually produce a corona. Source: National Weather Service JetStream - Online School for Weather. not completely covered. The sun and moon are usually easily seen through this type of cloud Source:
M4 Clouds Flying Saucer. Lenticular altocumulus showing remarkable symmetry. Wind flows through this stationary cloud. Source: ********************************************* M4 Clouds: Altocumulus (Ac) continually changing shape M4 Patches (often in the form of almonds or fish) of altocumulus, the greater part of which is semi-transparent; the clouds occur at one or more levels and the elements are continually changing in appearance. Notes: These clouds often appear to be dissolving in some places and forming in others. These clouds are usually thin and do not progressively invade the sky. They often resemble a net or honeycomb. They also often form in patches in the shape of almonds or lenses called Altocumulus Lenticularis (ACSL) or wave clouds. These formations are caused by wave motions in the atmosphere and are frequently seen in mountainous or hilly areas. They may be triggered off by hills only a few thousand feet high and may extend down wind for over 60 miles (100 km).The cloud elements form at the windward edge of the cloud and are M4 Clouds - Symbol = Lenticular Clouds Lenticular altocumulus clouds resemble flying saucers in the sky. They also look like a concentric stack of different sized pancakes. National Weather Service Air that moves over mountainous regions will often form slow moving lenticular clouds. The clouds are often thin, but well defined. The clouds are usually also confined to a smaller area and do not invade the sky although their formation can extend downwind 100 km away from a mountainous area. Source:
H4 Clouds: Cirrus (Ci) progressively invading the sky H4 Cirrus in the form of filaments, strands or hooks, progressively invading the sky and generally becoming dense Notes: These are the same clouds as H1 but they progressively invade the sky and generally become denser as a whole. They often seem to fuse together in the direction from which they come. The forward edge moves towards the opposite part of the horizon. The clouds occur most frequently in form of strands trailing from a small hook or tuft and less frequently in the form of straight or irregularly curved filaments. Source: National Weather Service JetStream - Online School for Weather H4 Clouds – Symbol = Cirrus Clouds with Hooks or Filaments Invading the Sky Cirrus clouds that seem to get denser and invade the sky are known as H4 clouds. National Weather Service While invading high cirrus clouds often indicate a frontal system approaching, there may also be no impending weather changes. The clouds will often form and seem to fuse together to make progressively larger and more invasive clouds. The appearance of H4 clouds is almost exactly the same as H1 clouds. If the wispy nature of high cirrus clouds appear to be progressively invading the sky, then they are H4 clouds rather than H1 clouds. Source:
H5 Clouds: Cirrostratus (Cs) increasing but below 45° elevation. H5 Cirrostratus progressively invading the sky and generally becoming denser, but the continuous veil does not reach 45° above the horizon. Notes: The next four classifications (H5-H8) are of the same cloud type. The only difference is the amount of the celestial dome that is covered by the cloud, whether the cloud is increasing or decreasing across the sky, and must be the predominate cloud. The reason is cirrostratus a good precursor of precipitation and if it is increasing then precipitation may occur within 12 to 24 hours. For the H5 classification, the main characteristic is cirrostratus invading the sky progressively but with its continuous part still less than 45° above the horizon. Cirrostratus not completely covering the sky may be H5 Clouds – Symbol = Increasing Cirrostratus Clouds Below a 45 Degree Elevation Above the Horizon Cirrostratus can indicate precipitation. While H5 cirrostratus invade the sky, the majority of the clouds are no greater than 45 degrees above the horizon. National Weather Service Shapeless, thick, and dense are ways to discuss cirrostratus clouds. Sometimes these clouds are thick enough to cover the sun or moon. But at other times these clouds are so thin that they are only visible because they change the sky color. These clouds do invade the sky, but not at an angle greater than 45 degrees above the horizon. The presence of cirrostratus in the sky often indicates precipitation will be on its way to an area within 12 to 24 hours. The edge of this band of invading clouds is usually irregularly shaped, but may also have more of a straightened edge as well. Source: