Workforms. contents. Note on copyright and reproduction

Size: px

Start display at page:

Download "Workforms. contents. Note on copyright and reproduction"

Drusilla Booker
5 years ago
Views:

1 Workforms contents Form 104 for Sight Reduction with Pub. 249 or 229 Form 106 for Sight Reduction with NAO Tables Form 107 for LAN Sights Form 108 Combined Sight Reduction Form 109 for Solar Index Correction Form 110 for Latitude By Polaris Form 111 for Sight Reduction with Pub. 249, Vol. 1 Note on copyright and reproduction These forms and the instructions to them are copyrighted by Starpath School of Navigation but students who have purchased our classroom or homestudy course may copy them for their own use.

Work Forms 1 WT h m s date body Hs WE S F ZD W E Form 108 Combined form for Almanac Daily Pages plus NAO Tables DR Lat DR Lon GMT h m s GMT date / LOP label log HE ft index corr.

12 Work Forms 1 WT h m s date body Hs WE S F ZD W E Form 108 Combined form for Almanac Daily Pages plus NAO Tables DR Lat DR Lon GMT h m s GMT date / LOP label log HE ft index corr. off on DIP Ha 2 GHA hr. vmoon planets Dec HP hr d moon 3 GHA m.s. SHA or v corr. GHA stars or moon, planets d corr. Dec Dec min additional altitude corr. moon, mars, venus altitude corr. all sights upper limb moon subtract 30 Ho 4 alon WE LHA 00 W / 60 E 5 6 Location on table pages Top Sides Latitude N S LHA SR Table > A same contrary A' N S Declination D B F D' B' F' Z 1 sign B = sign Z 1 if LHA = 0 to 90 if LHA = 91 to 269 if LHA = 270 to 360 bar top means rounded value 30' or 0.5 rounds up A F SR Table > 7 H H' P P' Z 2 if F = 0 to 90 if F = 90 to F' 9 A' Z 2 Aux > P Aux > same sign as Z 2 but reverse sign if F' = 30 to 59 if A' = 30 to 59 if A' = 0 to 29 Hc = Ho = 11 a = alat = C 1 C 2 A T take label of larger T A Z = N. Lat S. Lat Z > alon = 3 Zn = > LHA 0 to to > > Z > This is a combined form for those using NAO tables. The instructions for the top part are essentially the same as for Form 104. Instructions for the bottom part are the same as for the NAO tables. [1] Fill in sight data. [2] Get GP data from daily pages for whole hour. [3] Get minutes and seconds corrections. Sum for GHA, Sum for Dec. Copy Dec to line in 6. Mark N or S. [4] Choose alon and find LHA. Copy to line [6]. Choose alat, record in line [5]. Record alat and alon in line [11]. [5] Apply altitude corrections to get Ho. Copy Ho to space above [11]. [6]to[10] Follow standard NAO form instructions. [11] Find avalue as difference between Hc and Ho, and choose its label. Now all data needed to plot the LOP is at hand. 245

13 Starpath Form 110 for Polaris Sights Step Correct Hs to get Ho Record Index Correction IC (mark sign if off, if on) Record eye height (HE) and look up Dip Look up the altitude correction in the center of Ha Alt corr. Ho Find LHA Aries UTC date = 21 UTC Time in Hours, Minutes and Seconds UTC time = Step 2 o o Find GHA Aries on Left Hand Daily Page 22 of the Nautical Almanac (far left column) GHA Aries (hr) = for UTC Day and Hour Find GHA Aries minutes and seconds correction from Increments and Corrections pages 24 Sum the above two numbers to get GHA Aries 25 DR Longitude (W, E) GHA Aries (m, s) = GHA Aries = DR Lon = 26 LHA Aries (Combine previous numbers, round to nearest degree) LHA Aries = Step 3 Latitude Determination 31 Ho (from 16) 32 a0 from Polaris Table (using LHA Aries) HO = 33 a1 from Polaris Table (using DR Latitude) 34 a2 from Polaris Table (using Month) 35 Subtract 1 degree a1 = 36 ' ' ' ' Table A2, front of the Almanac 16 Sum the above two numbers to get Observed Height 23 ' HE (ft) 14 Sum the above to get Apparent Height of Polaris 15 Off On Dip 13 Correction on the righthand side of Table A2, front of Almanac o Hs Record Sextant Height of Polaris Sum the above five numbers to get Latitude a0 = a2 = 1º = Latitude = '

14 How to measure Index Correction using the Sun This is an old method, developed by those explorers who did most sights on land using an artificial horizon (Lewis and Clark, for example). It can be quite accurate and offers a quick check by measuring the sun s semidiameter at the time of the sight and comparing that with the value listed in the Nautical Almanac or computed by the StarPilot. It is not entirely clear, however, if this solar IC method is superior for routine sights at sea using a true sea horizon. In these cases, it could be that the conventional methods we discuss elsewhere might be preferred. For lunar distance sights, on the other hand, this solar method is likely best. Notes (1) we will be looking straight toward the sun and through a telescope to boot. So we must be very careful that all sun shades are in place and we do not somehow distort our view and look around the edge of the shades. Do not under any circumstances look directly at the sun without it being completely covered by the shades. (2) Use the highest power scope you have for this. Monocular 6x35 or 7x30 etc work well. (3) Adjust the shades if you have that option so the reflected and direct view of the sun appear as different colors. Procedure (1) Set the sextant to and look toward the sun on a clear day. You will see something like the following, where we use the convention that shaded sun is the reflected view on the right side of the horizon mirror and the unshaded one is the direct view through the clear glass of the left side of the horizon glass Side error Index error Step 1 Reflected view Direct view Step Index error Side error removed (2) Adjust the side error to remove it by first adjusting the Index mirror to be perpendicular to the frame of the arc and then adjusting the horizon mirror so it is parallel to the frame as well. Then you will see the picture to the right above which is almost all index error with no side error. Step 3 First we will measure the Toward value of the IC (3) Turn the micrometer Away from you until all of the reflected image is well below the direct image

15 (4) Now turn micrometer Toward you slowly and uniformly so the reflected image rises till the top edge of it just touches the bottom edge of the direct image. And read the dial. It should read something like 32 on the scale depending on your IC. Record this ON value. Accurate to the tenth. In this running example we will call this 34.0 ON. (5) Now continue to turn, slowly and uniformly, in the Toward direction until the bottom edge of the reflected image aligns with the top edge of the direct image. If you overshoot, we need to start all over again!. The idea is to be turning only in one direction when we stop. This time the dial will read about 28 but this will be an OFF the scale measurement, so we have to subtract whatever it reads from 60. In this example, let s assume micrometer read 29.2, which would be 29.2 = 30.8 OFF the scale. Record this OFF value. Step 4 Step (6) Now take the difference between the ON value and the OFF value and divide that by 2 to find your IC. Just subtract the smaller from the larger. The label of your result will be the same as the label of the larger value. In this example: = 3.2 and 3.2 /2 = 1.6 and since 34 was ON, the answer is ON, ie our IC is 1.6 ON the scale. (7) Now check your result by comparing to the actual semidiameter of the sun at the time of the sight. Our example was measured on 02/28/01 using an Astra 3b deluxe model sextant with traditional mirror. From the Nautical Almanac, we get that SD = The SD of the sun equals the ON value plus the OFF value divided by 4. In this example, = 64.8 and 64.8/4 = 16.2 which is right. More notes A quick and dirty method to measure the IC this way, or maybe to double check the result to see that it all makes sense, is just to align the reflected and direct images on top of each other and read the dial. That reading will be your IC, it is just that the above procedure is a more accurate way to get the value. In this case we would see what is shown here, depending on whether or not we had side error. In our example, the dial would read 1.6 ON the scale when either of the two rightside alignments were set. Now you can repeat the full process turning always in the Away direction. Careful data will often show a slight No side error With side error difference for the Toward and Away values, even for a metal sextant (see sample data to follow). For plastic sextants, on the other hand, the toward and away values will almost always be rather large, some few minutes or so.

16 Date 2/28/01 SD 16.2 Toward or Away = 30.8 = = = 1.6 on = = 30.2 = = = 1.8 on = = 30.8 = = = 1.7 = = 30.4 = = = 1.8 = = 4 6. = 2 = 4 Date 2/28/01 SD 16.2 Toward or Away = 31.2 = = = 1.2 on = = 31.0 = = = 1.2 = = 31.0 = = = 1.2 = = 30.8 = = = 1.4 = = 30.8 = = = 1.4 = = 2 = 4 average = ( ) / 4 = 1.7 On when turning in the Toward direction. average = ( )/5 = 1.3 On when turning in the Away direction. This data is from navigator Lanny Petitjean using Astra w. traditional mirror. He has since used the results to achieve numerous sights from land with accuracies all below 0.4 miles and lunar distance sights below 30 seconds. Thanks Lanny.

17 Date SD Toward or Away 1. 2 = 4 2. = 2 = 4 Date SD Toward or Away 1. 2 = 4 2. = 2 = = 4 4. = 2 = = 4 4. = 2 = = 4 6. = 2 = = 4 6. = 2 = 4 Form for solar IC measurements Starpath School of Navigation

18 See discussion at: Celestial Navigation Workforms Form 111, Pub. 249, Vol. 1 1 WT h m s date body Hs WE S F ZD W E UTC h m s DR Lat DR Lon UTC date / LOP label log HE ft index corr. off on DIP Ha 2 3 GHA hr. GHA m.s. GHA alon WE LHA LHA alat Star N S 00 W / 60 E } Pub. North Latitudes LHA greater than Zn = Z LHA less than Zn = 360 Z South Latitudes LHA greater than Zn = 180 Z LHA less than Zn = 180 Z copy copy 249, Vol. 1 4 altitude corr. (refraction) Ho Hc T A a = Zn = a Lat = a Lon = TA 5 1 WT h m s date body Hs WE S F ZD W E UTC h m s DR Lat DR Lon UTC date / LOP label log HE ft index corr. off on DIP Ha 2 3 GHA hr. GHA m.s. GHA alon WE LHA LHA alat Star N S 00 W / 60 E } Pub. North Latitudes LHA greater than Zn = Z LHA less than Zn = 360 Z South Latitudes LHA greater than Zn = 180 Z LHA less than Zn = 180 Z copy copy 249, Vol. 1 4 altitude corr. (refraction) Ho Hc T A a = Zn = a Lat = a Lon = TA 5

CHAPTER 20 SIGHT REDUCTION

CHAPTER 20 SIGHT REDUCTION BASIC PRINCIPLES 2000. Introduction Reducing a celestial sight to obtain a line of position consists of six steps: 1. Correcting sextant altitude (hs) to obtain observed altitude