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Blancia , Mary Jean R. BSMT II DELTA Navigation 4

Rules of Conversion from Arc to TimeTo convert Arc to Time.1) Divide degrees by 15 to obtain hours, and multiply the remainder by 4 to obtain minutes of time.2) Divide the minutes of are by 15 to obtain minutes of time and multiply the remainder by 4 to obtain seconds of time.3) Divide the seconds of are by 15 to obtain seconds and tenths of seconds of time.4) Bring down the number of hours and add minutes and seconds of time.

Examples:Convert the following Arc to time.1) 15 32' 39"15 15 = 1h32' 15 =2m 8s39" 15 = 2.6s15 32' 39" = 1h 2m 10.6s 2) 30 65' 15"30 15 = 2h65' 15 =4m 20s15" 15 = 1s30 65' 15" = 2h 4m 21s

3) 152 19' 30"152 15 = 10h19' 15 = 9m30" 15 = 18s152 19' 30" = 10h 9m 18s

4) 303 55' 30"303 15 = 20h 12m55' 15 = 3m 40s30" 15 = 2s303 55' 30" = 20h 15m 42s

5) 615 6' 36"615 15 = 41h6' 15 = 0m 24s36 15 = 2.4s615 6' 36" = 41h 0m 26.4s

Example:Convert the following Arc to time

1) 100 70' 15"2) 310 67' 45"3) 15 75' 100"4) 115 36' 45"5) 65 18' 54"

1) 100 70' 15"100 15 = 6h70' 15 = 44m15" 15 = 41s100 70' 15" = 6h 44m 41s

2) 310 67' 45"310 15 = 20h67' 15 = 44m45" 15 = 31s310 67' 45" = 20h 44m 31s

3) 15 75' 100"15 15 = 1h75' 15 = 5m100" 15 = 6.67s15 75' 100" = 1h 5m 6.67s

4) 115 36' 45"115 15 = 7h36' 15 = 42m45" 15 = 27s115 36' 45" = 7h 42m 27s

5) 65 18' 54"6515= 4h18'15= 21m54"15= 15.6s65 18' 54" = 4h 21m 15.6s

Conversion of the following from Arc to Time1) 360 99' 68"36015 = 24h99'15 = 6m 36s68"15 = 4.53s360 99' 68" = 24h 6m 40.53s

2) 510 260' 100"51015 = 34h260'15 = 17m 20s100"15 = 6.67s510 260' 100" = 34h 17m 26.67s

3) 488 66' 50"48815 = 32h 32m66'15 = 4m 24s50"15 = 3.33s488 66' 50" = 32h 36m 27.33s

4) 270 15' 3"27015= 18h15'15= 1m3"15= 0.2s270 15' 3" = 18h 1m 0.2s

5) 90 70' 36"9015= 6h70'15= 4m 40s36"15= 2.4s90 70' 36" = 6h 4m 42.4s

Conversion of Arc to TimeExample:1) 360 98' 45"36015 = 24h95'15 = 6m 32s45"15 = 3s360 98' 45" = 24h 6m 35s

2) 210 115' 65"21015 = 14h115'15 = 7m 40s65"15 = 4.33s210 115' 65" = 14h 7m 44.33s

3) 85 17' 30"8515= 5h17'15= 41m30"15= 10s85 17' 30" = 5h 41m 10s

4) 38 15' 65"3815 = 2h 32m15'15 = 1m65"15 = 4.33s38 15' 65" = 2h 33m 4.33s

5) 45 115' 65"4515 = 3h115'15 = 7m 40s65"15 = 4.33s45 115' 65" = 3h 7m 44.33s

Example of Conversion from Arc to Time1) 75 70' 30"7515= 5h70'15= 4m30"15= 24s75 70' 30" = 5h 4m 24s

2) 235 115' 30"23515 = 15h115'15 = 47m30"15 = 42s235 115' 30"=15h 47m 42s

3) 95 65' 45"9515 = 6h 20m65'15 = 4m 16s45"15 = 3s95 65' 45" = 6h 24m 19s

4) 85 36' 15"8515 = 5h 40m36'15 = 2m 24s15"15 = 1s85 36' 15" = 5h 42m 25s

5) 135 65' 30"13515 = 9h65'15 = 4m 20s30"15 = 2s135 65' 30"= 9h 4m 22s

Conversion of Arc to TimeExample:

1) 303 55' 30"30315 = 20h 12m55'15 = 3m 40s30"15 = 2s303 55' 30" = 20h 15m 42s

2) 15 55' 30"1515 = 1h55'15 = 3m 40s30"15 = 2s15 55' 30" = 1h 3m 42s

3) 75 45' 3"7515 = 5h45'15 = 3m3"15 = 0.2s75 45' 3" = 5h 3m 0.2s

4) 70 19' 7"7015 = 5h 40m19'15 = 1m 16s7"15 = 0.47s70 19' 7" = 4h 41m 16.47s

5) 360 65' 15"36015 = 24h65'15 = 4m 20s15"15 = 1s360 65' 15" = 24h 4m 21s

Conversion of Arc to TimeExample:1) 152 36' 30"15215 = 10h 5m36'15 = 2m 24s30"15 = 2s152 36' 30" = 10h 10m 26s

2) 120 45' 15"12015 = 8h45'15 = 3m15"15 = 1s120 45' 15" = 8h 3m 1s

3) 405 215' 115"40515 = 27h215'15 = 14h 20s115"15 = 7.67s405 215' 115" = 27h 14m 27.67s

4) 100 55' 15"10015 = 6h 40m55'15 = 3m 40s15"15 = 1s100 55' 15" = 6h 43m 41s

5) 25 7' 45"2515 = 1h 40m7'15 = 28s45"15 = 3s25 7' 45" = 1h 40m 31s

Rules of Conversion from Time to Arc

To convert time to arc:1) Multiply the hours by 15 to obtain degrees.2) Divide the minutes of time by 4 to obtain degrees, and multiply the remainder by 15 to obtain minutes of arc.3) Divide the seconds of time by 4 to obtain minutes and multiply the remainder by 15 to obtain seconds of arc.4) Add degrees, minutes and seconds of arc.

Examples of the following conversion of time to arc.1) 15h 36m 32s2) 34h 27m 12s3) 20h 15m 42s4) 10h 9m 18s5) 3h 50m 32s

Solution:1) 15h 36m 32s15h x 15 = 22536m 4 = 932s 4 = 8' 0"15h 36m 32s = 234 8' 0"

2) 34h 27m 12s34h x 15 = 51027m 4 = 6 45'12s 4 = 3' 0"34h 27m 12s = 516 48' 0"

3) 20h 15m 42s20h x 15 = 30015m 4 = 3 45'42s 4 = 10' 30"20h 15m 42s = 303 55' 30"

4) 10h 9m 18s10h x 15 = 1509m 4 = 2 15'18s 4 = 4' 30"10h 9m 18s = 152 19' 30"

5) 3h 50m 32s3h x 15 = 4550m 4 = 12 30'32s 4 = 8' 0"3h 50m 32s = 57 38' 0"

Example Time to Arc:

1) 15h 36m 32s15h x 15 = 22536m 4 = 932s 4 = 8' 0"15h 36m 32s = 234 8' 0"

2) 17h 32m 2s17h x15 = 25532m 4 = 82s 4 = 0' 30"17h 32m 2s = 263 0' 30"

3) 3h 15m 55s3h x15 = 4515m 4 = 3 45'55s 4 = 13' 45"3h 15m 55s = 48 58 ' 45"

4) 5h 25m 36s5h x15 = 7525m 4 = 6 15'36s 4 = 9' 0"5h 25m 36s = 81 24' 0"

5) 10h 18m 18s10h x 15 = 15018m 4 = 4 30'18s 4 = 4' 30"10h 18m 18s = 154 34' 30"

Convert the following from Time to Arc

1) 6h 27m 41s6h x15 = 9027m 4 = 6 45'41s 4 = 10' 15"6h 27m 41s = 96 55' 15"

2) 8h 32m 24s8 x 15 = 12032m 4 = 824s 4 = 6' 0"8h 32m 24s = 128 6' 0"

3) 3h 12m 28s3h x15 = 4512m 4 = 328s 4 = 7' 0"3h 12m 28s = 48 7' 0"

4) 9h 4m 96s9h x 15 = 1354m4 = 196s4 = 24' 0"9h 4m 96s = 136 24' 0"

5) 10h 32m 16s10hx 15 = 15032m 4 = 816s 4 = 4' 0"10h 32m 16s = 158 4' 0"

Example of Conversion from Time to Arc

1) 1h 2m 10s1h x 15 = 152m 4 = 0 30'10s 4 = 2' 30"1h 2m 10s = 15 32' 30"

2) 2h 4m 24s2h x 15 = 304m 4 = 124s 4 = 6' 0"2h 4m 24s = 31 6' 0"

3) 10h 16m 32s10h x 15 = 15016m 4 = 432s 4 = 8' 0"10h 16m 32s = 154 8' 0"

4) 20h 28m 36s20h x 15 = 30028m 4 = 736s 4 = 9' 0"20h 28m 36s = 307 9' 0"

5) 10h 20m 40s10h x 15 = 15020m 4 = 540s 4 = 10' 0"10h 20m 40s = 155 10' 0"

Conversion from Time to Arc

Example:

1) 7h 36m 16s7h x 15 = 10536m 4 = 916s 4 = 4' 0"7h 36m 16s = 114 4' 0"

2) 5h 20m 28s5h x 15 = 7520m 4 = 528s 4 = 7' 0" 5h 20m 28s = 80 7' 0"

3) 11h 12m 4s11h x 15 = 16512m 4 = 34s 4 = 1' 0"11h 12m 4s = 168 1' 0"

4) 16h 4m 8s16m x 15 = 2404m 4 = 18s 4 = 2' 0"16h 4m 8s = 241 2' 0 "

5) 9h 8m 42s9h x 15 = 1358m 4 = 242s 4 = 10' 30"9h 8m 42s = 137 10' 30"

Conversion Example from Time to Arc:

1) 6h 14m 8s6h x 15 = 9014m 4 = 3 30'8s 4 = 2' 0"6h 14m 8s = 93 32' 0"

2) 12h 16m 32s12h x 15 = 18016m 4 = 432s 4 = 8' 0"12h 16m 32s = 184 8' 0"

3) 2h 24m 32s2h x 15 = 3024m 4 = 632s 4 = 8' 0"2h 24m 32s = 36 8' 0"

4) 8h 3m 16s8h x 15 = 1203m 4 = 0 45'16s 4 = 4' 0"8h 3m 16s = 120 49' 0"

5) 5h 25m 32s5h x15 = 7525m 4 = 6 15'32s 4 = 8' 0"5h 25m 32s = 81 23' 0"

1) 24h 48m 8s24h x 15 = 36048m 4 = 128s 4 = 2' 0"24h 48m 8s = 372 2' 0"

2) 2h 4m 24s2h x 15 = 304m 4 = 124s 4 = 6' 0"2h 4m 24s = 31 6' 0"

3) 6h 36m 8s6h x 15 = 9036m 4 = 98s 4 = 2' 0"6h 36m 8s = 99 2' 0"

4) 14h 32m 28s14h x 15 = 21032m 4 = 828s 4 = 7' 0"14h 32m 28s = 218 7' 0"

5) 3h 27m 16s3h x 15 = 4527m 4 = 6 45'165 4 = 4' 0"3h 27m 16s = 51 49' 0"

Local Time and Dates of two places

The difference in times and dates at two places is equal to their difference of longitude expressed in time.

Example 1.The Longitude of which is 615 36' E , place A , the LMT and date is 15h 25m 36s Nov. 8. Find the LMT of B, the longitude of which is 310 30'.

Long of A = 615 36' ELong of B = 310 30' E DLo = 305 6' WDLo in time = 20h 20m 24sLMT of A = +15h 25m 36sLMT of B = 35h 45m 60s Nov 3 = -24 +1LMT of B = 11h 45m 60s Nov 4

Example 2.LMT of A = 15h 25m 36s of A = 41h 2m 24s GMT = 56h 27m 60s Nov. 3 = -24 +1GMT & Date = 32h 27m 60s Nov 4 of B (in time) = 20h 42m 0s LMT & Date of B = 11h 45m 60s Nov. 4

Example 3.Long of A = 230 65'Long of B = 15 32' 215 33'DLo (in time) = 14h 22m 12sLMT of A = +15h 36m 32sLMT of B 29h 58m 44s -24 +1LMT of B = 5h 58m 44s

Example 4.LMT of A = 15h 36m 32s of A = 15h 24m 20sGMT = 30h 10m 52s Nov 8 = -24 +1GMT & Date = 06h 60m 52s Nov. 9 of B (in time) = 01h 02m 08sLMT & Date of B = 5h 58m 44s

Example 5.Long A = 510 56' E B = 280 16' EDLo = 230 40 W

DLo (in time) = 15h 22m 40sLMT of A = 12h 16m 20sLMT of B = 27h 38m 60s Dec 8 = - 24 +1LMT of B = 3h 38m 60s Dec 9Example 1.LMT of A = 12h 16m 20s of A (in time) = 34h 3m 44sGMT = 56h 19m 64s Dec 8 = -24 +1GMT & Date = 32h 19m 64s Dec 9 of B in time = 18h 4m 04s 3h 38m 60s Dec 9

Example 2.Long A = 342 68' WLong B = 190 16' WDLo = 152 52' EDLo (in time) = 10h 11m 28sLMT of A = 18h 11m 10sLMT of B = 28h 22m 38s Jan 7= -24 +1LMT of B = 4h 22m 38s Jan 8

Example 3.LMT of A = 18h 11m 10s of A (in time) = 22h 52m 32sGMT = 40h 63m 42s Jan 7= -24 +1GMT & Date = 16h 63m42s Jan 8 of B (in time) = 12h 41m 4s LMT & Date = 4h 22m 38s Jan 8

Example 4.Long A = 420 48' WLong B = 300 16' WDLo = 120 32 EDLo in time = 8h 2m 8sLMT of A = 16h 13m 48sLMT of B = 24h 15m 56s July 6 = -24 +1LMT of B = 0h 15m 56s July 7

Example 5.LMT of A = 16h 13m 48s of A (in time) = 28h 3m 12sGMT = 44h 16m 60s July 6= -24 +1GMT & Date = 20h 16m 60s July 7 of B (in time) = 20h 1m 4s 0h 15m 56s July 7

Example 6.Long of A = 268 50'Long of B = 138 23'DLo = 130 27'DLo in time = 8h 41m 48sLMT of A = 20h 16m 30sLMT of B = 28h 58m 18s Feb 2= -24 +1LMT of B = 4h 57m 18s Feb 3

Example 7.LMT of A = 20h 16m 30s of A (in time) = 17h 55m 20sGMT = 37h 71m 50s Feb 2= -24h +1GMT & Date = 13h 71m 50s Feb 3 of b (in time) = 9h 13m 32s 4h 58m 18s

Example 8.Long of A = 175 10.5 WLong of B = 32 08.0 WDLo = 143 02.5 EDLo in time = 9h 32m 10s ELMT of A = 16h 02m 03s Dec 3LMT of B = 25h 34m 13s Dec 3 -24h +1LMT & Date of B= 01h 34m 13s Dec 4

Example 9.LMT of A= 16h 02m 03s Dec 3 of A= 11h 40m 42sGMT= 27h 42m 45s Dec 3- 24h + 1GMT & Date= 03h 42m 45s Dec 4 of B (in time)= 02h 08m 32sLMT & Date of B= 01h 34m 13s Dec 4

Example 10.Long of A= 180 01' 10" WLong of B= 100 59' 59" WDLo= 79 01' 11" EDLo (in time)= 5h 16m 4.73sLMT of A= 21h 09m Sept 08LMT of B= 26h 25m 4.73s Sept 08- 24h +1LMT & Date of B= 02h 25m 4.73s Sept 09

Example 11.LMT of A = 21 09' Sept 08 of A (in time) = 12 0' 4.67"GMT= 33h 09m 4.67s Sept 08- 24h +1GMT & Date = 9h 09m 4.67s Sept 09 of B= 6h 43m 59.93sLMT & Date of B= 02h 25m 4.73s Sept 09

Example 12.Long of A= 143 47' WLong of B= 57 36' WDLo= 86 11' EDLo (in time)= 5h 44m 44sLMT of A= 24h 00m 00s April 27LMT of B= 29h 44m 44s April 27- 24h + 1LMT & Date of B= 05h 44m 44s April 28

Example 13.LMT of A= 24h 00m 00s April 27 of A (in time)= 9h 35m 08sGMT= 33h 35m 08s April 27- 24h +1GMT & Date= 9h 35m 08s April 28 of B (in time)= 3h 50m 24sLMT & Date of B= 05h 44m 44s April 28

Example 14Long of A= 201 48' WLong of B= 157 24' WDLo= 44 24' EDLo (in time)= 2h 57m 36s ELMT of A= 23h 50m 00s June 16LMT of B= 26h 47m 36s June 16- 24h +1LMT & Date of B= 02h 47m 36s June 17

GMT AND ZONE TIMEIn converting ZT to GMT it must be remembered that the ZD is the number of whole hours that are to be added to or subtracted from ZT to obtain GMT and that, the plus or minus sign prefixed to the ZD indicates whether they are to be added to or subtracted respectively from the ZT.

Example:

1) The ZT at longitude 140 65' W is 15h 19m 68s what is the GMT?Solution:ZT = 15h 19m 68s+9ZD = +9h GMT = 24h 19m 68s

2) The ZT at longitude 188 6' 2" E is 9h 24m 30s. What is the GMT?ZT= 9h 24m 30s+13ZD= 13hGMT= 22h 24m 30s

3) The ZT at longitude of 160 18' E is 19h 10m 30s. What is the GMT?ZT= 19h 10m 30s+ZD= 11hGMT = 30h 10m 30s

4) The ZT at longitude of 250 68' W is 10h 16m 15s. What is the GMT?ZT= 10h 16m 15s+ZD= 17hGMT= 27h 16m 15s

5) The ZT at longitude of 250 133' 5" is 13h 17m 10s. What is the GMT?ZT= 13h 17m 10s+ZD= 17hGMT= 30h 17m 10s

Example of ZT to GMT

1) The ZT at longitude of 24 30 E is 10h 20m 3s. What is the GMT?ZT= 10h 20m 3s+ZD= 1hGMT= 11h 20m 3s


3) The ZT at longitude of 38 18 W is 15h 16m 8s. What is the GMT?ZT= 15h 16m 8s+ZD= 3hGMT= 18h 16m 8s




7) The ZT at longitude of 55 48 W is 9h 18m 12s. What is the GMT?ZT= 9h 18m 12s+ZD= 4hGMT=13h 18m 12s






13) The ZT at longitude of 100 55 E is 8h 3m 1s. What is the GMT?

ZT= 8h 3m 1s+ZD= 7hGMT=15h 3m 1s

GMT TO ZTIn converting GMT to ZT, a positive ZD is subtracted, and a negative one added, but its sign the same being part of the description.Example:1) The GMT is 16h 23m 05s. What is ZT at longitude 156 24' 3" WSolution:GMT= 16h 23m 05s+10ZD= (-) 10hZT= 6h 23m 05s

2) The GMT is 10h 30m 24s. What is ZT at longitude 95 60' 10" WSolution:GMT= 10h 30m 24s+6ZD= (-) 6hZT= 4h 30m 24s

3) The GMT is 9h 48m 16s. What is ZT at longitude 130 24' 18" ESolution:GMT = 9h 48m 16s+9ZD= (-) 9hZT= 0h 48m 16s4) The GMT is 12h 16m 39s. What is ZT at longitude 99 55' 20" WSolution:GMT= 12h 16m 39s+7ZD= (-) 7hZT= 5h 16m 39s

5) The GMT is 24h 0m 0s. What is ZT at longitude 60 5' 25" EGMT= 24h 0m 0s+4ZD= (-) 4hZT= 20h 0m 0s

6) The GMT is 15h 20m 13s. What is ZT at longitude 60 60' 50"GMT= 15h 20m 13s+4ZD= (-) 4hZT= 11h 20m 13s



9) The GMT is 13h 09m 18s. What is ZT at longitude 58 60' 45"GMT = 13h 09m 18s+4ZD= (-) 4hZT= 9h 09m 18s

10) The GMT is 14h 16m 20s. What is ZT at longitude 38 60' 58"GMT= 14h 16m 20s+3ZD= (-) 3ZT= 11h 16m 20s

Conversion from ZT to Another ZTWhen it is necessary to determine the ZT of a place in certain longitude corresponding to the ZT of another place in another longitude, convert first the given ZT to GMT and then apply to the GMT the ZD of the other place with the sign reversed.

Example No 1At longitude (A) 59 30' W the ZT is 1200. What is the ZT at B longitude 83 30' W?Solution:ZT of A= 1200+4 ZD= 4GMT= 1600+6 ZD= (-)6ZT of B= 1000

Example No 2

At longitude (A) 30 24' W the ZT is 1214. What is the ZT at B longitude 68 45' W?

Solution:ZT of A= 1214+2 ZD= 2GMT= 1414+ ZD= (-) 5ZT of B= 0914

Example No 3At place whose longitude is 73 29.2' W, the ZT is 20h 15m 43s or May 18. What is the ZT at place B where longitude is 119 17' 5" W?Solution:ZT of A = 20h 15m 43s May 18+5 ZD= +5GMT= 25h 15m 43s May 18+8 ZD= -8ZT of B= 17h 15m 43s May 18

Example No 4At place whose longitude is 93 20' E, the ZT is 18h 15m 12s on Nov 8. What is the ZT and date at place B whose longitude is 100 27' 30s.Solution:ZT of A= 18h 15m 12s Nov 8+6 ZD= 6hGMT= 24h 15m 12s Nov 8+7 ZD= -7hZT of B= 17h 15m 12s Nov 8

Example No 5The ship is leaving Australia in the 10ZD at noon of Dec. 4 for the Philippines in 10ZD, estimates that 15 days and 24 hours will be needed to make the trip. At what ZT and date will she arrive in the Philippines.Solution:ZT of Departure= Dec 4, 12h 00m 00s+ZD= +10hGMT of departure= Dec 4; 22h 00m 00sSteaming time interval= 15d; 24hGMT of Arrival at Dec 19; 46h 00m 00sPhilippines= +1 -24 Dec 20, 22h 00m 00s-10 ZD= Dec 20, +10ZT of Arrival at= 32h 00m 00sPhilippines+1 -24hZT of Arrival at Dec 21 8h 00m 00sPhilippines

Zone Time (ZT)

Zone Description (ZD) = The ZD indicates the number of hours to be added to or subtracted from the ZT to find GMT

Central Meridian is a meridian whose longitude is exactly divisible by 15.

Example of finding Zone description1) 130 E 15 = 8 40' 0" orZD = -9E

2) 136 W 15 = 9 4' 0" orZD = 9W

3) 68 W 15 = 4 32' orZD = 5W

4) 75 E 15 = 5 0' orZD = -5 E

5) 115 W 15 = 7 40 ' orZD = 8W

A. The common sources of error extant sights are: The sextant may not be rocked properly. Tangency may not be, judged accurately. A false horizon may have been used. Subnormal refraction (dip) might be present. The height of eye may be wrong. Time might be in error. The index correction may have been determined incorrectly. The sextant might be out of adjustment. An error may have been made in the computation.B. Define the ff. Sextant Altitude Corrections1.) Sextant Altitude (HS) must be corrected for errors of the instrument and observer, and other corrections depending on the celestial body being observed.2.) Observed Altitude (Ho) is the Hs value corrected to read as though the altitude had been measured with reference to the celestial horizon at the earths center, on a perpendicular plane passing through the observers zenith and the body.3.) Index Error of the sextant which is subtracted from the Hs if on the arc and added if off o the arc.4.) Height of Eye (dip) This is the depression of the visible horizon.5.) Refraction is the angle through which a ray of light is deflected in passing through the atmosphere to the eye of the observer.6.) Semi - diameter correction The altitude of a bodys center above the rational horizon is the quantity in navigational calculation.7.) Parallax Correction of the moon is the parallax corresponding to its altitude at the time of observation.8.) Horizontal Parallax (HP) of the moon is the parallax corresponding to its altitude at the time of observation.9.) Parallax in Altitude angle ZXE is the parallax for apparent altitude XZM.

Taking Sextant Altitude of Celestial BodiesA. Sun SightsThe expression taking a sight generally means sighting a celestial body for a sextant altitude with the purpose of establishing a sextant altitude with the purpose of establishing a celestial line of position (LOP). Sun sights therefore means taking the sextant altitude of the sun.

B. Moon SightsSights of the moon are best made during either daylight hours or that part of twilight in which the moon is less luminous.

C. 3 Methods or Steps of takin sextant altitude of star and planet sights

1) Set the index arm and micrometer drum on 0 and direct the line of sight at the body to be observed2) This is reverse of method No. 1. Instead of bringing the body down to the horizon, bring the horizon up to the body.3) Predict in advance the approximate altitude and azimuth of the body by a star finder or by used of sight reduction table.

3 Steps in Reading a Micrometer drum sextant

First Step: Read the degrees by noting the position of the arrow on the index arm in relation to the graduation on the arc.Second Step: Read the minutes lay noting the position of the zero mark on the Vernier* in the relation to the graduations on the micrometer drum.Third Step: Read the fraction of the minutes by noting which mark on the Vernier most nearly coincides with one of the graduations on the micrometer drum.

Reading On and Off the arcOne must remember that the smallest

1) The Classification of Sextant Errors

1) The non-adjustable error are: Centering Errors. This is an eccentric error due to failure to pivot the index arm exactly at the curvature of the limb. Prismatic Error. Prismatic error of the mirrors and shade glasses due to lack of parallelism of the two faces, or their non-perpendicularly to the limb. Graduation Error. This is the error in graduation. Either the limb or micrometer drum may have a slight imperfection in graduation.2) The adjustible errors are Perpendicularity error. The index mirror must be perpendicular to the frame of the sextant. Side error. An error resulting from the horizon glass being parallel to the plane of the sextant. Collimation error. An error resulting from the line of sight through the telescope not being parallel to the plane of the sextant. Index error. This error remaining after the perpendicularity error the side error and the collimation error has been removed.

2) Reading the sextantReading a micrometer drum sextant is done in three steps.First Step: Read the degrees by noting the position of the arrow on the index arm in relation to the graduation on the arc.Second Step: Read the minutes by noting the position of the zero mark on the Vernier* in relation to the graduations on the micrometer drum.Third Step: Read the fraction of the minute by noting which mark on the Vernier most nearly coincides with one of the graduations on the micrometer drum.

Define the following Frame, on which the other parts are mounted. The frame is normally made of brass, but some lightweight models are of aluminum alloy. Limb is the lower part of the frame and carries the arc which is graduated in degrees Index arm - is pivoted at the center of the curvature of the arc and is free to move around it. Micrometer drum is used to make fine adjustment of the index arm. Tangent Screw It is mounted on a shaft, having a pinion gear at the other end. Clamping lever or release lever are spring loaded clamps that hold the tangent screw against the teeth of the limb. Index Mirror - is mounted or the upper end of the index arm directly over its pivot point. Horizon Glass is mounted on the frame. Telescope is mounted with its axis parallel to the plane of the frame. Index shade glasses - are of optically ground glass mounted perpendicular to the arc, and are pivoted so that they can be swing into or out of line of sight between the index and the horizon mirror. Horizon shade glasses are similar to the index shades, but of lesser density and serve to reduce the glare of the reflected sunlight on the horizon. Handle usually of wood or plastic, is mounted on the frame at a location and angle for good balance and easy grip w/ right hand. Vernier is a small movable graduated scale for obtaining fractional parts of subdivision on a fixed scale.

Definition of the following1) Sextant is hand-held instrument that measures the angle between two points by bringing the direct ray from one point and double-reflected ray from the other into coincidence.2) Optical Principle Governing the construction of the sextantThe construction of the sextant is based on the following laws of optics. When a ray of light strikes a plane mirror, the angle of incidence is equal to the angle of reflection. The incident ray and the reflected ray arc in the same plane which is perpendicular to the plane of the reflecting surface. When a ray of light is reflected twice by two plane mirrors, the angle formed by the first and the last directions of the ray is equal of twice the angle formed by the plane of the two mirrors

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