191:
1009:
577:
1033:
985:
1021:
997:
678:
The second complication is that, assuming no deflection of the vertical, "overhead" means perpendicular to the ellipsoid at observer's location, but the perpendicular line does not pass through the center of the Earth; almanacs provide declinations measured at the center of the Earth. (An ellipsoid
650:
The first complication applies to all celestial objects: the object's declination equals the observer's astronomical latitude, but the term "latitude" ordinarily means geodetic latitude, which is the latitude on maps and GPS devices. In the continental United States and surrounding area, the
143:, and right ascension is likewise comparable to longitude. Points north of the celestial equator have positive declinations, while those south have negative declinations. Any units of angular measure can be used for declination, but it is customarily measured in the
121:(N.P.D.), which is equivalent to 90 – (declination). For instance an object marked as declination −5 would have an N.P.D. of 95, and a declination of −90 (the south celestial pole) would have an N.P.D. of 180.
348:. Upon flat terrain, the distance has to be within approximately 2 km, although this varies based upon the observer's altitude and surrounding terrain). Generally, if a star whose declination is
344:
Circumpolar stars never dip below the horizon. Conversely, there are other stars that never rise above the horizon, as seen from any given point on the Earth's surface (except extremely close to the
68:
159:, with 90° equivalent to a quarter circle. Declinations with magnitudes greater than 90° do not occur, because the poles are the northernmost and southernmost points of the celestial sphere.
818:
U.S. Naval
Observatory Nautical Almanac Office, Nautical Almanac Office; U.K. Hydrographic Office, H.M. Nautical Almanac Office (2008). "Time Scales and Coordinate Systems, 2010".
647:
When an object is directly overhead its declination is almost always within 0.01 degrees of the observer's latitude; it would be exactly equal except for two complications.
223:(including declination) are inherently relative to the year of their observation, and astronomers specify them with reference to a particular year, known as an
588:(green) and is positive northward (towards the top), negative southward (towards the bottom). The lines of right ascension (blue) divide the sky into
215:
The Earth's axis rotates slowly westward about the poles of the ecliptic, completing one circuit in about 26,000 years. This effect, known as
341:
which has a declination near to +90°, so is circumpolar as seen from anywhere in the
Northern Hemisphere except very close to the equator.
857:
817:
1053:
1063:
90:(red) on the celestial equator (blue). Declination is measured northward or southward from the celestial equator, along the
385:
Neglecting atmospheric refraction, for an observer at the equator, declination is always 0° at east and west points of the
227:. Coordinates from different epochs must be mathematically rotated to match each other, or to match a standard epoch.
758:
219:, causes the coordinates of stationary celestial objects to change continuously, if rather slowly. Therefore,
882:
708:
703:
220:
130:
49:
20:
693:
263:
975:
635:. Likewise, near the local winter solstice, the Sun remains below the horizon all day, which is called
243:
946:
367:
366:
never rises above the horizon, as seen by the same observer. (This neglects the effect of
8:
1037:
718:
652:
602:
533:
511:
318:
286:
833:
1025:
1013:
106:) means "a bending away" or "a bending down". It comes from the same root as the words
934:
754:
749:
U.S. Naval
Observatory, Nautical Almanac Office (1992). P. Kenneth Seidelmann (ed.).
585:
471:
402:
224:
57:
989:
920:
713:
529:
493:
440:
314:
271:
235:
216:
210:
202:
140:
79:
45:
926:
67:
961:
792:
775:
728:
723:
620:
334:
259:
194:
190:
71:
953:
56:. The declination angle is measured north (positive) or south (negative) of the
1058:
306:
175:
169:
144:
914:
321:
for objects with declinations less (i.e. more negative) than −90° −
1047:
656:
489:
267:
152:
148:
376:, then it never rises above the horizon as seen by an observer at latitude −
1001:
878:
632:
589:
275:
239:
117:
In some 18th and 19th century astronomical texts, declination is given as
942:
636:
156:
91:
61:
53:
405:, declination is uniform around the entire horizon, approximately 0°.
957:
680:
616:
338:
27:
258:'s direction remains nearly fixed due to its vast distance, but its
698:
628:
424:
414:
360:
is either positive or negative), then a star whose declination is −
302:
289:, celestial objects with declinations greater than 90° −
136:
87:
370:.) Likewise, if a star is circumpolar for an observer at latitude
624:
551:
386:
345:
310:
231:
83:
576:
612:
608:
570:
278:
objects change very rapidly compared to those of stars, due to
182:
The sign is customarily included whether positive or negative.
569:
Non-circumpolar stars are visible only during certain days or
279:
410:
255:
996:
900:. Sausalito, CA: University Science Books. pp. 200–5.
753:. University Science Books, Mill Valley, CA. p. 724.
915:
MEASURING THE SKY A Quick Guide to the
Celestial Sphere
748:
44:) is one of the two angles that locate a point on the
973:
895:
135:
Declination in astronomy is comparable to geographic
242:. Prior to J2000.0, astronomers used the successive
675:of a degree) but can be as great as 41 arcseconds.
337:for southern latitudes). An extreme example is the
898:Explanatory Supplement to the Astronomical Almanac
751:Explanatory Supplement to the Astronomical Almanac
623:, leading to the phenomenon of it being above the
619:latitudes, the Sun is circumpolar near the local
1045:
797:. New York: Macmillan Co. p. 125, art. 66.
389:. At the north point, it is 90° − |
82:. The primary direction of the system is the
16:Astronomical coordinate analogous to latitude
935:"(α,δ) – Right Ascension & Declination"
777:A Complete and Universal English Dictionary
262:and declination do change gradually due to
820:The Astronomical Almanac for the Year 2010
927:Celestial Equatorial Coordinate Explorers
822:. U.S. Govt. Printing Office. p. B2.
166:celestial equator has a declination of 0°
580:The night sky, divided into two halves.
575:
354:is circumpolar for some observer (where
238:. The prefix "J" indicates that it is a
189:
185:
66:
790:
773:
735:
642:
64:passing through the point in question.
1046:
932:
921:Celestial Equatorial Coordinate System
917:James B. Kaler, University of Illinois
607:The Sun's declination varies with the
285:As seen from locations in the Earth's
94:passing through the point in question.
230:The currently used standard epoch is
683:that is mathematically manageable).
305:) appear to circle daily around the
234:, which is January 1, 2000 at 12:00
896:P. Kenneth Seidelmann, ed. (1992).
395:|, and at the south point, −90° + |
13:
465:− for north latitude, + for south
459:+ for north latitude, − for south
14:
1075:
908:
201:(green) as seen from outside the
1031:
1019:
1007:
995:
983:
562:
556:
479:
1054:Astronomical coordinate systems
317:. This similarly occurs in the
246:B1875.0, B1900.0, and B1950.0.
1064:Technical factors of astrology
929:University of Nebraska-Lincoln
923:University of Nebraska-Lincoln
889:
871:
850:
826:
810:
801:
784:
767:
742:
124:
1:
883:U.S. National Geodetic Survey
78:as seen on the inside of the
794:An Introduction to Astronomy
791:Moulton, Forest Ray (1918).
709:Geographic coordinate system
704:Equatorial coordinate system
448:of non-circumpolar stars (°)
436:
131:Equatorial coordinate system
86:, the ascending node of the
50:equatorial coordinate system
21:Declination (disambiguation)
7:
881:. Silver Spring, Maryland:
694:Celestial coordinate system
686:
313:, and are therefore called
264:precession of the equinoxes
10:
1080:
807:Moulton (1918), pp. 92–95.
600:
309:without dipping below the
208:
128:
18:
430:
421:
178:has a declination of −90°
172:has a declination of +90°
947:University of Nottingham
453:of stars not visible (°)
270:, and cyclically due to
249:
834:"Celestial Coordinates"
774:Barclay, James (1799).
679:is an approximation to
596:
593:
368:atmospheric refraction
274:. The declinations of
221:equatorial coordinates
206:
95:
933:Merrifield, Michael.
655:) is typically a few
584:(blue) begins at the
579:
282:and close proximity.
193:
186:Effects of precession
139:, projected onto the
110:("bend forward") and
98:The root of the word
70:
736:Notes and references
643:Relation to latitude
592:, here 1 hour apart.
176:south celestial pole
170:north celestial pole
19:For other uses, see
816:see, for instance,
719:Position of the Sun
653:vertical deflection
603:Position of the Sun
418:
319:Southern Hemisphere
287:Northern Hemisphere
157:sexagesimal measure
119:North Pole Distance
114:("bend backward").
631:, which is called
594:
408:
207:
96:
52:, the other being
960:) – to determine
567:
566:
441:circumpolar stars
315:circumpolar stars
162:An object at the
58:celestial equator
1071:
1036:
1035:
1034:
1024:
1023:
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1000:
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954:Sidereal pointer
950:
902:
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838:www.austincc.edu
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782:
781:
771:
765:
764:
746:
714:Lunar standstill
674:
672:
671:
668:
665:
651:difference (the
530:Tropic of Cancer
494:Antarctic Circle
419:
407:
400:
394:
381:
375:
365:
359:
353:
332:
326:
300:
294:
244:Besselian Epochs
211:Axial precession
203:celestial sphere
141:celestial sphere
80:celestial sphere
46:celestial sphere
1079:
1078:
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761:
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729:Setting circles
724:Right ascension
689:
669:
666:
663:
662:
660:
659:(1 arcsecond =
645:
621:summer solstice
611:. As seen from
605:
599:
396:
390:
377:
371:
361:
355:
349:
335:negative number
328:
322:
296:
290:
272:annual parallax
260:right ascension
252:
213:
195:Right ascension
188:
133:
127:
72:Right ascension
24:
17:
12:
11:
5:
1077:
1067:
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1041:
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1028:
1016:
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972:
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909:External links
907:
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601:Main article:
598:
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543:
542:+66.5 to −66.5
540:
537:
525:
524:
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507:
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502:+23.5 to −23.5
500:
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478:
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467:
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463:
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307:celestial pole
280:orbital motion
251:
248:
209:Main article:
187:
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180:
179:
173:
167:
129:Main article:
126:
123:
84:vernal equinox
15:
9:
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4:
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939:Sixty Symbols
936:
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760:0-935702-68-7
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630:
626:
622:
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614:
610:
604:
591:
590:great circles
587:
583:
578:
574:
573:of the year.
572:
559:
553:
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516:
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437:
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428:
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404:
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393:
388:
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369:
364:
358:
352:
347:
342:
340:
336:
331:
325:
320:
316:
312:
308:
304:
301:= observer's
299:
293:
288:
283:
281:
277:
273:
269:
268:proper motion
265:
261:
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247:
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204:
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196:
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59:
55:
51:
47:
43:
42:
37:
34:(abbreviated
33:
29:
22:
1038:Solar System
967:
962:
938:
897:
891:
873:
859:
852:
841:. Retrieved
837:
828:
819:
812:
803:
793:
786:
776:
769:
750:
744:
677:
649:
646:
633:midnight sun
606:
581:
568:
452:
447:
438:
431:
422:
409:
401:|. From the
397:
391:
384:
378:
372:
362:
356:
350:
343:
333:is always a
329:
323:
297:
291:
284:
276:Solar System
253:
240:Julian epoch
229:
214:
198:
181:
161:
134:
118:
116:
111:
107:
103:
99:
97:
75:
60:, along the
40:
39:
35:
31:
25:
1026:Outer space
1014:Spaceflight
943:Brady Haran
879:"USDOV2009"
637:polar night
582:Declination
545:66.5 to 90
505:23.5 to 90
432:Declination
423:Observer's
413:visible by
199:declination
197:(blue) and
125:Explanation
100:declination
92:hour circle
76:declination
62:hour circle
32:declination
1048:Categories
860:baylor.edu
843:2017-03-24
657:arcseconds
560:+90 to −90
539:90 to 66.5
520:+45 to −45
499:90 to 23.5
217:precession
104:declinatio
54:hour angle
990:Astronomy
958:Torquetum
681:sea level
617:antarctic
534:Capricorn
523:45 to 90
339:pole star
151:(′), and
38:; symbol
28:astronomy
945:for the
699:Ecliptic
687:See also
629:midnight
517:90 to 45
512:midpoint
483:0 to 90
425:latitude
415:latitude
303:latitude
137:latitude
102:(Latin,
88:ecliptic
976:Portals
885:. 2011.
673:
661:
625:horizon
609:seasons
586:equator
571:seasons
552:Equator
477:90 to 0
462:
387:horizon
346:equator
327:(where
311:horizon
295:(where
232:J2000.0
155:(″) of
153:seconds
149:minutes
145:degrees
112:recline
108:incline
48:in the
757:
613:arctic
528:23.5 (
490:Arctic
488:66.5 (
1059:Angle
1002:Stars
865:(PDF)
411:Stars
403:poles
250:Stars
225:epoch
147:(°),
755:ISBN
670:3600
510:45 (
472:Pole
470:90 (
266:and
256:star
74:and
968:DEC
627:at
615:or
597:Sun
550:0 (
443:(°)
439:of
427:(°)
36:dec
26:In
1050::
963:RA
941:.
937:.
836:.
639:.
563:—
554:)
536:)
514:)
496:)
474:)
382:.
254:A
236:TT
30:,
978::
970:.
966:/
956:(
949:.
867:.
862:"
858:"
846:.
780:.
763:.
667:/
664:1
557:—
532:/
492:/
480:—
398:φ
392:φ
379:φ
373:φ
363:δ
357:δ
351:δ
330:φ
324:φ
298:φ
292:φ
205:.
41:δ
23:.
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