Celestial Navigation Theoryyyy

Zone Time

Time referenced to the observers central meridian

Inferior conjunction

When an inferior planet is between the Earth and the Sun

Latitude scale

______ is used as the standard reference along which distances can be measured on a Mercator chart

Parallel of Latitude

a circle ( or approximation) on the surface of the earth, parallel to the equator and connecting points of equal latitude

Vertical Circle

a great circle of the c.s. through the zenith and nadir. perpendicular to the horizon

Celestial Merdian

a great circle of the celestial sphere, through the celestial poles and the zenith. usually refers to the upper branch, coincides w/ the hour circle through the zenith and vertical circle through the elevated pole.

Meridian

a north-south reference line, particularly a great circle through the geographical poles of earth. divided into two branches, upper and lower

Latitude

a star is observed at lower transit. the line of position derived from this sight gives you a check on your _____

Altitude

angular distance about the horizon; the arc of a vertical circle between the horizon and a point on the c.s. measured upward from horizon. distance below horizon is called negative altitude/depression

Meridian Angle (t)

angular distance east or west of the local celestial meridian; the arc of the celestial equator between the upper branch of the local cm and the hour circle of a celestial body measured east/westward from the local cm through 180*

Polar distance

angular distance from a celestial pole; the arc of an hour circle between a celestial pole, usually the elevated pole and a pt on the c.s., measured from the celestial pole through 180*

Latitude

angular distance from a primary great circle of plane. terrestrial latitude is the angular distance from equator measured northward or southward through 90*

Greenwich Hour Angle

angular distance west of the greenwich c.m.; the arc of the c.e. between the upper branch of the greenwich c.m. and hour circle. measured westward from greenwich c.m. through 360*

Sidereal Hour Angle

angular distance west of the vernal equinox; the arc of the ce of the angle at the celestial pole between the hour angle of the vernal equinox and the hour circle. measured westward through 360*. the angular distance east of the vernal equinox through 24 hrs

Ecliptic

apparent annual path of sun eastward across the c.s. -great circle inclined 23* 27'

Geoidal Horizon

assuming observers eye level is at the surface of the Earth

Observed Altitude (Ho)

corrected sextant altitude; angular distance of the center of a celestial body above the celestial horizon of the observer, measured along a vertical circle from 0 to 90 degrees.

circumpolar

if a body can be seen both at upper transit and at lower transit the body is referred to as ______

False

in general, the most effective period for observing stars and planets occurs during the lighter limit of civil twilight

Nutation

irregulated in the precessional motion due to the disturbing effect of other celestial bodies, (moons precession is 18.6 yrs, nodal period)

Azimuth Angle (Z)

measured either clockwise or counterclockwise through 180* starting at north point of the horizon in northern latitude and the south point of the horizon in the southern latitude

Co-altitude (zenith distance)

ninety degrees minus the altitude

Co-latitude

ninety degrees minus the latitude, the angle between the polar axis and the radius vector locating a point

Retrograde motion

occurs when a planet appears to move backwards in the sky

Hour Circle (circle of declination)

on the celestial sphere, a great circle through the celestial poles.

meridian angle parallactic angle

one angle of the Celestial Triangle is Azimuth Angle. what are the the other two angles?

Geographic position and elevated pole

one vertex of the navigation triangle is located at the assumed position. what are the other two vertices?

Inferior planets

orbits of planets smaller than that of earth (mercury and venus) cannot reach opposition or quadrature

Twilights

period between when the sun disappears and darkness, allows brightest star to be seen along with horizon

Celestial Horizon

plane that is perpendicular to zenith/nadir through Earth's equator

Geometric Horizon

solely based on the observers height of eye (refraction is accounted for)

False

the GHA of a star increases at a rate of approximately 4* per hour

False

the GHA of the moon increases at a rate of approximately 12.2* per hour

GHA and declination

the GP of a body is determined from what two pieces of information__________

0*

the SHA of the Arcturus changes at about _____ per hour.

Sextant Altitude (Hs)

the altitude measured by the sextant BEFORE CORRECTIONS are applied

diurnal circle

the celestial path that a celestial body makes each day across the sky (parallel of declination

Elevated pole

the celestial pole above the horizon, agreeing in name with the latitude. the celestial pole below the horizon is called depressed pole

6080 60nm

the conversion factor commonly used in marine navigation to convert degrees of latitude into distance is 1' of arc = _____, or 1* of arc = _____

Zd and Zn

the direction and distance of the GP of cel. body from your position is determined by ______

Intercept

the distance in miles between the circle of equal altitude for the observed altitude (ho) and the circle of equal altitude for computed altitude (Hc) is called the _____

great circle curved straight

the intersection of the earth and a plane that passes through its center and divides it into two hemispheres is called a _____. if not perpendicular to the equator, it appears as a ______ line on a mercator chart, and as a _____ straight line on a gnomonic chart

50

the lunar day is about ____ minutes longer than the solar day

cel meridian hour circle

the meridian angle for a body is measured from the ____ to the ____ of the body

Sensible Horizon

the plane perpendicular to the zenith/nadir axis that passes through observers eye

First Point of Aries (vernal equinox)

the point of intersection of the ecliptic and the c.e., occupied by the sun as it changes from south to north declination on or about March 21st. the instant the sun reaches the point of 0 declination when crossing the c.e. from south to north. origin for measuring the SHA

False

the sidereal day is about 4 minutes longer than the solar day

Conjunction

the sun and a planet are on the same side

Principal vertical circle

the vertical circle passing through the north and south celestial poles. coincides with the celestial meridian

Azimuth (LOP) Compass Error Stars

what is the navigation triangle used for?

Quadrature

when a superior planet forms a right angle with the sun and earth

Superior conjunction

when a superior planet is behind the sun

Local Apparent Noon

when the apparent(true) sun is over the upper branch of the observers meridian

090*/290*

you wish to observe a cel. body to obtain a check on your long.. to be so the body have a true bearing

True Azimuth

Azimuth relative to true north. angle at the zenith measured clock-wise from true-north to the vertical circle passing through the body measured 0* through 360*

Opposition

Opposite sides in orbit

Longitude

angular distance along a primary great circle, from the adopted reference point. terrestrial longitude is the arc of a parallel, or the angle at the pole

Geographic position of Celestial body

the point on the earth at which a given celestial body is in the zenith at a specified time.

Equator

the primary great circle of a sphere, perpendicular to the polar axis, or a line. Terrestrial equator is 90* from the Earths terrestrial poles

Equinoctial (celestial equator)

the primary great circle of the celestial sphere, every 90* from the celestial poles; the intersection of the extended plane of the equator and the celestial sphere

Precession

the result of gravitational forces exerted principally by the sun and moon on earths equatorial bulge

Apparent Altitude (Ha)

the sextant altitude corrected for INACCURACIES IN THE INSTRUMENT and HEIGHT OF EYE

Prime vertical circle

the vertical circle perpendicular to the principal vertical circle. passes through the east and west points of horizon

Elevated pole Geographic pole Assumed position

three vertexes of the navigation triangle

True

when the elongation of Venus is maximum the planet is at the quadrature

Rotation

-body spinning around its axis. gives the affect of rising and setting bodies. -earth rotates from west to east, tilted 23.4*. -sun rises until it crosses the meridian at which it begins to set. -sets until it crosses the lower branch meridian at which it begins to rise. -causes apparent motion, sidereal day (23hrs 56min 4sec), and diurnal paths, counterclockwise motion from north pole -stars appear to shift 1* west per day as earth moves 1* east

Solstice

-when the earth and sun are farthest apart -december/winter: vertical rays are 23.5*S lat, on the 21st/22nd, tropic of capricorn, first day winter, hemisphere tilted away from sun -june/summer: vertical rays are 23.5* N lat, on the 21st/22nd, tropic of caner, hemisphere tilted toward sun

Equinoxes

-when the earth is the closest to the sun (September and march) - autumn/fall: suns rays are along the equator moving north to south, sept 22/23, axis not tilted -spring/ vernal: suns rays are along equator moving south to north, march 21/22, axis is not tilted

Declination

A measure of how far north or south an object is from the celestial equator

Visible Horizon

Height of observers eye (apparent line where sky and Earth appear to meet)

True Azimuth Azimuth Principal Vertical

In the horizon coordinate system, the altitude and the _____ of a body delineate its position. The _____ angle at the zenith of the observer is the smallest angle between the observer's _____ vertical circle and the _____ circle passing through the body.

Superior planets

Planets farther from the sun than the earth (Mars, Jupiter, Saturn, Uranus, Neptune)

Sexy Gorillas Can Violate George

Sensible Geoidal Celestial Visible Geometric

Tidal Cycles

Solar 12hrs Lunar 12hrs 25min Tropical month 27.33 days Anomalistic month 27.5 days

Primer Meridian

The 0* meridian of longitude, the greenwich england is almost universally used for this

Local Hour Angle

Angular distance west of the local c.m.; the arc of the c.e. between the upper branch of the local c.m. and hour circle. measured through 360*. At longitude 0* called GHA LHA= GHA +/- long.

True

A star is observed at lower transit. the line of position derived from the sight gives you a check on your latitude

Zenith Distance

Angular distance from the zenith or arc of vertical circle between the zenith and point of c.s. measured along vertical circle from 0* through 90*