Lesson 28: Astronomical Observation

Celestial Sphere

A better understanding of relationships in space and the procedures of practical field astronomy are easily simplified and achieved by the conceptof the ____________.

Celestial Sphere

For purposes of surveying, an assumption is made that the stars and other heavenly bodies are all fixed within a gigantic sphere.

Celestial Sphere

It rotates from east to west about a line which coincides with the earth axix.

360D59.14M/24H

The speed of rotation of the celestial sphere is ____________.

Celestial Poles

are the points on the surface of the celestial sphere pierced by the extension of the earths polar axis. It is designated by P and P' respectively.

Celestial Axis

It's the prolongation of the earth's polar axis.

Zenith

is the point where the plumb line at the place of observation projected above the horizon meets the celestial sphere.

Nadir

Is that point on the celestial sphere directly beneath the observer, the direct opposite to the zenith.

Great Circle

a great circle of a sphere is the trace on it's surface of the intersection of a plane passing through the center of the sphere.

Observer's Horizon

a great circle of the celestial sphere where a plane, perpendicular to the plumb line at the place of observation and passing through the center of the earth.

Observer's Vertical

a vertical line at the location of the observer which coincides with the plumb line and is normal to the observers horizon.

Celestial Equator

a great circle which is perpendicular to the polar axis of the celestial sphere.

Vertical Circle

a great circle passing through the observer's zenith and any celestial body. Such a circle is perpendicular to the horizon,and represents the line of intersection of a vertical plane of the celestial plane.

Hour Circle

a great circle joining the celestial poles and passing through a celestial body and whose plane is perpendicular to the plane of the celestial equator.

Meridian

is a great circle of the celestial sphere which passes through celestial poles and the observers zenith. This circle is both a vertical and hour circle.

Polaris

The north star

Ursa Minor

Little bear

Ephemeris

is an astronomical almanac containing tables giving the computef positions of the sun, the planets, and various stars for everyday of a given period.

The Almanac for GE

it is deigned to provide GE in the Philippines with necessary astronomical data using Philippine Standard Time.

Parallels

are lines formed by passing a series of imaginary planes perpendicular to the axis of the earth.

Equator

designated as the 0 degree parallel. also known as latitude.

Meridians

are formed by passing a series of imaginary planes through the earth's poles.

International Date Line

it is formed by 180 degree meridian

British Royal Observatory

The meridian which passes trough the former site of __________________________ near Greenwich, England is designated as 0 degree meridian.

Prime Meridian

the 0 degree meridian.

International Meridian Conference

In 1884 at Washington D.C. This conference agreed that the Greenwich meridian is the Prime Meridian.

Celestial Coordinate System

use to define the positions of heavenly bodies and points of reference on the celestial sphere.

Equatorial System

The primary great circle are used is the celestial equator and the secondaries are those of hour circles.

Hour Angle System

The primary reference circle is the celestial equator and the secondary is the hour circle through observers zenith.

Apparent Time

______________ or true solar time is determined with respect to the true sun.It is conveniently measured by means of a sun dial.

Sidereal Time

A sidereal day at any place on the earth's surface begins when the vernal equinox is on the observer's meridian and above his horizon.

Mean Solar Time or Civil Time

Since the sun us not convenient to use as an accurate time indicator, a fictious body, called the mean sun, has been devised.

PZS Triangle

A spherical triangle is the figure formed by joining any three pointson the surface of a sphereby arcs of great circle.

Point P

the north pole of the celestial sphere

Point Z

the observers zenith

Point S

the heavenly body observed which may be the sun or any other known star such as polaris.

Side PS or p

the polar distance or codeclination. It is equal to 90D minus the declination of the observed heavenly body.

Side PZ or y

the colatitude of Z. 90D minus the latitude of the observer.

Side ZS or z

the zenith distance or coaltitude of the observed heavenly body.

angle Z

true azimuth of the heavenly body

angle S

is the parallactic angle

angle t

it is known as meridian angle.

Refraction-

the change of direction when it passed from one medium into another of different density.

Parallax+

the different in direction of a heavenly body as seen from the surface and from the center of the earth.

Ecliptic

apparent path of the sun about the earth.

Equinox

If the equator and ecliptic intersect it is called ________________.

23D27M

Obliquity of the ecliptic

September 21

Autumnal equinox

March 21

Vernal equinox