Download North Celestial Pole

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Aries = ‫( برج الحمل‬March 21 - April 20 )
Taurus = ‫( برج الثور‬April 21 - May 21)
Gemini = ‫( برج الجوزاء‬May 22 - June 21 )
Cancer = ‫( برج السرطان‬June 22 - July 22 )
Leo = ‫( برج األسد‬July 23 -August 21 )
Vigro = ‫( برج العذراء‬August 22 - September 23 )
Libra = ‫( برج الميزان‬September 24 - October 23)
Scorpio = ‫( برج العقرب‬October 24 - November 22 )
Sagittarius = ‫( برج القوس‬November 23 - December 22)
Capricorn = ‫ ( برج الجدي‬December 23 - January 20 )
Aquarius = ‫( برج الدلو‬January 21 - February 19 )
Pisces = ‫(برج الحوت‬February 20- March 20)
‫وحمى الليث سنبل الميزان‬
ٌ ‫ومال دل‬
‫و بركة الحيتــــــــــان‬
‫حمل الثور جوزة السرطان‬
ٌ
‫عقرب بقوس الجدي‬
‫ورمى‬
 Is
not a property of stars themselves.
 It is an effect of our Earth’s atmosphere.
 Stars twinkle.
 Planets do not usually seem to twinkle.
 We
need to know an object’s direction to
observe it.
 Celestial sphere: large imaginary sphere, on
which all astronomical objects hung on its
inside surface.
 Longitudes:
half circles run from north
pole to south pole.


Longitude 0 passes through Greenwich.
Dhahran Longitude +49ْ 54’ 33” (East)
 Latitudes:
parallel circles that run
around Earth, all parallel to the equator.
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
Latitude 0 is the equator
Latitude ±90 the poles
Dhahran Latitude +26ْ 24’ 32” (North)
• The North Celestial Pole is the point
on the celestial sphere directly above
the Earth's North Pole.
• The South Celestial Pole is directly
above the Earth's South Pole.
• The star Polaris, in the constellation
Ursa Minor, is located very close to
the North Celestial Pole.
• The celestial equator is directly
above the Earth's equator.
• Right ascention = Longitude (East – West)
• Declination = Latitude (North South)
 Declination
corresponds to latitude
and is measured in the same way, but
relative to the celestial equator (0°
dec).
The north celestial pole is at 90° north
declination (+90° dec). The south
celestial pole is at 90° south declination
(-90° dec).
Circles of constant declination are all
parallel to the celestial equator.
 For
any position on the surface of the
Earth, the point on the celestial
sphere that is directly overhead is
called the zenith.
Since the Earth and the celestial
sphere are concentric, simple
geometry shows that the zenith will
always have a declination equal to
the latitude of the observer (such as
for Atlanta in the picture).

A star's position along a circle of constant declination
is described by a second number called right
ascension.
Right ascension corresponds to longitude, but
different units are used.
Instead of 360°, a circle is broken into 24 hours of
right ascension.
So, 360° = 24 h R.A., 15° = 1 h R.A., and 1° = 4 min
R.A.
Note that hours of right ascension is a unit of angle,
not time, although there is an obvious connection
due to the daily rotation of the celestial sphere.
 Right
ascension is measured from
the celestial meridian, chosen to be 0 h R.A.
(which is also the same as 24 h R.A.)
The celestial meridian is a semicircle
connecting the celestial poles and passing
through a particular point on the celestial
equator called the vernal equinox.
 Right ascension increases from west to east
(note that we are looking at the exterior of
the celestial sphere in the above picture).
 Although
the stars are fixed relative to each
other, the Sun moves relative to the stars.
Once a year, the Sun traces out a circle on
the celestial sphere called the ecliptic.
The ecliptic is tilted at an angle of 23.5°
with respect to the celestial equator.
(The Moon and planets also move near the
ecliptic.)

The Sun crosses the celestial equator at exactly
two points, called equinoxes, from the Latin
for "equal nights”.

The equinox where the Sun ascends from the
southern to the northern hemisphere is called
the spring or vernal equinox because the Sun
is there on March 21.
The vernal equinox is chosen to be 0 h R.A.

The Sun again crosses the celestial equator
halfway around, at 12 h R.A.
This position is called the autumnal
equinox because the Sun is there on September
23.

The positions where the Sun reaches its highest
and lowest points are called solstices, from the
Latin for "the Sun stops" as it changes direction.

The Sun is highest in the sky (in the northern
hemisphere) when it is at 6 h R.A.
This position is called the summer
solstice because the Sun is there on June 21.
The Sun then has a declination of +23.5°.

The Sun is lowest in the sky (in the northern
hemisphere) when it is at 18 h R.A.
This position is called the winter
solstice because the Sun is there on December
21.
The Sun then has a declination of -23.5°.
Event
Date
RA
Dec
VE
21 Mar.
0h
0
Equator
SS
22 Jun.
6h
+23.5ْ
Tropic of cancer
AE
23 Sep.
12 h
0
Equator
WS
22 Dec.
18 h
-23.5ْ
Tropic of Capricorn
The altitude of an object is the angle
between it and the horizon.
The horizon has an altitude of 0° and the
zenith has an altitude of 90°.
The azimuth of an object is the angle
between it and north, measured clockwise
along the horizon.
North has an azimuth of 0°, east has an
azimuth of 90°, south has an azimuth of
180°, and west has an azimuth of 270°.
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J2000 RA: 6h45m08.90s DE:-16°42'58.0"
Date RA: 6h45m38.31s DE:-16°43'41.2“
Dhahran 2010-12-20 2h59m
Sideral Time : 9h13m
Azimuth
:+223°47'
Altitude
:+33°59‘
Rise
:
19h04m Azimuth:+108°27'
Culmination :
0h32m
Set
:
6h00m Azimuth:+251°33‘
========================================
J2000 RA: 6h45m08.90s DE:-16°42'58.0"
Date RA: 6h45m38.38s DE:-16°43'41.4“
Dhahran 2010-12-30 2h59m
Sideral Time : 9h52m
Hour Angle
: 3h07m
Azimuth
:+231°43'
Altitude
:+27°27‘
Rise
:
18h24m Azimuth:+108°27'
Culmination :
23h53m
Set
:
5h21m Azimuth:+251°33‘
 J2000
RA: 6h23m57.10s DE:-52°41'45.0"
 Date RA: 6h24m11.70s DE:-52°42'08.0"
 Dhahran 2010-12-20 2h59m
 Sideral Time
: 9h13m
 Hour Angle
: 2h49m
 Azimuth
:+204°02'
 Altitude
:+03°00'
 Rise
:
20h48m Azimuth:+152°03'
 Culmination :
0h11m
 Set
:
3h33m Azimuth:+207°57‘
 Period
of 26000 years.
 Small correction of celestial
positions is needed.
 Small change (1/60ْ per
year).
 Latest is epoch 2000
 Sep.
22 Autumnal Equinox
 Sun has Dec. of 0ْ and RA of 12 h
 Sirius has Dec. of -16ْ 43’ and RA of 6h 45m
 A) what are the RA and Dec of the Sun on
March 21?
 B) what are the RA and Dec of the Sun on
June 22?
 C) What are the RA and Dec of Sirius on June
22?
 Bernard’s
Star has R.A. 17h 57.9m and dec.
+4ْ 41’
 It crosses the meridian facing south at
sidereal time 17h 57.9m
 At
what solar time does Bernard’s star cross
due south of you on September 22nd?
 It crosses the meridian facing south at
sidereal time 17h 57.9m
 On Sep. 22nd it corresponds to solar time 17h
58m
 On Sep. 26th it corresponds to solar time 17h
42m (16 min earlier)
 The
sun Today has RA of approximately 18 h
 At what sidereal time does the sun cross the
Meridian due south, today.
 Answer: at noon 11:40 am solar time = 18 h
sidereal time.
 Sirius
has RA 6h45m38.31s
 It will cross the Meridian due south at
6h45m38.31s (sidereal time) wich is
equivalent to 12:08 a.m.
 In
June: it will cross the Meridian at
6h45m38.31s (sidereal time) which is
equivalent to 12:23 p.m.