Transcript 3. Celestial Sphere Mark

Our Location on the Earth
Our Location on the Earth
North
West
East
South
Our Location on the Earth
North
you are here
West
East
South
Our Location on the Earth
North
West
East
South
Our Location on the Earth
North
Earth’s direction of rotation
West
East
South
Our Location on the Earth
North
West
East
South
Our Location on the Earth
North
West
East
Equator
South
Our Location on the Earth
North
West
Prime
Meridian
Equator
South
East
Our Location on the Earth
North
West
Prime
Meridian
Equator
South
East
Our Location on the Earth
North
West
Prime
Meridian
Equator
South
East
Our Location on the Earth
North
West
Prime
Meridian
longitude
Equator
South
East
Our Location on the Earth
North
latitude
West
Prime
Meridian
longitude
Equator
South
East
Our Location on the Earth
North
MTHS, WA
47o 57’ north latitude
122o 23’ west longitude
Our Location on the Earth
North
Brier, WA
The Earth turns
to the east
Our Location on the Earth
North
Brier, WA
Our Location on the Earth
North
Brier, WA
Our Location on the Earth
North
Brier, WA
Our Location on the Earth
North
Brier, WA
Dome of the Sky
Zenith
North
Horizon
meridoan Simulation
Nadir
Dome of the Sky
looking north
toward north star
Zenith
North
Horizon
looking south
Nadir
Dome of the Sky
zenith
toward North Star
north
south
Dome of the Sky
zenith
toward pole star
north
south
Dome of the Sky
Dome of the Sky
Dome of the Sky
Zenith
Meridian
Horizon
North
Dome of the Sky
Zenith
Meridian
Altitude
Horizon
Azimuth
East
North
Dome of the Sky
Zenith
Meridian
Altitude
Azimuth
North
Dome of the Sky
Zenith
Meridian
Altitude
Azimuth
North
Zenith
The point directly above the observer
Horizon
All those points that lie 90 degrees down from the zenith
Nadir
The point directly below the observer
Meridian A vertical circle defined by the path that starts at the zenith and
crosses the horizon at a point directly north
Altitude
The number of degrees along the vertical circle between the object
and the horizon
Azimuth
The number of degrees east of north between the northern horizon
and that point where the altitude line crosses the horizon
Celestial Sphere
Celestial Sphere
Celestial Sphere
Celestial Sphere
North Celestial Pole (NCP)
Celestial Sphere
North Celestial Pole (NCP)
Celestial Sphere
North Celestial Pole (NCP)
Celestial Equator
Celestial Sphere
North Celestial Pole (NCP)
Celestial Equator
Celestial Sphere
North Celestial Pole (NCP)
Declination (Dec)
Celestial Equator
Right Ascension (RA)
Celestial Sphere
NCP
Declination (Dec)
Celestial
Equator
Right Ascension
(RA)
Declination
Declination is analogous to latitude. It is measured in degrees above
(positive) or below (negative) the celestial equator going from –90
degrees to +90 degrees
Right Ascension
Right Ascension is analogous to longitude, but it is measured in time
units: hours, minutes, seconds, from zero hours to 24 hours
Celestial Sphere
Declination (Dec)
Right Ascension (RA)
One of the two points on the
Celestial Sphere where the
Ecliptic and the Celestial
Equator cross one another,
The First Point of Aries,
which is actually in Pisces,
defines the zero-point for
Right Ascension.
Declination
(Dec)
Right
Ascension
(RA)
When the Sun reaches the First Point of Aries, as it
does once each year, an equinox occurs. In the
northern hemisphere, this is the Vernal Equinox, the
first day of Spring.
The First Point of Aries is not a fixed point in space:
it moves along the Ecliptic at a rate of roughly one
degree every seventy years. When the Equinox was
first observed, thousands of years ago, the First Point
actually lay in the constellation of Aries. Due to the
effect of precession, the First Point of Aries crossed
into the neighboring constellation of Pisces in about
70 BCE. It has taken about 2,000 years to cross
Pisces, and it will soon cross into the next zodiacal
constellation, Aquarius, in about the year 2600.
Following its journey along the Ecliptic, it will
return to its starting point in Aries once again in
about 23,000 years.
The Sky from Here
From the ground, the sky looks like a big dome above us.
Both the “zenith” and horizon are locally defined.
Celestial Equator and Pole
We project the Earth into the sky, and its rotation
appears reflected there. The “diurnal” (daily) motion
of the sky is just due to the spinning Earth.
Celestial Coordinates
To “map” a given point in the sky, you can specify how
high it is, and in what direction (altitude and azimuth).
Or you can project latitude (declination) and longitude
into the sky, but since the Earth rotates, we must use
“right ascension” which is fixed on the stars.
Let’s set it all in motion
• Diurnal Motion – The rotation of the Earth
– This causes the stars to change during a night
– They rise in the East and set in the West
– Or rise in the SE and set in the SW
Motion of the Stars
Do all locations on Earth see the same
Visible Sky Simulation
motion of the stars?
Motion of stars as seen from Brier
Let’s set it all in motion
• Night sky changing through
the year
– Earth’s orbit around the Sun
– Stars up at sunset change
during the year
Zodiac Simulation
Let’s set it all in motion
Usefulness of the Constellations
• We can use the constellations to orient ourselves in the
sky
• Polaris - The north star
– in Brier our latitude is 48 degrees north
– Therefore Polaris is 48 degrees above the horizon
– This means you can always know your latitude in
the northern hemisphere by knowing were Polaris is
• Let’s look to the Northern Sky
Northern Sky
Usefulness of the Constellations
• The constellations can also tell you the time of
year by looking to the east around the time of
Sunset.
• Let’s look at the what you might see in the
Summer or Winter
Winter Triangle
Summer Triangle
Chart of the Sky
Note how the Sun appears to go North and South as the year
progresses. The zero point of Right Ascension occurs at the
Spring crossing of the Equator (vernal equinox). The
solstices occur at the maximum N/S excursions.