Transcript Celestial Sphere 1 Final

Introduction to Astronomy
and the Celestial Sphere
Astrology or Astronomy?
At one time, the two were considered to be
the same, but branched off into mythos and
science.
 Astrology – the non-scientific study of
horoscopes. Pseudoscience
 Astronomy – The scientific study of the
Universe.
There is a big difference, but this explains
why some of the terminology is similar.
Revolutionary Periods in Astronomy
There are two times that our understanding of the
universe changed within a single lifetime.
1)
2)
The 1600s- The Sun was placed at the center,
and the Earth and planets orbited the Sun.
Now – The Space Age. From 1957 – present.
What does Universe mean?
Universe- all existing matter and space
considered as a whole. The totality of all
space, time, matter, and energy.
Can there be “other” universes
by this definition?





Distances are commonly measured in:
inches
feet
centimeters
miles
kilometers
But space is HUGE, so we use other units.
 Light years (9.5X1012 km) - the distance that a
beam of light travels in one year
 Parsecs - 3X1013 km or 3.3 light years
 Astronomical Units (AU) 1.5X108 km – The
average distance from the earth to the sun
How fast is the speed of light?
 186,000 miles /sec
 300,000 km/s
 300,000,000 m/s, which is 3X108 m/s
 7 trips around the Earth’s Equator, each second!
How many stars exist within 1 LY of the Sun?
 NONE!
What is the closest star system to the sun?
 Alpha Centauri is actually made up of 3
stars and is 4.4 LY away from the sun
 Its name tells us that it is the brightest star
in the constellation of Centaurus
 Beta is used for the second brightest
 Proxima is used for the closest, so our
closest neighbor is Proxima Centauri
Constellation of Centaurus
Alpha Centauri, the brightest star
in the constellation, gets the
designation of “alpha”
Alpha Centauri
Constellation of Centaurus
Beta Centauri is the 2nd brightest
star in the constellation.
Beta Centauri
Alpha Centauri
Constellation of Centaurus
The 3rd brightest star in this
constellation is called
Proxima Centauri.
Beta Centauri
Alpha Centauri
Proxima Centauri
Constellation of Centaurus
Proxima Centauri
comes closer to
the Earth than any
other star.
Beta Centauri
Alpha Centauri
Proxima Centauri
How Many Stars in our Galaxy ?
There are about 200 billion (200,000,000,000)
stars in the Milky Way Galaxy.
Of those 200 Billion stars, we should potentially see
half of these at night (because the others are only
visible from the southern hemisphere)
That’s 100 billion stars
But we don’t…
 On the clearest of nights in the city, we can only
see about 2,000 stars.
 This is caused by light pollution
 Away from the city, we can only see about 6000
stars
 The rest are not visible because of our atmosphere,
light pollution stellar dimness, distance, and our
small eyes
Constellations
There is a natural tendency to see patterns
when we play “connect the dots” with stars.
 These patterns are called constellations.
 Constellations are human groupings of stars,
and can vary by culture
 In modern astronomy, we recognize 88
constellations
 12 of these are within the zodiac
 76 constellations are not.

Ecliptic - represents the sun's apparent (as seen from Earth)
path across the sky during the year.
Zodiac - a 16° band in the sky with the ecliptic in the center.
The apparent positions of the sun, moon, and most familiar
planets are found within this belt. It is divided into twelve
equal divisions or signs (Aries, Taurus, Gemini, Cancer,
Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius,
Pisces).
>>>
FYI, in astrology, a persons sign is defined as the
zodiac constellation the sun was supposedly in on their
day of birth. But it’s no longer the case.
Some constellations are very common.
The car
company,
Subaru, uses
The Pleides
as its logo.
The Pleides
Also known as
the Seven
Sisters, the
Pleides is
actually about
20 stars.
Is this the
Big Dipper?
Or is it the
Big (Great) Bear?
Actually, the correct name is neither The Big Dipper
nor The Big Bear.
 These are common names that are more
cultural.
 Its proper name is Ursa Major
 The “little dipper” is Ursa Minor
Orion, the Hunter
Notice the 3 stars
of his belt
Orion, the Hunter
3 stars of
his belt
Taurus the Bull
 Most constellations
do not really
resemble the object
for which they were
named
 instead, they were
named to honor a
figure from mythology
which was important
to the ancients.
Taurus the Bull
 For example, does
this look like a “bull”
to you?
 There may be a
resemblance, but
each constellation
has a cultural story
• Stars within a constellation are not close to each other and
are not at the same distance from Earth. So, constellations
are not real places.
The Celestial Sphere





An imaginary shell around the earth and
appears as a dome over our heads.
Stars seem embedded like tiny jewels
Ancient astronomers believed that all of the stars
were the same distance from the earth (but, of
course, they aren’t).
Useful model of what we see from Earth.
At any one time, we can see only ½ of the
celestial sphere (Where is the other half?)
Distance and Parallax
Parallax – The apparent motion of an object due
to the motion of the observer. Objects close to a
moving observer seem to move faster than
objects far away.
 Ancient astronomers did not see a change in the
position of stars as they moved from place to
place, so they knew that the celestial sphere
was very high in the sky.
 We still use parallax as a tool to measure
distances in space.
Descriptions of Celestial Sphere
The sky appears like
a dome overhead.
Zenith-directly overhead
Meridian – imaginary line
running north & south through
the zenith
Horizon – where the sky appears
to intersect the ground.
Altitude – height of a star above
horizon (degrees) to the
observer.
Declination – latitude lines,
extended out to celestial sphere
Right ascension – longitude
lines extended out into the
celestial sphere.
Descriptions of Celestial Sphere




North Celestial Pole (NCP)
– extension of Earth’s
rotation axis north onto the
sky.
South Celestial Pole extension of Earth’s rotation
axis south onto the sky.
Celestial Equator –
extension of Earth’s equator
onto the sky.
Ecliptic – apparent yearly
path of Sun. It appears
tilted because the earth is
tilted 23 ½ degrees in
space.
Rising and Setting of the Stars

The stars, sun, moon
and planets all appear
to rise in the east and
set in the west.

Reflection of Earth’s
rotation from west to
east.
Our view of Celestial Sphere



We live on the side of
the Earth.
Sky appears tilted at
an angle equal to our
latitude.
Stars appear to move
in arcs across the sky
that are not
perpendicular to
horizon.
Local Rising and Setting of the Stars


We live on the side of
the Earth.
NCP’s altitude equals
your latitude.
Circumpolar stars – these
stars appear close to the
NCP, so they never rise or
set. Instead, they circle
the NCP. Depends on
latitude.
Polaris




Polaris is more commonly known as the North Star
Almost directly above north celestial pole
At the North Pole, Polaris would be at the zenith
Polaris is found on the northern horizon at the
equator
Polaris
Zenith
Our view of Celestial Sphere


The sky appears to rotate around NCP.
Altitude of NCP is always equal to your latitude
on Earth's surface.
Polaris
 At the North Pole,
Polaris is found directly
overhead.
 As the Earth rotates on
its axis, all stars seem to
trace out circles around
Polaris.
 All stars at the North
Pole are circumpolar and
never rise or set
Polaris
Horizon
Horizon
Equator
 At the Equator, Polaris is found on the horizon.
 All stars rise and set, and none are circumpolar.
Circumpolar
Rise and
Set
 In El Paso and other middle latitudes, Polaris is
found between the zenith and the horizon.
 Some stars rise and set, and some are
circumpolar.
Comparing all three
North Pole
All stars are
circumpolar
Equator
El Paso, TX
No stars are
circumpolar
Some stars are
circumpolar
A space ship lands on an unknown planet.
The occupants notice that the stars never rise
or set but appear to move in circles parallel
to the horizon.
Where on the planet did the space ship land?
a) At the equator.
b) At 45 degrees latitude.
c) At one of the celestial poles.
d) Cannot be determined.
El Paso has a latitude of about 32 north degrees.
The star Polaris is very close to the Celestial North Pole.
What is the altitude of Polaris when viewed from El Paso?
a) 32 degrees
b) 45 degrees
c) 57 degrees
d) 90 degrees
This picture is a time exposure of the night sky showing star trails as the
stars appear to rotate around the NCP.
What is the name of the bright star near the center of the rock arch?
Where are the circumpolar stars?
Where could this
photo have been
taken?
Where could this
photo not have
been taken?
How close to the Equator
was this photo taken?