Download Foundation 1 - Discovering Astronomy

Að uppgötva
næturhimininn
Hvað heldur þú?
• Hve björt er norðurstjarnan, Pólstjarnan, í
samanburði við aðrar stjörnur?
• Eru stjörnumerkin aðeins goðfræðlegar
myndir á himninum?
• Hvað veldur árstíðaskiptum?
• Hvað eru stjörnumerkin mörg?
• Hvenær, er tunglið sýnilegt á daginn?
Stjörnumerkin auðvelda
staðsetningu stjarnanna
Notaðu
Stóra
björninn á
norðurhveli
himins tio
að finna
aðra hópa
stjarnanna
Notaðu vetrar
þríhyrningin
til að finna
suðurhimins
stjörnumerkin
á vetrarkvöldm
Notaðu Sumar Þríhyrninginn til að finna
suðræn stjörnumerki á sumarkvöldum
Hornið milli stjarna á himninum er
notað til að áætla fjarlægðir
Hornfjarlægð milli stjarna á
himninum eru mæld í gráðum
Ímyndað
Himinhvolf
sem
umlykur
Jörðina er
notað til að
túlka
himininn
Elements of the equatorial coordinate
system on the celestial sphere
• Vernal Equinox: The position of
the Sun on the first day of spring
• Right Ascension: How far east of
the Vernal Equinox an object is
located
• Celestial Equator: The line
separating the celestial sphere
into northern and southern
halves.
• Declination: How far above or
below the celestial equator an
object is located.
Earth’s
rotation
causes the
Sun and
stars to
appear to
move
Motion of Stars at the North Pole
Motion of Stars at the Equator
What about the Sun? It seems to move across
the celestial sphere on a path called the ecliptic.
Summer solstice
Winter solstice
Equinox position
Position of the “noon-time” Sun when
photographed every two weeks over a year
The “altitude” of the Sun impacts how much
energy is received on Earth resulting in seasons.
The seasons are caused by the tilt
of the Earth’s axis of rotation
In other words ...
• The Earth’s rotation on its axis determines
the length of the day
• The Earth’s orbit around the Sun
(revolution) determines the length of the
year
• The Earth’s tilt with respect to the ecliptic
causes the seasons.
Precession is a slow, circular motion
of the Earth’s axis of rotation
Precession causes
the position of the
NCP to change
over a period of
26,000 years.
The changing phases of the Moon originally
inspired the concept of the month
Moon Phase Names
•
•
•
•
•
New Moon
Waxing Crescent
First Quarter
Waxing Gibbous
Full Moon
•
•
•
•
•
Full Moon
Waning Gibbous
Third Quarter
Waning Crescent
New Moon
Although the
Moon is always
 lit from the
Sun, we see
different
amounts of the
lit portion from
Earth
depending on
where the
Moon is
located in its
month-long
orbit.
How long does it
take to go from new
moon to new moon?
lunar month
27.3 days
29.5 days
How long does it
take the Moon to
orbit Earth?
synodic month
Eclipses occur only when the Moon crosses
the ecliptic during the new or full phase
Types of Lunar Eclipses
• total eclipse
• penumbral eclipse
• partial eclipse
Solar
Eclipse
Annular Eclipse
Partial Eclipse
Total Eclipse
What did you think?
• How bright is the North Star, Polaris, compared to other
stars?
Polaris is a star of medium brightness compared to other stars visible to
the naked eye.
• Are constellations just mythic figures in the sky?
A constellation is an entire region of the celestial sphere and all that
stars in it.
• What causes the seasons?
The tilt of Earth’s rotational axis causes the seasons.
• How many zodiac constellations are there?
There are 13 zodiac constellations, the “unknown one is Ophiuchus.
• When, if ever, is the Moon visible during the daytime?
The Moon is visible during the day for half of the lunar cycle of phases.
Self-Check
1. Describe the nature and value of constellations.
2. Define the elements of the equatorial coordinate system on
the celestial sphere.
3. Define two solstices and two equinoxes; explain the
orientation of the ecliptic on the celestial sphere and how
it produces seasons on the Earth.
4. Describe what precession is, what effect it has on our
observations of stars, and why it occurs.
5. Explain by drawing a diagram showing how lunar phases
are controlled by the relative positions of the Sun and the
Moon.
6. Explain when and why solar and lunar eclipses occur and
why there are not such eclipses every month.