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Astronomy
1)In which months is the northern hemisphere most directly in the sun?
2)In which months is the southern hemisphere most directly in the sun?
3)Is there a time when the northern and southern hemispheres are equally exposed to
the sun?
4)What do you call the day when the Northern hemisphere is most directly in the sun
(the longest day of the year in the northern hemisphere)?
5)What do you call the day when the southern hemisphere is most directly in the sun
(the longest day of the year in the southern hemisphere)?
6)On what two days are the northern and southern hemispheres equally exposed to the
sun?
Day, Night, and the Seasons
• Day and Night- The earth rotates around an axis, meaning that
sometimes a particular point on earth faces the sun and other
times it does not.
• Seasons- The earth revolves around the sun, but its axis is
always tilted, meaning that sometimes the northern
hemisphere points towards the sun and sometimes it points
away.
– The day is longer when pointing towards the sun, meaning
it has more time to warm.
Summer solstice- day when the northern hemisphere receives the most exposure to the
sun; its longest day.
Winter solstice- day when the southern hemisphere receives the most exposure to the
sun; its longest day.
Autumn equinox- day in September when both northern and southern hemispheres
receive equal exposure to the sun.
Vernal equinox- day in March when both northern and southern hemispheres receive
equal exposure to the sun.
The lives of ancient and tribal peoples centered on the movement of the sun. Many
holidays and feast days are scheduled to coincide with the solstices, equinoxes, and
quarters of the year (half way between solstice and equinox).
Think of a few holidays, do they line up with any of these periods of the year?
June 21st
Beginning of August
September 22
Beginning of November
December 21st
Beginning of February
March 20th
End of April/Beginning of May
From what direction does the sun rise? Set?
If you know the date and time of day, can you navigate by the sun?
What are the cardinal directions?
Copy the compass below and fill in the missing directions.
N
NW
NNE
W
E
ESE
SSE
SW
S
Planetary Motion
What causes the revolution of the Earth around the sun?
Planets move around the sun on predictable paths called orbits
Johannes Kepler discovered that planets revolve around the Sun in elliptical
orbits.
Ellipse
Circle
Kepler also established three laws of motion describing planetary motion
•Kepler’s First Law- planets move around the sun in an elliptical orbit
•Kepler’s Second Law- planets move faster during periods of their orbit closer to the Sun
•Kepler’s Third Law- planets that are further from the sun take longer to revolve
Sir Isaac Newton clarified Kepler’s discoveries when he explained gravity
Law of Universal Gravitation- the force of gravity between two objects depends on
the masses of the two objects and the distance between them.
The Sun orbits us while we are orbiting it
Gravity works with inertia to produce this elliptical motion
Did we always know the Earth revolved around the Sun?
Geocentric Model
Claudius Ptolemy (140 CE)Theorized that the Sun and all
of the other planets revolved
around the Earth
Heliocentric Model
Nicolaus Copernicus (1543)Theorized that the Earth and all
other planets revolved around
the Sun.
The movement of the Earth, Moon, and Sun have effects beyond the seasons and day and
night.
They also cause tides of the Earth’s oceans, eclipses, and the phases of the moon.
Tides are caused by the gravitational pull of the moon and sun on Earth’s fluid surface.
-We experience two high tides and two low tides each day
-All four tides occur simultaneously
-High tide 1- Water is pulled by the moon’s gravity
-High tide 2- Water opposite the moon is left behind as the
Earth moves towards the moon
-Low tide 1+2- Water from the two remaining sides of the Earth
recede as the high tides draw away water.
The added pull of the sun’s gravity affects how extreme the tides develop.
Spring Tides- the sun adds to the moon’s pull and makes high tides higher and low
tides lower
Neap Tides-the sun pulls opposite the moon, making the difference between high
and low tides less extreme.
Eclipses take place when the sun, moon, and earth align causing either the moon or earth
to cast a shadow on the other.
Solar Eclipse- the moon comes between the earth and sun, causing its shadow
to block some of the earth (from the earth, the sun is eclipsed from view).
Lunar Eclipse- the earth comes between the moon and sun, causing its shadow
to block the moon from the sun’s light (the moon is eclipsed by the earth)
During an eclipse part of the moon or earth is completely blocked from the sun’s
light, while other parts are only partially blocked
Umbra- darkest part of the shadow, completely blocked
Penumbra- outer part of the shadow, partially blocked
Solar eclipses occur more frequently than lunar eclipses, but the shadow is smaller so
fewer people can see them.
You will see more lunar eclipses in your life than solar eclipses.
The phases of the moon are caused by relative positions of the moon, earth, and sun.
In order for you to see the moon it must be facing the Earth (so you can see it) and the
Sun (so there is light reflecting off of it).
Half of the moon is always facing the Earth
Half of the moon is always facing the Sun
You see the part of the moon facing both the Earth and Sun
Why do you always see the same side of the moon?
It rotates and revolves at the same speed, so the same side always
faces the Earth.
-Approximately one revolution/rotation a month
-Our 12 month calendar is called the lunar calendar
Our Solar System
• Our Solar System includes…
– 1 star
– 8 planets
– Moons orbiting the planets
– Dwarf planets
– Asteroids and meteoroids
– Keiper Belt bodies
– The Oort Cloud
The eight planets ordered by their distance from the sun are…
1) Mercury
2) Venus
3) Earth
4) Mars
5) Jupiter
6) Saturn
7) Uranus
8) Neptune
There are divided into two groups, terrestrial planets and gas giants
Terrestrial Planets – Mercury, Venus, Earth, and Mars
-made primarily of solid matter (rock), no rings, and few satellites (moons)
Gas Giants- Jupiter, Saturn, Uranus, and Neptune
-all have rings (Saturn has by far the most dramatic) and many moons
Mercury
-closest planet to the sun
-least mass and volume, second highest density
-no atmosphere
-drastic temperature changes between the day and night sides
of the planet
-most elliptical orbit
Venus
-2nd
planet from the sun
-3rd least mass and volume, but 3rd highest density
-thick sulfurous atmosphere, runaway greenhouse effect.
-hottest planet in the solar system
-Always appears in the sky near the sun
(it is closer to the sun than us)
Earth
-3rd planet from the sun
-5th highest mass and volume, most dense
-large electromagnetic field and biological functions support an
atmosphere and global temperature suitable for life.
-extensive liquid water on the surface
Mars
-4th planet from the sun
-2nd lowest mass and volume, 4th most dense
-2nd least gravitational pull, only slightly stronger than mercury
-Thin atmosphere and crater covered surface, lots of iron oxide (rust)
-Olympus Mons- largest mountain in the solar system
-Polar ice caps
Jupiter
-5th planet from the sun
-first planet outside the asteroid belt, first gas giant
-most mass and volume, 6th most dense.
-primarily gas (H and He), with a small solid or liquid core
-known for its giant storms lasting hundreds of years (example: Great
Red Spot)
-60+ satellites (moons)
Saturn
-6th planet from the sun
-2nd most mass, 2nd most volume, lowest density
-primarily gas, with a solid/liquid core
-known for its extensive rings
-60+ moons in addition to the rings orbit the planet
Uranus
-7th planet from the sun
-4th most mass, 3rd most volume, 2nd least dense
- Made primarily of gas, but has more ice and organic gases in its
atmosphere than Jupiter and Saturn.
-Has an unusually large tilt. Earth’s
tilt is approximately 23.5° from
vertical, Uranus is approximately
90°.
Neptune
-8th planet from the sun
-3rd most mass, 4th most volume, 5th highest density
-Similar composition to Uranus
-Approximately 30 x as far from the sun as Earth. One
Neptunian year is equal to almost 165 years on earth.
The solar system also has several dwarf planets, such as Pluto, Eris, and Ceres.
-these have enough mass and gravity to be round, but not enough to significantly
affect the objects around them like planets do.
It is also filled with Asteroids, Meteoroids, Comets, and dust particles. All
of these revolve around the sun like the planets do.
Asteroids are large rocks in space, not quite massive enough to have enough gravity to compact
themselves into a round shape.
-Meteoroids are small asteroids
-Meteoroids that enter earth’s atmosphere and burn up are called meteors
-Meteoroids that enter earth’s atmosphere and hit the ground are called meteorites.
Comets are similar to asteroids except they usually are partially or entirely made of ice
and usually have a long tail of dust and ice trailing behind them.
There are important areas of the solar system to know about.
-The Asteroid Belt – the area between Mars and Jupiter where most of the solar systems
asteroids and meteoroids orbit the sun.
The Kuiper Belt- area outside the planet Neptune, containing several dwarf planets as well
as smaller objects, dust-like ice, and organic gases.
The Scattered Disc- area outside the Kuiper Belt, made-up of similar material with the
addition of some comets. It’s objects tend to have odd or scattered orbits, stretched
ellipses, and sometimes a different orbital plane.
The Oort Cloud- Area outside the Kuiper Belt and Scattered Disc to the end of our solar
system (where the sun’s gravity is no longer strong enough to cause objects to orbit).
Primarily composed of comets and loose dust and ice.
Classification of Stars
Stars are organized by observing their color and temperature, size,
composition, and brightness.
-As the surface temperature of stars changes their color changes.
Blue = hotter Red = cooler
-
.
-One can determine the chemical composition of something by
using a spectrograph.
• Spectrograph: An instrument that separates light into colors
and makes an image of the resulting spectrum
Not all stars are equally bright. How bright they appear can be affected by their
distance from Earth and their absolute brightness.
-Apparent Brightness: The brightness of a star as seen from Earth.
-Absolute Brightness: The brightness a star would have if it were a standard
distance from Earth.
-Controlled by the star’s temperature, size, and chemical composition
So a dim star could really be dim or it could just be far away
A Herzsprung-Russell Diagram is used to graph this information
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•A star begins as a Nebula
-Nebula- a large cloud of gas and dust in space spread out in an immense
volume.
•Then gravity pulls it together into a protostar.
-Protostar- a contracting cloud of gas and dust with enough mass to form a star.
•From there it continues to condense until there is enough pressure for Nuclear Fusion
to begin. It is now a living star.
what is nuclear fusion?
Smaller atoms fuse together under immense pressure to
form larger, more complex atoms.
Death
•When it runs out of fuel for nuclear fusion, the core begins to collapse and the
exterior expands forming a red giant or a super red giant.
1)A red giant’s exterior will continue to expand until it dissipates into a cloud
called a planetary nebula
a.The still hot core is left behind as a white dwarf.
-White dwarf- the blue-white hot core of a star that is left behind
after its outer layers have expanded and drifted off into space.
2)A super red giant collapses so much that it eventually explodes in what is
called a supernova.
a.A black hole or a super dense neutron star is left in place of its core
- Supernova- the brilliant explosion of a dying supergiant star.
- Neutron star- the small, dense remains of a high mass star
after a supernova.
-Black hole- an object whose gravity is so strong that nothing,
not even light, can escape.
Stars, even in our own galaxy, are so far away that a larger unit of distance is needed
to measure them, so we use what is called a light-year.
light-year- distance that light travels in one year.~9,500,000,000,000 km
Nothing in the universe can travel faster than the speed of light.
It is like a universal speed limit.
-300,000 km/s
-186,000 mi/s
-The closest star is Proxima Centauri, it is 4.2 light-years away.
-The light we see from that star is 4.2 years old.
-The sun is approximately 8.3 light minutes from earth
Scientists measure the distance to stars by observing what is called their parallax.
-parallax- The apparent change in position of an object when seen from different
positions.
The closer objects are the more they appear to shift position.
The Big Picture:
Our solar system is just one star in our galaxy, the Milky Way.
Our galaxy is just one of billions of galaxies in the Universe.
What is outside the Universe and what its shape is remains a question.
.
What we know:
•Stars are usually in groups called star systems
•Double stars or Binary Stars = two stars
•Triple stars = three stars
•Open Clusters = loose grouping of a few thousand stars
•Globular Clusters = tight grouping of older stars, up to a million stars
-Eclipsing Binary- star system in which one star periodically blocks light from
another.
* one way to find planets around other stars is to look for objects eclipsing them.
-Galaxy- a huge group of single stars, star systems, star clusters, dust, and gas
bound together by gravity.
•There are several types of galaxies; spiral galaxies, elliptical galaxies, and
irregular galaxies.
spiral galaxy- galaxy with a bulge in the middle with arms that spiral out.
elliptical galaxy- galaxy that looks like round or flattened ball, less gas
and dust than a spiral galaxy.
irregular galaxy- smaller younger galaxy without a traditional shape, lots
of gas and dust to form new stars.
-There are also distant objects that resemble galaxies called quasars
The Universe- all of space and everything in it
•The Universe formed during the Big Bang about 14 billion years ago
Big Bang- theory that the universe formed in an instant in a massive explosion
•The Universe is still expanding, or stretching like an inflating balloon.