science Flashcards
nuclear fusion occurs in an environment of
extreme density and heat
heat and density cause the atoms to
lose their electrons and collide with great force
with nuclei that fuse during nuclear fusion
more energy is released which heats nearby nuclei
the proton-proton chain is
the dominant form of nuclear fusion
the proton-proton chain begins when
an ordinary hydrogen is stripped of its electron and becomes a single proton
four hydrogen protons are then
fused together to form a single helium nucleus
The end result of the proton-proton chain is
a helium nucleus composed of two protons and two neutrons, as well as a colossal amount of energy
lighter elements can be used to build
heavier elements
in the periodic table, lighter elements appear near the top while
heavier elements are farther down
Some stars that are hot enough have the ability to fuse helium nuclei to create
nitrogen, oxygen, carbon, and other elements
Nuclear fusion cannot produce elements heavier
than iron (symbol Fe
the formation of elements stronger than iron can only occur at
the very end of a star’s life
humans consume about
3.89 × 1020 joules of energy every year.
How long a star will live has a lot to do with its
mass
Stars with greater mass consume their fuel
much faster
A large star can put out
huge amounts of energy, and consumes its fuel incredibly quickly.
A smaller star consumes its fuel
very slowly
Stars with a greater overall mass are
brighter and hotter, and they consume their nuclear fuel faster.
Luminosity is the term for a star’s actual
brightness.
The HR diagram is a tool astronomers use to study how stars
evolve
Star’s color is determined by its
temperature
a star’s luminosity is determined by its
size.
Small and medium-sized stars begin their lives by gradually converting
hydrogen into helium.
Because small and medium-sized stars are cooler, they consume fuel very
slowly.
After all fuel resources have been used up, the star will emit enormous pulses of
energy
These pulses will push the outer layers of the star away, creating a cloud of
ionized gas.
At the center of this cloud is the
core of the star, (a white dwarf)
As the white dwarf cools, its light becomes
dimmer and redder.
Large stars go through the supernova stage where they collapse and turn into either a
neutron star or a black hole.
When a large star begins to exhaust its fuel supply, it starts fusing
hydrogen from outside its core
The result of the fusing is a
red supergiant.
A stellar nebula is a cloud of
interstellar gas and dust
a stellar nebula is also the
birthplace of a star
the collapse of a medium-sized star leads to a
planetary nebula
Before the formation of our solar system, there was a supernova event that sent out an enormous cloud of
gas and dust.
The cloud stabilized to form a slowly spinning
nebula.
The nebula that formed before our solar system was primarily composed of
hydrogen, helium, carbon, oxygen, nitrogen, and silicon.
the supernova event had produced heavy elements too, such as
gold, copper, uranium, and lead.
Although the nebula was spinning very slowly, the rotation was enough to cause it to
flatten out
Eventually, the disk-shaped nebula began to
shrink
This event marked the birth of the,
Sun
As gravity pulled the disk-shaped nebula inward
it spun faster and faster
The nuclear reactions occurring within the Sun grew stronger, and it began emitting tremendous amounts of
electromagnetic radiation.
These nuclear reactions created a lot of
heat
Because gases cannot condense at such high temperatures, the region close to the Sun became unsuitable for the formation of
gaseous planets.
outward pressure caused by the Sun’s radiation pushed many of the lighter elements to the farther reaches of the solar system. Once these gases were pushed out far enough, they could cool, condense, and begin to form the
gas giant and ice giant planets.
Close to the Sun, rocky materials rapidly orbiting the Sun frequently collided. In the process, they began to accrete to form.
planetesimals
As more and more rocks slowly joined the planetesimals, their mass, and therefore their gravitational influence, increased, becoming
protoplanets.
the bodies that make up our solar system are
planets, asteroids, comets, and meteoroids.
Terrestrial Planets
- solid outer surface
- dense and orbit closer to their stars
Other terrestrial planets in our solar system include
Mercury, Venus, and Mars.
Gas giants are extremely large planets made primarily of
hydrogen and helium in gaseous and liquid forms.
In our solar system, the gas giants are
Jupiter and Saturn.
The ice giants are composed of relatively
light elements.
ice giants have a different chemical composition than gas giants, and their interior is largely composed of frozen gases such as
oxygen, carbon, and methane.
In our solar system, the ice giants are
Uranus and Neptune.
Asteroids are small bodies made of
metal and rock
Comets are small, solid bodies made of
frozen gases.
Meteoroids are similar in composition to asteroids, but they are much
smaller
When they enter the atmosphere, they are known as,
meteors
Between the inner and outer planets is a region called the
asteroid belt.
the kuiper belt is a
region of icy bodies, located outside Neptune’s orbit
the kuiper belt also houses
pluto
Every object in the universe that has mass exerts a
gravitational pull on every other mass. this force is called gravity
Gravitational force between two objects depends on the
mass of the objects and the distance between them.
As the mass of any object increases,
its gravitational force grows stronger.
But if the distance between two objects increases,
the gravitational force between them grows weaker.
Planets formed gradually through the process of
accretion
The giant impact theory states that the Moon was formed by
debris during Earth’s collision with a Mars-sized planetesimal.
According to the capture hypothesis, the Moon was formed within the Sun’s orbit but far from Earth. As the Moon was passing Earth in its orbit around the Sun,
Earth’s gravity pulled it in.
The accretion hypothesis suggests that Earth and the Moon were formed at
the same time, from the same cloud of material, in the same general location, and by the same process.
Earth takes approximately 24 hours to complete an entire rotation about its
axis
Earth’s spin is the reason why parts of our planet are alternately
exposed to and shielded from the Sun.
This is the mechanism that creates the
daily cycle of sunrise and sunset.
Earth’s axial tilt also interacts with both Earth’s orbit and spin to cause seasonal changes in day and night. This interaction creates longer days than nights or longer nights than days in certain parts of the planet and at certain times of the year. The phenomenon is known as a
solstice
A solstice marks the beginning of either
summer or winter in a particular hemisphere.
During the summer solstice, the Sun’s rays reach their northernmost point on the planet. As a result, in the Northern Hemisphere,
daytime is longer than night.
The duration of daylight varies according to latitude. In some regions, the Sun stays above the horizon for more than 24 hours—a phenomenon called the
polar day.
During the winter solstice, the opposite occurs—
the night lasts longer than the day.
Tidal friction causes Earth to spin more
slowly
The Sun is Earth’s primary source of
energy
Earth’s journey around the Sun takes just over 365 days and is what defines a
year
While the Northern Hemisphere experiences summer, the Southern Hemisphere experiences
winter
There are also times in Earth’s orbit when the Sun shines directly on the equator, causing Earth’s surface to receive exactly 12 hours of day and 12 hours of night as it spins. This phenomenon is known as an
equinox
an equinox results in the seasons of
spring and autumn.
The first day of spring is marked by the vernal equinox around
March 21.
Likewise, the autumnal equinox occurs around
September 23.
photovoltaic (PV) cells convert sunlight into
electrical energy
The more sunlight a PV cell receives, the more
electricity it can produce.
However, when sunlight hits a PV cell at an angle other than 90°, the amount of energy delivered is
reduced
Solar trackers are moving mounts for PV cells. They adjust the position of the cell so that sunlight strikes the cell at as close to 90° as possible. This system ensures that PV cells always receive the maximum amount of
sunlight possible.
Solar trackers must be designed based on the type of
PV cell used.
The Moon’s orbit around Earth resembles Earth’s orbit around the
Sun
This phenomenon, in which an object’s rotational and orbital periods are the same, is called
tidal locking.
Due to tidal locking, Earth always sees the same
side of the Moon.
The common phrase “dark side of the Moon” refers to the side of the Moon facing
away from Earth.
At any given moment, precisely half of the Moon is
illuminated
when the Moon isn’t visible from Earth, it is called the
new moon.
When Earth lies between the Sun and the Moon, it is called the
full moon.
During the lunar cycle, the Moon goes through phases of
waxing and waning.
Waxing refers to an increase in the
illuminated portion as viewed from Earth.
Waning refers to the shrinking of the
illuminated portion as viewed from Earth.
During the new moon phase, the Moon is invisible from Earth. When it reappears, only a thin slice is illuminated. This is the young moon, or the
waxing crescent
Gradually, the illumination expands, and half the Moon becomes visible. This is the
first quarter moon.
The first quarter moon turns into the waxing gibbous and finally into the full moon. After the full moon, the visibility of the Moon gradually reduces. As it wanes, the Moon goes through three more phases—waning gibbous, last quarter, and waning crescent—before the
cycle begins again.
When the Sun, Earth, and Moon do line up perfectly, an
eclipse occurs.
A lunar eclipse occurs when
Earth casts a shadow on the Moon.
A solar eclipse occurs when the
Moon casts a shadow on Earth.
As the Moon orbits Earth, the planet’s ocean waters change position. The surface water on the side of Earth closest to the Moon, as well as the water farthest from the Moon
bulges in response to the Moon’s gravity.
Known as ocean tides, this movement of water helps
stabilize Earth’s orbit.
As Earth rotates, the locations of the two tidal bulges, known as high tide, follow the Moon’s
orbit
When the Sun and the Moon are aligned, their gravitational forces combine to create an event called
spring tide.
When the Moon is at a right angle to the Sun, a
neap tide occurs.
Qualifications for a planet:
a planet orbits a star but is not itself a satellite
a planet must have enough mass, and thus gravity, to assume a nearly spherical shape
a planet needs to have cleared the neighborhood around its orbit.
One way to calculate an orbit’s size is to measure the length of its
semimajor axis.
Another way to describe the size of an orbit is to measure its
orbital period.
