TCAP Review 6

Components of the Universe - StarsMain Sequence Stars: Main sequence stars

are usually medium sized stars. Our sun is a main sequence star.

Components of our solar systemThe Sun is by far the largest object in the

solar system. It contains more than 99.8% of the total mass of the Solar System (Jupiter contains most of the rest). Everything found in our solar system revolves around the sun.

PlanetsThere are eight major planets in our solar

system. A planet is a celestial body moving in an elliptical orbit around a star.

We have two systems of planets in our solar system:

The inner planets which are small dense and rocky.

The outer planets which are large and made of gases.

Dwarf PlanetsA dwarf planet is a celestial body massive

enough to be spherical, in orbit around the Sun, which are not satellites. The crucial factor dividing a planet from a dwarf planet is that a planet must have succeeded in clearing the area of its orbit from debris and other objects, whereas a dwarf planet has not.

MoonsMany people think that moons are smaller than

planets. This, however, is not true. There are several moons in the Solar System which are larger than both the planets Mercury and Pluto. Neither are the moons less exciting than the planets. There are moons with volcanos, atmospheres, and even quite possibly liquid water oceans. The difference between what we call a moon and what we call a planet has to do only with around what the world revolves, or circles. If the object circles the Sun it is called a Planet, however, if it circles another world instead of the Sun then it is called a moon.

Our Moon

CometsA comet is an icy small Solar System body that, when

close enough to the Sun, displays a visible coma (a thin, fuzzy, temporary atmosphere) and sometimes also a tail. Comets are often referred to as "dirty snowballs." They are left over from the formation of stars and planets billions of years ago. Before zipping around the Sun with their characteristic big tails, comets that we see in our solar system start out as big chunks of rock and ice just floating around in something called the Oort Cloud. When the gravity from a large passing body, like a star, becomes strong enough, some large chunks of ice get pulled away from the cloud and head toward the Sun. As that ball of ice gets close enough to the Sun, its heat begins to melt some of the ice that makes up the comet. The melted ice becomes a gaseous tail that extends away from the source of the heat (in this case, the Sun). The tail is pushed out by the Sun's solar wind.

Comet

AsteriodsAsteroids are metallic, rocky bodies without

atmospheres that orbit the Sun but are too small to be classified as planets. Known asteroids range in size from the largest -- Ceres, the first discovered asteroid in 1801 -- at about 600 miles (1,000 kilometers) in diameter down to the size of pebbles. Most asteroids are found in a belt between the orbits of Mars and Jupiter.

Meteoroid, Meteorite and MeteorA meteoroid is a small rock or particle of debris in

our solar system. They range in size from dust to around 10 metres in diameter (larger objects are usually referred to as asteroids).

A meteoroid that burns up as it passes through the Earth’s atmosphere is known as a meteor. If you’ve ever looked up at the sky at night and seen a streak of light or ‘shooting star’ what you are actually seeing is a meteor.

A meteoroid that survives falling through the Earth’s atmosphere and colliding with the Earth’s surface is known as a meteorite.

Meteoroid, Meteorite and Meteor

Rotation and RevolutionRotation means to turn on its axis. The Earth

and moon rotate on their axis. Prograde rotation is a planet spinning counterclockwise and retro grade is a planet spinning clockwise. Venus and Uranus are the only planets with retrograde rotation.

Revolution means to revolve around another body. The Earth revolves around the sun in an orbital path. The moon revolves around the Earth in an orbital path.

What makes a dayThe time it takes Earth to complete one

rotation is considered a day. It takes 24 hours to complete is responsible for day and night.

Why do we have seasons on Earth?The Earth's seasons are not caused by the differences in

the distance from the Sun throughout the year (these differences are extremely small). The seasons are the result of the tilt of the Earth's axis.

The Earth's axis is tilted from perpendicular to the plane of the ecliptic by 23.45°. This tilting is what gives us the four seasons of the year - spring, summer, autumn (fall) and winter. Since the axis is tilted, different parts of the globe are oriented towards the Sun at different times of the year.

Summer is warmer than winter (in each hemisphere) because the Sun's rays hit the Earth at a more direct angle during summer than during winter and also because the days are much longer than the nights during the summer. During the winter, the Sun's rays hit the Earth at an extreme angle, and the days are very short. These effects are due to the tilt of the Earth's axis.

Seasons

SolsticeA solstice is an astronomical event that occurs

twice each year as the Sun reaches its highest or lowest excursion relative to the celestial equator on the celestial sphere. As a result, on the day of the solstice, the Sun appears to have reached its highest or lowest annual altitude in the sky above the horizon at local solar noon.

The summer solstice is June 21. We have more daylight hours on this day than any other day of the year in the Northern Hemisphere.

The winter solstice is December 21. We have less daylight hours on this day than any other day of the year in the Northern Hemisphere.

Solstice

EquinoxAn equinox occurs twice a year, when the tilt

of the Earth's axis is inclined neither away from nor towards the Sun.

The fall equinox is September 21.The spring equinox is March 21.On these two dates we have equal amounts of

daylight and darkness all over the Earth.

Equinox

Moon PhasesThe moon goes through phases as it revolves

around the Earth because it reflects sunlight. It takes about one month for the moon to complete one lunar cycle, which is one revolution. It also takes the moon about one month to rotate on its axis. It revolves and rotates at the same speed.

Moon Phases

EclipseA lunar eclipse occurs when the moon passes through

the shadow of the earth ( During a Full moon). A lunar eclipse can last up to an hour and a half. During a lunar eclipse the moon may turn a reddish color. It is not dangerous at all to look at a lunar eclipse because the moon does not make its own light.

A Solar Eclipse occurs when the moon goes in front of the sun and blocks most of the sun's light from the earth (During a New Moon). During a total eclipse all you can see from earth is a ring of light around the moon which is part of the sun the moon did not cover. It is dangerous to look at a solar eclipse directly, even if you have sun glasses or smoked glass

Lunar Eclipse

Solar Eclipse

TidesThe moon's gravity pulls the oceans nearest it

towards it hence the high tide on the lunar side of the earth. The Moon's influence gets weaker with distance so the ocean on the far side of the Earth form the moon gets 'left behind'. In effect the Earth is pulled slightly more towards the moon than the oceans on the opposite side of the Earth. So there is a bulge or high tide at the same time on both sides of the Earth. Because of this there are two high tides and two low tides at each location on the earth every day.

Tides

Spring and neap tidesWhen the Sun, Earth & Moon are in alignment

with one another ( during new or full moons) spring tides occur. Spring tides happen twice a month Spring tides are higher than average. When the Sun - Earth line is at right angles to the Earth (During 1st and last quarter) we see "neap" tides, which are lower than average. A tide in which the difference between high and low tide is the least. Neap tides occur twice a month when the Sun and Moon are at right angles to the Earth. When this is the case, their total gravitational pull on the Earth's water is weakened because it comes from two different directions.

Spring and Neap tides