2.4. Objeto de la prueba
2.4.4. Costumbre admitida
On the Move
Transparency Teaching Tips
■ The concept introduced here is seasons. Ask the
students to explain why we have seasons. (Earth is tilted on its axis, and light from the Sun strikes Earth at different angles as Earth revolves about the Sun.)
Teacher Support & Planning
Earth
Moon Moon’s shadow
Area of total solar eclipse Area of partial solar eclipse
Sun
Earth Moon
Earth's shadow
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■ If possible, use a globe to point out that Earth’s axis
of inclination, or tilt, is 23.5°. Have a student pose as the Sun and walk the globe around him/her. Stop walking at winter (when the northern hemi- sphere is tilted away from the Sun) and again at summer (when the northern hemisphere is tilted toward the Sun).
■ Explain that this tilt causes seasonal changes.
■ The snow geese shown on the transparency
migrate from their summer breeding grounds in Greenland and the Canadian arctic to their winter homes in New Jersey and the Carolinas. Two of the triggering mechanisms for bird migration are changes in day length and intensity of sunlight, both related to seasonal change.
Content Background
■ Because Earth travels around the Sun in an
elliptical orbit, its distance from the Sun varies. For the northern hemisphere, Earth is actually closer to the Sun during winter. The tilt of Earth, however, is away from the Sun, which affects how the Sun’s rays strike Earth. During the summer, Earth’s tilt allows the rays to strike it at an angle closer to 90°. Such an angle allows for greater heating and more daylight hours.
■ In birds such as snow geese, changes in daylight
and temperature cause the pituitary gland to secrete hormones. The hormones affect various metabolic processes that cause the birds to begin their migratory flights.
■ Although not fully understood, the method by
which birds navigate great distances relates to their innate ability to use the stars, the Sun, and even Earth’s magnetic field as directional aids.
Answers to Student Worksheet
1. It must have been taken in the fall or spring.
Changes include day length, sunlight intensity, and temperature.
2. Answers will vary according to where you live.
Encourage discussions including temperature, precipitation, and length of day.
■ All asteroids are composed of rock and various
metallic elements. It has been hypothesized that asteroids are left over material from the formation of the solar system. The pieces were prevented from forming into a planet due to Jupiter’s enormous gravitational pull. It has also been suggested that asteroids are the remains of a planet destroyed in a collision.
■ Gaspra has been singled out for attention due to
its proximity to the trajectory of the spacecraft Galileo. In 1991, Galileo came within 1,600 kilometers (995 miles) of the Gaspra asteroid, sending back some intriguing photographs of the potato-shaped asteroid. The images appear to indicate that Gaspra is of fairly recent origin (300 to 500 million years ago) and is probably composed of silicates and chunks of pure metal. Note also the evidence of impact (the craters) in the image. Ask students what they think this might suggest about the size and composition of Gaspra.
Content Background
■ The smallest asteroids are no bigger than stones
you could pick up with your bare hand, and the biggest one, named Ceres, is 933 km (578 miles) in diameter.
■ It has been estimated that the total mass of all the
asteroids would be less than half that of the Moon.
■ Gaspra was discovered in 1917 by Grigoriy
Neujmin who named it after a Black Sea resort. The asteroid is 17 km (11 m) long.
■ Most meteoroids are asteroid fragments. Some
meteoroids are of cometary origin. Comets differ from asteroids in chemical composition and orbital characteristics (comets have irregular orbits). A meteoroid that enters Earth’s atmosphere is called a meteor. If it hits the ground, it is classified as a meteorite.
Answers to Student Worksheet
1. Answers will vary. Students might say it looks like
T14 The Solar System and Beyond
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Teacher Guide & Answers
(continued)■ Our Sun, shown on the transparency, is approxi-
mately 1,392,000 kilometers (865,000 miles) in diameter, or about 109 times bigger than the diameter of Earth. Its volume is 1.3 million times larger than Earth’s. The Sun’s core temperature is 15 million degrees Celsius (27,000,000°F), while its surface temperature is 5,500°C (10,000°F).
■ The stars visible in the night sky are enormous
distances from Earth. The Sun, at 150 million kilometers (93 million miles) is the closest star. The next nearest star, Proxima Centauri, is 25 trillion kilometers away. Light from this star takes over four years to reach Earth. There are stars in our own galaxy, the Milky Way, whose light takes 80,000 years to reach Earth.
Content Background
■ A star’s brightness is contingent upon how much
light energy it emits (which is related to tempera- ture) and its distance from Earth.
■ There are over 100 billion stars in the Milky Way
galaxy. The galaxy is about 100,000 light-years across and 300 light years thick.
■ For thousands of years, people have grouped stars
into constellations. Using the stars to create connect-the-dot patterns, people have seen animals, objects, and even people in the night sky.
■ The solar flare pictured on the transparency is
almost 591,000 kilometers (367,000 miles) across. Flares are caused by a jumbling of the Sun’s magnetic fields. This jumbling of magnetic forces results in an energy release of heat, light, electrons, and helium nuclei.
■ The picture was taken by Skylab 4 using an ultra-
violet spectroheliograph.
Answers to Student Worksheet
1. It would simply look like one of the stars you can
see in the night sky.
2. They group them in constellations.
3. A star’s perceived brightness depends on how
much light it emits and its distance from Earth.
Teaching Transparency (Page 47) Earth’s Revolution
Section 1
Transparency Teaching Tips
■ Use the transparency to discuss the seasons and
the reason for their occurrence.
■ Use a globe and a light source to demonstrate
Earth’s revolution around the Sun as you teach the transparency.
Reteaching Suggestion
■ Put the section vocabulary (rotation, revolution,
orbit, and eclipse) on the board and have the
students relate their significance to the transparency.
Extensions
Research: Have students research the solstices and
equinoxes, focusing on their relationship to Earth’s tilt and movements. Form small groups to present findings to the class.
Activity: In groups of three, have students model
the movements of Earth and the Moon. Assign one student to be the Sun, one Earth, and one the Moon.
Answers to Student Worksheet 1. rotation and revolution 2. rotation of the Earth on its axis 3. revolution
4. Earth’s tilt affects the way light from the Sun
strikes Earth. Summer comes to a region on Earth when the light is most direct; winter occurs when the light is least direct.
5. June; December
6. During a lunar eclipse, Earth moves between the
Sun and Moon. This means Earth’s shadow is cast over the Moon, causing a lunar eclipse.
Assessment Transparency (page 49) The Solar System and Beyond Section 3
Answers
1. C. For this question, students must read through
the table to identify which planet has the largest diameter. Choice C, Earth, has the largest diameter of the planets in the table, at 12,756 km.
2. F. Students must use the column headed Distance
from Sun to identify which planet is closest to the
Sun. Choice F, Mercury, is only 0.39 AU from the Sun and is therefore the closest of the inner planets.
3. B. In order to answer this question, students must
find the planet whose temperature most closely matches that of the planet in the question. Choice B, Venus, is the best match for a temperature of 470°C.
Test-Taking Tip
Remind students to bring extra pencils to the test and to sharpen them before the test begins.