1. I think it was the Big Bang Theory. It states that the universe was originally a small, immensely dense packet of energy that exploded causing the elements and space to form.
2. It's because of the Big Bang, even though it's a theory scientists still assume that's the reason why everything is moving away from each other. They even said something about planets and other things being formed because of it.
3. Gravitational force is a fundamental force which acts between any two bodies having mass. It is an attractive force. It is proportional to the mass of the two bodies and inversely proportional to square of distance between them.
It is due to gravitational force that holds planets with stars, moons with their planets and stars in galaxies. Had there been no gravitational force, the stars would not have formed and for the fact, any other body in this universe. Gravitational force causes the moons to revolve about planets, planets to revolve about star and star to revolve about the center of galaxy.
4. That part of the solar system is the sun. Of all the mass in the total solar system, more than 99% of it is in the sun.
5. Every object in the universe exerts a gravitational force on every other object, but the size of that force depends on the mass of the objects and the distance between them. The earth has more mass than the moon, so its gravitational pull affects the moon. The sun is more massive than any of the planets in the solar system and so its gravitational pull affects them and keeps them in orbit.
6. Earth is slightly closer to the sun in January than in July. However, summer is warmer because the tilt of the earth exposes the hemisphere to more direct light during the summer months.
7. If earth was not tilted on an axis, we wouldn't have any seasons. We wouldn't have seasons because the axis tilts us towards or away from the sun, and if you're tilted towards the sun, it would be summer. If you're tilted away from the sun, it would be winter. If there was no axis, the temperature would be the same everyday so therefore, we would not have seasons.
8. It shows the heliocentric idea of the solar system. In this view, the sun is at the center of the solar system with planets orbiting around it. In the geocentric view, the earth is at the center of the solar system.
9. On the summer solstice, the sun will shine directly on the Tropic of Cancer (23.5 degrees north ) , so the summer solstice should be picture B. While on the winter solstice, the sun will shine directly on the Tropic of Capricorn (23.5 degrees south), so the winter solstice is picture D. Because earth revolves in counter clockwise direction around the sun, the spring equinox will be picture A and the fall equinox will be picture C.
As for the dates, the spring equinox is on March 20 or 21, the summer solstice is on June 22 or 23, the fall equinox is on September 23 or 24, and the winter solstice is on December 22 or 23.
10. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
11. Mercury, Mars, Venus, Earth, Neptune, Uranus, Saturn, and Jupiter
12. Mercury, Mars, Uranus, Venus, Earth, Neptune, Saturn, and Jupiter
Earth
Earth, the third planet from the sun and the largest terrestrial
planet, is the only planet known to host living beings and the only one known to have liquid water on its surface. T
Jupiter
The largest and most distinctive of the storms, the Great Red Spot, is larger than Earth. Jupiter has 63 moons and a faint ring system.
Mars
Some of the surface features of Mars, such as dry river beds, hint to the possibility that water previously existed on the planet and may still flow under the surface.
Mercury
The planet Mercury is hot and cold at the same time. The part where it is facing the sun is so hot that it can reach up to 800 degrees Fahrenheit while the other side (not facing the sun) can be as cold as -279 F.
Neptune
Like all the outer planets, Neptune, like Uranus, has a diameter roughly four times that of Earth.
Saturn
Saturn has an extensive and complex ring system
Uranus
The ice giant Uranus spins on an axis parallel to its orbit.
Venus
The density of its atmosphere makes the air pressure at the surface 90 times that of Earth's. The heat and pressure make the planet decidedly inhospitable to life.