1. Galaxies, Solar Systems and Motion (35B/36A)
Galaxies are massive systems of stars, solar systems, remnants of stars, gas and dust, and dark matter held together by gravity.
Supermassive black holes are at the center of most galaxies and have the greatest mass in their galaxy. Galaxies move because of gravity.
Galaxies in the universe are categorized by their appearance: elliptical, spiral (ex. our Milky Way galaxy), or irregular.

2. Elliptical Galaxies-largest types of galaxy

3. Spiral Galaxies-most common type of galaxy

4. Irregular Galaxies-smallest types of galaxy

5. Lenticular Galaxies (Spiral is turning into an elliptical galaxy)

6. Our solar system is located in one of the “arms” of the Milky Way.

7. Know the names and order of the planets.

8. Galaxies, Solar Systems and Motion
Why can’t orbits be anything other than circular or like an oval?

9. Galaxies, Solar Systems and Motion
The gravitational pull of larger objects like stars brings smaller objects like planets into a circular/oval orbit around it. Gravity is always at work and never “stops working” so the shape of an object’s orbit can’t have any corners.

10. Based on the picture of the solar system, what 2 factors contribute to gravitational pull?
Gravitational pull is DIRECTLY PROPORTIONAL to mass and INVERSE to distance.
As mass increases, gravitational pull increases.
As distance increases, gravitational pull decreases.
As mass decreases, gravitational pull decreases.
As distance decreases, gravitational pull increases.

11. Which of the terrestrial planets has the most gravitational pull?

12. All of the planets feel a HUGE gravitational pull from the sun so why don’t any of the planets get pulled into the sun?

13. 1 AU = distance from Earth to the sun = 93 million miles!
Answer: Distance!
In the solar system, we measure distance in space by astronomical units (AU)
1 AU = distance from Earth to the sun = 93 million miles!
To scale down distance, we can choose a number (for example 10 cm) to equal 1 AU and multiply that scale value to the AU of other planets to give us that planet’s diameter value.
Planet AU
Distance Scale Value
Mercury
.4 AU
4 cm
Venus
.7 AU
7 cm
Earth
1 AU
10 cm

14. How can we make a model of the solar system if everything is so large?
Planet
Representative Object
Actual Diameter
Scaled Diameter Value
Mercury
4,789 km
Venus
12,104 km
Earth
12,792 km
Mars
6,779 km
Jupiter
139,822 km
Saturn
116,482 km
Uranus
50,724 km
Neptune
49,244 km
Which of the representative objects and scaled diameters should each planet be matched to? The Sun’s diameter is 1.4 million km and is represented by a gigantic beach ball 1,066 cm in diameter.
A marble (3.5 cm)
Rubber ball (13 cm)
Soccer ball (35 cm)
Ping pong ball (5 cm)
Basketball (85 cm)
Volleyball (37 cm)
Beach ball (105 cm)
A golf ball (12 cm).

15. How can we make a model of the solar system if everything is so large?
Planet
Representative Object
Actual Diameter
Scaled Diameter Value
Mercury
Marble
4,789 km
3.5 cm
Venus
A golf ball
12,104 km
12 cm
Earth
Rubber ball
12,792 km
13 cm
Mars
Ping pong ball
6,779 km
5 cm
Jupiter
Beach ball
139,822 km
105 cm
Saturn
Basketball
116,482 km
85 cm
Uranus
Volleyball
50,724 km
37 cm
Neptune
Soccer ball
49,244 km
35 cm
Which of the representative objects and scaled diameters should each planet be matched to? The Sun’s diameter is 1.4 million km and is represented by a gigantic beach ball 1,066 cm in diameter.