Earth has a diameter of approximately 8,000 miles (12,900 km), with a circumference near 24,000 miles (38,000 km). Our Moon has a diameter of about 2,170 miles (3,475 km), with a circumference of 6,800 miles (almost 11,000 km).
Our Sun has a diameter near 870,000 miles (1,390,00 km), which is over 100 times larger than the Earth! The circumference of the Sun is more than 2,700,00 miles (4,370,000 km).
Our Solar System is about 5.5 billion miles across (near 9 billion km). If we scaled down the solar system to the size of our classrooms, about 10 meters across, the Earth is smaller than a speck of sand (about 0.000014 meters, or 0.014 millimeter!), and the Sun is about the size of a piece of sand (about 0.0015 meters, or 1.5 mm)... albeit, a large bright piece of sand.
If we consider the Solar System to be disk, looking down at a 90-degree angle from the average ecliptic, then it's a disk with a circumference of 17.3 billion miles (27.6 billion-km). When we discuss distances of this size we usually discuss them in AUs (Astronomical Units), with 1 AU = average distance between the Earth and the Sun, or 93,000,000 miles (150,000,000 km). Thus, our Solar System is 59 AU across. For greater distances, we start using light years, the distance light travels in one Earth years. With light traveling at approximately 186,300 miles per second, a light year is about 6 trillion miles! Our Solar System is 0.0009 light years across.
We are about 30, 000 light years (180,000,000,000,000,000 miles) from the center of our Milky Way galaxy. The diameter of the Milky Way (across the disk) is about 100,000 light years!
We're about 2.2 million light years from the nearest similar galaxy to ours, the Andromeda Galaxy.
>GROUP ACTIVITY - 1: On the following chart, we have provided equatorial diameters for various space bodies. In groups, calculate the approximate equatorial circumference of each body and how long it would take you to walk around that body, assuming a walking rate of 20 miles per day. Note: all measurements are in kilometers, abiding by National Education Standards for Mathematics and Science.
RELATIVE SIZES (for this exercise II = pi =3.14)
Space Body Equatorial Diameter Equatorial Circumference Walking Time (around)
(diameter = d) (c=2 II r or II d) (20 miles/day-32 km/day)
Earth 12,756 km 40,074 km 1,252 days
Moon 3,476 km km days
Sun 1,390,000 km km days
Mercury 4,850 km km days
Venus 12,033 km km days
Mars 6,754 km km days
Jupiter 141,974 km km days
Saturn 119,306 km km days
Uranus 50,506 km km days
Neptune 48,318 km km days
Pluto 2,982 km km days
>GROUP ACTIVITY - 2: Now, in groups, develop a scale picture comparing the sizes of the planets, the Sun, our Moon, and a Saturn V rocket like the type used to carry our Apollo missions to the Moon. Use the scale that one meter (1 m) = the diameter of the Sun. Complete the following table first, and then obtain a piece of butcher paper or drawing paper and draw out these scaled down images, starting with the Sun and working down.
Calculation: 1 m/1,390,00 km = x in meters/diameter x in meters = diameter / 1,390,00 km
Space Body Actual Equatorial Diameter Scale Diameter
Sun 1,390,000 km 1 m or 100 cm
Mercury 4,850 km m or cm
Venus 12,033 km m or cm
Earth 12,756 km m or cm
Moon 3,476 km m or cm
Mars 6,754 km m or cm
Jupiter 141,974 km m or cm
Saturn 119,306 km m or cm
Uranus 50,506 km m or cm
Neptune 48,318 km m or cm
Pluto 2,982 km m or cm
Saturn V Rocket 0.11 km (length) m or cm
The following table provides distances and travel times from Earth (not from the Sun) and has obvious uses in mathematics classes as well as science classes.
RELATIVE DISTANCES: Travel Distance & Time From Earth
Destination Distance Jet Rocket Light/Laser/Radio
Moon 250,000 miles 16.5 days 9.4 hours 1.2 seconds
Sun 93,000,000 miles 17.7 yrs 4 months 8.5 minutes
Mercury 57,000,000 miles 10.8 yrs 3 months 5 minutes
Venus 26,000,000 miles 5.4 yrs 1.5 months 2.5 minutes
Mars 49,000,000 miles 8.8 yrs 2.5 months 4 minutes
Jupiter 90,000,000 miles 74.25 yrs 1.75 yrs 35 minutes
Saturn 794,000,000 miles 150.4 yrs 3.6 yrs 1.2 hours
Uranus 1.7 billion miles 318.5 yrs 7.6 yrs 2.5 hours
Neptune 2.7 billion miles 513.2 yrs 12.25 yrs 4 hours
Pluto 3.6 billion miles 690.1 yrs 16.4 yrs 5.4 hours
Alpha Centauri 25.2 trillion miles 4.8 million yrs 114,155.2 yrs 4.2 yrs
(Nearest star after our Sun)
Sirius 50.4 trillion miles 9.6 million yrs 228,310.4 yrs 8.4 yrs