To solve the problem, we will go through each part step by step.
Part I:
First, we need to convert the sun's diameter from kilometers to millimeters to have both measurements in the same unit.
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Convert Sun's Diameter:
- The sun's diameter is given as \(1.391 \times 10^6\) kilometers.
- We know that \(1\) kilometer = \(1,000,000\) millimeters.
- Therefore, we can convert the sun's diameter to millimeters as follows:
\[ \text{Sun's diameter in millimeters} = 1.391 \times 10^6 , \text{km} \times 1,000,000 , \text{mm/km} \]
\[ = 1.391 \times 10^6 \times 10^6 , \text{mm} \]
\[ = 1.391 \times 10^{12} , \text{mm} \]
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Earth's Diameter:
- The Earth's diameter is already given as \(1.2742 \times 10^{10}\) millimeters.
Since the Earth's diameter is already in millimeters and we converted the sun's diameter to millimeters as well, the best unit of measurement to represent the lengths of the sun and Earth's diameters is millimeters.
Part II:
Now that we have both diameters in millimeters, we can approximate how many times greater the sun's diameter is than planet Earth's.
- Calculate the Ratio:
\[ \text{Ratio} = \frac{\text{Sun's diameter}}{\text{Earth's diameter}} = \frac{1.391 \times 10^{12} , \text{mm}}{1.2742 \times 10^{10} , \text{mm}} \]
- Perform the Calculation:
\[ \text{Ratio} = \frac{1.391}{1.2742} \times \frac{10^{12}}{10^{10}} = \frac{1.391}{1.2742} \times 10^{2} \]
Calculating the numerical part:
\[ \frac{1.391}{1.2742} \approx 1.0909 \quad (\text{using a calculator}) \]
Now multiply by \(10^2\):
\[ 1.0909 \times 100 \approx 109.09 \]
Thus, the sun's diameter is approximately 109.09 times greater than the Earth's diameter.
Final Answer:
- Part I: The best unit of measurement for the lengths of the sun and Earth’s diameters is millimeters.
- Part II: The sun's diameter is approximately 109.09 times greater than planet Earth's diameter.