Question

revolving about the milky way
every 250 million years, our sun revolves once about the center of the milky way galaxy. find how many revolutions or parts of a revolution have occurred since the following events in earths history. show your work for each event.

1. earth formed 4600 million years ago.
2. oceans of water began forming 3800 million years ago.
3. animals with shells and skeletons first appeared 570 million years ago.
4. the appalachian mountains began forming 500 million years ago.
5. the first mammals appeared 225 million years ago.
6. the atlantic ocean basin began forming as africa, eurasia, and the americas began separating 190 million years ago.
7. the last dinosaurs died 65 million years ago.
8. the himalaya mountains began forming 53 million years ago.
9. the light we now see from the andromeda galaxy began traveling through space 2.4 million years ago.
10. the last ice age ended 10000 years ago.
11. the apollo astronauts first landed on the moon in 1969.

Explanation:

Step1: Recall the formula for number of revolutions

The number of revolutions $n$ of the sun around the center of the Milky - Way is given by the formula $n=\frac{t}{T}$, where $t$ is the time elapsed and $T = 250$ million years is the period of one revolution.

1. For Earth formed 4600 million years ago:

• Substitute $t = 4600$ million years and $T=250$ million years into the formula $n=\frac{t}{T}$.
• $n=\frac{4600}{250}=18.4$ revolutions.

1. For Oceans of water began forming 3800 million years ago:

• Substitute $t = 3800$ million years and $T = 250$ million years into the formula.
• $n=\frac{3800}{250}=15.2$ revolutions.

1. For Animals with shells and skeletons first appeared 570 million years ago:

• Substitute $t = 570$ million years and $T = 250$ million years into the formula.
• $n=\frac{570}{250}=2.28$ revolutions.

1. For The Appalachian Mountains began forming 500 million years ago:

• Substitute $t = 500$ million years and $T = 250$ million years into the formula.
• $n=\frac{500}{250}=2$ revolutions.

1. For The first mammals appeared 225 million years ago:

• Substitute $t = 225$ million years and $T = 250$ million years into the formula.
• $n=\frac{225}{250}=0.9$ revolutions.

1. For The Atlantic Ocean basin began forming 190 million years ago:

• Substitute $t = 190$ million years and $T = 250$ million years into the formula.
• $n=\frac{190}{250}=0.76$ revolutions.

1. For The last dinosaurs died 65 million years ago:

• Substitute $t = 65$ million years and $T = 250$ million years into the formula.
• $n=\frac{65}{250}=0.26$ revolutions.

1. For The Himalaya Mountains began forming 53 million years ago:

• Substitute $t = 53$ million years and $T = 250$ million years into the formula.
• $n=\frac{53}{250}=0.212$ revolutions.

1. For The light we now see from the Andromeda Galaxy began traveling through space 2.4 million years ago:

• Substitute $t = 2.4$ million years and $T = 250$ million years into the formula.
• $n=\frac{2.4}{250}=0.0096$ revolutions.

1. For The last ice - age ended 10000 years. First convert 10000 years to million years: $t=\frac{10000}{1000000}=0.01$ million years.

• Substitute $t = 0.01$ million years and $T = 250$ million years into the formula.
• $n=\frac{0.01}{250}=4\times10^{-5}$ revolutions.

1. For The Apollo astronauts first landed on the moon in 1969. Assume the current year is 2024, so $t = 2024 - 1969=55$ years. Convert 55 years to million years: $t=\frac{55}{1000000}=5.5\times10^{-5}$ million years.

• Substitute $t = 5.5\times10^{-5}$ million years and $T = 250$ million years into the formula.
• $n=\frac{5.5\times10^{-5}}{250}=2.2\times10^{-7}$ revolutions.

Answer:

1. 18.4 revolutions
2. 15.2 revolutions
3. 2.28 revolutions
4. 2 revolutions
5. 0.9 revolutions
6. 0.76 revolutions
7. 0.26 revolutions
8. 0.212 revolutions
9. 0.0096 revolutions
10. $4\times10^{-5}$ revolutions
11. $2.2\times10^{-7}$ revolutions