The table below shows the approximate distances of two stars from Earth.
| Name of star | Approximate distance from Earth (in light years) |
| :------------- | :--------------------------------------------- |
| Sirius | 8.6 |
| Epsilon Eridani | 10.5 |
A scientist uses a space telescope to photograph the two stars. Which of these is a correct conclusion about the photographs of the two stars as taken by the scientist?
A. It takes more than 10 years to photograph Sirius.
B. It takes more than 10 years to photograph Epsilon Eridani.
C. The photographs show a more recent picture of Sirius than Epsilon Eridani.
D. The photographs show a more recent picture of Epsilon Eridani than Sirius.
Answer (2)
The light from Sirius takes 8.6 years to reach Earth.
The light from Epsilon Eridani takes 10.5 years to reach Earth.
It takes more than 10 years to photograph Epsilon Eridani.
The photographs show a more recent picture of Sirius than Epsilon Eridani.
I tt ak es m ore t han 10 ye a rs t o p h o t o g r a p h Ep s i l o n E r i d ani .
Explanation
Problem Analysis We are given the distances of two stars, Sirius and Epsilon Eridani, from Earth in light years. We need to determine which of the given conclusions about the photographs of these stars taken by a scientist is correct.
Understanding Light Travel Time Since light travels at a finite speed, the light we see from these stars has taken years to reach us. The farther the star, the longer it takes for its light to reach us. Therefore, when we observe these stars, we are seeing them as they were in the past. The time it takes for the light to reach us is equal to the distance in light years.
Sirius's Light Travel Time The distance of Sirius from Earth is 8.6 light years. This means the light from Sirius takes 8.6 years to reach Earth. Therefore, when we photograph Sirius, we are seeing it as it was 8.6 years ago.
Epsilon Eridani's Light Travel Time The distance of Epsilon Eridani from Earth is 10.5 light years. This means the light from Epsilon Eridani takes 10.5 years to reach Earth. Therefore, when we photograph Epsilon Eridani, we are seeing it as it was 10.5 years ago.
Evaluating the Conclusions Now, let's evaluate the given conclusions:
'It takes more than 10 years to photograph Sirius.' This is incorrect because it takes 8.6 years for the light from Sirius to reach us, which is less than 10 years.
'It takes more than 10 years to photograph Epsilon Eridani.' This is correct because it takes 10.5 years for the light from Epsilon Eridani to reach us, which is more than 10 years.
'The photographs show a more recent picture of Sirius than Epsilon Eridani.' This is correct because the light from Sirius takes less time to reach us (8.6 years) compared to Epsilon Eridani (10.5 years). Therefore, we are seeing Sirius as it was more recently than Epsilon Eridani.
'The photographs show a more recent picture of Epsilon Eridani than Sirius.' This is incorrect because the light from Epsilon Eridani takes more time to reach us, so we are seeing it as it was further in the past compared to Sirius.
Final Answer Therefore, the correct conclusions are:
It takes more than 10 years to photograph Epsilon Eridani.
The photographs show a more recent picture of Sirius than Epsilon Eridani.
Selecting the Best Answer The question asks for which of these is a correct conclusion . Since there are two correct conclusions, and the question implies only one is correct, we must choose the most direct answer. The statement 'It takes more than 10 years to photograph Epsilon Eridani' is a direct consequence of the given data.
Examples
Understanding the time it takes for light to travel from distant objects is crucial in astronomy. For example, if astronomers observe a supernova (a star explosion) in a galaxy 100 million light-years away, they are witnessing an event that occurred 100 million years ago. This helps them study the evolution of stars and galaxies over vast timescales. Similarly, when planning space missions, scientists must account for the time delay in communication signals, which can be significant for probes exploring distant planets or galaxies.
The correct conclusion is that it takes more than 10 years to photograph Epsilon Eridani, as its light takes 10.5 years to reach Earth. Additionally, the photograph of Sirius shows it as it was more recently than Epsilon Eridani. Therefore, the best answer is option B.
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