Read the followingpassage and mark the letter A, B, C or D onyour answer sheet to indicate the correct answer to each of the questions
Stellar Astronomy
Many parameters are used to describe a star. One of them is its temperature, which can be determined by simple observation; the color of a star and its temperature are related. Once the color of a star is identified, its temperature can be calculated through the use of scientific principles such as Wien’s Law.
There are different types of stars in the universe. For our purposes, we can classify them into two categories: variable and binary. Variable stars are those which show some degree of variability in their luminosity and magnitude. Luminosity refers to the amount of energy radiated by a star, while magnitude refers to its brightness. At time the degree of variability may be high, requiring a telescope with an equally high light- gathering power. This can be achieved by using a lens of large diameter, such as that of a reflecting telescope.
Binary stars are those found in pairs that revolve around a common center. The closest star to the sun, Proxima Centauri, is a binary star. To observe a binary star, the resolving power of a telescope - its ability to distinguish between two close objects having a small angular separation - must be very high.
Stellar astronomy is possible for a everyone, well beyond mere looking at the sky with the naked eye in order to identify constellations. With two basic of telescopes and rudimentary knowledge, much exploration can be achieved.
Complete the summary by choosing one sentence (A, B, C or D) that is among the most important information to fill in the blank.
A. Variable stars may differ in the amount of energy they radiate or in their luminosity.
B. Variable stars change in brightness and luminosity, and require a telescope with a large lens
C. Proxima Centauri, the closest star to Earth, is a binary star and requires a large telescope for observation
D. Many different types of stars exist, but the most important categories are variable and binary stars.
Đáp án là B.
Câu B này chính là câu tóm tắt ý cho đoạn 2.