Quiz2

Question 3 We see red stars, white stars, and blue stars, but never a green star. Why? Answer: Any star whose blackbody spectrum peaks in green also emits enough other optical colours that it appears white, whereas reddish stars emit toward the infrared, and bluish stars emit toward the ultraviolet. You can play around with the following PhET that simulates the blackbody spectrum: Click me. But from the following figure, one can clearly observe that if the spectrum peaks at the green light, it also covers a large portion of the red and blue colors. Consequently, the observed light looks white-ish. Figure 2: The blackbody spectrum, when peaked at the green light, would also covers a good portion of red and blue. These colors combined gives a white color. Question 4 The fastest Earth-directed coronal mass ejections from the Sun can take ∼ 15 hours to reach Earth. What is the speed of the ejected particles expressed as a fraction of the speed of light? Answer: 0.009 We know that it takes about 8 minutes for light (obviously traveling at the speed of light) to reach from the Sun to the Earth. Let’s assume the distance between Sun and Earth is D , then by the usual equation D = v × t where v is the speed, and t is the time, we have D = c × 8 minutes = v × 15 hours = ⇒ v = 8 minutes 15 × 60 minutes c = 0 . 00888 c. 2