[AstroTech/4째주] 시험

[AstroTech/4째주] 시험

Question 1

천체 사진은 아름다움이 다는 아니죠. 아래 사진은 20등성의 밝기를 가진 처녀자리 성단을 청색 필터를 끼우고 사진건판으로 찍은 것을 디지털화 한 것. 망원경은 the UK Schmidt Telescope (image credit: http://www-wfau.roe.ac.uk/sss/index.html)



사진 건판으로 60초간 노출을 주어 찍은 사진인데 이보다 열배 어두운 대상을 담을 수 있는 방법은 무엇인가? 강의 비디오에 제시한 방법을 근거로 답하자.


(o) 사진 건판을 CCD 로 바꾸고 같은 량의 노출을 준다.
-> 강의 동영상에 의하면 CCD 는 약 80% 의 빛을 담을 수 있다. 이에 반해 사진 건판은 1%. 망원경이 동일하고, 노출시간도 동일하면 감지기를 바꿀것

()Use a telescope with a primary mirror which has twice the diameter of the original mirror
()Use the same telescope but integrate for twice as long
()Use a telescope with a primary mirror which has half the diameter of the original mirror

Question 2

하와이에 있는 영국 적외선 망원경(The United Kingdom Infrared Telescope in Hawaii)
(image credit: http://commons.wikimedia.org/wiki/ile:UKIRT_at_sunset_(straightened).jpg)



적외선 우주를 관찰할때 망원경을 사용하는 이유는?


()Infrared detectors reveal light emitted by hotter stars in our Milky Way galaxy
()Infrared detectors are sensitive to light emitted from material entering black holes

(o) 짙은 성간 먼지에 쌓인 별은 적외선으로 봐야한다.
-> 성간먼지들은 가시광을 대부분 차단. 파장이 길 수록 회절이 잘되어 통과된 빛을 볼 수 있음.

(o)우리은하내 낮은 온도의 별을 관측
-> 별에서 복사되는 빛의 파장은 온도가 높을 수록 짧아짐.

Question 3

An infrared photon in the K band has wavelength 2 microns (λ=2×10^-6 m), and an optical photon in the G band has wavelength 500nm (λ=5×10^-7 m). Which of the following is true:

()The IR photon has 4 times the energy of the optical one
()The IR photon has 1/16 the energy of the optical one
()The IR photon has 16 times the energy of the optical one
()Both photons have equal energy
(o)The IR photon has 1/4 the energy of the optical one

광자의 에너지량은 파장에 반비례

E= hc/(Lambda)

Question 4

Galaxies that are far away from us are observed to be more red than nearby galaxies because (pick one option)

()The further away a galaxy is, the further back in time we're seeing it, and hence the younger it is. Young galaxies are made of red stars and so the galaxy appears to be red.
()As light from a distant galaxy travels across the Universe, it slowly loses energy, like a car running out of gas. When the light reaches Earth the lower energy light looks red.
()The Universe is expanding. As light travels towards us across the expanding universe, space expands and stretches the light, so it's wavelength increases and the galaxy looks red.

(o)The Universe is expanding and hence all the galaxies are moving away from us. Their light experiences lots of little Doppler effect shifts as it travels towards us across the expanding Universe. The further away the galaxy is, the more little doppler shifts its light will experience, and the further its light is shifted towards the red.

우주는 빠르게 팽창하고 있음. 멀리 있는 은하일 수록 빠르게 멀어지고 있는 중임.

Question 5

Considering the same two photons from the question 3, and given that the optical one has energy 2.5eV, which one of these statements is true?

()Neither photon would be detected by a silicon photocell, but both would be detected by a MerCadTel photocell

(o)Only the optical photon would be detected by a silicon photocell
-> The optical photon has energy 2.5eV, which is greater than the silicon band-gap of 1.2eV. However, the IR photon has ~0.6eV, which is smaller than the band-gap
전자 빛 감지기용 물질로 사용되는 실리콘의 밴드 갭은 1.2eV 임.

()Both the optical and the IR photon would be detected by a silicon photocell
()Only the IR photon would be detected by a silicon photocell