[AstroTech/3주] 시험

[AstroTech/3주] 시험

Question 1
What are some problems of ground-based telescopes? (Pick all that apply)

(x) Ground-based telescopes can only see objects in our own Galaxy.
지구에서도 외계은하를 관측할 수 있음. 유명한 안드로메다 은하는 2백5십만광년이나 떨어져있음
(x) Telescopes on Earth are too expensive compared to space-based telescopes.
우주 망원경이 지상보다 훨씬 비쌈. 우주로 보내는 비용 때문.
(o) The atmosphere distorts light, blurring images.
(o) The Earth's atmosphere absorbs some wavelengths of light.

Question 2
Which image do you think was taken from a space telescope? (Ignore the slight rotation. Look for evidence of atmospheric blurring.)

허블 망원경으로 찍은 사진(고선명)


국립 갈릴레오 천문대 망원경사진(대기에 의한 흐림은 어쩔 수 없음)


Question 3
Which one of the following is NOT one of the main difficulties of operating a telescope in space?

() The heat and light from the sun must be blocked.
() Powering the telescope requires a large energy source.
(o) We can't make detectors which capture X-ray photons.
우주로 갈수록 X 검출이 용이함. X 선 감지기는 만들 수 있음
() Telescopes in space must be able to withstand collisions with human debris and natural dust particles.

Question 4
One solution to transmitting data from a telescope in space to the Earth is by using a satellite in geostationary orbit. A satellite in this orbit stays directly above the same spot on the ground, and thus goes around the earth in exactly one day. For an object to be in a geostationary orbit, it must orbit at an altitude of 5.6 Earth radii above the surface of the Earth (6.6 Earth radii from the Earth's center).

A geostationary orbit can be above a point on only one great circle of the Earth. Which is it?
() The International Date Line.
() The Tropic of Capricorn.
() The Prime Meridian.
(o) The Equator
우주 망원경은 관측 자료를 한 곳의 지상 지구국에 보내기 위해서 정지궤도에 있어야 함. 대략 지구상에서 지구 반지름의 5.5배 상공. 적도 바로위에 정지궤도.

Question 5
Cygnus X1 was one of the earliest black holes discovered. From the X-ray variability, the diameter of the accretion disk is known to be roughly 3000km. From the orbital dynamics of the companion blue supergiant, the mass inside the disk is roughly 16 times the mass of the Sun (note that the mass of the Sun is roughly 2×10^33g).

If all that mass were evenly distributed in a sphere of a diameter of 3000km, what would be the average density of Cygnus X1?
(o) 2.2×109g/cm^3
() 2.8×1023g/cm3
() 2.5×1030g/cm3
() 2.5×1025g/cm3

시그너스 X-1의 블랙-홀의 무게는 태양의 16배: 16*(2*10^33)g

구의 부피 = (3/4)*pie*r^3

지름이 3000Km(반지름 1500Km)인 구의 부피: 1.413*10^10 Km^3

밀도 = 무게/부피 = 3.2*10^34/1.413*10^10 = 2.28*10^24g/Km^3

부피를 cm 단위로 환산하면

밀도 = 2.28*10^9 g/cm^3

탁구공의 무게가 2백만 킬로그램인 셈!