[AstroTech/2째주] 시험

[AstroTech/2째주] 시험

Question 1
The amount of light collected by a telescope on a given celestial object is determined by which of the following:
a) the area of the secondary mirror
b) the area of the primary mirror
c) the thickness of the primary mirror
d) the size of the detector
Answer: c
지름이 큰 망원경을 원하는 이유는 더 많은 별빛을 모을 수 있기 때문입니다. 빛을 많이 모으면 확대 배율을 높여 관측해도 선명도를 유지할 수 있습니다. 망원경이 모을 수 있는 빛의 양은 대물렌즈(또는 반사경)의 면적(지름의 제곱)에 비례합니다. 천문대 건설 비용은 지름의 세제곱에 비례하죠.

Question 2
The smallest angular size that the human eye can resolve is:
a) 25 arcseconds (Diffraction only)
b) 1 arcminute
c) 30 arcminutes
d) 1 arcsec
Answer: b
인간의 동공 지름을 5mm로 보고 있습니다. 이정도 렌즈의 회절영향에 따른 한계 분해능은 25아크초. 여기에 구면 수차의 영향을 모두 감안하면 인간 분의 분해능 한계는 1 아크분. 1Km 거리에서 사람 머리를 구분할 정도.

Question 3
Which two techniques most effectively correct for blurring in astronomical images due to the atmosphere?
a) only observe targets when they are very close to zenith, i.e. when they are highest in the sky
b) only observe on the nights with the best weather and from the best sites.
c) put your telescope in space
d) observe a bright star with very, very short exposures and use that to correct for the atmosphere
e) only observe very bright targets
Answer: c,d

지상에서 천체 관측을 어렵게 하는 가장 근본적인 원인은 대기 때문입니다. 대기의 영향을 극복하기 위한 방법은 망원경을 우주로 보내는 것과 큰 망원경에 노출을 짧게 하는 적응광학을 적용하는 겁니다.

a) This might help achieve slightly better seeing (seeing is usually somewhat better at higher elevations), but still would be far from the diffraction limit of the telescope.
b) This might help, but still would not get you down to the diffraction limit of your telescope. In general, at the best sites in the very best seeing, you can get seeing-limited resolution down to 0.4 arcseconds. But there are ways to do even better...
c) This is an obvious but very expensive way not to have to deal with the atmosphere.
d) This technique is known as Adaptive Optics. After sensing the incoming wavefront using a bright star, you can then use a deformable mirror to cancel out aberrations in that wavefront.
e) Unfortunately, bright stars are just as affected by seeing and atmospheric turbulence as faint stars.

Question 4
How are stars distributed on a colour-magnitude diagram (a.k.a. HR diagram)?
a) The Sun is one of the most massive stars. Most stars are fainter than the Sun, so they appear lower on the diagram compared to the Sun.
b) The colors and luminosities of stars are mostly similar to that of the Sun.
c) The colors and luminosities of stars are randomly distributed
d) Most stars on the HR diagram would lie along the main sequence, with bright blue stars at the top of the diagram and dimmer red stars towards the bottom and right.
e) The Sun is a very low mass star and thus faint. Most stars are brighter than the Sun, so they appear higher up on the diagram compared to the sun.
Answer: d

별 중심에 수소를 태우는 동안 주계열에 머룹니다. HR도에서 주계열 별의 위치를 확인 해 봅시다.

During their hydrogen burning lifetimes, stars occupy a specific sequence along the HR diagram, with higher mass, bright blue stars near the top left and lower mass, fainter red stars near the bottom right.

Question 5
Stars are very massive, so gravity should force them to collapse. So, what holds up a main sequence star and prevents it from collapsing?
a) The energy produced by fusing helium atoms together produces pressure which counteracts gravity.
b) The energy produced by fission of iron nuclei produces pressure which counteracts gravity.
c) Neutron degeneracy in the core of the star prevents the star from collapsing.
d) The energy produced by fusing hydrogen atoms together produces pressure which counteracts gravity.
e) Electron degeneracy in the core of the star prevents the star from collapsing.
Answer: d

별 내부의 균형은 엄청난 질량으로 인해 중심으로 몰리는 압축과 내부에서 일어나는 수소 핵융합 반응의 결과로 발생되는 고에너지 방출에 의한 압력 입니다.

Main sequence stars fuse hydrogen together into helium. Some high mass stars can fuse heavier elements like helium together during their giant phase as well, but hydrogen burning is what keeps main-sequence stars from collapsing.