[AstroTech/5주] 시험

[AstroTech/5주] 시험

Question 1
What causes a meteor shower?

() The Earth's orbit passes through the orbit of a comet, and the comet strikes the Earth's surface.

(o)The Earth's orbit passes through a stream of debris left by a comet, and most of this debris burns up in the atmosphere.

유성우(Meteor Shower)는 혜성이 지나간 자리에 지구의 공전궤도가 지나면서 혜성이 남긴 찌꺼기가 지구의 대기에 떨어져 불타는 것임. 극히 일부가 지구에 떨어지기도 함

() The Earth's orbit passes through the orbit of a comet, which grazes the atmosphere and bounces off.
() The Earth's orbit passes through a stream of debris left by a comet, and most of this debris strikes the Earth's surface.


Question 2

If a CCD pixel can hold sixteen bits per pixel, and the CCD chip is a square with 1000 pixels on a side, approximately how many bytes can the CCD hold? (Note: we are using the "decimal" definition of megabytes, gigabytes etc, so one kilobyte = 1000 bytes, one megabyte = 1000 kilobytes and so on).

() 1 MB
() 2 KB

(o)2 MB
가로x세로 1,000 픽셀 인 영상의 크기. 픽셀당 2바이트
1000x1000=1Mx2 = 2MB

() 4 MB


Question 3

A modern sky survey will contain around one petabyte of data. How many bytes is this? (Remember we are using the decimal representation of bytes, so that one kilobyte = 1000 bytes, and so on).

() 10^18 bytes
() 10^6 bytes
() 10^12 bytes
() 10^9 bytes
(o)10^15 bytes

10^3 = K
10^6 = M
10^9 = G
10^12=T
10^15=P

Question 4

An astronomer is searching through a catalogue of half a billion objects to identify a small number of targets. She can store the catalogue on her laptop's hard drive. Once the data is transferred from the laptop's hard drive to the CPU, the laptop can process the data to find the targets in less than a second. But, each row of the catalogue has a transfer overhead of 2 milliseconds. She is looking to complete the processing work in 7 days, as she has a deadline to meet. Should she do a brute force search through all the objects?

() No, because the catalogue cannot be read into the CPU completely, and will be read in in chunks.
() Yes, because she will be able to complete the search in less than 7 days, and beat her deadline.
() Yes, because a brute force search is the only way to guarantee that she will find all her targets.
(o) No, because a brute force search will take longer than 7 days to process on her laptop, and she will miss her deadline.

"brute force" 방식의 데이터 베이스 검색은 시간이 많이 걸림. 시간을 줄이기 위해 인덱싱

---> Correct! Half a billion objects taking 2 milliseconds per object would take 1 million seconds, or 11.57 days to process. If she wants to process the data in time to beat her deadline, she will have to consider ways to reduce the number of objects to search. This problem has created a "service economy" in astronomy, where data centres optimise the way data is collected and stored, and save popular queries on large datasets for easy retrieval (much like search engines do for the Internet)


Question 5

In video 4, Catherine described an example of tracking an asteroid as it moves on the sky. Over a 7 day period, it moves an angular distance of half a degree. If we assume the asteroid is orbiting the Sun in a circle, then what is the asteroid's orbital period, and how far away is it from the Sun? (The gravitational constant G=6.67×10?11m3s?2kg?1, the Sun's mass is M=1.99×1030kg, and an astronomical unit is: 1AU=1.496×1011m. There are 3.16×107s in a year)

The orbital period is 14 years, and the asteroid is 5.7 AU away from the Sun.
This puts the asteroid in the vicinity of Jupiter, which orbits the Sun at 5.2 AU. This body could be one of Jupiter's Trojans!


주기:
Period = 360 * 7days / 0.5 = 14 year

Gravitational Force(중력)
F = GMm/r^2

Centrifugal Force(원심력)
F = m*v^2 / r

Speed (속도)
v = (2*Pi*r/P)^2

위의 세개 식을 정리하면,

r^3 = G*M*P^2 / (4*Pi^2)

계산기를 동원하여 풀것

r^3 = 6.67x10^-11 * 1.99x10^30 * (14 * 3.16x10^7)^2 / (4 * 9.86)