Evaluasi Bab 2 I. Esai
II. Pilihan Ganda
1. Andaikan sebuah bintang yang mirip Matahari (temperatur dan radiusnya sama dengan matahari) berada pada jarak 250 000 AU (1 AU jarak bumi – matahari, atau 1.5 x 108 km). Kita akan melihat terang bintang tersebut,…
a. 1,60 x 10-11 kali lebih lemah daripada Matahari b. 4,0 x 106 kali lebih lemah daripada Matahari c. 1,60 x 10-11 kali lebih terang daripada matahari d. 4,0 x 106 kali lebih terang daripada Matahari
e. Kita tidak bisa membandingkan terang bintang tersebut
2. Sebuah bintang yang temperatur permukaannya adalah 6000 K akan memancarkan spektrum benda hitam dengan puncaknya pada panjang gelombang .... A. 6000 m B. 5 x 10-7 nm C. 18 nm D. 5 x 10-7 m E. 1.8 x 10-7 nm
3. Dua buah bintang mempunyai ukuran yang sama, tetapi temperaturnya berbeda. Apabila kedua bintang dilihat dari jarak yang sama maka bintang yang lebih panas akan tampak
A. lebih biru dan lebih terang B. lebih merah dan lebih terang C. lebih biru, tapi lebih lemah D. lebih merah, tapi lebih lemah
E. sama terang dengan bintang yang lebih dingin
4. Tipe radiasi mana yang memiliki panjang gelombang yang lebih panjang dibanding cahaya tampak?
a. Gelombang mikro b. Gelombang radio c. Sinar-X
d. Radiasi infra merah e. Radiasi cahaya biru
5. Terang semu bintang menunjukkan ...
a) jumlah foton cahaya bintang yang sampai ke Bumi b) daya bintang
c) jarak bintang
d) banyaknya materi antar bintang e) diameter sudut bintang
6. Dua bintang terangnya sama, kemungkinan … a) jarak dan dayanya sama
b) jaraknya berbeda dayanya sama c) jaraknya sama dayanya berbeda
d) jarak dan radiusnya berbeda, dayanya sama e) jarak dan radiusnya sama, dayanya berbeda 7. Selain Matahari, bintang paling terang di langit…
a) bintang dengan daya paling besar b) bintang paling dekat dengan Matahari c) bintang paling panas
d) bintang berdiameter paling besar
e) kemungkinan dayanya besar dan jaraknya dekat 8. Bintang yang lemah cahayanya …
a) belum tentu bintang yang jauh
b) mungkin bintang yang sangat jauh dengan daya kecil c) mungkin bintang yang sangat jauh dengan daya besar d) bintang dekat berdaya besar dalam lingkungan nebula gelap e) semua jawaban benar
9. Two stars have the same luminosity. Star A is 5 times further away than Star B. Which is the true statement:
A. Star A and Star B appear equally bright in the night sky. B. Star A appears 5 times brighter than Star B in the night sky. C. Star A appears 5 times dimmer than Star B in the night sky. D. Star A appears 25 times brighter than Star B in the night sky. E. Star A appears 25 times dimmer than Star B in the night sky.
10. If a star has an apparent magnitude -2 and is located at 6.3 parsecs, what is the absolute magnitude of the star? (apparent magnitude = m, absolute magnitude = M)
a. -1 b. 1 c. -2 d. 2 e. -3
11. Of the regions of the electromagnetic spectrum listed below, which has the lowest frequencies? a. radio waves b. infrared radiation c. gamma rays d. visible light e. x-rays
12. Which star of the following apparent magnitudes will appear the brightest? A) 6.2 B) 1.0 C) 0.0 D) –1.4
13. Which list is in the correct order of electromagnetic radiation frequency, going from lowest to highest?
A) infrared, ultraviolet, gamma, radio B) gamma, x-ray, ultraviolet, visible C) radio, infrared, visible, ultaviolet D) radio, x-ray, ultraviolet, visible E) red, violet, blue, green
14. If a star was the same size as our Sun, but was 81X more luminous, it must be how many times hotter than the Sun?
A) 3x B) 81x C) 4x D) 9x E) 2x
m-M -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 15 20 Distance 2.5 4.0 6.3 10 16 25 40 63 100 160 250 400 630 1,000 10,000 100,000
15. If Vega is apparent magnitude zero, and Deneb is magnitude one, then: A) Vega appears 100 times brighter than Deneb.
B) Deneb is one magnitude brighter than Vega. C) Vega appears 2.5 times brighter than Deneb. D) Vega is 2.5 times more luminous than Deneb. E) Deneb is a main sequence star, and Vega is a giant
16. A new star is discovered; it is bright and hot, and emits mostly ultraviolet light. If we observe it with blue and yellow filters (separately), what would we find? A) More blue intensity than yellow
B) More yellow intensity than blue C) Equal yellow and blue intensity
D) Blue and yellow intensities are both zero E) Not enough information given.
17. If your naked eye limiting magnitude is 6.0, then using a 70 mm telescope, (with 100X the surface area of your pupil), which object would be near your new limiting magnitude?
A) seventh magnitude Titan, Saturn's largest moon B) eighth magnitude Neptune
C) ninth magnitude Barnard's Star
D) eleventh magnitude Tethys, Saturn's second largest moon E) thirteenth magnitude Pluto
18. Luminosity
a. Relatively dark spots of varying sizes found generally in groups on the solar surface that contain intense magnetic fields
b. Rate (per unit of time) that radiant energy is emitted over all wavelengths from the entire surface of a star
c. The limiting surface surrounding a black hole inside of which nothing can escape and thus it represents the last communication point with spacetime outside.
d. Gas and dust material that lies in between stars in the disk of our Galaxy and other spiral galaxies.
19. Apparent magnitude
a. A logarithmic measure of the brightness of a star as it appears in the sky.
b. Rapidly rotating neutron star emitting an intense beam of radiation that is sweep around, like a lighthouse beam, by the rotation.
c. An otherwise continuous spectrum in which appears a discrete number of dark absorption lines located at discrete wavelengths.
d. A body in a gravitational encounter that acquires sufficient kinetic energy to escape the gravitational attraction of the other body or bodies in the encounter. 20. Apparent magnitude is a measure of
a. the brightness of a star as it appears in the sky. b. the temperature of the stars photosphere.
c. the brightness a star would have if it was located at a distance of 32.6 ly or 10 pc from the Sun.
d. all of the above.
21. If Star A is hotter than Star B, and Star A is emitting most of its light at a wavelength corresponding to yellow light, which of the following statements is true?
a. Star B will emit most of its light at a wavelength longer than yellow b. Star B will emit most of its light at a wavelength shorter than yellow c. Star B will emit most of its light at the same wavelength as Star A d. more information is required to answer this question
22. What's the difference between a 2nd magnitude star and a 5th magnitude star? a. The 2nd magnitude star is brighter.
b. The 5th magnitude star is brighter c. The 2nd magnitude star is more massive d. The 5th magnitude star is more massive 23. The luminosity of a star is …
a. another name for its color or surface temperature. b. its brightness as seen by people on Earth.
c. its brightness if it were to be at a distance of 10 parsecs (32.6 light-years) from Earth.
d. its total energy output into all space, over all wavelengths.
24. If two stars in the sky are not hidden by gas or dust clouds, and have the same apparent brightness in our sky, then we know that…
a. they may be at different distances, in which case the farther one must have the greater luminosity.
b. they are necessarily at the same distance away from us. c. they have the same temperature
d. they may be at different distances, in which case the nearer one must have the greater luminosity.
25. The technique called photometry in stellar astronomy is the measurement of … a. the intensity of light from stars through several limited-bandpass filters from
which surface temperature, variability, luminosity, etc. of stars can be determined.
b. the relative absorption of light by different atoms and molecules in high resolution spectra of starlight, from which stellar temperatures can be estimated.
c. the precise positions and relative motions of stars in the galaxy, from which galactic structure and overall rotation can be determined.
d. the arrival times of photons from variable and pulsating stars, in order to determine accurately the pulsation or rotation periods of these stars.
26. The color index of a star, the difference between the apparent magnitudes B and V at two different colors, blue and visual, is directly related to which stellar property?
a. surface temperature c. Radius
b. Luminosity d. Distance from Earth
27. As the temperature of a radiating body is increased, the light emitted by the body …
A. becomes bluer and more intense. B. becomes redder and more intense. C. becomes redder and less intense. D. becomes bluer and less intense. E. shifts toward longer wavelengths.
28. Star A and Star B have the same apparent magnitude. If the absolute magnitude of Star A is 5 and the absolute magnitude of Star B is 3, then …
A. Star A appears brighter than Star B. B. Star A appears fainter than Star B. C. Star A is more luminous than Star B. D. Star A is closer than Star B.
E. Star A is farther than Star B.
29. Star A and Star B have the same parallax. If the apparent magnitude of Star A is 2 and the apparent magnitude of Star B is 3, then …
A. Star A appears fainter than Star B. B. Star A is less luminous than Star B. C. Star A is more luminous than Star B. D. Star A is closer than Star B.
E. Star A is farther than Star B.
30. Which is the correct ordering of the electromagnetic spectrum from long to short wavelength ?
a. Visible, ultraviolet, infrared, x-rays, microwaves, gamma rays, radio b. Radio, microwaves, infrared, visible, ultraviolet, x-rays, gamma rays c. Gamma rays, x-rays, ultraviolet, visible, infrared, microwaves, radio d. Ultraviolet, gamma rays, visible, x-rays, radio, infrared, microwave
31. Not all wavelengths of electromagnetic radiation can penetrate the Earth's atmosphere. Of the following types of waves that come from space which one are you likely to be able to detect most easily from our planet's surface:
a. x-rays b. gamma rays c. infrared waves d. ultraviolet waves
e. radio waves of the wavelength that carry FM broadcasts
32. Two stars are giving off electromagnetic radiation. The hotter star will: a. give off more radiation at all wavelengths
b. will have a higher average frequency of radiation c. will radiate energy at more than one wavelength d. will give off a continuous spectrum of waves e. all of the above
33. Two stars have the same Luminosity , but the star B is 3 times farther from us than star A. Compared to Star A, star B will look …
a. Three times brighter b. Nine times brighter c. nine times fainter d. three times fainter e. Just as bright as A
34. When an astronomer rambles on and on about the luminosity of a star she is studying, she is talking about :…
a. what color the star is
b. the total amount of mass in the star
c. the star's apparent size (the size seen from Earth) d. how much energy the star gives off each second e. the elements she can see in the star's spectrum
35. The apparent brightness of stars in general tells us nothing about their distances (i.e. we cannot assume that the dimmer stars are farther away.) In order for the apparent brightness of a star to be a good indicator of its distance, all the stars would have to be : …
a. at the same distance b. the same composition c. the same luminosity
d. by themselves instead of in binary or double-star systems e. a lot farther away than they presently are
36. The Sun's temperature can be determined if you find out ... a. the wavelength at which the Sun's spectrum is brightest b. the Sun's luminosity and radius
c. which elements are producing lines in the solar spectrum d. all of the above
e. none of the above
37. Two stars have the same apparent magnitude and are the same spectral type. One is twice as far away as the other. What is the relative size of the two stars ?
a. The nearer star is a fourth the size of the farther star. b. The nearer star is half the size of the farther star. c. The nearer star is twice the size of the farther star. d. The nearer star is a four times the size of the farther star.
38. The apparent visual magnitude of one star is three magnitudes greater than for another star. Therefore, the first star is approximately _________ than the second star?
a. three times brighter b. three times fainter c. six times brighter d. 16 times brighter. e. 16 times fainter.
39. If on a certain day the Sun has an apparent visual magnitude of -26.5, while in the evening the moon has an apparent magnitude of -12.5, how much brighter did the Sun appear on that day?
a.10 times b. 100 times c.1,000 times d. 10,000 times e. 1,000,000 times
40. Which of the following is not in itself useful for determining stellar temperature? a. spectral class
b. color index
c. absolute magnitude d. degree of ionization
e. wavelength of maximum intensity of the underlying spectrum. 41. Luminous stars with low temperatures …
a. have small diameters compared with the Sun b. have diameters comparable with that of the Sun c. have large diameters compared with that of the Sun d. are white dwarfs.
42. The sun's spectrum peaks at 5600 Å. What wavelength is the peak of a star whose temperature is twice that of the sun?
a. 1867 Å b. 2800 Å c. 11200 Å d. 16800 Å e. None of these. 43. Luminosity is …
a. energy per second per unit area in the visual region b. energy per second per unit area over all wavelengths c. a different word for magnitude
d. total energy per second radiated over all wavelengths.
44. Assuming that stars radiate like black bodies, you must know which of the following properties in order to infer the radius of a star?
A. luminosity and surface temperature. B. luminosity and distance.
C. luminosity and flux. D. luminosity and mass.
45. Manakah pernyataan di bawah ini yang paling tepat ?
a. Jika suhu bintang tiba-tiba berkurang, maka dapat kita ketahui dari turunnya panjang gelombang maksimum yang dipancarkan bintang tersebut
b. Jika radius bintang menjadi 2 kali semula tetapi suhunya turun menjadi ½ kali semula , maka luminositasnya akan menjadi 4 kali semula
c. Flux energi yang dipancarkan oleh bintang berbenading terbalik dengan kuadrat jarak (invers square law)
d. Jika magnitudo mutlak suatu bintang lebih besar daripada magnitudo semunya maka jaraknya pasti kurang dari 10 parsec.
e. Semakin besar sudut paralaks suatu bintang , semakin jauh jarak bintang tersebut dari kita.
46. Jika dua bintang memiliki temperatur yang sama, maka dapat dipastikan kedua bintang tersebut memiliki ... yang sama.
a. Luminositas
b. Flux energi yang diterima pengamat c. Flux energi yang dipancarkan d. Magnitudo
e. Luminositas dan spektrum
( tabel di atas untuk nomor 47 dan 48 )
47. Tentukan bintang nomor berapakah yang paling terang terlihat oleh mata anda ! a. No 1 , karena mV paling besar
b. No.2 , karena mB paling kecil c. No. 1 , karena mB paling besar
No. mB mV
1 8,62 8,82
2 7,45 7,25
d. No.3 , karena mV paling kecil
e. No.3, karena (mB + mV)-nya paling kecil
48. Dari tabel nomor 47, dapat kita simpulkan bintang paling panas adalah ... a. No. 1, karena nilai mB - mV nya paling kecil
b. No. 1, karena memiliki nilai mB paling besar
c. No. 2, karena nilai rata-rata mB dan mV nya paling kecil d. No. 3, karena nilai mB - mV nya paling besar
e. No. 3, karena nilai mV nya paling kecil
49. The star Phoenicis has an apparent magnitude of +3.4 and an absolute magnitude of +0.6. The North Star (Polaris) has an apparent magnitude of +2.0 and an absolute magnitude of +0.6. Assuming that no light has been absorbed or scattered by interstellar dust, we can say for sure that …
A) Both stars are the same distance away from us. B) Polaris is closer to us than Phoenicis.
C) Polaris is farther away from us than Phoenicis. D) Polaris appears fainter in our sky than Phoenicis E) We can’t conclude anything from information given
50. The apparent brightness of an object such as a star does not depend on … A. how fast the star is moving across our line of sight
B. the strength of the light emanating from the star C. the distance from us to the star
D. the amount and kind of obstacles between us and the star
Tentukanlah apakah pernyataan di bawah ini benar atau salah. Jika menurut Anda benar, tuliskan B dan jika menurut Anda salah, tuliskan S di lembar jawab Anda ! a. Kecerlangan sebuah bintang biasa (bukan bintang variabel) berubah-ubah di setiap
pengamatan karena tergantung kondisi pengamatan, tetapi nilai magnitudo semunya tetap (konstan).
b. Sebuah bintang yang tampak berwarna biru, berarti hanya memancarkan radiasi elektromagnetik pada panjang gelombang biru.
c. Dari spektrum sebuah bintang, dapat kita ketahui suhu, tingkatan evolusi (usia bintang), sudut paralaks dan komposisi penyusun bintang.
d. Hanya panjang gelombang optik, yang dilewatkan oleh atmosfer Bumi sampai ke permukaan Bumi.
e. Semakin jauh jarak sebuah bintang, maka pemandangan / penampakan bintang tersebut menunjuk pada waktu yang semakin lampau. Hal ini disebabkan oleh kecepatan cahaya yang terbatas.
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