THE SOUTHWORTH PLANETARIUM

207-780-4249 www.usm.maine.edu/planet

70 Falmouth Street Portland, Maine 04103

43.6667° N 70.2667° W

Altitude: 10 feet below sea level

Founded January 1970

Julian Date: 2458997.16

2019-2020: CLVII

THE DAILY ASTRONOMER

Friday, May 29, 2020

Remote Planetarium 44: Week 9 Quiz

As our week was shorter, the quiz will be, as well.

Fifteen questions instead of twenty: five questions from each class.

1. Which ONE of the following is not considered an "improper" stellar motion?

a. diurnal

b. annual

c. precessional

d. space

2. Diurnal motion shifts a star by about one degree every __________ minute(s).

a. 1

b. 2

c. 4

d. 8

3. If the star Betelgeuse rises at 9:00 p.m. on October 31st, what time will it rise on December 31st?

a. 9:00 p.m.

b. 1:00 a.m.

c. 5:00 p.m.

d. 12:45 p.m.

4. In 13,000 years, __________ will be the "north star."

a. Polaris

b. Errai

c. Thuban

d. Vega

5. A star's space velocity can be divided into __________ velocity and _________ velocity.

a. right ascension; declination

b. radial; transverse

c. sigma; omega

d. precessional; diurnal

6. A star's absolute magnitude equals its apparent magnitude from a distance of ___________.

a. 4 parsecs

b. 10 parsecs

c. 25 parsecs

d. 100 parsecs

7. What is the "distance modulus?"

a. the difference between apparent and absolute magnitude

b. the difference between parsec and light year

c. the difference between luminosity and absolute magnitude

d. none of the above

8. A star's absolute magnitude is directly related to the star's ___________________.

a. distance

b. luminosity

c. size

d. temperature

9. A star's spectral type reveals information about ______________

a. its temperature

b. its chemical composition

c. both a and b

d neither a nor b

e. none of the above

f. all of the above.

10. Log 10000 = _______

a. 1

b. 3

c. 4

d. 6

11. The H-R Diagram relates spectral type to ___________________

a. luminosity

b. absolute magnitude

c. temperature

d. all of the above

e. both a and b

f. both a and c

12. Every star begins its life on ________________

a. the main sequence

b. the asymptotic giant branch

c. in the red dwarf corner

d. at the lower left of the H-R Diagram.

13. The more massive a star is at birth the_________ it will be.

a. more long lived

b. more luminous

c. redder

d. metal rich

14. The majority of main sequence stars are _______________.

a. M type red dwarfs

b. O type dwarfs

c. G type dwarfs

d. none of the above

15. Which of the following statements about main sequence stars is/are correct?

a. they are all fusing hydrogen in their cores

b. they are all considered dwarf stars

c. their life spans are all equal

d. all of the above

ANSWERS

1. Which ONE of the following is not considered an "improper" stellar motion?

d. space

Improper motions are defined as apparent motions caused by Earth's movements. Diurnal motion refers to the westward migration of stars across the sky each day due to Earth's rotation. Annual motion refers to the changing positions of the stars relative to the Sun throughout the year. This motion results from the planet's revolutionary motion around the Sun. Precessional motion refers to the changing orientation of the stars relative to the North Celestial Pole due to Earth's "wobbling" motion. Space motion is the actual motion of stars through the galaxy.

2. Diurnal motion shifts a star by about one degree every __________ minute(s).

c. 4

Each night the stars move toward the west because Earth rotates in the opposite direction. During each 24 hour period, the star will traverse 360 degrees in the sky. Twenty hours equals 1440 minutes. 1440 divided by 360 = 4 minutes.

3. If the star Betelgeuse rises at 9:00 p.m. on October 31st, what time will it rise on December 31st?

c. 5:00 p.m.

Remember the two hour rule. Unless a star is circumpolar, it will rise four minutes earlier each day due to Earth's revolutionary motion. Four minutes a day adds up to about half an hour a week and two hours every month. So, if Betelgeuse rises at 9:00 p.m. on October 31st, it will rise four hours earlier two months in the future, or at 5:00 p.m.

4. In 13,000 years, __________ will be the "north star."

d. Vega

Precession is causing Earth's north pole to describe a wide circle through space over a 26,000 year period. The pole's alignment will shift during this time so that it will point toward different stars. In 13,000 years, the NCP will point toward Vega, the brightest star in Lyra the Harp. While the NCP won't be as close to Vega as it currently is to Polaris, Vega will still serve as the north star for Earthbound observers.

5. A star's space velocity can be divided into __________ velocity and _________ velocity.

b. radial; transverse

A star's space velocity is a combination of its radial velocity (the motion along the sight line) and the transverse velocity (the motion across the sight line.) The proper motion is primarily affected by the transverse motion.

6. A star's absolute magnitude equals its apparent magnitude from a distance of ___________.

b. 10 parsecs

The Sun's absolute magnitude is 4.83, meaning that if the Sun were 10 parsecs away from us, it would appear as a 4.83 magnitude star: not particularly bright. As the Sun is instead only 0.0000005 parsecs from us, it appears blindingly bright.

7. What is the "distance modulus?"

a. the difference between apparent and absolute magnitude

The distance modulus equation m - M = 5log(d) - 5

relates apparent magnitude (m), absolute magnitude (M) and the distance(d) expressed in parsecs. The actual distance modulus is the relation m - M.

8. A star's absolute magnitude is directly related to the star's ___________________.

b. luminosity

If you know a star's absolute magnitude you will also know its intrinsic brightness or luminosity. Knowing the absolute magnitude alone will not give you specific information pertaining to the star's size or temperature.

9. A star's spectral type reveals information about ______________

a. its temperature

b. its chemical composition

A star's spectrum reveals a sequence of absorption lines caused by the presence of atoms within its outer layers. These lines are akin to a barcode that identifies different chemicals within the star. The spectral type is also related to the star's effective temperature. The O stars are the hottest, while the M stars are the coolest.

10. Log 10000 = _______

c. 4

When the subscript number does not appear in the logarithmic expression, base 10 is assumed.

Log 10000 is asking: 10000 equals 10 raised to the power of which number? 10 raised to the 4th power equals 10000.

11. The H-R Diagram relates spectral type to ___________________

e. both a and b

The H-R Diagram relates spectral type (or temperature) to luminosity (or absolute magnitude). In many H R diagrams, luminosity will be listed along one side of the diagram and absolute magnitude on the other.

12. Every star begins its life on ________________

a. the main sequence

When a star first becomes active it would be plotted on the H-R Diagram's main sequence. Once it reaches the next evolutionary stage, it will migrate off the main sequence toward the right.

13. The more massive a star is at birth the_________ it will be.

b. more luminous

The more massive a star is, the more luminous it will be. Along the main sequence, the lowest mass stars are the red dwarfs at the lower right. The highest mass stars will be at the upper left.

14. The majority of main sequence stars are _______________.

a. M type red dwarfs

Approximately 76% of all main sequence stars are red dwarfs. These are the low mass stars that just became hot enough to ignite and sustain core thermonuclear fusion reactions. Only 0.000003% of main sequence stars are the ultra hot O type dwarf.

15. Which of the following statements about main sequence stars is/are correct?

a. they are all fusing hydrogen in their cores

b. they are all considered dwarf stars

When a star first becomes active, it will be a main sequence star and will begin fusing hydrogen in its core. A star will move off the main sequence once its core hydrogen reactions cease. Even the most massive main sequence stars are still considered "dwarf" or luminosity class V stars.