Question 1

A unique characteristic of type O stars is ionized helium lines in its spectrum.

Accepted Answer

Type O stars are the hottest stars and have temperatures high enough to ionize helium, which results in ionized helium lines in their spectra.

Question 2

A +6.0 magnitude star is brighter than a +3.0 magnitude star.

Accepted Answer

In the astronomical magnitude scale, lower numbers indicate brighter objects, so a +3.0 magnitude star is brighter than a +6.0 magnitude star.

Question 3

The Hipparcos satellite has extended our accurate parallax distance measurements to over 200 parsecs.

Accepted Answer

The Hipparcos satellite, launched by the European Space Agency (ESA) in 1989, was designed for high-precision astrometry, which includes measuring stellar distances through parallax. It significantly extended the range of accurate parallax measurements, indeed reaching beyond 200 parsecs for some stars, thereby improving our understanding of stellar distances and motions within our galaxy.

Question 4

Hydrogen lines are strongest in class A stars.

Accepted Answer

Class A stars have the optimal temperature range (around 7,500 to 10,000 K) for hydrogen lines to be most prominent in their spectra, as this temperature maximizes the excitation of hydrogen atoms.

Question 5

A 3rd magnitude star appears 2.5 times brighter than a 4th magnitude star.

Accepted Answer

The magnitude scale is logarithmic, where a difference of 1 magnitude corresponds to a brightness ratio of about 2.5 times. Therefore, a 3rd magnitude star is indeed 2.5 times brighter than a 4th magnitude star.

Question 6

Two stars have the same absolute magnitude, but one lies twice as far from Earth as the other. It will appear half as bright.

Accepted Answer

The brightness of a star decreases with the square of the distance, so if one star is twice as far away, it will appear one-fourth as bright, not half as bright.

Question 7

A parsec is slightly more than 200,000 AU.

Accepted Answer

A parsec is equivalent to approximately 206,265 astronomical units (AU), which is indeed slightly more than 200,000 AU.

Question 8

A type B9 star is hotter than a type A0 star.

Accepted Answer

A type B9 star has a higher surface temperature than a type A0 star.

Question 9

A parsec is about 3.3 light- years.

Accepted Answer

A parsec is a unit of distance used in astronomy, equivalent to about 3.26 light-years, which is close to the given value of 3.3 light-years.

Question 10

Our nearest stellar neighbor is a little less than 1 parsec away.

Accepted Answer

The nearest stellar neighbor, Proxima Centauri, is about 1.3 parsecs away from Earth.

Question 11

Combining a star's proper motion and its distance allows us to determine its transverse velocity.

Accepted Answer

The transverse velocity of a star is calculated by combining its proper motion (angular movement across the sky) with its distance from us. This allows us to determine how fast the star is moving sideways relative to our line of sight.

Question 12

The parallactic angle is the total shift observed over a six- month interval.

Accepted Answer

The parallactic angle refers to the angle between the celestial object and the zenith, changing as the Earth rotates, not specifically to a total shift observed over a six-month interval.

Question 13

At its brightest, Venus, at magnitude - 4, is 100 times brighter than a 1st magnitude star.

Accepted Answer

The magnitude scale is logarithmic, where a difference of 5 magnitudes corresponds to a brightness factor of 100. Since Venus at magnitude -4 is 5 magnitudes brighter than a 1st magnitude star, it is indeed 100 times brighter.

Question 14

Of all the stars in the sky, Barnard's star, the next closest beyond Alpha Centauri, appears to move the fastest.

Accepted Answer

Barnard's Star exhibits the largest proper motion of any known star relative to the Sun due to its proximity and relatively high velocity through space.

Question 15

If a star has a parallax of 0.25", then its distance is about 13 light- years.

Accepted Answer

The parallax of a star is the angle at which it appears to move from two different points on Earth's orbit around the Sun. The distance to a star can be calculated using the formula distance = 1/parallax. In this case, the parallax is 0.25", which means that the distance to the star is 1/0.25 = 4 light-years.

Question 16

The nearest star system to our Sun, Alpha Centauri, is still over a parsec distant.

Accepted Answer

Alpha Centauri is about 1.34 parsecs (or approximately 4.37 light-years) away from the Sun, making it the closest star system to our own.

Question 17

A type B star is bluer than a type G star.

Accepted Answer

Type B stars are hotter and emit more blue light compared to the cooler, yellowish type G stars, making them appear bluer.

Question 18

The Sun, at absolute magnitude +4.8, would be one of the brightest stars in the sky if seen from 32 light- years distance.

Accepted Answer

Absolute magnitude measures a star's intrinsic brightness as if it were located 10 parsecs (about 32.6 light-years) from Earth. The Sun's absolute magnitude of +4.8 actually means it would be rather dim, barely visible to the naked eye under perfect dark-sky conditions, and certainly not one of the brightest stars in the sky.

Question 19

To get the space velocity of a star in three dimensions, you need its proper motion, distance, and radial velocity.

Accepted Answer

The space velocity of a star in three dimensions is determined by combining its proper motion (motion across the sky), distance (to convert proper motion from angular to linear velocity), and radial velocity (motion towards or away from us).

Question 20

Fewer than 100 stars lie within 5 parsecs of the Sun.

Accepted Answer

There are approximately 63 known stellar systems within 5 parsecs (about 16.3 light-years) of the Sun, which include multiple stars in some systems, but the total number of individual stars is still fewer than 100.

Quiz 11: Measuring the Stars: Giants, Dwarfs, and the Main Sequence