Parallax and Standard Candles

The distances to two stars are being determined using trigonometric parallax.

The intensity received (radiation flux) from star P is greater than that from star Q, and the parallax angle for star P is greater than that of star Q.

Which of the following is a correct deduction about the stars?

• Star P has a greater luminosity than star Q.

• Star P has the same luminosity as star Q.

• Star P is closer than star Q.

• Star P is the same distance from the Earth as star Q.

In the early 20th century, Hubble determined the distances to a range of nearby galaxies.

Which of the following methods would have allowed him to do this?

• measuring trigonometric parallax

• observing Cepheid variables

• using radio waves

• using the formula v = H₀d

The brightness of a star depends upon its luminosity and

• core temperature.

• distance from the observer.

• initial mass.

• surface temperature.

Trigonometric parallax is used to determine the distances to two stars, P and Q. The radiation flux from P is greater than that from Q. The parallax angle for P is smaller than that for Q.

Which of the following is a correct deduction about these stars?

• P has a greater luminosity than Q.

• P has the same luminosity as Q.

• P is closer to the Earth than Q.

• P is the same distance from the Earth as Q.

Two stars are being observed.

Star X is twice as far away as star Y and the intensity (radiation flux) received from star X is half that from star Y.

Which of the following statements is correct?

• Star X has half the luminosity of star Y.

• Star X has the same luminosity as star Y.

• Star X has twice the luminosity of star Y.

• Star X has eight times the luminosity of star Y.

Star X has a luminosity L and is a distance x from the Earth. The intensity (radiation flux) received

from this star is F.

Star Y has a luminosity 3L and is a distance 2x from the Earth.

What is the radiation flux received from star Y?

• 3F/4

• 2F/3

• 4F/3

• 3F/2

Standard candles can not be used to determine distances to

• nearby stars.

• distant stars.

• nearby galaxies.

• distant galaxies.

Cepheid variable stars are examples of standard candles.

A standard candle is a star with a known

• frequency.

• luminosity.

• intensity.

• radius.

Stellar parallax is used by astronomers to determine the distances to stars.

Why can this method only be used for some stars?

• The effect is too small for nearby stars.

• The effect is too large for nearby stars.

• The effect is too small for distant stars.

• The effect is too large for distant stars.

Astronomers are collecting data for two stars X and Y.

What can be concluded about the luminosities L_X and L_Y of star X and star Y?

*radiation flux is the intensity received at Earth.

• L_X > L_Y

• L_X = L_Y

• L_X = (L_Y)²

• L_X < L_Y