distance between stars

other methods

Even with the most precise instruments available, parallax is too small to measure the distance to stars that are more than a few hundred light years away. For these more distant stars, astronomers must use more indirect methods of determining distance. Most of these methods involve determining how bright the star they are looking at really is. For example, if the star has properties similar to the Sun, then it should be about as bright as the Sun. The astronomer compares the observed brightness to the expected brightness.

parallax

Distances to stars that are relatively close to us can be measured using parallax. Parallax is an apparent shift in position that takes place when the position of the observer changes. To see an example of parallax, try holding your finger about 1 foot (30 cm) in front of your eyes. Now, while focusing on your finger, close one eye and then the other. Alternate back and forth between eyes, and pay attention to how your finger appears to move. The shift in position of your finger is an example of parallax. Now try moving your finger closer to your eyes, and repeat the experiment. Do you notice any difference? The closer your finger is to your eyes, the greater the position changes because of parallax. As Figure 1.1 shows, astronomers use this same principle to measure the distance to stars. Instead of a finger, they focus on a star, and instead of switching back and forth between eyes, they switch between the biggest possible differences in observing position. To do this, an astronomer first looks at the star from one position and notes where the star is relative to more distant stars. Now where will the astronomer go to make an observation the greatest possible distance from the first observation? In six months, after Earth moves from one side of its orbit around the Sun to the other side, the astronomer looks at the star again. This time parallax causes the star to appear in a different position relative to more distant stars. From the size of this shift, astronomers can calculate the distance to the star.

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instructional diagrams

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questions

parallax is used to measure the distance of

a) all stars.

b) stars that are anywhere in the milky way galaxy.

c) stars that are only a few light years from us.

-->  d) stars that are no more than a few hundred light years from us.

to test parallax, put your finger about one foot in front of your eyes and then look at it from one eye and then the other.

-->  a) true

b) false

to use parallax to determine the distance to a star, astronomers must observe that star

-->  a) relative to more distant stars at two opposite sides of earths orbit.

b) relative to more distant stars at two times of day, 12 hours apart.

c) relative to the sun, at two different times, 6 months apart.

d) relative to the sun, at two different times of day, 12 hours apart.

when observing stars, this is the furthest apart two locations on the earths orbit can be.

a) 1 au

-->  b) 2 au

c) 3 au

d) 4 au

even with the most precise instruments available, parallax is too small to measure the distance to stars that are more than a few hundred light years away.

-->  a) true

b) false

the more distant the star, the more accurate our estimate of its distance.

a) true

-->  b) false

to determine the properties of a distance star, astronomers compare that star to

a) the nearest star to our solar system, alpha centauri

b) betelgeuse in the constellation orion.

-->  c) the sun.

d) jupiter.

au stands for _ and it is the distance between _.

a) astrology units; earth and the nearest star

-->  b) astronomical units; earth and the sun

c) astrology units; earth and the sun

d) astronomical units; earth and the nearest star

to determine the distance of a star that is far away, astronomers

a) compare observed size to expected size.

b) determine its color.

c) use parallax with more precise instruments.

-->  d) compare observed brightness to expected brightness.

diagram questions

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