1. astronomers measure the angle that the star appears to jump when viewing it from two different points in earth's orbit. what is this technique called? a) parsecs b) parallax c) luminosity d) mass transfer 3. what properties of a star are needed to calculate the stars's luminosity? a) size and apparent brightness b) mass and distance to the star c) temperature and diameter of the star d) apparent brightness and distance to the star 4. which cool and bright stars are located in the upper right of the h-r diagram? a) red giant b) neutron stars c) white dwarfs d) main sequence 5. what color are stars that are very hot and very bright? a) red b) blue c) white d) yellow

1. B) Parallax

3. D) Apparent brightness and distance to the star

4. A) Red giant

5. B) Blue

Explanation:

1. In order to measure the distance to a nearby star, astronomers use parallax method. In this method, parallax angle is measured. The star appears to move against a fixed background when viewed from two different position of Earth in its orbit.

where, d is the distance in parsecs and p is the parallax angle in arc-second.

2. Luminosity of a star is the energy emitted by a star's surface. It measured in watts. In order to measure the luminosity of a star, apparent brightness (b) and distance to the star (d) is required. Following formula can be used to measure the luminosity of a star:

3. The H-R diagram is the plot of stars based on their luminosity, color and temperature. In the upper right of the H-R diagram, red giants are located. These are the cool and bright stars. An average mass star like the sun expands and becomes a red giant when it runs off its fuel before ending up as a white dwarf.

4. Color of a star indicated its surface temperature. A star emits different wavelengths but a peak wavelength can be observed from its spectrum which indicates the star's effective temperature. So, cool stars are red in color where as hot and bright stars are blue in color.

convex lenses are thicker at the middle. rays of light that pass through the lens are brought closer together (they converge). a convex lens is a converging lens. when parallel rays of light pass through a convex lens the refracted rays converge at one point called the principal focus.

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