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25
Properties of Stars
| Question | Answer |
|---|---|
| What are constellations? | Patterns of stars. They are used to divide the sky into units. Can be used as a "map" of the night sky. 88 constellations are recognized today. |
| What is the clue to a stars temperature? | Color. Very hot stars with a surface temperature of above 3,000 K emit most of their energy in the form of short wave-length and appear blue. |
| Are red stars hotter or cooler than blue stars? | Red stars are much cooler. Most of their energy is emitted as longer-wavelength red light. |
| What are the temperatures of yellow stars? | Between 5000 and 6000 k appear yellow, like the sun. |
| What are binary stars? | Pairs of stars pulled away from each other by gravity. |
| What star property are binary stars used to determine? | Its mass. The mass of a body can be calculated if it is attached by gravity to a partner. |
| How do binary stars calculate mass? | Binary stars orbit each other around a common point called the center of mass. For stars of equal mass, the center of mass lies exactly halfway between them. If one star is more massive than its partner, their common center will be closer to the more ma |
| What is parallax? | The most basic way to measure star distance. It is the slight shifting in the apparent position of a nearby star due to the orbital motion of Earth. |
| How is parallax determined? | By photographing a nearby star against the background of distant stars. Ten six months later, when the Earth has moved half way yaround its orbit, a second photograph is taken. When these photographs are compared, the position of the nearby star appears |
| Which stars have the largest parallax angles? | The nearest stars have the largest parallax angles, while those of distant stars are too small to measure. |
| Are parallax angles large or small? | Small |
| What is a Light year? | A unit to express stellar distanct. It is the distance light travels in one year. |
| What is the measure of a star's brightness? | it's magnitude |
| What is apparent magnitude? | A star's brightness as it appears from Earth. |
| What are the three factors that control the apparent brightness of a star as seen from Earth? | How big it is How hot it is How far awa it is |
| How do Astronomers rank apparent magnitude? | They use numbers. The larger the number is, the dimmer the star. A first magnitude star is about 100 time brighter than a sixth magnitude star. Two stars that differ by 5 magnitudes have a ratio in brightness of 100 to 1. |
| What is absolute magnitude? | How bright a star actually is. |
| Does two stars that have the same absolute magnitude have the same apparent magnitude? | not necessarily because one may be much further away from us than the other. The one that is further away will appear dimmer. |
| What did Einar Hertzsprung and Henry Russell develop? | A graph to study stars, called a Hertzsprung-Russell diagram. It shows the relationship between the absolte magnitude and temperature of stars. |
| Are hottest main-sequence stars brightest or dimmest? | Brightest |
| What are red giants? | A grop of very bright stars above and to the right of the main sequence in the H-R diagram. |
| How are red giants size be estimated? | By comparing them with stars of known size that have the same surface temperature. |
| what are supergiants? | Extremel large stars |
| What are Cephid Variables? | stars that get brighter and fainter in a regular pattern. |
| The longer the light period of a Cepheid, the _______________ its absolute magnitude is. | greater |
| What is a nova? | A sudden brightening of a star. |
| What is nebulae? | Clouds of dust and gases in between stars. |
| What is bright nebulae? | When interstellar matter is close to a very hot star, it will glow. |
| What are the two main types of bright nebulae? | emission nebulae and reflection nebulae |
| what is emission nebulae? | Consists largely of hydrogen. They absorb ultraviolet radiation radiation emitted by a nearby hot star. |
| What is the conversion of ultraviolet light to visible light? | Fluorescence |
| What is reflection nebulae? | Reflects the light of nearby stars. thought to be composed of bright dense clouds of large particles called interstellar dust. |
| What are dark nebulae? | Nebulae that are not close enough to a bright star. They can easily be seen in starless regions when viewing the Milky Way. |
| Are nebulae very dense? | No, they are made up of thinly scattered matter. |
| Where are stars born? | In dark, cool interstellar clouds |
| How is a star born? | Some nebulae become dense enough to contract. A shock wave from an explosion of a nearby star may trigger the contraction. Once the process begins, gravity squeezes particles in the nebula, pulling every particle toward the center. As the nebula shrink |
| Protostar | A developing star not yet hot enough to engage in nuclear fusion. The initial contraction spans a million years or so. As time passes, the temperature of this gaseous body slowly rises until it is hot enough to radiate energy from its surface in the fo |
| How does a star become a stable-main sequence star? | Heat from hydrogen fusion causes gases to increase motion, this causes an increase in outward gas pressure. At some point this outward gas pressure exactly balances the inward force of gravity.When this balance is reached, the star a stable main-sequence |
| What is a stable main-sequenced star? | it is balanced between two forces: gravity, which is trying to squeeze it into a smaller sphere, and gas pressure, which is trying to expand it. |
| Main-sequence stage | from this stage until the star dies, the internal gas pressure struggles to offset the unyielding force of gravity. |
| Do all starts age at the same rate? | No. Hot, massive blue stars radiate energy at such an enormous rate that they deplete their hydrogen fuel in only a few million years. The least massive main-sequence stars may remain stable for hundreds of billions of years. A yellow star, the sun, re |
| What percentage does an average star spend as a hydrogen-burning main-sequence star? | 90% of its life |
| Once the _______________ _____ in the star's core is depleted, it evolves rapidly, and dies. | hydrogen fuel |
| How can a star delay its death? | By fusing heavier elements and becoming a giant. |
| Why does the red giant stage occur? | Because the zone of hydrogen fusion continually moves outward, leaving behind a helium core. |
| What happens when the core contracts? | it grows hotter by converting gravitational energy into heat energy. This energy is radiated outward, increasing hydrogen fusion in the star's outer shell. This energy heats and expands the star's outer layer. The result is a giant body hundreds of thous |
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jclicurse
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