Astronomy Chapter 17 Quiz
What is the defining difference between a brown dwarf and a true star?
A brown dwarf object has less than 7.5% of the sun's mass and is not warm enough for hydrogen fusion to happen. A true star gives off 100% of its energy to the fusion of hydrogen into helium
What two factors determine how bright a star appears to be in the sky?
A star's distance and luminosity determines how bright it appears in the sky.
Do stars that look brighter in the sky have larger or smaller magnitudes than fainter stars?
Fainter stars have larger magnitudes while brighter stars have smaller magnitudes.
Order the seven basic spectral types from hottest to coldest.
O, B, A, F, G, K, M
The star Antares has an apparent magnitude of 1.0, whereas the star Procyon has an apparent magnitude of 0.4. Which star appears brighter in the sky?
Procyon because its apparent magnitude is smaller.
Name five characteristics of a star that can be determined by measuring its spectrum. Explain how you would use a spectrum to determine these characteristics.
Radial velocity, temperature, chemical composition, rotation, and atmospheric pressure.
What did Annie Cannon contribute to the understanding of stellar spectra?
She changed the order of the 7 classes from hotter to coolest.
How do objects of spectral types L, T, and Y differ from those of the other spectral types?
Spectral types L are hotter than stars that are type M. They are warmer than category M stars in the range of 1300 type L. They have temperatures from 1300 and 2400 K. Most give off red color. The spectrum includes mainly metal hydride layers and alkali metal layers(such as teide 1). Types are warmer than Type L stars. Temperatures range from 700 to 1300 K. They are generally colored Magenta. The spectrum mainly involves methane lines due to their low temperature. Gliese 229B is an example. Y types are warmer than Type T stars. They have a temperature of less than 700 K. Because of its low temperature, ammonia lines and infrared part are included in the spectrum. Example: WISE 1828 + 2650.
What elements are stars mostly made of? How do we know this?
Stars are mostly made of hydrogen and helium. We know this by studying the light that they emit since different elements(that make up a star) give off different colors in their emission spectrum making it possible for us to tell them apart.
Based on their colors, which of the following stars is hottest? Which is coolest? Archenar (blue), Betelgeuse (red), Capella (yellow).
The coolest is Betelgeuse and the warmest is Archenar.
What is the main reason that the spectra of all stars are not identical? Explain.
They absorb different elements based on their different temperatures.
Explain why color is a measure of a star's temperature.
Wien's law shows that a star's color depends on its temperature. The shade of the illumination doesn't change with distance to the object even though the light frequency doesn't change with distance.
Giant
a star that is very large in size with an extended photosphere
Brown dwarfs
an object with size between a planet and star the mass range is from about 1/100 of the mass of the Sun up to the lower mass limit for self-sustaining nuclear reactions, which is around 0.075 the mass of the Sun, brown dwarfs are capable of deuterium fusion, but not hydrogen fusion
Magnitude
an older system used to measure the amount of light we get from a star or other object, the larger the magnitude; the less radiation we get
Radial velocity
movement going towards or away from the observer, the element of relative velocity that lies in the line of sight(is visible)
Proper motion
the angular change in the path of a star seen from the Sun per year
Color index
the difference between the magnitudes of a star(or other object) measured in 2 different regions of the spectrum, blue minus visual (B-V) magnitudes
Apparent brightness
the measure of the amount of light Earth receives from a star or other object, how bright an object appears in the sky compared to its luminosity
Luminosity
the rate at which a star or other object releases electromagnetic energy into outer space
Spectral class
the rate at which a star or other object releases electromagnetic energy into outer space
Space velocity
the(three-dimensional) speed and direction with which an object travels through space relative to the Sun
