Measurements of various properties of stars allowed astronomers to determine a more physically meaningful way of ordering the different spectral types than just by the strength of their hydrogen absorption lines. Study this table of properties, and use it to determine how the stars should be ordered. Choose the list of spectral types that is ordered by decreasing strength of any given property or properties from the table. Choose one: mathrm(O) 5, mathrm(BO), mathrm(AO), mathrm(FO), mathrm(KO), mathrm(GO), mathrm(MO) mathrm(MO), mathrm(KO), mathrm(GO), mathrm(FO), mathrm(AO), mathrm(BO), mathrm(O) 5 mathrm(AO), mathrm(BO), mathrm(FO), mathrm(GO), mathrm(KO), mathrm(MO), mathrm(O) 5 mathrm(O) 5, mathrm(BO), mathrm(AO), mathrm(FO), mathrm(GO), mathrm(KO), mathrm(MO), mathrm(O) 5

To determine the correct ordering of spectral types, we need to understand how stars are classified based on their spectral properties. The spectral classification system orders stars by their surface temperature, which correlates with other physical properties such as color and strength of hydrogen absorption lines.<br /><br />The standard order of spectral types is:<br /><br />**O → B → A → F → G → K → M**<br /><br />This sequence corresponds to decreasing surface temperature, where:<br />- **O-type stars** are the hottest and most massive, with strong ionized helium lines.<br />- **M-type stars** are the coolest and least massive, with molecular absorption features.<br /><br />### Explanation of the Choices:<br />1. \( \mathrm{O} 5, \mathrm{BO}, \mathrm{AO}, \mathrm{FO}, \mathrm{KO}, \mathrm{GO}, \mathrm{MO} \) <br /> This matches the correct order of spectral types from hottest (O) to coolest (M). <br /><br />2. \( \mathrm{MO}, \mathrm{KO}, \mathrm{GO}, \mathrm{FO}, \mathrm{AO}, \mathrm{BO}, \mathrm{O} 5 \) <br /> This is the reverse order, going from coolest (M) to hottest (O), which does not match the standard classification.<br /><br />3. \( \mathrm{AO}, \mathrm{BO}, \mathrm{FO}, \mathrm{GO}, \mathrm{KO}, \mathrm{MO}, \mathrm{O} 5 \) <br /> This is an incorrect order because it places A before B and O at the end, which contradicts the standard classification.<br /><br />4. \( \mathrm{O} 5, \mathrm{BO}, \mathrm{AO}, \mathrm{FO}, \mathrm{GO}, \mathrm{KO}, \mathrm{MO}, \mathrm{O} 5 \) <br /> This repeats the O-type star at the end, making it inconsistent with the standard classification.<br /><br />### Correct Answer:<br />**\( \mathrm{O} 5, \mathrm{BO}, \mathrm{AO}, \mathrm{FO}, \mathrm{GO}, \mathrm{KO}, \mathrm{MO} \)**