astro quiz 7
What basic characteristics/properties of stars are we trying to understand? - correct answer To understand how something works we need to know their basic characteristics:
- Size, shape, distance
- Energy output, temperature
- Mass
What's parallax and how do we use it to measure the distance to a nearby star? - correct answer For nearby stars use Parallax -measure position against background stars -use angle to calculate distance The distance in parsecs is , with the angle measured in arc-seconds
This simple technique was argued by Tycho Brahe
How do we actually calculate the distance? What are the units of angle and distance that we use? - correct answer Parallax is measured in very small angles
How small? arc seconds! 360 deg (of arc)= 360 X 60 min (of arc)= 360 X 60 X 60 sec (of arc) = 1,296,000 arc-sec
-parallax angle: lets your brain judge how close or far an object is from you (p) half the angle by which Earth shifts positions through the year as seen from the star (measured in arcseconds) distance to a star in parsecs = 1/parallax angle of that star in arc second
What is apparent magnitude? What does it measure? Relative to what? - correct answer -The brightnesses of stars measured without regard to their distances from Earth are called apparent magnitudes, denoted by the lowercase m.
→ the brightest stars were designated m = +1, those that appeared half as bright were said to be second magnitude stars (m = +2) and so forth down to the sixth magnitude stars, the dimmest ones visible to the
unaided eye
→ The scale used today begins by giving the star Vega an apparent magnitude of 0.0
→ Because some bodies are brighter than Vega, astronomers assign negative numbers to the apparent magnitudes of the very brightest objects.
→ Sirius, the brightest star in the night sky has an apparent magnitude of m = -1.44 -Remember: objects with negative apparent magnitudes appear brighter than those with positive apparent magnitudes, the more negative, the brighter
What objects have what brightness using the magnitude scale? What is the Sun's apparent mag'? - correct answer [sirius, the brightest star, is -1.44, Venus, -4.4, full moon -12.6, sun -26.7]
What is absolute magnitude? What does it measure? - correct answer -Absolute magnitude, M, is the brightness each star would have at a distance of 10 pc (32.6 ly).
-Light moving outward from a source spreads over increasingly larger areas of space, and therefore its brightness decreases with increasing distance
→ The inverse-square law provides the rule for just how quickly the brightness of an object changes with
distance
The inverse-square law can be summarized mathematically as follows → apparent brightness decreases inversely with the square of the distance between the source and the observer
What do we need to know for calculating the absolute magnitude (actual brightness) of a star? What's the absolute mag' of the Sun? - correct answer -Absolute magnitudes are usually determined by calculations based on apparent magnitudes → We can calculate the absolute magnitude of a nearby star by first measuring its apparent magnitude and then finding its distance by measuring its parallax angle
-Absolute magnitudes range from roughly M = -10 for the brightest stars and M = +17 for the dimmest
-sun is 4.8
What two ways do we have to measure the temperature of a star? What part of the star are we referring
to? - correct answer -Like the Sun, all stars are very nearly perfect blackbodies → meaning their color is determined by their surface temperature
-Different blackbody curves are associated with blackbodies of different temperatures. These curves differ in both their intensities and the locations of their peaks, as described by Wien's law
-to accurately determine the peaks of stars' blackbody spectra and, hence, their surface temperatures, astronomers need to know which blackbody curve most accurately describes each star
→ Photometry provides this information → in this process, a telescope collects starlight that is then passed through one of a set of colored filters and recorded on a CCD.
→ By plotting the three data points and finding which unique blackbody curve they fit on, we can determine that star's surface temperature
What basic characteristics/properties of stars are we trying to understand? - correct answer To understand how something works we need to know their basic characteristics:
- Size, shape, distance
- Energy output, temperature
- Mass
What's parallax and how do we use it to measure the distance to a nearby star? - correct answer For nearby stars use Parallax -measure position against background stars -use angle to calculate distance The distance in parsecs is , with the angle measured in arc-seconds
This simple technique was argued by Tycho Brahe
How do we actually calculate the distance? What are the units of angle and distance that we use? - correct answer Parallax is measured in very small angles
How small? arc seconds! 360 deg (of arc)= 360 X 60 min (of arc)= 360 X 60 X 60 sec (of arc) = 1,296,000 arc-sec
-parallax angle: lets your brain judge how close or far an object is from you (p) half the angle by which Earth shifts positions through the year as seen from the star (measured in arcseconds) distance to a star in parsecs = 1/parallax angle of that star in arc second
What is apparent magnitude? What does it measure? Relative to what? - correct answer -The brightnesses of stars measured without regard to their distances from Earth are called apparent magnitudes, denoted by the lowercase m.
→ the brightest stars were designated m = +1, those that appeared half as bright were said to be second magnitude stars (m = +2) and so forth down to the sixth magnitude stars, the dimmest ones visible to the
unaided eye
→ The scale used today begins by giving the star Vega an apparent magnitude of 0.0
→ Because some bodies are brighter than Vega, astronomers assign negative numbers to the apparent magnitudes of the very brightest objects.
→ Sirius, the brightest star in the night sky has an apparent magnitude of m = -1.44 -Remember: objects with negative apparent magnitudes appear brighter than those with positive apparent magnitudes, the more negative, the brighter
What objects have what brightness using the magnitude scale? What is the Sun's apparent mag'? - correct answer [sirius, the brightest star, is -1.44, Venus, -4.4, full moon -12.6, sun -26.7]
What is absolute magnitude? What does it measure? - correct answer -Absolute magnitude, M, is the brightness each star would have at a distance of 10 pc (32.6 ly).
-Light moving outward from a source spreads over increasingly larger areas of space, and therefore its brightness decreases with increasing distance
→ The inverse-square law provides the rule for just how quickly the brightness of an object changes with
distance
The inverse-square law can be summarized mathematically as follows → apparent brightness decreases inversely with the square of the distance between the source and the observer
What do we need to know for calculating the absolute magnitude (actual brightness) of a star? What's the absolute mag' of the Sun? - correct answer -Absolute magnitudes are usually determined by calculations based on apparent magnitudes → We can calculate the absolute magnitude of a nearby star by first measuring its apparent magnitude and then finding its distance by measuring its parallax angle
-Absolute magnitudes range from roughly M = -10 for the brightest stars and M = +17 for the dimmest
-sun is 4.8
What two ways do we have to measure the temperature of a star? What part of the star are we referring
to? - correct answer -Like the Sun, all stars are very nearly perfect blackbodies → meaning their color is determined by their surface temperature
-Different blackbody curves are associated with blackbodies of different temperatures. These curves differ in both their intensities and the locations of their peaks, as described by Wien's law
-to accurately determine the peaks of stars' blackbody spectra and, hence, their surface temperatures, astronomers need to know which blackbody curve most accurately describes each star
→ Photometry provides this information → in this process, a telescope collects starlight that is then passed through one of a set of colored filters and recorded on a CCD.
→ By plotting the three data points and finding which unique blackbody curve they fit on, we can determine that star's surface temperature
