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ASTR 1346 Exam 1 2026-Authentic
Questions And Verified Answers
The Electromagnetic Spectrum - correct-answer -Visible light is the particular type
of electromagnetic radiation --- to which our eyes happen to be sensitive.
There is invisible EM radiation, which goes undetected by our eyes. - correct-
answer -radio, infrared, ultraviolet, x rays and gamma rays
The only characteristic distinguishing one from another is.. - correct-answer -
wavelength or frequency.
Absolute brightness (luminosity) and apparent brightnes - correct-answer --
Luminosity: It is the intrinsic property of a star, so, is independent of distance and
location. It is the measure of total energy output the star. Measured in Power
Units: Energy/second emitted by the object (e.g., Watts or ergs/sec or joules/sec
etc.)It is sometimes also referred as absolute brightness.
-Apparent brightness: It is the measure of how bright an object appears to be as
seen by a distant observer (i.e brightness that we see here on the Earth). It
, 2
depends on the distance to the object and hence it is not the measure of total
energy but of energy flux. Measured in Flux Units: Energy/second/area received
from the object
Magnitude System/ scale:Traditional system - correct-answer -Traditional system:
Dating to classical times (Hipparchus of Rhodes, c. 300BC).Rank stars into 1st, 2nd,
3rd, etc. magnitude.• 1st magnitude are brightest stars,• 2nd magnitude are next
brightest,• and so on...The faintest stars visible to the naked eye are 6th
magnitude
Magnitude System/ scale: Modern System - correct-answer -Modern System:
(now we also use negative and non-integers as well)Modern version quantifies
magnitudes as:• 5 steps of magnitude = factor of 100 in brightness. Examples:•
10th mag star is 100x fainter than a 5th mag star.• 20th mag star is 10,000x fainter
than a 10th mag star. Computationally convenient, but somewhat obtusely
defined (it is backwards: larger magnitudes = fainter stars)
Apparent Brightness/ Magnitude - correct-answer --The Apparent Brightness (B)
of a source is inversely proportional to the square of its distance (d):
--In Words:2-times Farther = 4-times Fainter3-times Farther = 9-times
Fainter[Credit: R. Pogge, OSU]
-The Apparent Brightness is also directly proportional to the luminosity:
, 3
Spectra and Stars: spectral classification of stars (O, B, A...) and their sub-
classification; relation of spectral class with temperature - correct-answer --
Astronomers further subdivide each spectral classification into 10 subdivisions.
-Temperature: is the direct measure of heat or motion of constituent particles.
Temperature of stars is measured by their colors or spectra
Is there any correlation between temperature and luminosity of stars? - correct-
answer -Yes, and this correlation was first studied, independently in1912 by a
Danish astronomer Eljnar Hertzsprung and an American astronomer Henry Norris
Russell for nearby stars.
-Now it is know as HR diagram which is a graph between temperature from
hottest to coolest along the horizontal axis, and luminosity from faintest to
brightest along the vertical axis.
HR diagram (what we plot on X-axis and Y-axis); position of main sequence stars
(red dwarf, blue giant) - correct-answer -90% stars, including the Sun, lie along a
diagonal band in the H-R Diagram called the Main Sequence (MS) Stars.
• Most of them are Red Dwarfs.(K and M stars with low luminosity)
• A few are Blue Giants.(Hot, luminous stars)• A very few are Blue
Supergaints.(Very hot and very luminous stars)
White dwarfs and Red Giants - correct-answer -White Dwarfs
ASTR 1346 Exam 1 2026-Authentic
Questions And Verified Answers
The Electromagnetic Spectrum - correct-answer -Visible light is the particular type
of electromagnetic radiation --- to which our eyes happen to be sensitive.
There is invisible EM radiation, which goes undetected by our eyes. - correct-
answer -radio, infrared, ultraviolet, x rays and gamma rays
The only characteristic distinguishing one from another is.. - correct-answer -
wavelength or frequency.
Absolute brightness (luminosity) and apparent brightnes - correct-answer --
Luminosity: It is the intrinsic property of a star, so, is independent of distance and
location. It is the measure of total energy output the star. Measured in Power
Units: Energy/second emitted by the object (e.g., Watts or ergs/sec or joules/sec
etc.)It is sometimes also referred as absolute brightness.
-Apparent brightness: It is the measure of how bright an object appears to be as
seen by a distant observer (i.e brightness that we see here on the Earth). It
, 2
depends on the distance to the object and hence it is not the measure of total
energy but of energy flux. Measured in Flux Units: Energy/second/area received
from the object
Magnitude System/ scale:Traditional system - correct-answer -Traditional system:
Dating to classical times (Hipparchus of Rhodes, c. 300BC).Rank stars into 1st, 2nd,
3rd, etc. magnitude.• 1st magnitude are brightest stars,• 2nd magnitude are next
brightest,• and so on...The faintest stars visible to the naked eye are 6th
magnitude
Magnitude System/ scale: Modern System - correct-answer -Modern System:
(now we also use negative and non-integers as well)Modern version quantifies
magnitudes as:• 5 steps of magnitude = factor of 100 in brightness. Examples:•
10th mag star is 100x fainter than a 5th mag star.• 20th mag star is 10,000x fainter
than a 10th mag star. Computationally convenient, but somewhat obtusely
defined (it is backwards: larger magnitudes = fainter stars)
Apparent Brightness/ Magnitude - correct-answer --The Apparent Brightness (B)
of a source is inversely proportional to the square of its distance (d):
--In Words:2-times Farther = 4-times Fainter3-times Farther = 9-times
Fainter[Credit: R. Pogge, OSU]
-The Apparent Brightness is also directly proportional to the luminosity:
, 3
Spectra and Stars: spectral classification of stars (O, B, A...) and their sub-
classification; relation of spectral class with temperature - correct-answer --
Astronomers further subdivide each spectral classification into 10 subdivisions.
-Temperature: is the direct measure of heat or motion of constituent particles.
Temperature of stars is measured by their colors or spectra
Is there any correlation between temperature and luminosity of stars? - correct-
answer -Yes, and this correlation was first studied, independently in1912 by a
Danish astronomer Eljnar Hertzsprung and an American astronomer Henry Norris
Russell for nearby stars.
-Now it is know as HR diagram which is a graph between temperature from
hottest to coolest along the horizontal axis, and luminosity from faintest to
brightest along the vertical axis.
HR diagram (what we plot on X-axis and Y-axis); position of main sequence stars
(red dwarf, blue giant) - correct-answer -90% stars, including the Sun, lie along a
diagonal band in the H-R Diagram called the Main Sequence (MS) Stars.
• Most of them are Red Dwarfs.(K and M stars with low luminosity)
• A few are Blue Giants.(Hot, luminous stars)• A very few are Blue
Supergaints.(Very hot and very luminous stars)
White dwarfs and Red Giants - correct-answer -White Dwarfs
