Lab4
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Boston University *
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Course
102
Subject
Astronomy
Date
Dec 6, 2023
Type
Pages
7
Uploaded by CommodoreMoon11903
Page
6
AS102
-
Day
Laboratory
Exercise:
Luminosity
and
Brightness
DAY
LABORATORY
EXERCISE
#2:
LUMINOSITY
AND
BRIGHTNESS
Name/ID#
TA’s
Initials:
Class/Section:
AS102/
Date
due:
Station
1:
Light
and
Distance
Table
1
Checkerboard
Distance
Distance
in
Units
of
Number
of
Squares
Fraction
of
Light
per
from
the
Bulb
Filament
30cm
(d)
[Mluminated
Square
(b)
30
cm
1
1
1
60
cm
90
cm
120
cm
e
What
do
you
infer
about
the
proportionality
between
the
apparent
brightness
(b)
of
any
individual
square
on
the
checkerboard
and
its
distance
from
the
light
filament
(d)?
o
Explain
your
reasoning.
Why
is
the
proportionality
of
the
form
you
deduce?
How
should
the
luminosity
of
the
light
bulb
be
incorporated
into
the
mathematical
relation?
AS102
—
Day
Laboratory
Exercise
Luminosity
and
Brightness
Page
7
Station
2:
Differential
Photometer
e
With
the
classroom
dark
and
the
200
W
bulb
turned
on,
what
do
you
see
happen
to
the
photometer
as
you
move
it
toward
and
away
from
the
light?
e
What
do
you
see
on
the
side
of
the
photometer
which
is
not
illuminated?
e
Based
on
your
observations,
describe
how
the
photometer
works.
What
is
the
function
of
the
aluminum
foil?
Of
the
wax
slabs?
e
Meter
stick
with
two
100
Watt
light
bulbs.
e
With
the
bulbs
at
the
ends
of
the
meter
stick,
where
does
your
formula
from
Station
1
predict
you
should
place
the
photometer
so
that
it
will
show
a
balance
of light
brightness?
Page
8
AS102
-
Day
Laboratory
Exercise:
Luminosity
and
Brightness
e
Do
the
experiment.
Was
your
prediction
correct?
Why
or
why
not?
e
Meter
stick
with
one
100
W
and
one
60
W
bulb.
e
With
the
bulbs
at
the
ends
of
the
meter
stick,
where
do
you
predict
you
should
place
the
photometer
to
see
a
balance
of light
brightness?
What
is
the
basis
of
your
prediction?
e
Do
the
experiment.
Was
your
prediction
correct?
Why
or
why
not?
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AS102
—
Day
Laboratory
Exercise
Luminosity
and
Brightness
Page
9
e
60
W
bulb
and
unknown
wattage
bulb:
e
With
the
60
W
bulb
at
one
end
of
the
meter
stick
and
the
unknown
at
the
other
end,
adjust
the
placement
of
the
photometer
until
the
brightness
balanced
from
both
sides
of
the
photometer.
e
Measure
the
distances
between
the
bulbs
and
the
photometer.
e
(alculate
the
wattage
of
the
unknown
bulb.
SHOW
ALL
YOUR
WORK!
e
Wattage
of
unknown
bulb
=
e
Unknown
wattage
bulb
and
candle.
e
With
the
unknown
wattage
bulb
at
one
end
of
the
meter
stick
and
a
candle
at
the
other
end,
adjust
the
placement
of
the
photometer
until
the
brightness
is
in
balance
on
both
sides
of
the
photometer.
Measure
the
distances
between
the
bulb
and
the
photometer
and
the
candle
and
photometer.
e
(alculate
the
luminosity
of
the
candle
as
you
did
for
the
unknown
wattage
bulb.
e
Wattage
of
candle
=
Page
10
AS102
-
Day
Laboratory
Exercise:
Luminosity
and
Brightness
Station
3:
Solar
Luminosity
and
Temperature
e
Distance
between
the
200
W
bulb
and
the
photometer
when
the
photometer
shows
a
balance
of
brightness
for
the
Sun
and
the
bulb.
e
(Calculate
the
luminosity
of
the
Sun,
SHOWING
ALL
YOUR
WORK.
Note
that the
Sun
is
1.49x10!!
meters
away.
e
Using
the
luminosity
you
calculated
for
the
Sun
and
the
relationship
described
in
the
introduction,
calculate
the
temperature
of
the
Sun
(in
Kelvin
degrees).
The
Sun
has
a
radius
of
6.96x10®
meters.
SHOW
ALL
YOUR
WORK.
AS102
—
Day
Laboratory
Exercise
Luminosity
and
Brightness
Page
11
Summary
Questions
1.
Betelgeuse
is
a
bright
red
supergiant
star
located
in
the
winter
constellation
Orion.
Calculate
its
luminosity
if
its
radius
is
300
times
that
of
the
Sun
and
its
temperature
is
4200°
K.
SHOW
ALL
YOUR
WORK.
2.
How
many
Watts/m?
get
to
Earth
from
Betelgeuse
if
it
is
at
a
distance
of
150
parsec
(1
pc
=
3x10'®
meters)?
SHOW
ALL
YOUR
WORK.
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Page
12
AS102
-
Day
Laboratory
Exercise:
Luminosity
and
Brightness
3.
What
is
the
ratio
of
brightness
of
Betelgeuse
to
the
Sun,
as
measured
at
the
Earth?
The
brightness
of
the
Sun
as
seen
from
Earth
is
1400
W/m?.
SHOW
ALL
YOUR
WORK.
4.
From
your
measurement
of
the
luminosity
of
an
average
candle,
what
is
the
absolute
“candlepower”
of
the
Sun?
(The
Sun’s
luminosity
is
equivalent
to
how
many
candles?)