AST 309-TIME
Elementary Astrolabe Use
This assignment is DUE on October
21.
Reduced credit if late!
Name_________________________ Birthday______________
This assignment asks you to do some simple astrolabe manipulations
on your birthday, to get practice with using the astrolabe.
Note that this is for any year (the astrolabe doesn't know about
year numbers).
Set the astrolabe for 0 hours sidereal time (the line for the
Vernal Equinox should point to the "12" on the top of
the astrolabe). Set the sun pointer for the day of your birthday.
Express all your answers in terms of a 24-hour clock.
1) What is the local apparent solar time (on a 24-hour
clock) of 0 hours sidereal time, on your birthday? ___________________
2) On the back of the astrolabe, determine the correction for
the Equation of Time for this date. Be sure to write down the
sign. Subtract this from the local apparent solar time
to get the local mean solar time. What is the result? _________________
3) Look up the longitude correction for Austin, Texas, on the
back of your astrolabe. Subtract this from the local mean
solar time to get the Central Standard Time of 0 hours
sidereal time. What is the result?_______________________
4) If your birthday falls during a time that Daylight Savings
Time is in effect, add one hour to get the Central Daylight
Savings Time of 0 hours sidereal time. For the sake of this
calculation, take Daylight Savings Time to be in effect during
the months April-October. This is what your watch would read.
_________________________
5) Find a prominent named star or star group that is above the
horizon. Describe its position in the sky: Has it recently risen,
or is it near the meridian, or is it about to set, or is it somewhere
in between one of these positions?
____________________________________________________________________
6) Now determine the local apparent solar time of midnight, Central
(Standard or Daylight) Time, on your birthday. (Reverse steps
4, 3 and 2 above, but start with CST or CDT of 0 hours. This means,
when it says add, subtract; when it says subtract, add. You are
"undoing" what steps 2-4 do.). What is the local apparent
solar time of this instant? _______________________
7) Set your astrolabe for this local apparent solar time.What
is the local sidereal time of this instant? ___________________________
8) Find a prominent named star or star group that is above the
horizon. Describe its position in the sky: Has it recently risen,
or is it near the meridian, or is it about to set, or is it somewhere
in between one of these positions?
____________________________________________________________________
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