On the 10th of august 2007 a star Gacrux (on the southern cross)
has a transit time 15h 11m 31s and it’s
right ascension is 12h 31m 33.72s
Explain how this tells you how eastern standard time is related to local sidereal time?
the answer to this should let me
Estimate (without skymap) when next (if ever) local sidereal time will coincide with eastern standard time?
.
The two questions are the same only back to front
firstly
right ascension is 12h 31m 33.72s is the time that gacrux will transit the meridian on the equinox’s, the next equinox is the autumnal equinox ( which is your vernol equinox if you live in the south) on about sept 22 which is 43 days after the 10th of august also the transit time is about 160 minutes after the RA then 160 /43 ≈ 4 min per day so this tells you that
LST ≈ EST + [4 min per day * (# of days)]
the second question is the same but in reverse
assume you know there is 4 min per day (approx) difference then since transit and RA are 160 minutes apart, the times will coincide in 160 /4 = 40 days gives september 20 as an estimate
note: the inaccuracy of sept 20 is expected since the angular speed of the earths orbit around the ecliptic isn’t constant
Religion is a fairytale so keep on burning…lol
the end
.
September 30th, 2009 at 1:45 pm
Siderial time (star time) varies daily by about 4 minutes. Transit times are local times while the Right Ascension lines rotate around us daily. So at the time of transit, siderial time for your location will be 12h 31 minutes 33 sec. If stargazing you can set your clock/watch to that time and track siderial time for the night. If you have the RA and Dec of any object you can then adjust your scope and find the item without using your finder.
References :
September 30th, 2009 at 2:15 pm
The two questions are the same only back to front
firstly
right ascension is 12h 31m 33.72s is the time that gacrux will transit the meridian on the equinox’s, the next equinox is the autumnal equinox ( which is your vernol equinox if you live in the south) on about sept 22 which is 43 days after the 10th of august also the transit time is about 160 minutes after the RA then 160 /43 ≈ 4 min per day so this tells you that
LST ≈ EST + [4 min per day * (# of days)]
the second question is the same but in reverse
assume you know there is 4 min per day (approx) difference then since transit and RA are 160 minutes apart, the times will coincide in 160 /4 = 40 days gives september 20 as an estimate
note: the inaccuracy of sept 20 is expected since the angular speed of the earths orbit around the ecliptic isn’t constant
Religion is a fairytale so keep on burning…lol
the end
.
References :