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VTB
newbie
Reged: 10/17/09
Posts: 2
Loc: Monkton, Maryland
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Recently purchased a 125-PE.
In scrolling through the handset, I noticed if I held the Mode key for 2 seconds or more, I get to screens dealing with the Finder, Lat, Long, etc.
One of them lists Time on the top line and LST on the bottom.
The top will display the correct time after I enter it when the scope is turned on.
The LST displays a different time in 24 hour format.
There appears to be no correlation between them, i.e.,
Time: 6:51:29
LST: 20:18:28
What is this "LST" ?
Local Standard Time ???
Are the times supposed to be different?
If so, why?
If not, how does one correct ?
Thanks
Tim Bambrick
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Fish
sage
Reged: 10/13/07
Posts: 470
Loc: Norridgewock, ME
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Tim,
I believe that is "Local Sidereal Time"; that is, the current Right Ascension transiting your local meridian. By this definition, midnight LST is when the hour angle of the vernal equinox transits your local meridian.
Now you have me curious: where's my ETX hiding?
Regards, Marc
--------------------
Goseck Observatory
Kunming 152 f/5.9 & Baader Wedge
Orion ED80 & LS75FHa2/B1200
Meade 102ED & LS18CaKMDd2
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Bob Griffiths
Postmaster
Reged: 10/10/05
Posts: 6592
Loc: Frederick Maryland
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I take it to mean >>>> Local Sidereal Time...
Which runs 5 hours behind Universal time...here in Maryland.
But 20:18:28 corresponds to 8:18 PM which would be 9:18 PM with daylight savings time still in effect...I have no clue where you got 6:51:19
Bob G.
--------------------
CPC1100
Nexstar 8i + GPS & Rays Brackets
Denk S1 power switch
Orion 100 mm Refractor
Meade LXD 55 ...AR-5 127 mm Refractor
Exploradome Observatory S.I.E. (Smiling Irish Eyes)
Gerbring Heated Motorcycle clothing in the winter
39*21'03" N
77*28'12" W
The sky over my head....
Edited by Bob Griffiths (10/29/09 08:01 PM)
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brianb11213
Carpal Tunnel
Reged: 02/25/09
Posts: 2119
Loc: 55.215N 6.554W
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Quote:
Local Sidereal Time...
Which runs 5 hours behind Universal time...here in Maryland.
Local solar time may be about 5 hours behind UT - though even that varies, the "equation of time" is a correction which can run to +/- 16 minutes depending on the season of the year, this is caused by the earth rotating at a constant rate but its orbital motion not being constant because of the eccentricity of the earth's orbit.
But sidereal time doesn't even run at the same rate as solar time. The earth rotates 366.25 times in a year with respect to the stars, 365.25 times with respect to the Sun (orbital motion again) therefor sidereal time runs faster than solar time by nearly 4 minutes per day.
Local sidereal time is simply the same as the right asension of an object on the meridian. e.g. if Betelgeuse is due south, then the local sidereal time is 5h 55m 43.1s
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VTB
newbie
Reged: 10/17/09
Posts: 2
Loc: Monkton, Maryland
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In response to Bob G.'s comments re TIME:
When the Autostar controller is turned on, it prompts you to enter the date, time and whether it's Daylight Savings or not.
Last night I entered the time at 6:49pm or thereabouts.
After going to the screen in question, the top line was displaying the current time, i.e., 6:51:19 and was "ticking".
The bottom line LST displayed the 20:18:28 at the same moment and was also "ticking".
OK...to reaffirm my amateur status, for purposes of aligning, etc., the difference between TIME and LST is of no consequence and can be ignored. Yes ???
Tim Bambrick
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Joe Lalumia
Post Laureate
Reged: 01/24/07
Posts: 3616
Loc: Rockwall, Texas, USA
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Yes-- It has no bearing for normal GOTO operation.
--------------------
LX90 8" LNT, SV Nighthawk & TelePOD, SV 80/9D & M4 mount, ETX 90, Orion XT10i, 20x80 binoculars, SV-BV3s-- www.texasastro.org
"Great minds discuss ideas;Average minds discuss events;Small minds discuss people." Unknown
Edited by Joe Lalumia (10/30/09 10:01 AM)
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rmollise
Post Laureate
Reged: 07/06/07
Posts: 4598
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Quote:
Recently purchased a 125-PE.
In scrolling through the handset, I noticed if I held the Mode key for 2 seconds or more, I get to screens dealing with the Finder, Lat, Long, etc.
One of them lists Time on the top line and LST on the bottom.
The top will display the correct time after I enter it when the scope is turned on.
The LST displays a different time in 24 hour format.
There appears to be no correlation between them, i.e.,
Time: 6:51:29
LST: 20:18:28
What is this "LST" ?
Local Standard Time ???
Are the times supposed to be different?
If so, why?
If not, how does one correct ?
Thanks
Tim Bambrick
LST is a different animal... (Rod puts on college astronomy instructor's hat)...
LST is "Local Sidereal Time," and is equal to the Right Ascension of the line of Right Ascension currently on the meridian.
In simpler terms, if stars, planets, constellations, whatever with an RA of 21:30 are on your meridian (the imaginary line that runs from the North Celestial Pole, through the Zenith, down to the south horizon and back around) it is now 21:30 LST 
--------------------
Uncle Rod
Rod's New Book:
Choosing and Using a New CAT
Available now!
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JT5
professor emeritus
Reged: 11/08/07
Posts: 588
Loc: Ozarks of Missouri
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Yes to all of the above. If you do not have a manual with the scope, you can find it online. The "finder" section is important to you and you need to read the manual. It is a great scope if you learn how to use it and both Joe and Rod are experts on this. You may also want to familiarize yourself with Mike Weasner's Mighty ETX website.
John
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