Solar ephemeris

Larry I have not looked at my MICA in years. With that being said you can find what you are looking

for in?ÿ"The Astronomical Almanac " year xxxx. You can purchase the book from U.S. Govt. Pub.

Office ( http://bookstore.gpo.gov)?ÿ you will want to look at page C6 - C21.

This should be online but since I get the book I have not checked that.

?ÿ

JOHN NOLTON

PS?ÿ If you have some specific day (or days) I can put it here.?ÿ

I'm very confused concerning your question.?ÿ ?ÿMirror ?ÿcoronagraph (MICA) daily images at several observatories measure ?ÿthe inner solar corona with high temporal and spatial resolution in two spectral ranges: the well known green (~1.8 MK) and red (~1.0 MK) coronal lines at 5303 A and 6374 A respectively, which are the most accurate determinations of the sun's diameter in near real time.?ÿ But that has little to do with how the eye lines up the sun's limb through a telescope.

?ÿIf you're observing the sun for azimuth using tripod mounted?ÿtheodolites the major effect on the sun's apparent diameter is its distance from the earth which varies annually, and is readily available in astronomic tables.?ÿ It's easy to negate the effect of the sun's diameter and observer bias?ÿ by inversion, observe the left limb, then the right limb, correct for time and average them.?ÿ Similarly for altitude observations.?ÿ Best if you're in a hurry is a Roelofs prism which is not affected by semidiameter.

I'll admit I'm an old timer; ran solar transit lines while working for the BLM (+-1?ø), then lots of solar alignment?ÿ azimuths for microwave & cell tower sites which were maybe +-1/2?ø.?ÿ Really tight azimuths required Polaris observations over several nights and could get to 15" or less.

But I realize those days are gone and a simple GPS procedure can determine azimuth with two stations a few thousand feet apart suffices now at much lower cost.?ÿ So what is your question?

@mike-marks

MICA:

Multi year?ÿ

Interactive?ÿ

Computer

Almanac?ÿ

@john-nolton

well I calculated it. MICA outputs AU, so I get about the same second in diameter the hard way. And thatƒ??s 0.5ƒ? worst case different than JPL.?ÿ

I did see that the JPL Horizons uses 696,000 km radius. But, Iƒ??ve found 696,345 km elsewhere, multiple source, and that is 1 arcsecond in diameter.?ÿ

Every year January is update my spreadsheet month. With USNO still down Iƒ??ve had to revise my routine. Which is for the good. You learn stuff the hard way.?ÿ

MICA is the Multiyear Interactive Computer Almanac from the US Naval Observatory.?ÿ The USNO has mostly disabled their web site for over a year now with an overdue promise to update it.?ÿ I got the program from Willmann-Bell Publishing, but later saw they didn't have it in stock.

The solar diameter can be found in MICA using Calculate / Configurations / Major Solar System Bodies

?ÿ

I found a previous thread about USNO and MICA.?ÿ If you are interested in the program, note that it being a government-sponsored program I felt it okay to post it there for downloading (~125 megabytes).

https://surveyorconnect.com/community/gnss-geodesy/usno/

@bill93

Good to know. I screwed around and did it the hard way with AU. itƒ??s just not all in one place. But, I can get used to MICA. It has stars! JPL doesnƒ??t ?ÿ

thanx?ÿ

@bill93

i saw that. And Iƒ??m now mica adapted?ÿ

For extra fun MICAƒ??s GAST is a pain. I pulled that from ICE a while back. Funny ICE from way back in DOS 3.0 days has GAST to within 0.01ƒ? of current?ÿ

Iƒ??m good for now.?ÿ

You can find SD under calculate...physical ephemeris...sun...topocentric

@john-hamilton

its always a good way to start the year. The first test sun shot of ƒ??21 hit inverse for 2.3ƒ? at 12 miles.?ÿ

Q: how to convert geocentric ephemeris. I load topocentric, but Iƒ??d like to use geocentric.?ÿ

NASA website, wife says how the heck you know what they talking about??ÿ

All the while, freaking level 23 of Candy Crush is driving her batty.?ÿ

@samlucy3874

I just look at the pictures.?ÿ

John Nolton

Is there any place online wgere you can get the Ephemeris in the format that Jerry Wahl used to post in his web page and also in the format of the old BLM Ephemeris. There is a difference between the two, BLM's was based on apparent noon Grenwich and the other like the old K&E at midnight GMT?

John Nolton

Is there any place online where you can get the Ephemeris in the format that Jerry Wahl used to post in his web page and also in the format of the old BLM Ephemeris. There is a difference between the two, BLM's was based on apparent noon Grenwich and the other like the old K&E at midnight GMT?

@larry-scott?ÿ I stand corrected.

MICA sidereal time output is interesting.

mean sidereal time 09-Jan 0:00:00 UT:
07:14:60.9421

Apparent sidereal time is only given in seconds:
59.9523

Why? In spreadsheet itƒ??s not really an issue, but you have to be careful.?ÿ

@larry-scott?ÿ ?ÿthe Sun semi-diameter for 9 Jan 2021 is?ÿ16m 15.87 s and I get the same

values you post above but my print out only gives 3 places to the right of the decimal place.

Good enough for any geodetic work.

?ÿ

JOHN NOLTON

@charles-l-dowdell?ÿ ?ÿ ?ÿNot that I know of(?). When this covid-19 is over with we will do a Polaris shot

and then Sun the next day. For Polaris you will have to remember the FK6 number is 907 and the

HIP Star No. is 11767 and I will show you where to get the data.

JOHN NOLTON

@john-nolton

Iƒ??ve filled in all the parts and pieces for my 2021 spread sheet, and tested. Mica has everything, if you look around for it. I calculated the semi diameter, then compared that JPL and MICA. A worthwhile calc.?ÿ

The last post was just pointing out the way mica handles apparent and mean time. The mean time HMS seconds exceeds 60. And the apparent time, output in only seconds can just be substituted. Just something to lookout for. Especially if accidentally using mean time.?ÿ