Last updated: 27 January 2005
Subject: Additional data for the sun-as-asteroid page Sent: Tuesday, January 25, 2005 20:59:21 From: Richard Seymour (firstname.lastname@example.org) Many people ask for a "TLE file" which can be dragged-and-dropped into the Autostar Updater to add the Sun-as-Asteroid as described below. Here it is. The line (for those who wish to edit their own files) is: Sun|2005 01 1.500|0.01671|1.0|-0.0001|168.7394|114.2078|2000|357.5172|-12.0|1.00|1.0 Or, if you'd like it as a "file", it's also "attached" have fun --dick
This tip updates the earlier ones from 2001 that follow it. --Mike
Subject: Sun as Asteroid... Improved! Sent: Saturday, September 11, 2004 18:18:49 From: Richard Seymour (email@example.com) A few years ago a student who worked with me came up with a simple set of orbital elements to allow Autostars to GoTo the Sun. Unfortunately they were -too- simple, and had quite a bit of periodic error. So i posted a note on the Astroprogramming Yahoo group ( http://groups.yahoo.com/group/astroprg/ ) requesting better Keplerian elements for the Sun. Juan Lacruz responded with a set of numbers derived from a JPL site ( http://ssd.jpl.nasa.gov/ ), specifically the Earth's elements: ( http://ssd.jpl.nasa.gov/elem_planets.html ), adjusted to create an asteroid on "the other side of the sun". Converting from JPL's notation to the terms requested by the Autostar, and rounded to match its input fields, we get the following "Asteroid" elements: Name: Sun epoch: 1.5 jan 2000 eccentricity: 0.016710 semi major axis: 1 inclination: -0.0001 long asc node: 168.7394 arg of peri: 114.2078 mean anomaly: 357.5172 abs mag: -12 mag slope: 0 At the moment, they're yielding a 2 arcminute prediction error when compared to StarryNightPro. have fun --dick
Subject: if the moon's a balloon, does that make the Sun an Asteroid? From: firstname.lastname@example.org (Dick Seymour) A couple of months ago Mike's site was full of questions about "how to point an ETX at the Sun?", primarily driven by the November transit of Mercury. Meade, as a safety measure, doesn't provide the Sun as an object in their database. But they -do- provide the ability to add Satellites, Comets and Asteroids... so I wondered, what could we call the Sun given those categories? Not a Satellite... the Autostar just thinks those circle the earth. Not a comet... too weird parameters (he says without looking). But an Asteroid... they're Sun-related... maybe one with a zero orbital radius? So I tried that: Name: Sun, zero for a semi-major axis, zero for everything else, 21-Mar-1999 for Epoch (see below). Then tell the Autostar it's 3pm, and Select/Enter/GoTo... ...the word "Calculating..." appears.... and stays, and stays.. and stays... "Mode" fails to gain its attention. Finally the "Power" switch breaks the spell... (for those of you over 45, this brings to mind the old Freiden electro-mechanical calculators... set them to divide-by-zero and you were in for an infinite spell of noisily spinning gears and digits...) So a zero-orbital-radius asteroid won't work. So I started asking friends of an astronomical (and calculational) bent: what -would- serve as orbital parameters for the Sun (as an asteroid)(and zero won't work)? The responses were unanimous: "I'll get back to you on that..." And then one of them did: a young physics student tried to model it with an old version of Voyager on her Macintosh. When she gave it "zero" for a radius, it wouldn't allow it. So she thought a little more, asking "What else could the telescope be looking at to see the Sun?" And the answer was elegantly simple: an asteroid... in the Earth's orbit, but on the other side of the sun. Any attempt to see it would have an "inconvenient" sun in the way. Bingo! True out-of-the-box thinking. She ran the Voyager simulation ahead a dozen years or so, viewed from both above the sun and from the earth's surface. The "asteroid" dutifully remained hidden behind the sun. She reported the numbers to me, and I tried them in the Autostar... they seem to work. They are: Name: Sun, Epoch: 21-Mar-1999 (see below), Semi-major axis: 1.0 (that's one Astronomical Unit, the earth's orbital radius). We cheated and called the eccentricity zero, decreeing the asteroid to having a circular orbit. The earth's eccentricity is 0.016, but for the purposes, zero is probably accurate enough... When you're entering a satellite, comet or asteroid, part of what you're telling the Autostar is: "on -this- date we saw it -there-, and the rest of the numbers tell you how to forecast where it'll be with -that- as a starting point". That date is the "Epoch". By choosing the Vernal Equinox (the date the "body" crosses the celestial equator headed north) (21-Mar-1999 in Greenwich) as the Epoch , the rest of the orbital angular parameters all fall to zero... because (by definition) spring starts when the Sun crosses the celestial equator as it moves along the ecliptic. *And* that point is where 0 degrees (or Hours) of Right Ascension is located. Likewise the Mean Anomaly is zero, since that's the measure from that crossing point to where the object is at the time of the Epoch. For a "magnitude" (brightness) I just said "12" and gave it a slope of zero. And that seems to work... if I set the Autostar's idea of "time" to a few minutes on either side of sunrise and sunset, it either reports "below horizon" or GoTo's the appropriate zone of the sky. Unfortunately for my testing, I live in Seattle, and the Sun isn't forecast for visibility anywhere in the next ten days. So I haven't been able to verify its pointing accuracy. Now some notes: DO NOT TRY THIS ... unless you have **real astronomical grade** Solar Filters for your telescope. You -will- damage things, including your eyes. (Want to see -my- 35-year old retinal scars?) Don't even let the scope point that way with the cover on... unless you've *also* covered the viewfinder. My testing and analysis of how the Autostar "thinks" reveal that it only calculates the "asteroid's" position when you first Select it. After that it assumes it's motionless against the background of stars. It's not. The Sun moves about a degree a day (ok, ok: 0.98561 (thanks, Tami!)) as it makes its yearly journey around the ecliptic/zodiac. That means about a half-degree between sunrise and sunset. You can check the Autostar's idea on this: set the time to a bit after sunrise (use Event to get the time), tell the Autostar to locate the Asteroid/Sun. Write down the R.A. and Dec result. Then reset the Autostar's clock to just before sunset and, again, Select the Asteroid/Sun. Note the different numbers. That's how far the Autostar calculates that the sun will have moved during that day cycle. So (very) long-period solar photography won't currently work using the Autostar. However, that day-long half-degree shift is only a half of the 26mm eyepiece's field of view, so visual work should have no problems. Other fun notes: The Autostar won't GoTo something "below the horizon" (i.e. Altitude less than zero)... but it will happily -track- something -to- below the horizon... it doesn't -stop- tracking when the Altitude drops below zero... so don't leave your telescope unattended with low western objects. When playing with different numbers for the orbital parameters, I was surprised that the Autostar didn't allow 1.0 as an eccentricity ("Invalid Number"), but that it did allow the obviously problematical 0.0 as an orbital radius. I repeat: DO NOT TRY SUN POINTING ... unless you have **real astronomical grade** Solar Filters for your telescope. You -will- damage things, including your eyes. You'll damage the inside of the telescope too. Don't even let the scope point that way with the main cover or filter on... unless you've *also* covered the front (sky) end of the viewfinder. Clear (night) skies... --dickMike here: I remember the Freiden machines. We used them when I was an undergrad working in the Astronomy Department's Minor Planet Center.
Quicky follow-up... due to a local weather amusement called the Puget Sound Convergence Zone, the Sun just shown on my smidge of Seattle long enough to test the 'scope's new Asteroid. Result: (working from alignment marks magic-markered on masking tape to allow instant "home" alignment for "setup") it worked! The scope's shadow became a circle, and the sun ended up well within the viewfinder. (I -don't- yet have a proper solar filter for the main lens, so that remained closed...but I do have eclipse filters suitable for the viewfinder) The Autostar's beeping of the completed tracking was quickly followed by the sound of my arm breaking as it patted my back...
Subject: RE: Tracking the sun Sent: Sunday, February 11, 2001 09:12:28 From: email@example.com (Mike Hadey) Hi Mike, I just read the following on your Site this morning: > Subject: Tracking the sun > Sent: Thursday, February 8, 2001 22:43:14 > From: firstname.lastname@example.org (Frederic Hawley Jr.) > I have 2.1ek loaded on my Autostar and I'm trying to add the SUN into > the user objects. I've tried to follow the instructions listed on the > Autostar Info page ("Adding the Sun"), but I think things in the > Autostar may have changed since these instructions were written. ........ > > Mike here: Yes, that old trick won't work with 2.1ek. > However, you can still track the Sun by just having the RA > tracking start (see the "Quick "Align" with the Autostar on > the Autostar Information page) and then manually slewing to > the Sun's position (using the shadow technique). Using the A2.4 uploader with 2.1Ek FW, I just now added the Sun per Dick's instructions on Autostar Info page. I think that there was (is) a problem when Using the A2.3 SW version to upload 2.1Ek FW that went away when I uploaded 2.1Ek with A2.4. This also seems to have solved the "Lunar Eclipse" bug I mentioned earlier. Initially I just added "Sun as Asteroid" instructions manually in the Autostar and it seemed to work. I thought I would try to add the Sun Asteroid as TLE data. I made up two .txt files (see attached) in the appropriate format. One for 1999 Epoch and one for 2001 Epoch. By using TLE format you can enter fractional information for the time of the Vernal Equinox crossing. I haven't a clue whether or not the Autostar uses the fractional data. To get the TLE data in the Autostar, I fired up the A2.4 uploader and quickly got the main screen. By making the Windows Explorer Folder that contain the .txt files visible at the same time as the uploader main screen, you can just drag and drop the two files on to the Asteroid button. This effectively adds the TLE data to the LibAseroid.ROM file in the Ephemerides folder and marks them as <selected for Hndbox>. Next you need to click on each of the Asteroid, Comet, Satellite, Tours, etc. buttons, one at a time, and select <Send all to Autostar> (or whatever selection you want). Otherwise when you click on the "Send To" button the only thing that goes up is the two Sun Asteroids. Although the Sun is not really out over here today (as usual) I set up in front of the patio sliders where I could see the bright spot in the clouds with roughly the correct polar alignment. Turned the scope on, did and Easy align (just hit enter when it got through slewing to the two chosen stars). Selected 1st "Sun Asteroid" (1999 Epoch) hit [Enter]../..\.Autostar displayed RA and date, hit [GO To]... and sure 'nuff the scope pointed pretty close to the bright spot in the clouds. I then selected the 2nd (2001 Epoch), repeated above, and when I hit [GO TO] it slewed a small amount and carried merrily on tracking. I compared the RA and Dec values against a Freeware Astro program I have (Adastra) and here are the results: RA Dec Adastra 21hr 42.5m -13deg 51' 0 Sun (1999 Ep.) 21hr 42.0m -13deg 47' Sun (2001 Ep.) 21hr 43.0m -13deg 42' Should be good enough to get you real close. I'll find out for sure if the Sun comes out in the near future. I can't remember if it was Rick or Dick (Rick I think) that was having trouble with "Sun as Asteroid". Have any of you guys tried this after uploading 2.1Ek with A2.4? I don't remember reading anything about success if you have. I have worked this new A2.4/2.1Ek combo pretty hard for a while now and I am pretty happy. I know Clay has been waiting for the rest of the results to come in (sorry to hear about your cat accident, Clay). Other than the scope pointing 180 deg. away from where it should have (twice, could have been operator error, but I'm not sure), the pointing accuracy in Polar mode seem much better than with A2.3. In Polar mode there seems to be no "snap back" (but maybe a slow "creep after beep"). By not downloading the astronomical data as soon as it starts A2.4 made a big difference for me in the "user hos tility" rating. Other than the fact that you can't download the Tour data from the handbox and the TJ tour doesn't work at all (even with no error message on uploading) I can definitely live with this combo (so far). Now that I've reduced the Read Wait value in the registry I can easily make data changes quickly ("although not as quickly as I originally thought" he says choking down the stale crow and wiping the egg off his face). Cheers, Mike H.Click to download sun-tracking.zip (337 bytes).
From: email@example.com I did a cut and paste of the data above into a file called Sun.ast on which I did a drag and drop into AU A2.4. There were no problems with AU and no problems with 2.1Ek. I also have Dick's original hack, using an eccentricity of 0, in my handbox. Not too surprisingly, there's a slight difference of opinion between it and your two data sets. However, put to the test this afternoon, comparing Sun (RS) and 2001 Sun, the difference was perhaps 20% of the FOV of my 8x25 finder. Comparing 1999 Sun against 2001 Sun, the difference wasn't worth worrying about. I'm sure there was a slight difference but it simply didn't matter. Please bear in mind that my scope alignment was very much a seat of the pants guess which may have contributed to the small error seen. FWIW, after tracking the Sun for a while, I turned to Venus. The error seen in going from the Sun to Venus was on the order of the same distance as Dick's initial "Sun as asteriod" versus your work. BTW, I was working in equitorial mode. Cheers, Rick
Subject: Adding the Sun as an Asteroid Sent: Tuesday, February 13, 2001 06:19:40 From: firstname.lastname@example.org (Autostar Software Review Project) Clip the enclosed to a text file, call it something clever like "Sun.ast", drag and drop it on the AU's Asteroid button, and upload the ephemeris. You can compare the results of using the two different epochs. 1999 Sun |1999 03 21.072|0.016|1.0| 0.0|0.0 |0.0 | 1999| 0.0 | 12.0 | 0.0| 0.00 2001 Sun |2001 03 20.056|0.016|1.0| 0.0|0.0 |0.0 | 2001| 0.0 | 12.0 | 0.0| 0.00 Cheers, RickAnd:
From: email@example.com (richard seymour) Rick sent the numbers, so i'll just send the commentary. What they are are the parameters for an object orbiting in the Earth's orbit, 180 degrees away from us. They were originally developed by a physics student who works at my lab... i was asking everybody there "what would be the orbital parameters of the sun, if it were viewed as a satellite of the earth?". Blank stares.... but she took it home and thunk about it, and came up with the out-of-the-box answer... which she then tested on her Mac with the program Voyager. Then, since an asteroid's parameters are: Epoch Date: WHEN and RA of Ascending Node: WHERE the object crosses the celestial equator into the northern hemisphere, the date is Vernal Equinox, and everything else becomes Zero. (by definition of RA). Eccentricity and radius matches us. I still wonder about inclination. Something i haven't checked is: from the Keypad, you can only enter Epoch day-number, not fractional. I don't know if shuffling it in with the Updater improves upon that by truly getting the fractional component into the Autostar. (it won't show on a keypad editing session) And that's the story behind the story... --dick
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