Discussions: Stars missing in star databases.


Question of Lorenzo:

--And finally, a curiosity; I have noted it is reported by HNSKY Tycho has 1,055,115 stars, but other sources say Tycho has 1,058,332 and actually some stars seem to be missing in hnsky (see list later) similar annotations also apply to the Hipparcos (hnsky reports 117,955 vs. 118,218 official)   SAO (hnsky 257,529 vs. 258,977)   why? is there a particular reason for this? here are some missing stars present in skymap pro 6 (shareware), which uses tycho1 too:

TYC 4774-954-1 (mag.4.98) - HIP 26220 BM Orionis

TYC 4774-937-2 (mag.6.56) - HIP 26257

TYC 9538-74-1 (mag.13.64) - HIP 36649

TYC 773-609-2 (mag.7.30) - HIP 36843

regards, Lorenzo Lodi



Yes your observation confirmed.

Whouuw this took some time to answer ! I had to unpack and analyze the Tycho source file of 300 Mbytes. I lost my second harddisk a week ago but for searching (not so easy in 300 Mbytes) I used now the DOS /Windows command find.exe to search for "4774 " and redirect it to a file using .......FIND "4774 " tyc_main.dat >1.txt......... Anyhow I attached the results to this message. I checked the two first stars you mention and no magnitude is given in the orginal file. But they have ( 4774-953 and 4774-954) the same HIP number 26220 ???.

I you check in Tycho-2, TYC 4774-953 has a magnitude of 6.6 and TYC 4774-954 7.5

I you check in Tycho-1, TYC 4774-953 has a magnitude of 5.0

I you check in Hip, the corresponding HIP-26220 has a magnitude of 5.0

The TYC 4774-953 and 954 are both missing in GSC 1.1 and GSC_ACT, but show up in GSC 1.2 with both a magnitude of 11 !!!

They are not included in SAO and PPM. This becomes a great puzzle.

You can also see that position of TYC 4774-953 and Hip 26220 match !!! (visual, just change star files in HNSKY) So my possible conclusion is that Skymap-6 is using wrong magnitudes ! If I can trust the latest TYcho-2. In Tycho1, TYC 4774-954 has no defined magnitude. This is later fixed in Tycho-2.

There is also a X marker that it should not be used for astrometric purposes ??.

I you check in Tycho-2, TYC 4774-937-2 has a magnitude of 8.4 and TYC 4774-937 (-1) 6.4. So same story.

Back to SAO. Some stars where marked as double entries or non existent and so on. They are not included as marked in the original SAO file.

Tycho-2. Here I lost some stars maybe 100/200 ? during testing/conversions while the last entries of files where not written to disk or closed properly. I'm still thinking of re-doing the whole excersise, but first it will take about 1 week computer time and secondly several hours to upload. So for now I like to keep it as it is.

I should put this story in my webpage. This is a very interesting observation. Yes I will do.

P.s How did you find out. Good observation. Please send more of these.

Best regards, Han Kleijn


Han, later:

I just had a clear moment.

Now I understand. Those stars are in the middle of M42 !!. Possible trapezium stars.

Time to go to bed.


And then a story of Bill Anderson:                            Dated 2001-5-9

There will come a time when you get tired of being complimented for HNSKY if you are not already so. However, several things have happened in the last week that have pointed out to me VERY CLEARLY just how valuable HNSKY is to me. So, at the risk of making you mad at me, I felt the need to send this memo.

Part of the hassle I have had this last week is the new GSC-ACT that I got from Bill Gray of GUIDE. It is massive, as indeed is also the GSC 1.1. I have been working with it a lot and have found out that it really does not answer the basic questions that I have had all along. I have been using as a test object the Double-Double in Lyra (epsilon). I have found that only Tycho 1 shows all four component stars. Neither Tycho 2 nor the GSC 1.1 does. I mentioned this to Bill Gray and his response was the cause of some of my distress that I have been feeling. He said that his efforts to correct the GSC into GSC-ACT involved JUST the RA/DEC and NOTHING ELSE. This means that whatever problems there are with the GSC 1.1 are, for the most part, still in the GSC-ACT. The coordinates have been corrected, though the correction values are rather small. In fact, the correction values likely will not be visible on the screen of the standard computer unless the image is at very narrow field of view. Even then, the corrections likely will, for a person like me, not be of much concern as I need only an approximate representation of the field as a finder chart.

This brings up a thought I had last night that was to a very real degree quite a revelation to me. Most of the planetaria that are available today, be they commercial, shareware, freeware, or whatever, have built-in databases that are the base for the program to use. There may, and in many instances there are, possibilities for the user to add supplemental databases that augment the main data bases used by the program. However, often there are no ways to choose which data the program is to use. Even GUIDE has some magical mix of databases that are unknown to the users generally, so when the user has a field represented on the screen there is no real way to know which stars come from which databases. I can tell a little by the Epsilon LYRAE test, but that may not be conclusive.

A similar thing can be said about the data that represents objects. Many programs use the SAC data as well as the NGC/IC data from the government or elsewhere. Also there are a number of other databases too numerous to mention that are available that can show globulars, opens, galaxies, and so on and so on. However, the user is, for the most part, limited to the data that is recognized by the program as being valid. Perhaps the format of the data is dictated by the program and is in some style that the user has very little, if any, ability to change or expand upon.

I mentioned in a memo to you some time ago that one of the BIG ADVANTAGES of HNSKY is that the data can be ENTIRELY USER dictated. Yes, there are some databases supplied, but whether those choices are the ones the user makes or not is totally the decision of the user. I have made a number of my own databases for objects and stars that I use in place of the supplied databases. I am quite comfortable with this.

I have just in the last day realized just how important this quality is. The fact that the user has complete control of the data used by HNSKY makes it, in my humble opinion, the absolute winner in first place of all planetaria. The release of this data or that data from the government or observatory or university is not material. HNSKY is independant of the relative date or newness of the data. So, HNSKY is, in a very real sense, timeless and changeless. Certain features you have introduced in the several years the program has been out make the program nicer or more appealing to use, but the basic operation of the program is the same. It easily shows the data the user wants in a most appealing manner. If I should have some wierd desire to use some VERY OLD data of the 1800's, no problem. I can do that very easily.

The first place award I give to HNSKY is based partly on the databases, but also on the way the data appears on the screen. I have observed often that HNSKY has the nicest "looks" on the screen. I can almost kid myself into thinking that the view I see is like the view in the telescope. Many programs I have looked at (and it has been many) make the sky look totally artificial and cartoonish. The views presented by HNSKY are quite believable and aesthetic.

Another major plus to HNSKY is in the quality of the printouts. They are really quite nice. One small observation I can make, and I am not sure it is really to the degree of a suggestion is that it may be nice to have the option of not having any legend printed out. I don't need to have the date or time and such on the printout. However, this is a very minor point.

So, the main point of this memo is to say that I have finally placed HNSKY at the top of the list as far as planetaria are concerned. There might be things for which another program like GUIDE may be used, but for general, aesthetic, pleasing, quality use, HNSKY beats out everything else. You will notice that I have copied my scoping friends with this memo. I have been quite disturbed over the last several days with my revelations and have sent them some of my thoughts. It is only fitting that I send them these as well.

Well, I must get to work.

Clear skies to you.