Re: [guide-user] My asteroids disappeared

Bob Elliott Feb 14, 2004

At 21:10 2004-02-14 +0100, Jean Francois wrote:
>
>Hello the list,
>
>I thank you all for your answers, that bring me new questions
>
>First, I managed to access my asteroid database which was copied on the
>hard drive and I added the file soft02bright.txt in the guide directory.
>I noticed that the magnitude is not displayed for the asteroid that I
>copied on my hard drive ( from the guide CD)
>but I could see the magnitude of the asteroids that come from the
>soft02bright.txt file (asteroid that are in opposition in 2004).
>
>Secondly, I wondered if it is possible to see graphically the asteroids
>that come from the file inserted with ' Extra, Add asteroid from MPC '
>and those that are in the asteroid directory or in the MPCorb.dat.
>
>It would be useful for example if we want to gaze only the asteroids
>that are in opposition ( = soft02bright.txt )
>
>Finally, is it possible to remove the data which come from the file
>inserted in ' Extra, Add asteroid from MPC '.
>It seems to me that the only way to remove them is to enter the
>comets.dat file and delete them.


Hello Jean Francois.

I don't have an answer to your question about the Magnitude of Ceres being
0.0, but here is some information about selecting a particular group of
asteroids to be displayed in Guide. You might also want to look at the
following URLs.

http://www.projectpluto.com/update7.htm and
http://www.projectpluto.com/hist_idx.htm

which give lots of information about additions to Guide that you can use.

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(30 Jan 2000) Filtering of asteroids: Previously, Guide allowed you to
filter asteroids solely on the basis of magnitude.
You could tell it to drop asteroids fainter than, say, magnitude 15.4, but
that was the limit of your ability to select which ones
appeared.

For most people, this limitation is not particularly troublesome. But it
can be pleasant at times to filter asteroids on the basis
of orbital parameters, and this is now possible. For example: suppose you
wanted Guide to display only Jupiter Trojan
asteroids. These are distinguished by having a semimajor axis (a) that is
between 5.05 and 5.4 AU. To tell Guide to display
only these asteroids, you would edit GUIDE.DAT and add this line:

ASTFILTER=5.05 < a & a<5.4

(This is worth giving a try, by the way... do it and turn asteroids 'On',
and you can see two distinct clouds of Trojan-belt
asteroids, 60 degrees ahead of and behind of Jupiter.)

Alternatively, if you dislike text editors, you can hit Alt-J and get a
little dialog box asking you to "Enter a test flag:" You can
then enter the text ASTFILTER=5.05 < a & a<5.4, and click OK.

You can also filter on the basis of limits in q (perihelion distance), Q
(aphelion distance), e (eccentricity), i (inclination), P
(orbital period), and d (distance from the earth). By combining these, you
can define most of the major asteroid groups and
families. For example, to define the Nysas, you would use:

ASTFILTER=2.41<a & (a < 2.5) & (e > .12 & e < .21) & (1.5 < i & i < 4.3)

(As the above indicates, you can use parentheses and spaces as you wish.)
You can also filter on the basis of x (right
ascension, in degrees) and y (declination, again in degrees.) The only real
situation I can think of where you would want to do
this is as follows. Let's say that you can't really image any asteroids
below dec -20 (too close to your southern horizon). Let's
say that the opposition point is currently at about RA=1h (15 degrees), and
you want to know which asteroids are within 25
degrees of opposition. You could set up the following:

ASTFILTER=(y>-20) & (x>350 | x<40)

(The '|' means 'or'. I realize it's not as obvious as the '&' meaning
'and', though C programmers will find it a familiar usage.)
Do this, fire up Guide, and you can go into 'Tables... List Asteroids', and
get a list of asteroids in that area down to your
desired limiting magnitude.

Also, if you want to filter out Guide's built-in asteroids, using only
those added with the 'Edit Comet/Asteroid Data' and 'Add
MPC Comets/Asteroids', you would use this:

ASTFILTER=b

I don't actually envision many people making use of these filters, but they
can be educational and (in rare cases) actually
useful.
----------------------------------------------------------------------------
------

Be very careful about deleting data from the "Add comets and asteroid" files.

The number of objects in that file must match the number at the top of the
file.


Regards.

Bob Elliott