S Dor
The S Dor type of variable star is a very luminous
star that will irregularly (sometimes cyclically) erupt in
brightness by one to seven magnitudes. They are usually
the most luminous stars in their galaxy (S Doradus is the
most luminous known star, about 500,000 times more so
than the Sun). They are usually young, blue-hot stars
surrounded by nebulae.
SAx.0
SA1.0
SA2.0
The SA1.0, or "Selected A1.0" CD-ROM, contains about one-tenth
of the stars listed in the A1.0 (about 50 million) and therefore
fits on one CD-ROM. SA2.0 does much the same thing for the newer
A2.0 catalog. In situations where their differences don't matter,
both catalogs are referred to as SAx.0.
Unlike the Ax.0 catalogs, SAx.0 is easy to get; and, like Ax.0,
it can be viewed in Guide through the Get Ax.0 Data option.
The only bad part is that the tenth of the stars selected are not
the brightest 10%. SA1.0 is therefore mostly useless for star charts
(and was never intended for that purpose anyway). It is a good
dataset for astrometry, because the 10% selected have high-quality
positions and guarantee an even density of stars over the entire sky.
SAC
The SAC (Saguaro Astronomy Club) database was compiled
from a variety of sources, including the RNGC, NGC 2000,
RC3, and many others. It incorporates corrections to most
of these catalogs, and is generally a more reliable source
than the RNGC and NGC 2000. Full documentation is in the
\SAC directory of this CD-ROM. A partial list of those
involved in the creation of this database includes:
Bill Anderson Alan Gore Paul Maxson
Steve Coe Steve Gottlieb John McGrath
Dean Corn Mike Janes Tom McGrath
Dr. Harold Corwin Jim Knott Brian Skiff
A. J. Crayon Alister Ling Steve Stanford
Bob Dahl Gene Lucas Dan Ward
Paul Dickson Jim Lucyk Jeffrey Weintraub
Jean Goddin Dr. Jack Marling Mike Willmoth
SAO
The SAO catalog is a list of 258,997 stars compiled by
the Smithsonian Astronomical Observatory. It has most
stars down to magnitude 8.5, plus a few dimmer stars.
You can find a star's SAO number by clicking on it with
the right mouse button. (Of course, it may not have
one.) You can go to any SAO star by using the Go to SAO
option in the Go to Star menu under the Go To menu.
Saturn
Saturn is best known for its bright system of rings.
They are not solid, but made up of orbiting chunks of
ice, either material that came from tides ripping a
satellite apart or from a satellite that never formed.
Inspection through a modest telescope shows some sub-
divisions in the rings. The major one, the Cassini gap,
separates the 'A' (outermost) ring from the 'B' (bright)
ring. Just inside the B ring is the somewhat dimmer 'C'
(crepe) ring. If you zoom in on Saturn in this program,
down to about level 13, you will see these rings. You
won't see the innermost 'D' (dusky) ring, which is very
faint. Saturn takes 29.5 years to orbit the Sun; during
that time, the angle at which we see the rings changes.
At times, the rings are edge on to us, and you can't
see them in a telescope.
Inspection by the probes Voyager 1 and 2 showed a lot
of finer structure. There are smaller subdivisions not
noticeable from the Earth, 'spokes' that show radial
brightenings and dimmings of the rings, and even some
'braided' rings. The dynamics of the rings are still not
fully understood, and probably won't be until we send
another probe out there to take a longer look.
Saturn has eight major moons; the biggest, Titan, is
the largest in the Solar System. Because it's big and is
so far from the Sun (therefore cold), it holds on to an
atmosphere denser than our own. Many have thought it a
possible place for life to form.
Saturn System I
Saturn System II
Saturn System III
Measuring longitude values on Saturn is made difficult
by the fact that the planet rotates more rapidly near the
equator than it does at the poles. So three systems are
used. Of the three, Guide currently reports only Saturn
System I.
Save a Mark
}
Let's say that you've set up a particular view that
you like and want to save your location in the sky and
everything about that view for later use. This is the
function you use to do that. When you click on this
option, you will be asked to provide a mark name. Enter
this and hit Enter, and the position and display
settings will be stored.
When you want to go back to this mark, you can use
the Go to Mark option.
This item can be reached at any time via the }
hotkey; or, you can reach it from within the File menu.
Schmidt
A Schmidt telescope (or "camera") is a specialized
telescope for taking images of large areas of the sky.
Most telescopes are not good for this purpose; their
images become too blurry at the edge of a large field.
Schmidt telescopes use a combination of a special lens of
complex shape and a spherical mirror to avoid this
problem.
Scope Pad
For many telescope systems, the Scope Pad menu option appears once
you configure the telescope in the Scope Control dialog. Select that
option, and a small floating dialog is shown.
The top of the dialog contains arrow buttons and a central "stop"
button, along with four radio buttons providing speed controls.
This design was taken from the LX-200 keypad; for that telescope,
all the buttons work. For most other systems (Sky Commander, Ultima
2000, etc.), the slew/speed/stop buttons do nothing.
screen fonts
printer fonts
In Windows, you can change the fonts used, both on screen
and in printouts, with the Screen Fonts and Printer Fonts
options. Select one of these, and Guide will show a dialog
box with the settings for the currently selected fonts.
Change them and select OK, and that font will be used on all
subsequent charts.
screen size text
zoom level
1-9
ALT-1...9
The third line of the legend shows your zoom level.
This can range from 1 (seeing the maximum amount of sky,
roughly an entire hemisphere) down to level 20 (seeing
an incredibly small part of the sky).
At Level 1, you see only those stars visible to an
unaided eye; at each successive level, you see dimmer
and dimmer stars up to about Level 10. At this point,
the dimmest stars you see are of about magnitude 14 or
15.
Also, this line shows how high the screen is at your
present level. You can change your zoom level by using
the Zoom In and Zoom Out options. You can also zoom
in and out by hitting the * and / keys, no matter in
which menu you are. You also can go to any particular
zoom level from 1 to 9 by hitting the key corresponding
to that digit. You can reach level 10 by hitting the 0
key, and levels 11 to 19 by hitting ALT-1 through ALT-9.
Finally, you can set your zoom level by hitting
). This key brings up a control panel of twenty
buttons, one for each level; hit a button, and you go
to that level.
Select Printer
The Select Printer menu lets you tell Guide what kind
of printer you have. The menu lists most popular
printers; if your printer isn't listed, it's a good bet
that it can at least emulate one that is on the list.
Which one, and how you get it into that emulation
mode, is probably described in your printer manual. You
can also select "no printer" (the default), or you can
"print", so to speak, to a .PCX file at any of three
resolutions.
If you select a printer capable of printing at more
than one resolution, Guide will then list the different
possible resolutions and allow you to choose one.
select printer output
In this menu, you select where you want printing
output to go. If you select PRN or an LPT port, Guide
will know to send data to that port and will ask no
further questions. If you select a COM (serial) port,
Guide will ask for the baud rate and parity. If you
select disk file output, Guide will ask for the name
of the disk file. You can copy the resulting file to
the printer using
copy (filename) prn /b
This option is useful in two cases. First, suppose
you want to make more than one copy of the printout. It
may be faster to make a disk file, then copy it twice
using the above command. Secondly, if the printer is on
a machine other than the one Guide is running on, you
can make the disk file, then copy it via floppy or other
means to the machine with a printer. (Several users who
run Guide at home but have access to better printers at
work do this.)
Select resolution
This menu lets you select the resolution of printouts.
Be aware that a higher resolution printout will look
better, at the cost of taking longer. It may take some
experimentation to decide what tradeoff is acceptable to
you, and you may decide to change this from printout to
printout.
selenographic
The term selenographic is the lunar equivalent of the
term geographic. Just as there is a geographic system of
latitude and longitude, there is a selenographic system
of these coordinates used for maps of the moon.
When you "click for more info" on the moon, Guide will
show the current selenographic position of the Sun. This can
be used, with a lunar atlas, to show what parts of the moon
are near the terminator, and therefore, are in good
positions to be observed. The position given is the point on
the moon where the sun would be directly overhead; any point
90 degrees away from that point would be on the terminator.
semidetached eclipsing binary
In a semidetached eclipsing binary, the two stars are
close enough that one is about at the point where tides
from its companion star are about to rip some matter from
it.
Semimajor axis
This line shows the semimajor axis, or mean distance
from the Sun, of the asteroid. Most asteroids will be
in the 2 to 5 AU range, putting them between Mars and
Jupiter. Some will be closer in (and possibly cross the
Earth's orbit); some are far from the Sun, like 5145
Pholus (20 AU, out around the distance of Uranus).
Semiregular long-period
Semiregular long-period stars are variable stars,
giant or supergiant, whose variations in brightness are
noticeably regular. Sometimes the regular changes are
accompanied by or interrupted by irregularities. The
periods run from 20 to more than 2000 days, and the
changes run from a few hundredths to several magnitudes.
This class can be subdivided into Z Aqr, RR CrB, Mu Cep,
and SX Her types.
separation
When you look at a double star in a telescope or with
an interferometer, you can measure how far apart the two
stars seem to be, that is, their angular separation,
measured in arcseconds.
By itself, this doesn't tell you how far apart the
stars really are. They could be close to Earth and
therefore very close to each other, or they could be very
far away and therefore not close to each other at all. If
you can, by some other technique, find out how far the
stars are from you, you can get the real, physical
distance between them.
SERC-J1
This plate in the GSC was taken using the U.K. SERC
Schmidt telescope, using a singlet corrector, IIIaJ
emulsion, and GG 395 filter.
SERC-J2
This plate in the GSC was taken using the U.K. SERC
Schmidt telescope, using a doublet corrector, IIIaJ
emulsion, and GG 395 filter.
SERC-V
This plate in the GSC was taken using the U.K. SERC
Schmidt telescope, using a doublet corrector, IIaD
emulsion, and GG 495 filter.
Set Location
Location dialog
The Location dialog, found under the Settings menu, provides a
way to specify your "observing viewpoint". The very first line asks
you to set your home planet. By default, Guide shows you the sky
as seen from Earth; but you can select other planets and satellites from
this list, allowing you to see, for example, the sky as seen from Mars.
The next three lines ask you to set your latitude, longitude, and
altitude. These do continue to have a meaning on other planets, by
the way. For example, if you set latitude=longitude=0 on the moon, your
viewpoint will be at the center of the side of the moon facing the earth;
from this position, the earth will always be at the zenith.
Next is a checkbox for "use geocentric position". Normally, your
viewpoint will always be from the surface of a planet; but you can use
this option to view from the center of a planet. (It was convenient to
call this option "geocentric"; of course, if your home planet is
the moon, then it is really "selenocentric", and so on.)
Finally, there are options to reset the humidity, pressure, and
temperature of your observing site. Right now, these are only used
when on the earth, in a topocentric (non-geocentric) location. They
are used to compute refraction and the visual magnitude limit given
in Quick Info.
Setting the animation rate
In Windows, the animation rate is shown on a button in
the Animation Dialog that is turned on in the Animation
menu. In DOS, the animation rate is shown in the menu
itself.
In either case, you can reset the animation rate by
clicking on it. When you do so, Guide will prompt you to
enter a new animation step size. You can enter both a number
and units; for example, "13 s" or "13 sec" will be read as
"thirteen seconds per step"; "41 m" or "41 min" as
"forty-one minutes per step"; "11 h" or "11 hr" as "eleven
hours per step"; and "3 d" or "3 days" as "three days per
step".
Settings menu
ALT-S
The Settings menu provides the following controls:
Set Location (lets you set your latitude, longitude,
altitude above sea level, home planet, and other parameters)
Colors menu (lets you set which colors are used to
draw most objects and markings) (DOS only)
Time dialog (lets you set Guide's time, time zone and
calendar)
Level size (lets you set the angular size used for the
current zoom level)
Scope control (lets you set up and communicate with an
LX-200 or Sky Commander telescope control system)
Language menu
Margins menu
RA/dec format (also lets you switch from English to metric units,
set format used for latitude/longitude, and more)
TLE=(filename)
Projection menu
Set Video mode (DOS only)
Toolbar dialog (used to determine which buttons are shown on the
toolbar)
Sharpless
Sh2-
The Sharpless catalog of nebulae lists several
hundred of the more important emission nebulae.
Shift-F1
In the DOS version, you can use the Shift-F1 hotkey to reset
the rotation of the chart. Hit this key, and you will be
prompted to enter the rotation, in degrees (by default, this is
zero).
In both versions, one can instead reset the rotation in the
Inversion dialog.
shift-f2
By default, when Guide sends a command to an LX-200
or Sky Commander telescope control system, it will wait
for 15 seconds for a reply. That's ample time for both
systems. Some people with home-built telescopes emulating
the LX-200 are using slower slew rates, and wanted a way
to change that waiting time.
When you hit the Shift-F2 hotkey, Guide will prompt
you to enter the new delay, in seconds.
SHIFT-F3
Add to Print Queue
SHIFT-F4
Flush Print Queue
The Add to Print Queue and Flush Print Queue options
are used for batch printing. Batch printing allows you to
set up a series ("queue") of charts to be printed, then
to print them all at once ("flush the queue").
To do this, you set up each of the charts you want
printed, with the chart settings exactly the way you want
it for that printout. You set up the chart as desired,
then hit "Add to Print Queue" to add it to the list to be
printed. Each time you do this, Guide will tell you
the number of printouts currently in the queue.
When you're done and are ready to print the queue,
hit "Flush Print Queue". Depending on what you're
printing, it may take several minutes for Guide to flush
all the printouts.
You can add to the print queue from anywhere in the
program with the SHIFT-F3 hotkey, and can flush the print
queue from anywhere with the SHIFT-F4 hotkey.
Shift-F5
This option leads to a menu showing all the overlays
Guide knows about. Those currently set "on" are marked.
You can toggle some overlays on or off, then return to
the previous menu.
You can reach this menu at any point with the @
hotkey.
Short-period Beta Cep
Short-period Beta Cep type variable stars are different
because they have periods of usually less than a week and
take almost equal amounts of time to climb in brightness
as to decline. Otherwise, they are simply normal Beta
Cep type objects.
Show Eclipse
This option, in the Extras menu, is slightly mislabeled. It also
finds occultations and transits. But "Show Eclipse/Occultation/Transit"
is a mouthful; the generic term "eclipse" will be used.
The option provides a way to show the path on the earth cast by
an eclipse or similar event. To use it, first set the date and time
close to that of the event in question (no great precision is required)
and select the objects involved in the event. For example, for a
solar eclipse, you would right-click on the Sun and then click "OK";
then you would right-click on the Moon and then click "OK". (The order
isn't important.) For a case where a star is occulted by an asteroid,
you would right-click on those two objects instead.
After you do this, the Show Eclipse option will no longer be
grayed out. Click on it, and Guide will first determine that an
eclipse exists (you'll get a "No eclipse found!" message otherwise).
Guide will then clear the screen and show a world map with the eclipse
path superimposed.
You can then drag open boxes and zoom in and out, much as if it
were a star chart instead of an "earth chart". When done, you can
click on "Show Eclipse" again, to return to the "normal" star charting
mode. The menus will be vastly different in eclipse mode; many things
appropriate to star charts (constellation boundaries, for example)
make little sense on earth charts.
Shut off images
The Shut off Images option provides a way to temporarily turn off
the display of DSS images.
side labels
Side labels are labels on the edge of the screen showing
intervals of right ascension and declination. Common on
most star charts, this program lets you turn the display of
side labels on or off and to adjust their spacing within the
measurements dialog; or by right-clicking on a side label
and then clicking "Display".
The Margins menu has four check-boxes so you can decide which
edges will get side labels when printing.
sidereal
mean solar day
An object's sidereal rotation period refers to its rotation
relative to the stars. For example: the moon's sidereal orbital
period is about 27.3 days. This means that, if you were standing
on the moon, you would see the stars rotate around you once every
27.3 days.
Because the moon would, during those 27.3 days, move a bit
around the Sun, you would see the Sun rotate around you about
once every 29.5 days. This would be the mean solar day for
the Moon.
For similar reasons, those of us on the Earth see stars
rotate around us once every 23 hours, 56 minutes, 4 seconds
(the "sidereal day"), but see the Sun rotate around us once
every 24 hours (the "mean solar day" for the Earth).
Sidereal Time
Local Sidereal Time
Greenwich Sidereal Time
LST
GST
Sidereal time, or "star time", is a time system used to
express what portions of the sky are on the meridian. For
example, if the Local Sidereal Time (LST) is 13:32:50,
then objects on the meridian will have a right ascension of
13h32m50s. Thus, just as the "normal" time system used in
everyday life closely matches the apparent motion of the sun,
sidereal time matches the apparent motion of the stars.
The two systems have almost, but not quite, the same
rate of advance. The difference comes about because the
sun appears to circle the earth once a day; the stars do
so once every 23 hours, 56 minutes, 4.09 seconds, which
is 3 minutes, 55.91 seconds less than a day. The result
is that a sidereal clock put next to a solar clock would
appear to run a little too fast.
Just as there are different time zones used to describe
where the sun appears from different parts of the world,
one uses Greenwich Sidereal Time (GST) to describe what
stars are visible from Greenwich, and Local Sidereal Time
to describe what stars are visible from where you are.