Sigma Leonids 
Lyrids 
Mu Virginids 
Alpha Bootids 
Phi Bootids 
Alpha Scorpiids 
Eta Aquarids 
Kappa Serpentids 
Delta Draconids 
Virginids 
April Fireballs 
Showers in April and May 
  Apr.  4 Kappa Serpentids: Radiant--near Corona Borealis. 4 or 5
per hour from Apr. 1 to 7.
  Apr. 7 Delta Draconids: Radiant--near Cepheus border. From Mar. 28
to Apr. 7.  Slow meteors at about 5 per hour.
  Apr. 10 Virginids: Radiant-- near Gamma in bowl of Virgo. 20 per
hour.
  Apr. 15 April Fireballs: Radiant-- between The Water Jar and
Scutum, very erratic. From April 15 to 30 many bright bolides from
Southeastern sky.
  Apr. 17 Sigma Leonids: Radiant-- at Leo-Virgo border, actually
has moved into Virgo in recent years. Weak shower of 1 to 2 per hour.
  Apr. 22 Lyrids: Radiant-- near Vega. 15 per hour, bright and
long lasting meteors. From Comet Thatcher.
  April 25 Mu Virginids: Radiant--near Libra. 7 to 10 per hour
of medium speed meteors.
  Apr. 28 Alpha Bootids: Radiant-- near Arcturus. From Apr. 14
to May 13. Slow meteors with fine trails.
  May 1 Phi Bootids:  Radiant--near Hercules. From Apr. 16 to
May 12. 6 per hour.
  May 3 Alpha Scorpiids: Radiant-- Near Antares. From Apr. 16
to May 9.
  May 4 Eta Aquarids: Radiant-- near  Water Jar. From Apr. 21
to May 12. 21 per hour, yellow with bright trails. Comet Halley
debris.

Size on red POSS 
Size on blue POSS 
   The POSS,  or Palomar Observatory Sky Survey,  shows
objects on red and blue sensitive photographic plates.
Some galaxies may be measured on both plates.  The
difference between plates can tell you something about
the distribution of red (usually older) stars versus the
distribution of blue (mostly younger) stars.

slope parameter 
   The slope parameter of an asteroid is a number describing
how the magnitude of the asteroid varies as a function of
changing illumination,  or phase angle.  Most asteroids are
brightest when the sun illuminates them fully (near opposition),
and their brightness drops off when partly illuminated.  The
extent of that dropoff is specified by the slope parameter.
The slope parameter can then be used in reverse to predict
the asteroid magnitude for any given illumination.  It is usually
given the symbol 'G'.
   For almost all asteroids,  the slope parameter is about .15.
In fact,  if the asteroid has not been closely studied,  it's
common to simply assume a slope parameter of .15.

Slow irregular 
   The slow irregular type of variable star either shows
no signs of being periodic,  or isn't consistently so.
Stars are often considered this simply because they have
not been studied long enough to determine their real
nature.  As a rule,  these are giant stars.

Solar central meridian 
   Solar observers often need to refer observations to the
solar central meridian,  which,  together with the tilt
of the pole,  indicates the part of the Sun currently
turned toward us.  In reality,  different parts of the
Sun rotate at different rates,  much as on Jupiter and
Saturn.  By convention,  the Sun is assumed to rotate
once every 25.38 days;  because we are orbiting the sun,
it appears to rotate only once every 27.2752 days.

solar constant 
planetary solar const 
planetary solar constant 
   The solar constant is a measure of the amount of radiated energy,
at all wavelengths,  emitted by the Sun.  At our distance from the
Sun (one astronomical unit),  it is 1367.6 watts per square meter.
   Each planet has its own planetary solar constant,  ranging from
Mercury (9936.9 watts per square meter) to Pluto (.87 watts per square
meter).  This is given in "more info" for that planet.

Solar rotation number 
   Solar observers often make use of the solar rotation
number in describing their data.  This system starts with
rotation #1 on 9 Nov 1854,  and a new rotation begins when
the solar central meridian is equal to zero (that is,  the
sun has made one apparent rotation).  That takes about
27.275 days,  on average.
   This is useful in describing the behavior of solar
features.  One can say,  for example,  that "the sunspot I
saw on rotation number 1923 moved north by rotation 1924,
and had faded out by 1925."
   When you click for "more info" on the Sun,  Guide will
report the current rotation number and the date on which
it began.

solstice 
summer solstice 
winter solstice 
   The solstices (meaning "the sun stands still") mark the
points where the sun appears at its maximum and minimum
declination.  The summer solstice marks its greatest
declination,  and usually occurs within a day or two of
June 21.  It marks the beginning of summer in the Northern
Hemisphere.  The winter solstice marks the sun's lowest
declination,  and usually occurs within a day or two of
December 21.
   The times of the solstices are given in the "click for
more info" section for the sun,  as are times for the
vernal equinox and autumnal equinox.

spectral type 
   A star's spectrum is usually first classified by
spectral type.  The spectral type consists of one of
the letters O, B, A, F, G, K, M, R, N, S,  followed by
a digit.  (Generations of astronomy students have been
able to remember the letters through "Oh Be A Fine Girl,
Kiss Me Right Now, Sweetheart".)  The numbers provide
gradations between letters;  an F9 star,  for example,
is only slightly hotter than a G0 star.
   The type gives an idea of the star's color and
temperature.   Type O stars are young,  blue,  extremely
hot stars,  with surface temperatures of about 40,000
degrees Kelvin (about 70,000 F.)  As you progress through
the letters,  one reaches successively cooler stars and
the color changes to white (for A stars),  yellow (G
stars),  orange (K stars),  and red (M stars).  M stars
have surfaces as "cold" as 3000 degrees Kelvin (5000 F.)
(Notice that these are all surface temperatures.  The
cores of stars usually run more in tens of millions of
degrees.)
   R, N, and S stars are somewhat off the scale.  These
are extremely old stars.  Your average star,  such as the
Sun (which is type G2),  produces energy by fusing
hydrogen nuclei into helium.  R, N, and S stars are so old
that they have mostly run out of hydrogen to fuse.  They
produce energy by fusing helium nuclei into carbon nuclei,
which is why they are also called carbon stars.

Spectroscopic Binaries 
   Some binary stars are so close together that even the
largest telescopes see them as one point of light.
However,  if you examine their spectrum,  you may find
that each line is doubled.  This is caused by the Doppler
shift.  One star is approaching us,  and its lines are a
little bluer than usual;  the other is receding,  and its
lines are redder.  The difference tells you their relative
speeds.  As they orbit one another,  the lines switch
places,  telling you their period,  their relative masses,
and other useful information.  Such stars are called
spectroscopic binaries.

spectrum 
spectra 
   You have probably seen at some point a picture of white
light passing through a triangular prism,  and coming out
split into colors running from red to blue.  This is the
visible part of the spectrum.  A similar color-splitting
phenomenon produces rainbows.
   If you take such a prism and put it behind a telescope,
you can split the light from a star into its component
colors.  The result isn't equally bright in all colors.
Some colors will appear with greater or lesser intensity.
These colors correspond to different elements being heated
up on the star's surface and atmosphere,  so the presence
and absence and intensity of certain colors (or "lines",
so-called because they show up as lines in the spectrum)
tells you what elements are in that star and in what
quantities they occur.  You can also find out how fast the
star is approaching or receding relative to the Earth,
or determine if it is a close binary star,  or (roughly)
how fast it spins on its axis,  or how hot it is.
   Astronomers first classify a star's spectrum by
spectral type;  for stars from the SAO catalog,  this is
all the information on their spectrum that this program
has.  For Bright Star Catalog stars,  the type is usually
followed by the star's luminosity class,  and sometimes
a list of chemical elements apparent in the spectrum plus
added information.

speed of apparent motion 
   In observing asteroids,  it's sometimes helpful to have
some idea as to how rapidly they appear to be moving
across the sky.  This is especially true with those passing
near the Earth,  which can move at apparent speeds of up
to several degrees per hour.
   When you click for "more info" about an asteroid,  Guide
will calculate the apparent angular speed and the position
angle of the motion (the direction in which the asteroid
is headed).  This is shown as the speed of apparent motion.

Spin Left 
   Click on this menu option to rotate the CCD frame
five degrees to the left.  You can also explicitly set
the tilt angle of the camera with the "Angle=" menu
option.

Spin Right 
   Click on this menu option to rotate the CCD frame
five degrees to the right.  You can also explicitly set
the tilt angle of the camera with the "Angle=" menu option.

SS Cyg 
   SS Cyg stars are a subclass of U Gem stars.  These
variable stars increase in brightness by 2 to 6 magnitudes
over one or two days,  then go back to normal over a few
days.  They repeat this semi-periodically.  The period
between outbursts for a given star can range from ten to
a few thousand days.

Starting/stopping animation 
Ctrl-A 
   In Windows,  animation is mostly controlled with five buttons
on a toolbar in the Animation Dialog option in the Animation
menu.  (In DOS,  the same five buttons appear directly inside
the Animation Menu.) The buttons look like this:


   The "double left arrow" causes animation to run backwards,
into the past.  The "double right arrow" makes it run into
the future.  The single arrows animate by one step each time
they are clicked.  The square in the center stops animation
completely.
   In Windows,  there are four additional radio buttons used to
select slightly different ways in which animation can work.  The
default is the "RA/dec" button.  In this mode,  stars are fixed, and
your viewpoint remains centered at the same RA/dec position as time
changes.  (This is the only mode available in DOS.)
   The second button,  "Moving",  can only be selected after you
have clicked on a moving object (asteroid,  comet,  planet,  natural
or artificial satellite).  When this button is selected,  your viewpoint
will be kept centered on the moving object.  As the object moves,
stars will drift by in the background.
   The third button,  "Horizon",  keeps your viewpoint centered on
the same alt/az position as time changes.  If you are looking to the
southeast and start animation in this mode,  you will remain looking
to the southeast while stars appear to rise on the screen.  If you've
turned the horizon on,  the horizon will stay fixed.
   The fourth button,  "Proper Motion",  resembles the first "RA/dec"
in that you will stay centered on the same RA/dec position as time
changes.  But the stars will be moved according to proper motion.
Because this is a very slow movement indeed,  you generally need an
enormous step size (say,  10 years/step) to see it at all.

@m 50,80    dbl left
@l 57,70
@l 57,90
@l 50,80
@m 57,80    dbl left
@l 64,70
@l 64,90
@l 57,80
@m 75,80    sing left
@l 82,70
@l 82,90
@l 75,80
@m 95,72    box
@l 105,72
@l 105,88
@l 95,88
@l 95,72
@m 125,80   sing rt
@l 118,70
@l 118,90
@l 125,80
@m 143,80   dbl rt
@l 136,70
@l 136,90
@l 143,80
@m 150,80   dbl rt
@l 143,70
@l 143,90
@l 150,80

Str 
Reference: O. Struve and W.C. Straka: 1962, Publ. Astron. Soc. Pac.
74.474. Notes on diffuse galactic nebulae.

SU UMa 
   SU UMa stars are a subclass of U Gem stars.  They are
different because along with normal U Gem type outbursts,
they have occasional "super-outbursts".  A super-outburst
is about two magnitudes brighter than a normal one and
lasts more than five times as long,  but occurs about
three times less frequently.  These stars complete an
orbit in less than 2 or 3 hours.

Sun 
   The Sun is far and away the closest star to us.  The
second closest,  Proxima Centauri,  is about 250,000 times
farther away.
   The Sun is an enormous ball of (mostly) hydrogen and
helium.  It has a diameter 109 times that of the Earth,
and is 333,000 times more massive.
   The Sun and other stars produce their energy by nuclear
fusion.  Deep in the Sun's core,  the temperature and
density are sufficient to push hydrogen nuclei together to
form helium nuclei.  Each second,  the Sun converts
1,500,000 million pounds of hydrogen into 1,490,000 pounds
of helium.  The difference is accounted for by changing
mass into energy, according to the well-known E=mc
squared.  This is an immense amount of power.  The Sun
produces enough energy to boil every drop of water in the
ocean,  every second.  It has done this every second for
five billion years,  and is expected to do so for another
five billion.
   Examination of the Sun with telescopes reveals the
occasional appearance of sunspots,  areas that are a
little cooler than their surroundings.  Their appearance
follows a fairly irregular 11 year cycle,  although some
cycles have been much shorter or longer and sometimes no
pattern at all has been apparent.  Sunspots are linked
with emissions of radio energy and of charged particles,
causing the aurora to be seen on Earth.

supernova 
   Supernovae are extremely rare events.  One occurs in
our galaxy,  it is estimated,  about once every three
centuries or so.  When it does happen,  one star can
suddenly produce,  at its peak,  more power than the
entire galaxy is producing.
   We have not been so fortunate as to see a supernova
in this galaxy since the early 1600s,  just before the
invention of the telescope.  However,  several supernovae
have been seen in other galaxies,  including one in the
Large Magellanic Cloud (a very nearby galaxy) in 1987.
Supernovae are now found in other galaxies at the rate
of about one a month.   We also can look at the remains
of these explosions,  such as the nebulae left behind.
After the explosion,  the star generally becomes either
a neutron star,  white dwarf or black hole.
   Supernovae come in two types, Type I supernovae and
type II supernovae.
   Supernovae are not named in the same way as other,
more "normal" stars.  They are named by year and a letter,
as in 1993J or 1885A.  You can find them with the
Go to Supernova option in the Go to Star menu.

supplemental plate 
   The Hubble Guide Star Catalog,  or GSC,  was originally
made with a few "problem areas",  mostly places near very
bright stars where the light from the bright star washed
out dimmer stars nearby.  Those problems,  seen in the
first version (number 1.0),  were fixed in version 1.1 by
taking some supplemental plates to patch those areas.
Regrettably,  the usual information about exposure start
and so on isn't available for these plates.

Switch To/From Red 
Normal colors 
Red mode 
ALT-R 
   It is possible that you may have some desire to use
this program at night out in the field.  If so,  having
your eyes adjust to darkness would be tough if you looked
at a bright white screen.
   On the other hand,  red light is not very destructive
to night vision.  Clicking on this option turns all stars,
objects and menu items to (or from) red,  making the
screen easier on night-adapted eyes.
   This item can be toggled at any time via the ALT-R
hotkey;  or,  you can reach it from the display menu.
   In Windows Guide,  this can only affect the charts
drawn by Guide.  The colors of the menu and title bars
are controlled by Windows;  you can reset them in the
Control Panel (Win3.1) or Color Manager in the system
group (Win95).

SX Arietis 
   SX Arietis type variable stars are blue-hot (spectral
type B) stars with uneven distributions of helium and
strong magnetic fields.  As they rotate,  the amount of
helium seen in the spectrum and the intensity of the
magnetic field appear to vary,  while the brightness
changes by about .1 magnitude.  These stars,  also called
helium variables,  are high-temperature versions of the
Alpha CVn stars.

SX Her 
   The SX Her type of variable star has a fairly regular
period of variation of 30 to 1100 days in length.  Most
semiregular long-period variables are older,  cooler stars
of spectral type M, R, N, or S,  but the SX Her type is
apt to be of type F, G, or K,  not very unlike the Sun.
This type varies from .1 up to 4 magnitudes in brightness.

SX Phe 
   The SX Phe type of variable star is much like a Delta
Sct type star.  They are pulsating subdwarf stars (smaller
than the Sun) with spectral type A2 to F5.  They are found
in globular clusters.

Symmetric RR Lyrae 
   Symmetric RR Lyrae variables are RR Lyrae stars that
have a light curve that looks much like a sine wave,  a
smooth variation from dark to light.

Synchronous rotation 
   An object that has synchronous rotation has an orbital period that
matches its rotational period.  This is true of the Moon (and of
almost all satellites in the solar system).  The result is that,
for example,  the Moon keeps one face toward the earth,  and Io
keeps one face toward Jupiter,  and so on.

T Tauri 
   T Tauri type stars are probably about the youngest
visible stars.  They form in rich clouds of gas:  as a
lump in the gas forms,  it creates a gravitational field
that sucks in more gas,  creating more gravity,  and so
on.  As this takes place,  the gas falling in starts to
form an accretion disk around the star.  All of this
releases a lot of energy,  most of which is soaked up by
the surrounding gas and released as infrared (heat) and
microwave radiation.
   Also,  this energy will often cause jets to erupt from
the poles of the star.  Almost always,  these stars are
found in diffuse nebulae.

Tables menu 
table menu 
Shift-F9 
   The tables menu provides several options for generating
tables of events such as a "lunar data table" (rise and
set times and libration), lunar apogee and perigees,
lunar eclipses,  Jupiter's satellite events and Great
Red Spot appearances,  and tables showing what comets or
asteroids are visible down to a desired magnitude.  There
is also a Create Star List option to list all stars in the
area currently shown on the screen,  down to a desired limit.
   For each option, you'll be asked to provide a number of
days, or of phases, or a magnitude limit.  Guide will then
show that list,  and you can save it to a file or print it if
you wish.
   In DOS,  you can also reach the Tables Menu with the Shift-F9
hotkey.

Tau Herculids 
Scorpiids 
Arietids 
Ophiuchids 
June Lyrids 
June Draconids 
Delta Aquarids 
Capricornids 
Perseids 
Kappa Cygnids 
Andromedids 
Alpha Aurigids 
Showers in June,  July,  August,  and September 
 June 3 Tau Herculids: Radiant--near Corona Borealis. About a
month long, 15 per hour max, most quite faint.
  June 5 Scorpiids: Radiant--near Ophiuchus. 20 per hour with
some fireballs.
  June 7 Arietids: About 30 per hour. Slow moving with some fireballs.
  June 13 Ophiuchids: Radiant-- near Scorpius. Only 3 per hour but
fast moving bolides are common. Duration--25 days
  June 16 June Lyrids: Radiant--near Vega. Another part of May
Lyrid meteor stream. 15 per hour, faint blue meteors.
  June 20 Ophiuchids: Radiant-- near Sagittarius. Rate varies from
8 to 20, with occasionally many more.
  June 30 June Draconids: Radiant--near handle of Big Dipper.
Rate varies from 10 to 100 per hour. Pons-Winnecke Comet is parent.
  July 28 Delta Aquarids: Radiant--near Capricornus. 25 per hour,
slow (24 km/sec) with yellow trails. Duration--40 days
  July 30 Capricornids: Radiant--near Aquarius. Tough to tell these
from Delta Aquarids. 10 to 35 per hour with bolides.
  Aug 10 Perseids: Radiant--near Double cluster. 50 to 100 per hour,
yellow with trails and bolides. The best modern dependable shower.
Duration--5 days.
  Aug 20 Kappa Cygnids: Radiant--near Deneb. 12 per hour with many
fireballs. Duration--15 days.
  Aug 31 Andromedids: Radiant-- near Cassiopeia. Occasionally
spectacular, usually 20 per hour. Some red fireballs with trails.
Biela's Comet parent.
  Sept 23 Alpha Aurigids: Radiant-- near Capella. 12 per hour,
fast with trails.