home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
GEMini Atari
/
GEMini_Atari_CD-ROM_Walnut_Creek_December_1993.iso
/
zip
/
astronmy
/
ybs_hap.lzh
/
YBS.TXT
< prev
Wrap
Text File
|
1991-09-10
|
16KB
|
360 lines
Yale Bright Star Catalog Application by R. Quance
--------------------------------------------------------------
A demonstration of the capabilities of HyperLINK through a simple
application. This is the beginning of a star catalog that has over
9000 stars. The Yale Bright Star Catalog (YBS) contains information
on stars down to about magnitude 6 (or about the limits of the naked
eye). The information describes the properties of individual stars,
including size, distance, color, type, motion and others. Only the
first 20 entries have been entered, if you're not lazy like me you
can find the data for the remaining stars in the Spaceport R/T on
GEnie. The files are: YBS1CAT.ARC through YBS8CAT.ARC. There are a
few catalog readers also in the Spaceport libraries such as
YBS_ST2.ARC to help you read the information in these files.
How to use
------------
Load the HAP and its files into the HyperLINK directory. Run
HyperLINK and load in the YBS.HAP application, looks nice don't it.
Using the arrow buttons you can scroll through the data. When you hit
YBS No. 7 move the mouse down to the "?" in the bottom left corner
and click on it. This shows you a picture of the constellation where
the star will be found ( it looks better in monochrome ).
There are a few indexes that can be used in sorting the data as well
as online help. By double-clicking on the label for each field you will
get a description of what the field is telling you and how the data
is used, there is room for expansion here.
Field Descriptions
--------------------
YBS No. : This is the YBS Catalog number for the selected star.
There are over 9000 stars in the actual catalog. Only the
first 20 are shown here, others can be added if you wish
to add them yourself.
R.A. : To understand R.A. (Right Ascension) we have to get a picture
in our minds of what we are looking at when we look at the
night sky. Imagine the Earth is surrounded by a huge black
hollow sphere with pinholes through it. The light shining
through the pinholes marks the locations of the stars. Now to
get the coordinates of the stars we'll have to lay a grid
over the inside of the "Celestial Sphere". We're going to need
lines similar to lines of longitude (vertical) on a globe,
but what do we use for a scale, Hmmm... Let's see, the Earth
rotates once every 24 hours, that's it, we'll use 24 segments.
We can further divide each down into minutes (60 minutes) and
seconds (60 seconds). So, every 1 hour of R.A. is divided down
into 3600 smaller segments (seconds). Hmmm, so where do we start
counting from and which direction do we go? We'll just have to
use some event that occurs every year to mark the staring point,
the "Vernal Equinox" is what we'll use, or the point where the
sun crosses the Equator in the springtime.
Since it varies from year to year we'll have to specify a
date to use as a reference, or Epoch. Most stars catalogs are
based on a particular Epoch, e.g. 2000.0 or 1950.0. This
means that the locations of the stars are measured from the
point where the sun crosses the Equator on that Epoch date.
So, which way do we go? Well, if we point our telescope at a
particular star and don't move it for 1 hour, we will be
looking at a point 1 hour of R.A. east of the star we had it
pointed at, that's the direction we'll use. We can use the
Earths rotation as a clock to find our way around the sky. If
we're looking at a star that is 1 hour of R.A. above the
eastern horizon and we want to look at a star that has an
R.A. of 2 hours more than the star we are looking at. We'll
have to wait 2 more hours for it to appear in the same
position as the first star. Confusing, I know, but that's
about as simple an explanation as I can give...
Dec. : To understand Declination (Dec.), we have to go back to the
"Celestial Sphere" we created in the R.A. section above. We
have the vertical lines (R.A.), but we still need the
horizontal lines that represent lines of latitude. These
lines start at the "Celestial Equator", which closely matches
the position of our own equator. The scaleing is the same as
we use on our globe, with +90 degrees and -90 degrees, starting
with 0 degrees at the celestial equator and ending at the
celestial North and South poles. Each degree of declination
is further broken down into minutes (60 minutes) and seconds
(60 seconds). Now we can find the coordinates for a particular
star by using the R.A. and Declination of the star, it's just
like looking from the inside of a globe of the Earth. We can
see the vertical and horizontal lines marking longitude and
latitude, only it's dark and we only see points of light not
the back of the continents on this sphere...
Distance : This is the distance from the Earth in "Light Years". The
light year is the distance light will travel in one year.
It's actually quite a long distance, since light travels
186,282 miles per second. Let's use a little math to
figure out the distance. How many seconds in a year?
There are 60 seconds in a minute, 86,400 seconds in one
day and 31,536,000 seconds in one year. Multiply that by
186,282 and you get the idea. That's quite some distance
isn't it?
Parallax : Since the Earth revolves around the Sun each year with
an orbit that is 186 million miles in diameter, the
stars that are closer the our solar system appear to
move in little circles against the more distant
background stars. This apparent motion is known as
parallax. The parallax angle is the angular difference in
the postion of a star when viewed from opposite sides of
the sun. When the star is closer to the ecliptic (or the
path of the Sun across the sky) it becomes more elliptical
(oval). As a result we'll have to use the longest
distance from the center of the ellipse ( semi-major axis )
to make all our measurements. This information can be
useful in determining the distance of nearby stars...
Type : This tells you whether the star is all by itself or is made
up of multiple stars. Double stars are actually two stars
that appear close together but are actually some distance
apart, they just happened to appear along the same path.
Binary stars are multiple stars that are in close proximity
to each other and actually orbit around each other.
Annual Proper Motion (R.A.) : Since all things are never permanent so
it is with stars too. Although you can't notice it, except
over long periods of time, the stars are actually moving. The
Annual Proper Motion (R.A.) is a measure of how far the star
will have moved over a period of one year. A positive number
means that the star is moving eastward, a negative number
means it's moving the opposite way. We can use this
information to help determine the distance the star is away or
speed the it's traveling or where it will be sometime in the
future.
Annual Proper Motion (Dec.) : Represents how far the star has moved
in Declination over a period of one year. If the number is
postive then it's moving in a northward direction, if it's
negative then it's moving south. This information is of the
same importance as that mentioned in the Annual Proper Motion
(R.A.) above....
Spectral Class : We can classify stars according to characteristics
in their spectra. You have probably noticed, on a clear night,
that stars have different colors. There are seven basic types
of spectral class, based on the colors emitted at varying
surface temperatures of these stars. Depending on the
elements present within the star, certain bands of light will
be absorbed by these elements. They appear as black lines in
the spectral color of the star and are called, of all things,
"Absorbtion Lines". The basic spectral types are described
here with their absorbtion lines (elements):
Type Absorbtion Lines
-------------------------------------------------------------
O Ionized Helium (He II)
B Neutral Helium, first appearance of Hydrogen
A Hydrogen dominant, plus singly ionized metals
F Hydrogen weaker, ionized calcium (Ca II)
G Ca II prominent, weak Hydrogen and neutral metals
K Neutral Metals prominent
M Molecular Bands, mostly Titanium Oxide (TiO)
Each of these seven types is further divided into 10 classes,
with a class of "5" occuring half way between two types. (e.g.
A5 is half way between A0 and F0). The age of a star can be
determined by the elements present within it. The types O, B,
and A are of the "early type", with K and M being of the
"late type".
Since within each type, a brighter star can be more luminous
(emit more light), the absorbtion lines tend to get narrower.
So to take this into account, we add a "Luminousity Class" to
each star. We use Roman numerals to add the luminousity
class to our star, they are shown in the list here:
Luminousity Class Description
-------------------------------------------------
I Supergiants
II Bright Giants
III Giants
IV Subgiants
V Main-Sequence Dwarfs
VI Subdwarfs
VII White Dwarfs
Some of these classes, especially the Supergiants, can be
divided further with suffixes (e.g. a, ab and b). You might
see a spectral class like " K0III " or " M2Iab", can you
figure these out? If there are any non-standard features
found within a stars spectra, they will be noted by small
letters following the luminousity class. Here is a list of
these features:
Feature Description
--------------------------------------------------------
e Emmision Lines (f in some O-type stars)
m Metallic Lines
n Nebulous Lines
p Peculiar Spectrum
q Blue Shift absorbtion and Red Shift emmision
(presence of an expanding shell)
v Variable Spectrum
I'll bet you're really confused now!!! Hang in there...
Absolute Magnitude : Magnitude is a measure of the brightness of a
star. Since stars at a greater distances may be just as
bright as stars nearby, but at greater distances they appear to
be fainter, we'll have to find way to describe their actual
brightness. We do this by calculating the brightness of a
star if it were at a standard distance away. We use 10
parsecs (33 light years) as the standard distance. The result
is the "Absolute Magnitude" or the magnitude the star would be
if it were 10 parsecs away.
Visual Magnitude : This is a measure of the brightness of a star as
it appears to the human eye. There are no corrections applied
to this measurement, what you see is what you get. The
magnitude scale is based on an early scale used by Hipparchus
in the 2nd century B.C. It classed stars into 6 catagories,
the brightest stars were magnitude 1, the next less bright
were magnitude 2, and so on to magnitude 6 which were the
faintest stars visible to the naked eye. This scale was
later expanded, to help with telescopic measurements, to
include postive (+) and negative (-) magnitudes. As well it
was found that a 1 magnitude difference worked out to a
difference in brightness by a ratio of 2.5, and a 5 mag.
difference in brightness between two stars resulted in a
brightness ratio of 2.5^5, or nearly 100. The brightest
star in the sky would now be -1.46 mag. (Sirius),
according to the new scale and the faintest stars seen in a 3"
telescope are at the 11th magnitude...
Color : The electronic measurement of a stars brightness is usually
done through four different color filters. These colors are
(U)ltraviolet (350 nm), (V)iolet (410 nm), (B)lue (470 nm) and
(Y)ellow (550nm). The "Color Index" is the difference in
magnitude of a star measured through two of the filters,
usually B-V or U-B. In this case we are using the B-V
difference.
Common Name : This is the name of the selected star. It can be the
proper name (e.g. Rigel), the Bayer letter ( e.g. mu Cygni),
Flamsteed numbers (e.g. 31 Orionis). The Bayer letter is
usually a Greek letter followed by the constellation name and
the Flamsteed number is a number followed by the constellation
name. The Greek alphabet is difficult to represent here, we
will have to use the following representation of the
characters (e.g. Gamma Orionis - Bellatrix):
Alpha Beta Gamma Delta Epsilon Zeta
Eta Theta Iota Kappa Lambda Mu
Nu Xi Omicron Pi Rho Sigma
Tau Upsilon Phi Chi Psi Omega
Constellation : There are 88 constellations that represent fixed
areas of the sky. They were originally determined by the
early Greeks to represent characters from their mythology
and are still used today. The following is a list of the
constellations and their abbveviations:
Name Genitive Abbreviation
--------------------------------------------------------------------
Andromeda Andromedae And
Antlia Antliae Ant
Apus Apodis Aps
Aquarius Aquarii Aqr
Aquila Aquilae Aql
Ara Arae Ara
Aries Arietis Ari
Auriga Aurigae Aur
Bootes Bootis Boo
Caelum Caeli Cae
Camelopardalis Camelopardalis Cam
Cancer Cancri Cnc
Canes Venatici Canum Venaticorum CVn
Canis Major Canis Majoris CMa
Canis Minor Canis Minoris CMi
Capricornus Capricorni Cap
Carina Carinae Car
Cassiopeia Cassiopeiae Cas
Centaurus Centauri Cen
Cepheus Cephei Cep
Cetus Ceti Cet
Chamaeleon Chamaeleontis Cha
Circinus Circini Cir
Columba Columbae Col
Coma Berenices Comae Berenices Com
Corona Australis Coronae Australis CrA
Corona Borealis Coronae Borealis CrB
Corvus Corvi Crv
Crater Crateris Crt
Crux Crucis Cru
Cygnus Cygni Cyg
Delphinus Delphini Del
Dorado Doradus Dor
Draco Draconis Dra
Equuleus Equulei Equ
Eridanus Eridani Eri
Fornax Fornacis For
Gemini Geminorum Gem
Grus Gruis Gru
Hercules Herculis Her
Horologium Horologii Hor
Hydra Hydrae Hya
Hydrus Hydri Hyi
Indus Indi Ind
Lacerta Lacertae Lac
Leo Leonis Leo
Leo Minor Leonis Minoris LMi
Lepus Leporis Lep
Libra Librae Lib
Lupus Lupi Lup
Lynx Lyncis Lyn
Lyra Lyrae Lyr
Mensa Mensae Men
Microscopium Microscopii Mic
Monoceros Monocerotis Mon
Musca Muscae Mus
Norma Normae Nor
Octans Octantis Oct
Ophiuchus Ophiuchi Oph
Orion Orionis Ori
Pavo Pavonis Pav
Pegasus Pegasi Peg
Perseus Persei Per
Phoenix Phoenicis Phe
Pictor Pictoris Pic
Pisces Piscium Psc
Piscis Austrinus Piscis Austrini PsA
Puppis Puppis Pup
Pyxis Pyxidis Pyx
Reticulum Reticuli Ret
Sagitta Sagittae Sge
Sagittarius Sagittarii Sgr
Scorpius Scorpii Sco
Sculptor Sculptoris Scl
Scutum Scuti Sct
Serpens Serpentis Ser
Sextans Sextantis Sex
Taurus Tauri Tau
Telescopium Telescopii Tel
Triangulum Trianguli Tri
Triangulum Australe Trianguli Australis TrA
Tucana Tucanae Tuc
Ursa Major Ursae Majoris UMa
Ursa Minor Ursae Minoris UMi
Vela Velorum Vel
Virgo Virginis Vir
Volans Volantis Vol
Vulpecula Vulpeculae Vul
If there are any questions or comments, please send them to me at
my GEnie address:
R.QUANCE
I hope you enjoy using this HyperLINK application and find it of
some use. I will eventually find a way to load the data for all
9000 stars into this HAP, so stay tuned.....
Robert W. Quance
