User`s guide

Sky Data 75
***Heliocentric X, Y, Z: Heliocentric
co-ordinates reference your position in
space with respect to the Sun. Heliocentric
co-ordinates of (0, 0, 0) would place you at
the center of the Sun. The X and Y
co-ordinates mark your position along the
ecliptic plane (the plane of Earth’s orbit
around the Sun). The Z co-ordinate
indicates your distance from the ecliptic
plane. Earth travels along the ecliptic
plane, so if you are on Earth’s surface,
your heliocentric Z value will be close to
0. Heliocentric co-ordinates are given in
astronomical units (AU’s). 1 AU is the
average distance between Earth and the
Sun, about 150 000 000 km.
***Distance from Sun/Angle from Ecliptic
Plane/Phi:
Another set of heliocentric
co-ordinates, using angular measures
instead of X, Y, Z co-ordinates. Phi
specifies the angle along the ecliptic plane,
with the zero point being the position of
Earth on the autumnal equinox.
4 Hertzsprung-Russell:
Expand the Hertzsprung-Russell layer to
view a special kind of graph known as an
H-R (Hertzsprung-Russell) diagram.
An H-R diagram tells us about a star’s age
and its mass. Each dot on the diagram
represents a star. The diagram plots star
luminosity (amount of light & energy
emitted by the star) on the vertical axis
versus star temperature on the horizontal
axis. Young stars which are still burning
hydrogen in their cores are found in the
“Main Sequence”, the curve along the left
side of the graph. The larger and heavier a
star is, the farther it will be to the upper
left along this curve. Older stars in the “red
giant” phase of their life are no longer on
the main sequence, and will be found in
the upper right corner of the H-R diagram.
Finally, “white dwarf” stars will be found
along the bottom left of the H-R diagram,
beneath the main sequence.
The stars plotted in the H-R diagram are
the same stars shown onscreen in the main
window. You can click on any star in the
H-R diagram, and Starry Night will draw a
circle around this star on the main window,
allowing you to identify it. This makes it
easy to identify stellar oddballs, such as
white dwarfs, supergiants, and extremely
massive main sequence stars. Conversely,
you can point the cursor at any star in the
main window, and Starry Night will
highlight this star’s position (with a red
dot) on the H-R diagram.