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.
Tip: The H-R diagram is fully dynamic. If you scroll around the screen or change your field of view, the stars shown onscreen will change, and the H-R diagram will update to plot these new stars.
H-R Diagram Options:
Expand the H-R Options layer beneath the H-R diagram to access options that affect the appearance of the diagram.
Use Absolute Magnitudes: Unchecking this option will plot apparent magnitude instead of absolute magnitude on the vertical axis.
Automatic ranges: Checking this option will cause Starry Night to select the smallest possible ranges for the X and Y axes that still manages to include all stars visible onscreen.
Image Brightness: This slider controls how bright the star dots in the H-R diagram are drawn.
Distance Cut-Off: This plots only those stars with distances from Earth that lie between the minimum and maximum distances that you specify.
Labels: Unchecking this option draws a blank graph with no labels. Checking this option allows you to turn on any of the label options listed below.
￼Gridlines: Draws gridlines from the vertical and horizontal axes.
B-V: Uses a stars B-V colour as the field along the horizontal axis. Hotter stars have a lower B-V value.
Kelvin X 1000: Plots star temperature (in thousands of degrees Kelvin) along the horizontal axis. Degrees Kelvin are equal to degrees Celsius + 273.
Spectral Class: Plots star spectral class along the horizontal axis.
Main Sequence: Draws a line representing stars on the main sequence. Any star that appears close to this line is probably a main sequence star (a star that is still burning hydrogen fuel).
Regions: Labels the areas of red giants, white dwarfs, and main sequence stars. Note: White dwarfs are very dim and few are in Starry Night's star catalogues (the Hipparcos/Tycho-2 catalogues), so few will be found in Starry Night's H-R diagrams.
Dim Labels: Draws the diagram labels much dimmer than the stars.