H-R Diagram Help

This feature is only available in SkySafari Plus and Pro.

The Hertzsprung-Russell Diagram (H-R Diagram) is a special kind of graph that tells us about a star's age and its mass. Each dot on the diagram represents a star. Young stars burning hydrogen in their cores are found in the "Main Sequence" along the left side. Older "red giant" stars are in the upper right. "White dwarf" stars are along the bottom left.

Using the H-R Diagram

The stars plotted in the H-R diagram are the same stars shown onscreen in the sky chart. You can tap on any star in the H-R diagram to identify it. Conversely, tap any star in the sky chart to highlight its position on the H-R diagram.

Tip: The H-R diagram is fully dynamic. If you scroll or change your field of view, the H-R diagram updates to plot the new stars.

Visibility

• Show H-R Diagram: Toggles the H-R Diagram on/off in the sky chart.
• Show Region Labels: Labels the areas of red giants, white dwarfs, and main sequence stars.
• Show Main Sequence: Draws a line representing stars on the main sequence.
• Show Grid Lines: Draws gridlines from the vertical and horizontal axes.

X-Axis Options

• Color: Uses a star's B-V color index.
• Temperature: Plots star temperature in thousands of degrees Kelvin.
• Spectrum: Plots star spectral class (O, B, A, F, G, K, M).

Y-Axis Options

• Absolute Magnitude: How bright stars would appear at 10 parsecs distance.
• Visual Magnitude: Brightness as seen from Earth.
• Luminosity: Amount of light and energy emitted by a star.