Age:
* Hertzsprung-Russell Diagram (HR Diagram): This diagram plots stars' luminosity against their surface temperature. Stars of similar age tend to fall along specific evolutionary tracks on the HR Diagram. By comparing a star's position on the HR Diagram to theoretical models, scientists can estimate its age.
* Stellar Evolution Models: These models simulate the life cycle of stars, taking into account factors like mass, composition, and energy output. By comparing observations to model predictions, scientists can infer a star's age.
* Cluster Ages: Stars within a star cluster are born around the same time. By observing the ages of the oldest stars in a cluster, scientists can estimate the age of the entire cluster, including younger stars.
* Radioactive Dating: Some stars contain elements like lithium, which decays at a known rate. Measuring the amount of lithium remaining can provide an estimate of the star's age.
Mass:
* Binary Star Systems: By observing the orbital motions of binary stars, scientists can apply Kepler's laws of motion to calculate the stars' masses.
* Spectroscopic Parallax: This method uses the star's spectral type and luminosity to estimate its distance. Knowing the distance and apparent brightness allows for the calculation of the star's absolute luminosity, which is related to its mass.
* Stellar Models: Similar to age estimation, stellar models can predict a star's mass based on its observed properties.
Rotation Period:
* Spectroscopic Observations: Analyzing the Doppler shift of spectral lines in a star's light can reveal the velocity of its rotation.
* Photometric Variations: Some stars exhibit brightness variations caused by their rotation. By measuring these variations, scientists can determine the rotation period.
* Starspots: Darker regions on the surface of stars (like sunspots) can be used to track the rotation period.
Important Considerations:
* Error Margins: Each method has limitations and uncertainties, so the determined values are often estimates with error bars.
* Evolutionary Stages: The methods used depend on the star's evolutionary stage. For example, direct mass measurement is easier for young stars than for older stars.
* New Discoveries: Ongoing research and new technologies constantly improve our understanding of stars, refining these methods and revealing new insights.
It's important to remember that while we have sophisticated tools to study stars, their ages, masses, and rotation periods are not always known with absolute certainty. The knowledge we gain is a result of continuous scientific investigation and refinement of our understanding of the cosmos.
