The brightness of the variable star fluctuates apparently. This variation is caused by a change in the emitted light. It can also be caused by something that is partly blocking the light. Most of the stars have at least some variations in luminosity i.e., the energy output of our Sun. For example, varies by about 0.1 per cent over an 11-year solar cycle. The first variable star was identified when Johannes Holwarda observed that Omicron Ceti pulsated in a cycle taking 11 months.
Classification of Variable Stars
Variable stars are either intrinsic or extrinsic.
- Intrinsic Variable Stars: The variability in the stars is because of changes in the physical properties. Intrinsic variable stars are divided into three subgroups.
- Pulsating variables are the stars whose radius expands and contracts alternately. This activity is like a part of their natural evolutionary ageing processes.
- Eruptive variables are the stars who experience eruptions on their surfaces like flares or mass ejections.
- Cataclysmic or explosive variables are the stars that undergo a cataclysmic change in their properties like novae and supernovae.
- Extrinsic Variable Stars: The variability of stars is because of external properties like rotation or eclipses. There are two main subgroups of extrinsic variables:
- Eclipsing binaries, these are double stars as seen from Earth’s vantage point the stars occasionally eclipse one another as they orbit.
- Rotating variables, stars whose variability is due to phenomena related to their rotation. For examples stars with extreme sunspots. This affects the apparent brightness of stars. It can also be stars that have fast rotation speeds causing them to become ellipsoidal in shape.
Observation of Variable Star
There are many reasons why the study on variable stars and the collection of data on variable stars is an essential and useful activity. Research on these stars gives a wealth of information on stellar properties such as the mass, luminosity of stars, radius of stars, and the composition of stars. This information can be useful to study other stars as well. These stars are observed for decades. These stars determine their long-term behaviour.
Anyone can be a variable star observer. Following are the things to keep in mind to begin observation of variable stars:
- A pair of binoculars or a telescope
- Variable star chart to help you navigate
- Some basic instructions
- A little patience
Variable star-gazers are familiar with the procedures of observing variable stars. These gazers cover dozens of stars a night swinging from one star to another without the help of charts.
FAQs on Variable Star
Question: Why do variable stars change their brightness?
Answer: Variable stars change brightness because of many reasons. For instance, pulsating variables shrink and swell because of internal forces. It is the same as an eclipsing binary that dims when it is obscured by a faint partner and then brightens when the occulting partner moves apart. The different causes for light variation in variable star render stimulus for classifying stars into different categories as per their action.