What are the Cepheids

Most stars shine with almost constant brightness – the Sun’s brightness, for example, varies by only 0.1% over a period of 11 years. Yet some stars vary significantly in brightness and over much shorter time periods. Some of them shrink and expand as their internal structure changes because they are exhausting the fuel in their interior, a type of variation called pulsation.
.One of the most common and best studied types of pulsating star is the Cepheid variable. These are older stars, usually yellow giants, that vary quite regularly over a period of 1 to 50 days. They brighten and dim as they physically expand and contract, acting like a spring. The gas of the star’s envelope compresses due to gravity, causing it to heat and brighten. Eventually pressure overcomes gravity, the envelope of gas rebounds, and the temperature drops causing the brightness to decrease. Then, the pressure decreases, gravity takes over, and the cycle begins again. One might expect
that the pulsations would eventually stop because of energy losses in each cycle, but in fact, a complex phenomenon due to the ionization of helium in the star’s envelope sustains the pulsation.
The first variable star of this type was discovered in 1784 by John Goodrick, a Dutch amateur astronomer who paid for the discovery with his life: he caught pneumonia while making his long nocturnal observations – he was not yet 22 when he died. The object of his interest was the star  Cephei in the constellation Cepheus, which gave its name to this class of variable star.Cepheids play a crucial role in astronomy because, as demonstrated by the American astronomer Henrietta Swan Leavitt in 1912, the period of a Cepheid’s variation is related to the intrinsic luminosity of the star, and can thus serve as a “standard candle” to measure large distances. Cepheids are very bright, with up to 10 000 times the luminosity of the Sun, making it possible to detect them even in relatively distant galaxies. Once a Cepheid is found and monitored, its pulsation period supplies its intrinsic luminosity. The comparison of the intrinsic luminosity to the apparent brightness provides the distance to the star’s home galaxy. It was this method that Edwin Hubble used in 1929 to demonstrate the expansion of the Universe, and was again used recently with the Hubble Space Telescope in order to determine its rate of expansion with greater precision.

Pic Source: Wikipedia

What will happen to the Earth when the Sun dies????

 The scenario is catastrophic and inescapable. The Sun will shine normally for the next several billion years, but its temperature will steadily rise, making living conditions on Earth challenging well before our star’s final convulsions. In approximately 1 billion years, the Sun will be 10% hotter than at present, and some think that this will destabilize the Earth’s climate and biosphere, boiling off most of our water and transforming the surface of our planet into desert. In 3.5 billion years the Sun’s temperature will be 40% higher than now, and temperatures on Earth will be so high that any remaining oceans will have evaporated into space. The Earth will then share the fate of Venus: no water, no life. In 6.5 billion years, the Sun will inflate to become a red giant, triggering hellish conditions in the inner solar system. The Sun’s outer layers will grow to encompass Mercury. Temperatures on Earth will reach 2500◦C, and melt the planet, transforming it into a ball of magma. As it continues to inflate, the Sun will suffer a significant loss of mass and, as a consequence, the orbits of the remaining planets will expand. Venus will be swallowed up, and though Mars may escape, it will not be habitable. The Earth is predicted to barely escape vaporization at the fringes of the red giant’s surface. The giant outer planets (Jupiter, Saturn, Uranus, Neptune) are likely to survive this cataclysm, but will be modified significantly. After this final fiery gasp, our Sun will evolve into a slowly cooling white dwarf and the entire solar system will become very cold.

Red Giant:


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White Dwarf:

 

What is the future of our sun ???

The Sun is close to mid-life now. It will continue to shine normally for about another 6 billion years, although gradually increasing in volume and luminosity. At the age of 10.9 billion years, the Sun’s central hydrogen reserve will be exhausted and our star will rapidly enter into a new phase that will trigger the burning of its centralhelium, inflating it into a red giant . Then, 1.7 billion years after that, with itshelium exhausted and being unable to burn other elements, it will eject most of its
envelope as a planetary nebula. The Sun will thus finish its life as a white dwarf

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