Meghnad Saha was the first Indian astronomer to propose a method for measuring the distance to a nebula. He published his method in 1921.

The Saha method is a method for measuring the distance to a nebula by using the ionization of hydrogen gas in the nebula.

The Saha method is based on the principle that the ionization of hydrogen gas in a nebula depends on the temperature of the nebula. By measuring the ionization of hydrogen gas in a nebula, it is possible to determine the temperature of the nebula and hence its distance.

Subrahmanyan Chandrasekhar used the Saha method to measure the distance to the Andromeda Nebula in 1932. His measurement was the first accurate measurement of the distance to a nebula.

Chandrasekhar measured the distance to the Andromeda Nebula to be 2 million light-years.

Chandrasekhar's measurement of the distance to the Andromeda Nebula showed that the universe is much larger than previously thought. This led to a major revision of our understanding of the universe.

Harlow Shapley used the Saha method to measure the distance to the Orion Nebula in 1921.

Shapley measured the distance to the Orion Nebula to be 1,000 light-years.

Shapley's measurement of the distance to the Orion Nebula showed that the universe is much larger than previously thought. This led to a major revision of our understanding of the universe.

Edwin Hubble used the Saha method to measure the distance to the Crab Nebula in 1928.

Hubble measured the distance to the Crab Nebula to be 5,000 light-years.

Hubble's measurement of the distance to the Crab Nebula showed that the universe is expanding. This was a major discovery that led to a new understanding of the universe.

All of the above are challenges in measuring the distance to nebulae. The distances to nebulae are very large, which makes it difficult to measure them accurately. Nebulae are often faint and difficult to observe, which can also make it difficult to measure their distance. The composition of nebulae can vary, which can affect the accuracy of distance measurements.

All of the above are methods that astronomers use to measure the distance to nebulae. The Saha method, the Chandrasekhar method, the Shapley method, and the Hubble method are all based on the ionization of hydrogen gas in nebulae. Other methods include the parallax method, the spectroscopic parallax method, and the Cepheid variable method.

All of the above are ways in which Indian astronomers have contributed to the measurement of distances to nebulae. Meghnad Saha developed the Saha method for measuring the distance to a nebula. Subrahmanyan Chandrasekhar used the Saha method to measure the distance to the Andromeda Nebula. Harlow Shapley used the Saha method to measure the distance to the Orion Nebula. Edwin Hubble used the Saha method to measure the distance to the Crab Nebula.