Why is it difficult to collect evidence about the sky

How are isotopes of the same chemical element alike? how are they different?

Large helium-filled balloons are used to lift scientific equipment to high altitudes. what is the pressure inside such a balloon if it starts out at sea level with a temperature of 10.0ºc and rises to an altitude where its volume is twenty times the original volume and its temperature is – 50.0ºc ?

Why does a plastic bottle that is sealed at a high altitude change it’s shape when taken to lower altitude