How have observations in the sky enabled humans to explore and travel?

Observations of the sky allowed explorers to mark the passage of time both in hours and through the months of the year. Early astronomers also realized that the night sky does not look the same from different places on the Earth.

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

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since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.