Talvez eu esteja errado mas eu acho que você confundiu o "é" o
It is é sim um "é" mas no inglês em muitos casos é preciso indicar o sujeito que no Verbo to Be é o
IT.
E no exemplo que citou Galaxy assume o papel do
Ite o outro motivo possível é a virgula mas esta parte não tenho certeza outra pessoa pode dar certeza.
Our galaxy,
which is called the Milky Way, is quite small compared to others.
a parte em negrito pode ser retirada sem qualquer perca do sentido da frase.
Our
galaxy is quite small compared to others.
como bonus vai umas dicas em relação as virgulas retiradas do site BBC learning English
www.bbc.co.uk/learningenglish/english/course/towards-advanced/unit-1/session-1Summary
1. You can remove a non-defining relative clause and the sentence will still make sense. It adds extra information about the noun.
Their dog, which spent its first year living on the streets, didn't like sleeping in the house.
Their dog didn't like sleeping in the house.
2. You can always identify a non-defining relative clause because there is a comma after the noun it's describing. There will always be a comma at the end of the non-defining clause as well unless it finishes the sentence.
Her hair, which was naturally brown, was dyed blonde.
She had blonde hair, which was dyed.
3. Non-defining relative clauses always need the correct relative pronoun (which, who, whom). In defining relative clauses, these pronouns are often replaced with 'that'. It's also not possible to leave the pronoun out of a non-defining relative clause.
Correct: Their car, which was 20 years old, had begun to fall apart.
Wrong: Their car, that was 20 years old, had begun to fall apart.
Wrong: Their car, was 20 years old, had begun to fall apart.
4. Non-defining relative clauses can add extra information about the quantity of objects described. We do this by using expressions such as many, some, all, a few, half followed by the correct relative pronoun.
The people, half of whom had never voted before, elected a new leader.
The patients, many of whom smoked, were suffering from lung conditions.
5. You can comment on a whole sentence using non-defining relative clauses.
The pigeons, which were all over the town square, left a terrible mess, which was disgusting.
The children, who were having a wonderful time, didn't want to go home, which didn't surprise me.
To do
