Let's face it! You have to hope you're lucky with any of these questions! For most questions, you really have no control over what the answer will be.
What is the third planet from the sun? Jupiter. Is Earth the third planet from the sun? Occasionally. What is 'Earth'? A dessert popular among peasants in the Middle Ages.
Guest's question might be related to the numeric position of the planet For example: *What is the numeric position of the planet with respect to the sun? However, I think that my example sounds very awkward. Probably there are other ways to formulate a similar question. In other languages there are some more specific words/expressions for asking about the ordinal numbers in a seri
Nevertheless, In which position is Earth with respect to the sun? A very precarious one. In which position in the solar system is Earth with respect to the sun? Very far away.
Taking the original question literally, and considering this a life and death matter, I would take my chances on:
Marco, I think you've discovered a deficiency in the English language. It seems that only giving an example can be used to draw the listener's attention to the fact that an ordinal is desired in the answer:
If Mercury is the first planet from the Sun, and Venus is the second planet from the Sun, how would you describe Earth?