3 जनवरी के आसपास पृथ्वी सूर्य के निकटतम स्थिति में होती है, यह स्थिति क्या कहलाती है?

If the Earth's axis were not tilted, which of the following changes would most likely occur?

What name is given to the imaginary great circle that divides the Earth into the illuminated hemisphere (daytime) and the dark hemisphere (nighttime)?