Venus will be high up in the western evening sky after sunset today October 30, 2021 as it reaches its greatest eastern elongation.
A planet’s elongation is the angular separation between the Sun and the planet. For the inferior planet Venus and Mercury, the greatest elongations happen at two points on their orbit where the angle between Earth, the inferior planet and the Sun is at a maximum of 90°. When the inferior planet is visible in the western evening sky after sunset, the greatest elongation is called the greatest eastern elongation, as the planet is east of the Sun. When the inferior planet is visible in the eastern morning sky before sunrise, the greatest elongation is called the greatest western elongation, as the planet is west of the Sun.
During the greatest elongations, the angular separation between the inferior planets and the Sun will be the greatest as seen from Earth. The angle of maximum separation for Mercury is between 18° and 28°, while for Venus it is between 45° and 47°. The values differ due to the eccentricity and inclination of their orbits around the Sun. During its greatest eastern elongation today, Venus will be 47° away from the Sun.
Due to the geometry of the positions of the Earth, the inferior planets and the Sun, if you observe them during their greatest elongations through a small telescope, you will see them exhibiting a near half phase like the quarter moon.
Check it out tonight!