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The moon is well known to have phases observed by a viewer on Earth: new, growing, quarter, gibbous and full. These phases are caused by the relative angles of the sun and the moon with respect to the Earth. When the moon turns around the Earth, the sun shines on different areas of the moon and we see the illuminated areas.
However, this phenomenon is not unique to the Earth and our moon. Other planets in the solar system also seem to go through phases, as can be seen from Earth.
Venus and Mercury have the most obvious phases compared to other planets. This is because of their orbits relative to the Earth. Mercury and Venus are both lower planets, which means that they are in orbit closer to our parent star than the Earth. As a result, we see that these planets pass through distinct phases similar to that of the moon.
When Venus is at a lower solar conjunction – that is, almost directly between the Earth and the sun – Venus will appear almost completely dark. This can be compared to the way we see a new moon. Other phases of Venus include the largest western elongation (similar to the first quarter moon), the upper solar conjunction (full moon), and the largest eastern elongation (last quarter moon).
Mercury also observes these phases, although they are not always noticeable because of the size and darkness of Mercury.
The higher planets (those whose orbits are further away than the sun seen from the Earth) do not undergo visible phases. We still see most of their sides illuminated because the Earth and the sun are located in the same relative direction of each higher planet. Often, the phases we observe with the higher planets, if we see them, appear only as a slight shadow on the edge of their surface. The only exception is Mars. Due to the near orbit of Mars, the shadow can sometimes be very noticeable.
If you are interested in seeing the phases of Venus, he is approaching his greatest lengthening to the east. August 17. Subsequently, he will reach his inferior conjunction on October 26 and will reach the next two phases in 2019.
Want to know more about astronomy? Join us at dusk on July 21st in the Niabi Zoo parking lot at Coal Valley for a free and public viewing event.
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