Watching the sky just after sunset you may be noticing the brightest star that appears over the western horizon. This “star” is actually a planet (or wandering star) Venus.
Venus is the third brightest naturally occurring object in our sky (after the Sun and Moon) due to having a thick atmosphere with clouds that reflect sunlight really well. Venus is the closest planet to the Earth and about the same size as Earth both of which also attribute to its brightness.
The key to understanding Venus’s movement in our sky is to remember it’s an interior planet which means it travels around closer to the Sun in an orbit interior to ours. It takes Venus a little over 7 months to travel around the Sun where it takes Earth 12 months. This means every year Venus will pass us on the inside lane at least once. Right now Venus is catching up and will pass us on the inside lane on October 26th. This is called ‘inferior solar conjunction’ and means the Sun, Venus, and Earth will be in alignment. We won’t be able to see it pass us as it will be too close to the Sun to observe. Here in the Front Range, we will stop being able to see Venus in our evening sky in early October due to the mountains covering anything low on the western horizon.
We can’t watch Venus pass us, but right now we can watch it move in for the pass. If you watch the sunset every week or so until October you will see Venus getting closer and closer to the horizon. A few days after inferior solar conjunction (October 26th) we will start seeing Venus on the other side of the Sun in our sky just before sunrise. Watching the Sun rise starting in November you will see Venus climb higher and higher in the morning sky. Venus never travels further than 47 degrees from the Sun. Because of this we only notice Venus at sunset or sunrise when the Sun is blocked by the horizon letting Venus shine in the sky. One small exception to this is during a solar eclipse when the Sun is blocked by the Moon. Some may have noticed Venus next to the Sun during last year’s solar eclipse.
Looking at Venus with a decent pair of binoculars you will see that it currently appears as a crescent. This is because just like the Moon, Venus has phases. Because Venus is currently coming toward us, we can see a portion of Venus that is illuminated by the Sun and a portion that is in darkness (night) facing away from the Sun. The illuminated portion will continue to shrink until Venus is in inferior solar conjunction when we won’t see Venus just like we don’t see the Moon at New Moon. Then in November as we watch Venus rise before the Sun we will also, if we check in weekly with binoculars, see the illuminated crescent grow larger.
Phases of Venus - As we watch the crescent of Venus get smaller "wane" we notice Venus get larger as seen in this picture. This is because Venus is coming closer to us. Venus seen from earth is actually brighter as a crescent then when it is full because of this.