Venus, the second planet from our nearest star, has a sidereal rotation period of 243 days but it’s near circular orbit period is approximately 225 days. This makes a Venusian day longer than a Venusian year. (Reflect on that concept for a bit… Would you celebrate your birthday every day?)
As close as it is to the Sun, the surface never sees direct sunlight since thick clouds always cover the entire surface. It’s the reflection of Sunlight off of this cloud-base that is responsible making Venus not only the brightest natural object in our nighttime sky but also bright enough to be seen in the middle of the day.
When Venus is in position between the Earth and the Sun (inferior conjunction), it makes the closest approach to Earth of any planet. It reaches inferior conjunction, on average, every 584 Earth days (5 Venutian Solar days) with a recent occurrence on 29 Mar 2009 (± 2 days) 1 It has since ”passed” the Earth in it’s orbit around the Sun and went from being visible after Sunset to now visible before Sunrise.
Like our Moon, Venus exhibits “phases” but only in telescopic view. This could only be possible if the planet orbited the Sun and this discovery in the 17th century by Galileo supported the unfathomable 16th century Copernican heliocentric, or Sun-centered, idea that we are not the center of the Universe (although I know a few who’d probably still argue that point to date ;) ).
A couple of Carl Sagan Astronomy Videos on YouTube:
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John,
Thanks for sharing information about Venus. It’s fascinating to me that a day in Venus is longer than a year. I never knew that. You also raise an interesting question about birthdays, I was also wondering if they’re celebrated every day. Ha ha!
Venus has been rather bright lately in the west sky. I also didn’t know about the phases of Venus and I wonder if the brightness through the naked eye is affected by its phase. For example, if Venus is “full,” is it a brighter magnitude than if it is “half full”?
Chris
Chris,
And how does her orbit come into play with your initial question? For us to see her as “Full”, she’d have to be at the furthest possible distance, no? So considering direction of orbit, she’s been getting closer to us while the phase wanes – to what we’d call Moon’s 1st qtr since being Full, the reverse of Luna I’ve since concluded thanks to you.
Is the proximity (in millons of miles) enough to contribute to our naked eye brightness/phase observations? If we were “back in the day”, we’d have to wait a few months to find out, but now I guess we can research what others have noted.