Here on Earth, we tend to take time for granted, never suspected that the increments with which we measure it are actually quite relative.
The ways in which we measure our days and years, for example, are actually the result of our planet’s distance from the Sun, the time it takes to orbit, and the time it takes to rotate on its axis.
The same is true for the other planets in our Solar System.
While we Earthlings count on a day being about 24 hours from sunup to sundown, the length of a single day on another planet is quite different.
In some cases, they are very short, while in others, they can last longer than years – sometimes considerably! Let’s go over how time works on other planets and see just how long their days can be, shall we?
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A day on Mercury:
Mercury is the closest planet to our Sun, ranging from 46,001,200 km at perihelion (closest to the Sun) to 69,816,900 km at aphelion (farthest). Since it takes 58.646 Earth days for Mercury to rotate once on its axis – aka. its sidereal rotation period – this means that it takes just over 58 Earth days for Mercury to experience a single sunrise and sunset.
However, it only takes Mercury 87.969 Earth days to complete a single orbit of the Sun (aka. its orbital period). This means a year on Mercury is the equivalent of about 88 Earth days, which in turn means that a single Mercurian (or Hermian) year last exactly one and half Mercurian days. What’s more, Mercury’s northern polar regions are constantly in the shade.
This is due to it’s axis being tilted at a mere 0.034° (compared to Earth’s 23.4°), which means that it does not experience extreme seasonal variations where days and nights can last for months depending on the season. On the poles of Mercury, it is always dark and shady. So you could say the poles are in a constant state of twilight.
A day on Venus:
Also known as “Earth’s Twin”, Venus is the second closest planet to our Sun – ranging from 107,477,000 km at perihelion to 108,939,000 km at aphelion. Unfortunately, Venus is also the slowest moving planet, a fact which is made evident by looking at its poles. Whereas every other planet in the Solar System has experienced flattening at their poles due to the speed of their spin, Venus has experienced no such flattening.
Venus has a rotational velocity of just 6.5 km/h (4.0 mph) – compared to Earth’s rational velocity of 1,670 km/h (1,040 mph) – which leads to a sidereal rotation period of 243.025 days. Technically, it is -243.025 days, since Venus’ rotation is retrograde (i.e. rotating opposite of its orbital path around the Sun). So if you were above Venus’ north pole and watched it circle the Sun, you would see it is moving clockwise, whereas its rotation is counter-clockwise.
Nevertheless, this still means that Venus takes over 243 Earth days to rotate once on its axis, which means that many days pass between a single sunrise and sunset. This may seem odd, until you consider that a single Venusian (or Cytherean) year works out to 224.701 Earth days. Yes, Venus takes a little more than 224 days to complete a single orbital period, but over 243 days to experience a single sunrise and sunset.
So basically, a single Venusian day is longer than a Venusian year! Good thing Venus has other things in common With Earth, because it is sure isn’t its diurnal cycle!
A day on Earth:
When we think of a day on Earth, we tend to think of it as a simple 24 hour interval. In truth, the Earth’s sidereal rotation period is exactly 23 hours 56 minutes and 4.1 seconds long. So really, a single day on Earth is actually the equivalent about of 0.997 Earth days.
Odd, but then again, people prefer simplicity when it comes to time management, so we round up. At the same time, there are variations in the length of a single day on the planet based on seasonal cycles. Due to Earth’s axial tilt, the amount of sunlight experienced in certain hemispheres will vary. The most extreme case of this occurs at the poles, where day and night can last for days or months depending on the season.
At the North and South Poles during the winter, a single night can last up to six months, which is known as a “polar night”. During the summer, the poles will experience what is called a “midnight sun”, where a day lasts a full 24 hours. So really, days are not as simple as we like to imagine. But compared to the other planets in the Solar System, time management is still easier here on Earth.
See the rest of the story at Business Insider