Category: Astronomy

The Universe Today readers are always asking great questions. ”How long is a day on Jupiter?”, is one of them. A day on Jupiter, also known as the sidereal rotation period, lasts 9.92496 hours. Jupiter is the fastest rotating body in our Solar System. Determining the length of a day on Jupiter was very difficult, because, unlike the terrestrial planets, it does not have surface features that scientists could use to determine its rotational speed.

Scientists cast about for ways to judge the planet’s rotational speed. An early attempt was to do some storm watching. Jupiter is constantly buffeted by atmospheric storms, so the theory was that you could locate the center of a storm and get some idea of the length of a day. The problem scientists encountered was that the storms on Jupiter are very fast moving, making them an inaccurate source of rotational information. Scientist were finally able to use radio emissions from Jupiter’s magnetic field to calculate the planet’s rotational period and speed. While other parts of the planet rotate at different speeds, the speed as measured by the magnetosphere is used as the official rotational speed and period.

All of the planets are oblate spheroids with varying degrees of flattening. Jupiter’s extremely fast rotation flattens it more than any other planet. The diameter of the equator is 9275 km more than the distance from pole to pole. Another interesting effect of Jupiter’s rotational speed is that, because Jupiter is not a solid body, its upper atmosphere features differential rotation. The atmosphere above the poles rotates about five minutes slower than the atmosphere at the equator.

Jupiter is almost a solar system unto itself. Many astronomers believe the the planet is simply a failed star, just lacking the mass needed to ignite fusion. Many people are aware of its four largest moons, the Galilean moons Io, Europa, Ganymede, and Callisto, but few realize that Jupiter has 50 confirmed moons and at least 14 provisional moons. The four largest moons are all very interesting to scientists. Io is a volcanic nightmare. Europa is covered in water ice and may have oceans of slushy ice underneath. Ganymede is the largest moon in the Solar System, even bigger than Mercury, and is the only moon known to have an internally generated magnetic field like Earth’s. Callisto is interesting because its surface is thought to be very ancient; perhaps original material from the birth of the Solar System.

Knowing ”how long is a day on Jupiter” just scratches the surface of the intrigue that is the Jovian system. You could spend months researching the planet and its moons, yet have more to research to do.

Here’s an article on Universe Today that shows how Jupiter can be very flattened, and an article about how the powerful windstorms are generated from its rotation.

NASA’s Ask an Astronomer also has an answer for the question, “how long is a day on Jupiter?” And a cool video of Jupiter’s rotation.

We’ve also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter’s Moons.

Sources:
NASA
Caltech Cool Cosmos

A year on Earth is obviously 1 year long, since it’s the standard of measurement. But we can break it down further.

A year is 365.24 days. Or 8,765 hours, or 526,000 minutes, or 31.6 million seconds.

The tricky one is the number of days. Because the earth year doesn’t work out to exactly 365 days, we have the leap year. If we didn’t, days in the calendar wouldn’t match up with the position of the Earth in its orbit. Eventually, the months would flip around, and the northern hemisphere would have summer in January, and vice versa.

To fix this, we put on extra days in some years, called leap years. In those leap years, a year lasts 366 days, and not the usual 365. This gets tacked onto the end of February. Normally, February only has 28 days, but in leap years, it has 29 days.

When to you have leap years? It’s actually pretty complicated.

The basic rule is that you have a leap year if you can divide the year by 4. So 2004, 2008, etc. But years divisible by 100 are not leap years. So 1800, 1900 aren’t leap years. Unless they’re divisible by 400. So 1600 and 2000 are leap years. By following this algorithm, you can have an Earth orbit that lasts 365.24 days.

With the current system, it’s not actually perfect. There’s an extra 0.000125 days being accumulated. Over course of 8,000 years, the calendar will lose a single day.

Here’s an article about how astronomers might use cosmic rays to measure time on Earth.

And here is more information on how to calculate leap years from timeanddate.com.

We did an episode of Astronomy Cast just on the Earth. Give it a listen, Episode 51: Earth.

The driest place on Earth is in Antarctica in an area called the Dry Valleys, which have seen no rain for nearly 2 million years. There is absolutely no precipitation in this region and it makes up a 4800 square kilometer region of almost no water, ice or snow. Water features include Lake Vida, Lake Vanda, Lake Bonney and the Onyx River. There is no net gain of water. The reason why this region receives no rain is due to Katabatic winds, winds from the mountains that are so heavy with moisture that gravity pulls them down and away from the Valleys.

One feature of note is Lake Bonney, a saline lake situated in the Dry Valleys. It is permanently covered with 3 to 5 meters of ice. Scientists have found mummified bodies of seals around the lake. Lake Vanda, also in the region, is 3 times saltier than the ocean. Temperatures at the bottom of this lake are as warm as 25 degrees Celsius.

The next driest place in the world measured by the amount of precipitation that falls is the Atacama Desert in Chile and Peru. There are no glaciers that are feeding water to this area; and thus, very little life can survive. Some weather stations in this region have received no rain for years, while another station reports an average of one millimeter per year.

The lowest point on land is the Dead Sea that borders Israel, the West Bank and Jordan. It’s 420 meters below sea level.

The Dead Sea sits on top of the Dead Sea Rift, a tectonic fault line between the Arabian and the African plates. The movement of these plates causes the Dead Sea to sink about one meter per year! The Dead Sea used to be connected to the Mediterranean Ocean, but over a geologic time scale, it became cut off and evaporation concentrated the salt in the water so that today, the Dead Sea is 30 to 31 percent mineral salts. It has the highest level of salinity of any body of water in the world. Just a side note, I’ve had a chance to swim in the dead sea, and it’s one of the strangest experiences I’ve ever had.

The lowest point on land in the Western Hemisphere is Death Valley in California at 86 meters below sea level.

The lowest point on the Earth’s crust is the Mariana’s Trench in the North Pacific Ocean. It is 11 kilometers deep. Like many of Earth’s extremes, the Mariana’s Trench is caused by the Pacific tectonic plate subducting beneath the Philippine plate; this means that the Pacific Plate is sliding underneath the Philippine plate. The point where the Philippine plate overlaps is Mariana’s Trench.

When people learn that energy output from the Sun is increasing, and will boil away the planet’s oceans within a billion years, they wonder if there’s any way to stop the process. Obviously, we can’t stop the Sun from shining and increasing its energy output. But is there a way humans could move the Earth further away from the Sun?

The answer is yes. Well, it’s theoretically possible. Not with today’s technology, and not without an enormous amount of energy, but the laws of physics say it’s possible. In fact, nature does it all the time.

The trick is to replicate a natural process called a 3-body interaction. This is what happens when you have nice orbit perturbed by a 3rd object. In this case, we’ve got the Earth nicely orbiting the Sun. But if we could have an asteroid pass by the Earth in just the right way, its gravity would pull our planet out of its orbit just a tiny bit.

Instead of its current elliptical orbit, the Earth would start to spiral outward from the Sun, slowly drifting further and further away. This is very similar to how the Moon is slowly drifting away from the Earth.

If you timed things right, and used several asteroid passes, you could make the Earth spiral outward as the Sun’s energy output is increasing. Instead of getting roasted, we would slowly drift away from the Sun, matching the expanding habitable zone. This would give life on Earth billions more years, instead of a few hundred million.

Of course, playing pool with asteroids is a dangerous game. Give an asteroid the wrong trajectory and it could crash into our planet and end humanity in an instant. And if you get the calculations wrong, you could end up spiraling the Earth away from the Sun too quickly, and freeze the planet. You’ve got to get it just right.

Everyone has wanted to dig a hole down to the center of the Earth at some time in their lives. I think I was in the 3rd grade, and my friends and I tried to dig down as far as we could go. I never told them my goal, but in my heart, we were going all the way through. In the end we actually got down about 2 meters, but the bottom kept filling in with water.

Of course, digging down to the centre of the Earth was always out of reach.

In order to be able to dig down to the center of the Earth, my friends and I would have needed to dig our way through 6,378 km of rock, mantle, and iron. Most of this journey would be through temperatures hot enough to melt rock, getting as high as 7,000 Kelvin at the center.

The first 35 km or so of digging would be through the outer crust of the Earth. Assuming we could actually get through the solid rock, and keep water from filling back into our super deep hole, we might actually be able to make some progress through this.

Temperatures rise as you get deeper, though. One of the deepest mines in the world is the TauTona gold mine in South Africa, a mere 3.6 kilometers deep. Even though this just scratches the surface of the Earth, temperatures at the bottom of TauTona already get as high as 55°C.

Once you break through the crust, you’re into the Earth’s mantle. At this point, you’re looking at about 3,000 km of rock heated to such a high temperature that it’s a liquid. Volcanoes are points on the Earth when magma from the mantle breaks through to the surface.

How we’d dig through that… I have no idea. But let’s say we could.

Then we’d break through into the core of Earth. This region extends for another 3,500 km or so, and its comprised almost entirely of iron, with a little nickel, and some other trace metals. And it’s even hotter than the mantle above it. This is where temperatures get to 7,000 Kelvin. Assuming we could bore through the iron, and could withstand the heat, we could get down to the center of the Earth.

At this point, we would have traveled 6,378 km to complete our journey. And then another 6,378 km to get through the other side and visit the folks in China.

Sources:
http://en.wikipedia.org/wiki/Earth_radius
http://en.wikipedia.org/wiki/TauTona_Mine
http://en.wikipedia.org/wiki/Mantle_%28geology%29