Solar System - Mercury

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Things you don't know about the Solar System

I've always found space fascinating, and among my first books was a book about astronomy. It was just a small, general guide that had a number of interesting facts about the solar system and the stars and galaxies. This was 1980 or before, and we've made a LOT of discoveries since then, and I've kept up on it, partly thanks to Ars Technica, the Science Channel, and NASA.

I'm going to present a few curious things to you about what surrounds you that I'll bet you don't know. It's time to discover the planet closest to the Sun and therefore the hardest to observe: Mercury.


Mercury is the fastest planet, swinging around the Sun in just under 3 months. It's so close that it's within the Sun's warped space. For a long time, people thought there was an even-closer planet that was perturbing Mercury's orbit, a truly hellish world they dubbed Vulcan.
However, Vulcan was never discovered, because it wasn't there to be found, yet Mercury's orbit was still not conforming to Newton's predictions. Something else was going on. It wasn't until Einstein's Theory of Relativity that the answer was found.

You've heard that a circle is 360 degrees around, right? Well, massive objects like the Sun distort the space around them. Close to the Sun, where Mercury is, a complete circle is slightly less than 360 degrees, and as a result, Newton couldn't predict where Mercury would be.

Here's something else you don't know about Mercury: it experiences a double sunrise and a double sunset every day. How? This will only take a moment to explain.

Mercury is a big rock, much like the Moon, except it’s really hot because it’s so close to the Sun. The Earth’s distance to the Sun, the famous 93 million miles, has a much easier name to remember, called the AU, which means Astronomical Unit. Earth is 1 AU from the Sun. Mercury is about 2/5 of this distance, and as a consequence, it zooms around the Sun in only 88 Earth-days, which is just under 3 months.

Mercury rotates very slowly compared to Earth. The Earth rotates in 24 hours - one day - but Mercury needs about 59 Earth-days to turn a full 360 degrees. This means a Mercury-day is very long, about 2 months.

Did you notice something there? Its day is 2 months and its year is 3 months? That means that Mercury has 3 “days” for every 2 “years”. Those are incredibly long days!

One other thing you need to know: in its travels around the Sun, Mercury’s orbit is not a perfect circle. Sometimes it’s closer to the Sun than normal, and sometimes it’s farther away. When it’s closer, it goes faster, and when it’s farther, it goes slower. This makes its orbit somewhat elliptical.

You’re already aware that the Moon always keeps the same side facing the Earth, right? This is because the Moon’s “day” is equal to it’s “year”. However, because the Moon also doesn’t have a perfectly circular orbit, this means that sometimes the Moon goes faster and sometimes it goes slower, and because of this, it’s possible to see more than 50% of the Moon’s surface from Earth over the course of a year. Here’s a page and animation I found that explains and shows this wobble...

Click here to see the Moon’s libration!

When Mercury rotates, the Sun comes up over the horizon very slowly. When it is close to the Sun, its increased orbital speed is fast enough that when seen from the ground, the Sun goes back down! Then when the planet moves farther away from the Sun, it slows down and now the sunrise can continue. The same thing happens in reverse on the other side of the planet with the sunset.

To put it another way, the Sun heads west across the sky, then when Mercury is close to the Sun and outrunning its rotation, the Sun goes east for a while, then when Mercury moves away from the Sun, the Sun heads west again.

And so, Mercury’s double-sunrise and double-sunset are caused by this combination of very slow rotation, very fast revolution around the Sun, and orbiting faster than it can spin for a small part of the local “day”.

It’s important to note that, because of the relationship between its “day” and it’s “year” — it’s a ratio of 3 to 2 known as a resonance — this means that these doubles are visible only from small portions of the planet’s surface, and nowhere else. Anywhere else on the day side, you’ll instead see the Sun going backwards for a little while before it resumes its trek across the sky. This isn’t like a Solar eclipse of the Moon, which can happen pretty much anywhere on Earth in narrow swaths for a given event; if you build your house somewhere on Mercury where you saw a double-sunrise, you’ll always be able to see these double sunrises from your house every other “year”.

I haven’t done the math to see if double-sunrises and double-sunsets can be seen from the same locations, but it seems unlikely.

Bonus points for those of you who were also able to figure out that, on certain small locations on the Moon, you can watch the Earth rise and fall over the horizon over the course of a lunar “day” in the same manner!

I think that's enough knowledge to boggle your mind about Mercury. Next up: Venus.

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Further reading to whet your appetite for knowledge:
Solar System - Venus
Solar System - Sun
To Your Health - Part 1

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You Might not Know the Value of a Dollar

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Things you Might not Know

In my travels about the Earth, I have uncovered various truths. It seems there are a lot of people out there who aren’t aware that they don’t know how to drive, or that they don’t know the value of a dollar, or various other Earth-shattering problems. To help regular folks find out if they know this or not, I created some questionnaires so my friends and fans could find out if they are afflicted with these dangerous or inconvenient problems. We’re all often blind to our own problems, right? So take these tests to find out yours.

You Might not Know the Value of a Dollar

I have to wonder if I’m the only person who has ever had to struggle with money, as in, not having a lot of it. I was born in the lower middle class, I’ve had to ask my mom not to buy me Christmas presents so she could pay the heating bill, and my sister says I can get 15 cents out of a dime. If you have any reason to believe that you don’t know the value of a dollar, please take this test and keep track of the YES answers. Scores will be tabulated at the end.

This one is a bit more difficult to do, because inflation drives prices up constantly. Frex, I haven’t paid more than $6 for a 24-pack of pop EVER, nor will I pay more than about $1 for a regular Arby sandwich. I also frequently shop for computer components at Newegg because of their excellent service and they usually have the lowest price. I shop at Walmart for their low prices, and their lack of price-increasing, privacy-invading “discount” cards too. But because people are willing to pay ever-higher prices for things, they continue to rise, and stores that overcharge continue to do business, and so it’s impossible to say “If you pay more than $6 for a 24-pack of pop, you might not know the value of a dollar” because in a few years, that price may be impossible to find. I’ve been paying that (or less) for most of my life, and if it becomes impossible to do so, then I’ll simply do without. So few people are willing to do without unimportant things, though.

So instead of saying how ridiculous you have to be to pay $2 for a candy bar, I have to be more general.

1. Do you frequently shop at the convenience store?

2. Do you ever buy refreshments while at the movie theater?

3. Have you ever bought anything, especially food, at an interstate rest area vending machine, or a toll road service area?

4. Do you hate coupons or sales?

5. Are you usually the first to own some cool new thing, like a spiffy new game, game machine, computer component, music CD, car, or some other thing that will have its price cut in half next month but you’re too anxious to own it right now?

6. Have you ever used a “buy one get one free” coupon to buy a 69 cent hamburger when you could have instead used it to buy a 5 dollar double quarter pounder with cheese?

7. Have you ever been named customer of the year?

8. Do you buy your gasoline at the expensive stations when the station across the street is selling the exact same gasoline for 20 cents less per gallon?

9. Do you shop at supermarkets that have “discount cards”?

10. Are you unaware that even WITH that discount card, you could probably still get a better price somewhere else?

11. Do you shop at the mall a lot, when there are discount outlets nearby you could go to instead?

12. Are you afraid to buy things over the internet?

13. Do you play the lottery regularly?

Scoring

0             Excellent! You probably know the value of a dollar.

1-2         You’re not very savvy with your cash.

3+          Please hire me to do your shopping for you. I’ll get you the exact same stuff, you’ll pay the exact same price, and I’ll keep the savings. I’ll make millions in just a few days!