SUNRISE, SUNSET

Normally I spend time writing about things of political importance or philosophical pointlessness. But I finally understood something - I think - that has puzzled me for years, and I wanted to share the explanation that worked for me.

You know that days get longer in the summer and shorter in the winter. You also know that this happens because the Earth's axis is tilted relative to its orbit around the sun. In June, the northern hemisphere tilts toward the sun, so the northern hemisphere is in its summertime while the southern hemisphere is in the dark of winter. The longest day of the year in the northern hemisphere this year is June 21, and the shortest day is December 22.

You might think that the earliest sunrise and latest sunset would also occur on June 21, since that is the longest day of the year. You might think that the latest sunrise and earliest sunset would occur on December 22. But that is not true.

In summer, the earliest sunrise occurs about a week or so before the longest day. The latest sunset occurs about a week or so afterwards.

In winter, the earliest sunset occurs a week or so before the shortest day. The latest sunrise occurs about a week or so afterwards.

You can see for yourself by following this link and looking 30 days before and after the summer and winter solstices at your location.

http://www.100tools.com/100tools/pages/calculators/sunriseSunset.asp

What is going on here? I've looked up different explanations that describe analemmas and equations and they've never made sense to me. But now I have a better explanation.

We think of the Earth as orbiting around the sun in a circle. But that's not quite true. Actually the Earth's orbit is an ellipse. Sometimes it is a little closer to the sun, sometimes a little farther away than if its orbit were a perfect circle. It turns out that Earth is closest to the sun in early January, around January 4. That's also when the Earth is moving at its fastest orbital velocity through space. It is farthest away from the sun on July 4. That's when it is moving its slowest.

So from July 4 to January 4 each year, the Earth is heading towards its point of maximum velocity. It is speeding up in its orbit a little more each day. From January 4 to July 4 the Earth is moving towards its slowest point. It is slowing down in its orbit a little each day.

This is important because of the way we define "one day". One day is the time from noon to noon, the time it takes for the sun to appear again at its highest point in the sky. This is not the same as the amount of time it takes the Earth to make one revolution! Since the Earth is moving through space, "one day" takes just a little more than one revolution, the time required to turn the Earth just little more to face the sun again. Imagine being in a moving car and turning a full circle to look at a person outside the car. If you started by looking exactly sideways out the window and then spun around 360 degrees, you would still have to turn a little farther backwards to look at the same person because he appears to have moved backwards a little.

If the Earth moved in a perfect circle, it would always orbit at the same speed, and each day would be the same length. But the Earth's orbit is not a perfect circle. It is slightly elliptical. As I explained, the Earth is speeding up from its slowest orbital motion near July 4 to its fastest orbital motion near January 4. Because the Earth's motion gets faster and faster, the extra rotation required to face the sun again gets larger and larger. It looks to us like the sun is running late - noon is a little later than we expected every day. This effect pushes the whole day later - sunrises are later, noontimes are later, sunsets are later.

But because the Earth's orbit is very nearly circular, this orbital effect is very small. We almost never see it, because the effect caused by the Earth's tilted axis is so much bigger. Except...

Except when the Earth is near its longest day or its shortest day. During those periods, when the effects of the Earth's tilted axis are near maximum and minimum, the day-to-day differences of this effect are practically zero. That's when we can observe the smaller effect of Earth's varying orbital speed. It's like listening to someone whispering next to someone playing a tuba. Most of the time, you can't hear the whispering. But when the tuba player takes five, then you can.

The increasing orbital speed of the Earth around the longest day makes the sun seem to be running a little late. From the Earth tilt effect, sunrises should be getting earlier and earlier, but the small orbital effect takes over before the solstice arrives and starts sunrises on a downward trend a few days sooner. Sunsets should be getting later and later, and the small orbital effect adds to that trend. It takes a few extra days after the solstice before the changing length of the day overwhelms the small orbital velocity effect and sunsets once again start happening earlier.

A similar thing happens around the shortest day of the year at the winter solstice. The effect of the increasing orbital speed of the earth adds to the trend of later and later sunrises, pushing the latest sunrise past the solstice. The orbital effect is opposite to the trend of earlier sunsets, and makes the earliest sunset occur before the solstice.

If the Earth's axis weren't tilted, we'd only see the effects of changes in its orbital velocity. The longest day of the year would be January 4, when the Earth is closest to the sun and traveling fastest along its orbit. The shortest day of the year would be July 4, when the Earth is farthest from the sun and slowest. As it is, we don't even notice effects of Earth's changing speed, except during the two times each year when day-to-day effects of its tilted axis are minimal.

It finally makes sense. And I look forward to experiencing early and late sunsets and sunrises around the solstices, and recalling that they are being caused by the mad 65,000+ mph rush of the Earth through space in its orbit around the sun.

Wow.

A BLANK PAGE

It's been a while since I last wrote.

I felt very distressed by the lies and crimes and thievery and betrayal of the Bush-Cheney administration. I felt hopeful - but still deeply concerned - when this country finally rejected neocon fascism and turned again towards our American ideals by electing Barack Obama.

But I felt extremely sick and disgusted by the return of Congress to the Republicans.

This country had a opportunity to be great. If we had not allowed the election of 2000 to be stolen by political toadies in the state of Florida and on the bench of the Supreme Court, we could have had the sane and effective leadership of Al Gore. There would have been no 9/11, because Richard Clarke would have remained on the Security Council and Al-Qaeda would have remained a top defense priority. There would have been no invasion of Iraq, because Gore would not have been in league with oil companies and the military-industrial complex. And there would have been no economic meltdown in 2008, because the federal government would not have failed in its obligation to regulate economic activities to protect the public interest, would not have taken the position that national economic policy should be set by the greediest, most corrupt and irresponsible sleazeballs in the private sector.

This country may yet succeed in living up to its inspiring ideals, that governments derive power from the consent of the governed, that individual rights of conscience and expression and faith are supreme to every government authority, that freedom and tolerance will prevail.

But many in this generation have failed their test. In response to warmongering and fearmongering and propaganda and scapegoating these Americans fell into line and followed their leaders into darkness and destruction. They are the dark side of the American dream, the ones who use Christian language to don hoods and burn crosses and to murder the innocent. They are the fifth column of American politics, who smile as our Constitutional rights are shredded by the right wing and stockpile guns, ammunition, and paranoid delusions when Their Fuhrer loses an election. They are born Americans, but they are the most dangerous enemies of America.

I thought today, I would try to start writing again, that I would start with a blank page.

But there is no blank page.

Our present is the product of our past, and this country has been badly damaged by the viciousness of these un-American Americans. For my children's sake, I hope the wounds are not fatal.

But every day, I see the powerful becoming more powerful and reckless. I see the future of our country being sacrificed to the greed and delusions of divisive private interests. I see the tenor and truth of our national discourse sinking into oblivion.

Sometimes it seems hopeless.

Today is Memorial Day. It is a day when we honor those who died for our country, and all veterans who served and stood ready to make the same sacrifice. Many of them marched forward into hopeless battles and did not retreat. Their example can inspire us - or shame us - into facing our own national enemies, our enemies from within.

And today I will rededicate myself to that end.

To telling the truth as I see it when the liars and thieves bray their calls to the unwary.

I don't suppose it will make any difference or that anyone will listen.

I will be a small voice in a tempest.

But I will honor the memory of those who created this country, who gave us this noble heritage.

Perhaps we can not escape the past, and start each day with a blank page and unlimited hope.

But we can imagine an America that cherishes and defends its ideals.

And each day we can take one step more into that bright future.

It's worth a try anyway.

OK. Here we go again.