skytalk

Take a break from taxing matters


Lunar Eclipse late tonight/early tomorrow – First of two lunar eclipses this year. The October 8th eclipse is less favorable for us in the Northeast, (moon sets during totality at sunrise) but will be completely visible on the west coast. Most important eclipse to for us to know about is the total solar of 2017 Aug 21. It sweeps from nw to se right through central South Carolina. Start planning now! Equation of time is zero tomorrow. – That is when apparent solar time and mean solar time are equal: our faked system of when noon occurs (exactly 24h apart day to day) is in sync with the natural instance of noon which shifts during the year because of axial tilt of the planet and eccentricity of our orbit. ‘Fast’ by 16:33~Nov. 3, ‘slow by 14:06 Feb 12; zero April 15, June 13, September 1 and December 25.


April 14, 2014

 

[Dave Heller] There’s an out-of-this-world incentive for procrastinators to complete their 2013 tax returns this evening. Details from Derrick Pitts, chief astronomer at the Franklin Institute. I’m all ears, Derrick.

[Derrick Pitts] Well you could also say that for those who really procrastinate, here’s a little break they can take in the middle of the night, because as it turns out tonight / early tomorrow morning we have a total lunar eclipse visible from the Philadelphia area. Starts at about 1:00 in the morning, but the really significant portion where you can see color on the surface of the moon as it passes into the shadow of the Earth starts around 2 a.m. and goes until about 3:30, 3:45 or so in the morning. Then the final portions of the eclipse where there isn’t very much color on the moon will complete the whole cycle for the evening.

And then you can pick up your paper and your calculator and continue on with your taxes.

And you’ll have until midnight Tuesday night, I guess it is.

And for those still struggling, is there a subsequent opportunity soon again to see a full lunar eclipse?

Just as you could apply for an extension to file your taxes — that would then require you to do something by October — as it turns out, there also happens to be another total lunar eclipse coming up this fall, October 8.

Now are all lunar eclipses equal, or is there a handicapping system making one better than another?

Well in fact, yes, there is a handicapping system in a sense in that it depends which part of the Earth is going to be facing the eclipse at the time. So for the eclipse tomorrow morning, it really favors us very well. So we’ll be able to see all of the eclipse without any problem at all. The lunar eclipse that happens on the 8th is not really very good for us, so we won’t be able to see very much of it here.

It’s been a long time since we had the opportunity to talk about a total solar eclipse in our area.

Yes, that’s true. And it’s going to be a little while until we have that opportunity again because as it turns out, there is a total solar eclipse coming, but it’s not until the year 2017, the 21st of August to be exact. Now this eclipse won’t happen in the Delaware Valley. It will appear as a partial eclipse here, but a short drive away right down route 95 right through central South Carolina, we’ll be able to come across the path of totality and we’ll easily get to see a total solar eclipse right here in our region.

Now let’s get back to those tax filers — there’s another equation to ponder as we reach the zero hour tomorrow.

Yes, it’s actually the zero minute if you think about it. And this zero minute refers to the fact that tomorrow we reach this interesting point at which we say the equation of time equals zero.

The equation of time?

Yes, the equation of time. You know about the equation of time? Not quite? Well, let me refresh your memory. We always expect noon to be right at 12:00 as we see it on our watches and clocks. But the truth of the matter is “noon” — the point where the sun is halfway through its motion across the sky during the day — varies throughout the year. It only matches our watch time exactly on four dates through the course of the year: April 15, June 13, September 1 and December 25. During the rest of the year, the times vary up and down. Now, if we were to say that “clock noon” happens before the sun reaches its halfway point, then we say that the sun is slow, it’s behind clock time. But if we get to a point where its the other way around where the sun has already reached and passed noon of the day by the time 12:00 noon on our watches rolls around, then we say that the sun is fast.

Tomorrow, the sun and our watches will be in exact synchronization for when noon is. Now the extremes go like this: the sun can be as much as 16 minutes, 33 seconds fast — and that happens early November; or the sun can be 14 minutes, 8 seconds slow — and that happens in February. So we’re just coming around to the point where the sun is coming up from being slow; it’s come to the equilateral point when noon on your watch and the sun’s noon are equal. And now what will happen is time will pick up and it will seem as if its sun fast and we’ll go back and forth through the variations, meeting the equal time again on June 13, September 1 and December 25.

Ironically this wasn’t an issue when the preferred mode of telling time was the sundial.

No, in fact it was not. It was not a problem at all because if you just went by the sundial, you’d be following exactly when it is that the sun reaches its halfway point across the sky, and that worked out just fine for most people. But that’s because we didn’t really have a need to try to fix our days as having exactly 24 hours. Now this is caused by two things: the axial tilt of the Earth and the fact that the orbit around the sun is not a perfect circle. It is actually an elipse; we have a little bit of eccentricity. And if we were a planet that had a vertical axis of rotation and a perfectly circular orbit around the sun, we would have no difference in time at all — clock noon and sun noon would equal each other every day of the year.

We have a moment left: What’s available in the night sky this week?

Beautiful observing in the evening. There are three evening planets if we go from east to west just after sunset. We find Jupiter high in the west, if we look all the way over to the eastern side of the sky we can see that Mars is above the horizon at sunset too, or we can see it just after sunset as the sky darkens. And then Saturn, the ringed planet, rises at about 9 p.m., high enough to be seen above buildings at about 10 p.m. But now if we switch ourselves around to early morning in the predawn sky — 5:30, quarter to 6 — we find that we have Mars on the western horizon, Saturn high in the south, and brilliant Venus over on the eastern horizon, very easy to see and recognize.



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