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It's All About Lag

The Calendar >

This week on our calendar marks a special time of the year when movements in the heavens would be cause for celebration among different “old world” people groups. Our high tech modern age is apparently above all that, but it’s still worth investigating. It’s summer solstice time: for some the beginning of summer, for others a special time called midsummer.

Regular visitors here will recall that the solstices and equinoxes get their fame from the unsung hero here - the tilt of our planet relative to the sun. The summer solstice is when we in the Northern Hemisphere are tilted most toward it. Thus the sun rises earlier, sets later, travels highest in the sky, and provides us with the most direct rays of energy – all the ingredients necessary for long, hot, miserable days. Oh joy.

But if the summer solstice was the longest day (June 21 this year), that means the days are now getting shorter. Wait! - the “first day of summer” is when days actually start getting shorter? If so, it should be getting cooler, right? But we know with a high degree of certainty that our thermometers will be showing higher degrees, not lower! And why do some countries refer to this first day of summer as midsummer, anyway? Is there a connection??? Confusion abounds!

It’s all about lag.

Here’s what I mean. The hottest time of the day should be noon, correct? After all, the sun is highest and its rays are burning with the most direct intensity. Well, sorta. It takes a while for the atmosphere to heat up.

It’s not unlike boiling a pot of water. It takes time for the water to absorb the energy from the stove and for its temperature to rise. Even after the water has been on the flame for a couple minutes one can still stick in a hand and not get scalded.

So it is with the local environment. It takes time to get really hot - there is a lag - so the hottest part of the day is usually around 3 o’clock in the afternoon.

On the big planet-wide scale the same thing happens. There is a lag between when the sun provides us with the highest energy input (around solstice) and when the climate temps really kick in. The lag here is a month or so after solstice, into late July and August.

And this lag gives us the differences of opinion about when “midsummer” really is. The calendar most of us use now has the beginning of summer on the solstice – usually on June 21. Midsummer Day would fall about a month and a half later, at the beginning of August.

But another calendar system places the equinoxes and solstices not as the beginnings, but as the climaxes of their seasons. Under that system summer begins on May Day. And the solstice, the height of the season, June 21, is Midsummer Day.

Today, in many northern European countries - countries which have a special reverence and appreciation for the sun - this version of midsummer is celebrated as St John’s Day (usually on June 24) and signals the end of the sowing season. The hard work of harvest and hay-making lay ahead in preparation for the cold of winter. Great bonfires are lit and people sing and dance and play games and carry about in tradition-rich ways celebrating their precious, life-giving sun.

But whether you see the solstice as the first day of summer or Midsummer itself, one thing is guaranteed - the heat is on its way.

Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com.

Posted by Administrator at 2003.06.22 01:25 PM | Comments (0)

Waxing Your Knowledge About the Moon

The Solar System >

It's been my experience in teaching and sharing astronomy with people that one of the most common everyday occurrences - the changing face of the Moon --- is also one of the least understood.

The best way to show the Moon's phases is for you to demonstrate it for yourself. You might even make this a family thing, or use it in a homeschooling situation. You'll need all of one golfball, a strong direct light source like a flashlight, and a darkened room.

The strong light source represents the sun. The golfball represents the Moon. Your head is the third heavenly body here --- the Earth.

Hold the golfball at arm's length. Hold it in the same direction as the strong light source, a direction which we'll refer to as the traditional "12 o'clock" position. Notice that it isn't too easy to see the ball due to the blinding light of our "sun." This is what is called New Moon, and is the time when solar eclipses can occur.

Slowly orbit the tiny ball to the left (counterclockwise) to about the 11 o'clock position. You should see just a sliver of a crescent Moon. We always see this phase just after the sun has set.

Continue now to the 9 o'clock position. See how half the ball is lit up, and the other half is in shadow? It has taken a week to go a quarter way around the Earth, to reach this phase called First Quarter.

Notice also that the divots in the golfball are strikingly detailed. This is the phase which, when looking at the Moon through a telescope, is the most fascinating. The sun casts long shadows along the day/night line that cuts through the Moon and vividly reveals the stark details of lunar valleys and craters.

Moving along to the 8 o'clock and 7 o'clock positions notice that the golfball-moon is growing in brightness --- it is a "waxing" Moon. The lit part of the Moon appeared to the ancients as a hump; the Latin for hump is gibbous. Thus, in astrospeak, we are seeing a waxing gibbous. And that is the Moon we have at the moment. Look for it this evening!

We now come to the 6 o'clock position, two weeks through our orbit, to a point on the opposite side from the sun. You should see a fully lit golfball-moon, a "Full Moon." Notice also that the dramatic shadows are gone. So it is with the very bright, but very flat, Full Moon that we'll be seeing a couple days from now.

Going on through the rest of the trip from the 5 to 4 to 3 o'clock position we see the lit side getting smaller and smaller from our point of view. We are now in the "waning" phases of the Moon.

At the 3 o'clock position --- three weeks and three quarters of the way around now --- we have the Third Quarter Moon. Few of us see this phase because it doesn't even rise above the horizon until after midnight.

We finish our orbit with a very "old" Moon, nearly back at the 12 o'clock location again, with a tiny sliver seen only before sunrise and just days before it gets back to New Moon.

This whole show takes about 29.5 days, which is essentially a month. Can you now guess where the word "month" comes from? "Month" is a word derived, to no one's surprise, from the word "moon," and reflects the time taken by our lunar companion to complete an entire roundtrip flight.

Until next time, clear skies!

Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com.

Posted by Administrator at 2003.06. 7 01:28 PM | Comments (0)



Looking for something?	« May 2003 \| Main \| July 2003 » It's All About Lag The Calendar > This week on our calendar marks a special time of the year when movements in the heavens would be cause for celebration among different “old world” people groups. Our high tech modern age is apparently above all that, but it’s still worth investigating. It’s summer solstice time: for some the beginning of summer, for others a special time called midsummer. Regular visitors here will recall that the solstices and equinoxes get their fame from the unsung hero here - the tilt of our planet relative to the sun. The summer solstice is when we in the Northern Hemisphere are tilted most toward it. Thus the sun rises earlier, sets later, travels highest in the sky, and provides us with the most direct rays of energy – all the ingredients necessary for long, hot, miserable days. Oh joy. But if the summer solstice was the longest day (June 21 this year), that means the days are now getting shorter. Wait! - the “first day of summer” is when days actually start getting shorter? If so, it should be getting cooler, right? But we know with a high degree of certainty that our thermometers will be showing higher degrees, not lower! And why do some countries refer to this first day of summer as midsummer, anyway? Is there a connection??? Confusion abounds! It’s all about lag. Here’s what I mean. The hottest time of the day should be noon, correct? After all, the sun is highest and its rays are burning with the most direct intensity. Well, sorta. It takes a while for the atmosphere to heat up. It’s not unlike boiling a pot of water. It takes time for the water to absorb the energy from the stove and for its temperature to rise. Even after the water has been on the flame for a couple minutes one can still stick in a hand and not get scalded. So it is with the local environment. It takes time to get really hot - there is a lag - so the hottest part of the day is usually around 3 o’clock in the afternoon. On the big planet-wide scale the same thing happens. There is a lag between when the sun provides us with the highest energy input (around solstice) and when the climate temps really kick in. The lag here is a month or so after solstice, into late July and August. And this lag gives us the differences of opinion about when “midsummer” really is. The calendar most of us use now has the beginning of summer on the solstice – usually on June 21. Midsummer Day would fall about a month and a half later, at the beginning of August. But another calendar system places the equinoxes and solstices not as the beginnings, but as the climaxes of their seasons. Under that system summer begins on May Day. And the solstice, the height of the season, June 21, is Midsummer Day. Today, in many northern European countries - countries which have a special reverence and appreciation for the sun - this version of midsummer is celebrated as St John’s Day (usually on June 24) and signals the end of the sowing season. The hard work of harvest and hay-making lay ahead in preparation for the cold of winter. Great bonfires are lit and people sing and dance and play games and carry about in tradition-rich ways celebrating their precious, life-giving sun. But whether you see the solstice as the first day of summer or Midsummer itself, one thing is guaranteed - the heat is on its way. Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com. Posted by Administrator at 2003.06.22 01:25 PM \| Comments (0) Waxing Your Knowledge About the Moon The Solar System > It's been my experience in teaching and sharing astronomy with people that one of the most common everyday occurrences - the changing face of the Moon --- is also one of the least understood. The best way to show the Moon's phases is for you to demonstrate it for yourself. You might even make this a family thing, or use it in a homeschooling situation. You'll need all of one golfball, a strong direct light source like a flashlight, and a darkened room. The strong light source represents the sun. The golfball represents the Moon. Your head is the third heavenly body here --- the Earth. Hold the golfball at arm's length. Hold it in the same direction as the strong light source, a direction which we'll refer to as the traditional "12 o'clock" position. Notice that it isn't too easy to see the ball due to the blinding light of our "sun." This is what is called New Moon, and is the time when solar eclipses can occur. Slowly orbit the tiny ball to the left (counterclockwise) to about the 11 o'clock position. You should see just a sliver of a crescent Moon. We always see this phase just after the sun has set. Continue now to the 9 o'clock position. See how half the ball is lit up, and the other half is in shadow? It has taken a week to go a quarter way around the Earth, to reach this phase called First Quarter. Notice also that the divots in the golfball are strikingly detailed. This is the phase which, when looking at the Moon through a telescope, is the most fascinating. The sun casts long shadows along the day/night line that cuts through the Moon and vividly reveals the stark details of lunar valleys and craters. Moving along to the 8 o'clock and 7 o'clock positions notice that the golfball-moon is growing in brightness --- it is a "waxing" Moon. The lit part of the Moon appeared to the ancients as a hump; the Latin for hump is gibbous. Thus, in astrospeak, we are seeing a waxing gibbous. And that is the Moon we have at the moment. Look for it this evening! We now come to the 6 o'clock position, two weeks through our orbit, to a point on the opposite side from the sun. You should see a fully lit golfball-moon, a "Full Moon." Notice also that the dramatic shadows are gone. So it is with the very bright, but very flat, Full Moon that we'll be seeing a couple days from now. Going on through the rest of the trip from the 5 to 4 to 3 o'clock position we see the lit side getting smaller and smaller from our point of view. We are now in the "waning" phases of the Moon. At the 3 o'clock position --- three weeks and three quarters of the way around now --- we have the Third Quarter Moon. Few of us see this phase because it doesn't even rise above the horizon until after midnight. We finish our orbit with a very "old" Moon, nearly back at the 12 o'clock location again, with a tiny sliver seen only before sunrise and just days before it gets back to New Moon. This whole show takes about 29.5 days, which is essentially a month. Can you now guess where the word "month" comes from? "Month" is a word derived, to no one's surprise, from the word "moon," and reflects the time taken by our lunar companion to complete an entire roundtrip flight. Until next time, clear skies! Mark Ritter teaches astronomy at Temecula Valley High School and can be reached at mritter@firstlightastro.com. Posted by Administrator at 2003.06. 7 01:28 PM \| Comments (0)
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