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Study of air tides: phases of the moon versus barometric pressure

Study of air tides: phases of the moon versus barometric pressure

Introduction: (Initial Observation)

Every object in the world is constantly subject to gravitational forces by other objects specially large bodies such as planets and moons.

On the earth, the earth gravity is the largest gravitational force. However, objects on the earth are subject to gravitational forces of moon and sun as well.

You weight less at the times that moon is above your head than other times that moon is on the other side of the earth.

One of the major affects of moon’s gravity on the earth is known as tide. Tide is a shift of the earth’s surface water toward the moon. So if the moon is above, water level will rise and when moon is on the other side of the earth, water level will fall.

A similar thing happens to the air layer, covering the earth. Air layer is always shifted toward the direction of the moon. That will cause higher air pressure in some areas (where moon is above) and lower air pressure on the opposite side.

In this project we will study the effects of air tides on air pressure.


If you have any questions, click on the help button at the top of this page to send me your questions. I may respond by email, but often I update this page with the information that you need.

Project Advisor

This is a meteorology related project. Meteorologists use such information to predict weather conditions and issue necessary warnings.

Information Gathering:

Gather information about tides caused by moon. Read books, magazines or ask professionals who might know in order to learn about the effect of moon’s gravitational force on objects on the earth. Keep track of where you got your information from.

Following are samples of information that you may find:

New studies have shown that not only are there tides in the oceans but also in the earth and the air. Only recently, with very highly sensitive instruments, have scientists been able to see a tidal range of about twenty two inches. Compared to the oceans tides, that number is very small, but still a change is occurring every day. Also, this crustal tide is due to the same factor as the ocean tides, the sun and the moon. WE can neither see, nor feel it, because like a ship on the sea, we move with the crust’s flood and ebb. How did scientists then figure out the earth was moving, when even the instruments on it would be moving as well? As I said, highly sensitive instruments were used, such as the horizontal pendulum, and the gravimeter, they are used to measure the amount of gravitational pull from the moon. There is a set standard for these measurements, and after every possible precaution was taken to make sure there were no errors, and the tests were done, there showed a smaller gravitational pull from the moon. The only feasible explanation was that the earth itself had moved, and the instruments with it, altering the gravitational pull from the moon. Proving that the air does, in fact, have tides! Like the oceans, the air has tow high tides, and two low, the average range being between eight and twelve inches. Also, the flooding and ebbing of the sea causes a downward and upward tilt of the land. When the ocean’s tides are rising millions of gallons of water move into coastal regions, adding pressure and pushing the land down. When the ocean tides ebb, it releases the pressure, and the crust tilts upward. This wave of motion does not happen only at end coastal regions though, it extends far inland. A man named Pierre Simon de Laplace, discovered tides in the air. It took him eight years of reading his barometer every day four times a day to come to the conclusion that the air also flows similarly to the ocean tides. Puzzlingly, though, these tides did not follow the moon, as did the ocean, and earth tides, no these tides followed the clock. High tides were at 10:00 am and pm, and low tides were at 4:00 am and pm. Unlike ocean tides, that flow an hour later each day, these times remained constant, disproving the theory that the tides are following the sun and moon. Scientists now believe that they followed the heat of the sun, and that was what caused the pressure to rise and fall. There is some tidal movement like that of the oceans, in the air, but to a very small extent. Further studies are being done in the outer atmosphere, we have yet to know.

From: http://members.tripod.com/~CovenK/ (Editions have been made)

While developing an explanation for sea tides, Isaac Newton pointed out that there should also be gravitational tides in Earth’s atmosphere. He realized that air tides would be barely discernable in England, because tidal effects are maximized at the equator and decrease rapidly toward the poles.
Air tides at the mid-latitudes are indeed at the edge of detectability. At around 10 microbars, or 0.01 millibars, they were only discovered after scientists carefully analyzed records kept over a long period of time. These tiny variations are almost nonexistent when compared to a standard atmospheric pressure of 1013 millibars.

But atmospheric tides are about 100 times stronger at the equator. This still makes them small, but far easier to detect. Seafaring people armed with barometers always saw air pressure in the tropics go up and down with an amplitude of about 1 millibar.

Like sea tides, atmospheric tides have 12-hour cycles, but that’s where the similarity ends. Observers soon discovered that air tides came in intervals of 12 solar hours. This made the tides they were measuring different than the sea tides, which came in twelve-hour intervals related to the moon’s position.

In the 1870s, the British physicist Lord Kelvin raised an obvious point. If these tides were in synch with the Sun, they must be forced by heating. But if this were the case, why 12-hour tides instead of 24? He surmised it had everything to do with how heat is shunted throughout the Earth’s atmosphere.

Armed with his observations, Kelvin made some pretty insightful hunches about how the atmosphere layered itself. Many of his guesses were wrong, but the questions posed by Kelvin were the first time anyone ever suggested using air tides as a tool to plumb the atmosphere. This new line of thinking launched an age of upper-atmospheric science.

It turns out that the main force for a 12-hour thermal tide is heating in the ozone layer. Our atmosphere allows 12-hour oscillations to propagate from the ozone layer to the surface, but it traps 24-hour oscillations.

Thermal tides could be the cause for more dramatic effects on Venus, a planet that orbits closer to the Sun’s heat and has a completely different atmosphere than Earth’s. Venus’ atmosphere circulates 50 times faster than the planet spins.


Author(s): John Shibley ( http://www.earthsky.com/2001/es010407.html )

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to see the effect of air tides caused by moon on air pressure.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variable (also known as manipulated variable) is the position of moon in relation to your current position.

Dependent variable (also known as responding variable) is the air pressure.

Controlled variables are weather condition and temperature. (In this project air tides are not the only factors that may affect air pressure. Other factors such as weather conditions and temperature may also affect the air pressure.)

Constants are experiment location, experiment tools.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

My hypothesis is that the change in air pressure caused by air tides is so small that can not easily be noticed or detected with home made or consumer quality barometers.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

Effect of moon position or air pressure


In this experiment you will use a consumer quality barometer to monitor and record the air pressure while moon is located at different positions in relation to your location. Barometers are commercially available from different stores. You may also purchase them online. Some barometers are in a set known as weather station that include barometer, thermometer and hygrometer.


  • Observe the position of the moon and find out when the moon is above your head in your area. (Almost 12 hours after that, the moon will be in the other side of the earth). You may use some internet websites to calculate the position of the moon even before it is visible.
  • Prepare a schedule for your observations. You must make 4 observations in each 24 hours. When the moon appears in horizon (moonrise), when the moon is all the way above, when the moon is setting in the horizon (moonset) and finally when the moon is in the opposite side of the earth.
  • In each observation record the air pressure, temperature and weather condition.
  • Record your results in a table like this:
    Period Start Date moonrise moon above moonset moon in opposite side

* Period start date is the date of moonrise recording.

* Values in the table are pair of numbers. First number is the air pressure and second number is the temperature.

  • Repeat your observations and recordings for at least 15 days
  • From your results table, eliminate all results that are recorded during weather changes.
  • Calculate and compare the average air pressure for different moon positions.

Make a bar graph for air pressure:

Draw a bar graph to show the average air pressure in different moon positions.

Use one vertical bar for each moon position. The height of each bar will represent the average air pressure for that specific moon position. Write the moon position below each bar.

Make a bar graph for air temperature:

Draw a bar graph to show the average temperature in different moon positions.

Use one vertical bar for each moon position. The height of each bar will represent the average temperature for that specific moon position. Write the moon position below each bar.

Experiment 2:

(Make a mercury barometer)

Pour the mercury into the barometer tube, filling it completely. Pour the remaining mercury into a beaker. Place a finger over the open end of the tube and invert the tube, lowering it carefully into the beaker containing the remainder of the mercury. Clamp the tube upright on the stand.

Mark a scale of inches and half inches on the cardboard, and label it from 24 to 36 inches. With the yardstick, measure the actual height of the mercury column and attach the scale to the proper spot on the tube.

Watch the day-to-day variations in the height of the mercury. Record your readings. Compare them with radio and newspaper reports of local barometric pressure conditions.

NOTE: Be very careful that the mercury does not come in contact with any jewelry you may be wearing.

Experiment 3:

(Make an air barometer)


  • Glass or aluminum, or hard plastic bottle.
  • plastic tube
  • Gum or glue
  • water or colored water

Bend a thin clear plastic tube to make a U shape with an attachment. Put some water in the U section of your tube. (Colored water is more visible). Secure your tube on the side of a cardboard. Insert the attachment tube into a glass bottle and use some glue or gum to make it air tight.

Your bottle can be mounted horizontally or can stand vertically.

What’s happening

High pressure will make the colored water go up on the bottle side and low pressure will make it go down on the bottle side. Movement of water in the opposite side of our U tube will be reverse.


What happens to your barometer when moon is above? What happens when moon is on the other side of the earth. Make and record your observations for about 2 weeks. Can you use your barometer to show the effect of air tides?

Position of the moon (Optional Activity)

One of your activities in the above projects is observing and recording the position of the moon. For example you need to know the time of moonrise and moonset.

Hear is a sample guideline on how to track the position of the moon.


  • Compass
  • Large piece of cardboard
  • Large piece of butcher paper
  • Colored pencils, crayons and markers
  1. Begin by checking your local newspaper for the rising and setting times of the moon as well as its phases. Ideally, you should start this activity around the time of the first quarter moon. The quarter rises about six hours before sunset, so it should be more than halfway across the sky when you go out in the early evening.
  2. Next, you’ll want to choose your observation spot. Pick an open view of the sky facing south, as close to home as possible. If you’re not sure which direction is south, make a quick check with a compass.
  3. Cover a large piece of cardboard with a piece of butcher paper. In daylight, draw the southern skyline, including any houses, tall trees, electric poles or other landmarks.
  4. At the appointed time, head outdoors to chart the moon. First, see how to do a “sky measurement.” Choose a landmark below the moon, clench one fist out at arm’s length and, keeping it steady, place the other fist on top as if you are handing off on a baseball bat. Count how many fists from the top of the landmark are there to the moon?
  5. Draw the moon as you see it in the sky. Be sure you draw the right shape, and label the moon with the date and time.
  6. Every night at the same time, draw another picture of the moon on the paper, skipping a night if it’s cloudy. Try to draw as many moons as possible for as long as you want to continue the activity. How much change is there from night to night? When do you have to stop the project and why? Is the moon moving or are we? Why do we not always see a full moon?

Materials and Equipment:

For mercury barometer:

  • Glass barometer tube 36″ long, closed at one end
  • Small glass or beaker
  • Mercury
  • Ring stand with clamp
  • Cardboard strip, 2″ x 10″
  • Scotch or masking tape
  • Yardstick

For air barometer:

  • Glass or aluminum, or hard plastic bottle.
  • plastic tube
  • Gum or glue
  • water or colored water

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


No calculation is required for the above experiments.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.


List your References in your project report.