182 FAQs about the Earth (The Astronomy Cafe)

View your home from space TerraServer , Your Longitude and Latitude

Basic statistics and facts: A NASA Data Book , NASA/NSSDC FactSheet

Today's earthquake live: US Geological Service Event List

Today's space weather forecast: NOAA Space Environment Center

Satellite Data Archive NASA CDAWeb , Dynamics Explorer

Geophysical data archive: National Geophysical Data Center , Real-time solar wind data

Introductory geophysics papers America Geophysics Union

When does Spring arrive?: Table of dates and times

What If...

  1. What would happen if the magnetic field of the Earth suddenly changed?
  2. What would happen if the rotation axis of the Earth suddenly changes?
  3. What would happen if the Earth stopped spinning?
  4. If the Earth left the Sun's orbit, would we be able to tell immediately?
  5. If the Earth were to rotate once every 365 days, would you really get 1/2 year of daylight and 1/2 year of night?
  6. If I could float above the ground, would the Earth rotate underneath me?
  7. What would happen to your weight if you traveled to the center of the Earth?
  8. What would happen if you traveled through an aurora?
  9. If the Sun stopped shining, how long would the Earth cool to Absolute Zero in a few days?
  10. If the Sun stopped shining, how would the temperature of the Earth change?
  11. If the Sun mysteriously vanished, what would happen to the Earth?
  12. What would happen if the Earth were suddenly stopped in its orbit?
  13. If the Sun suddenly became a black hole, what would happen to the Earth's orbit?

Earth rotation and time:

  1. Does the Earth wobble as it spins?
  2. By how much does the axis of the Earth shift when it wobbles?
  3. What kinds of things cause the Earth to wobble?
  4. By how much does the Earth wobble?
  5. At the Autumnal Equinox in San Francisco we get more than 12 hours of daylight. Why is this?
  6. In which direction is the analema tilted from Earth?
  7. At what Central Standard Time will spring arrive in 1999-2019?
  8. Do the precession of the equinoxes, and the Earth's orbital eccentricity affect weather?
  9. Why does the earliest sunset occur almost 2 weeks before the December solstice?
  10. Why doesn't the longest night of the year have the earliest sunset or the latest sunrise?
  11. On which day of the year is the Earth closest to the Sun?
  12. How do you calculate GHA and SHA for celestial navigation?
  13. Why isn't the length of day symmetric about the noon hour?
  14. How can I find the Sidereal Time for my location?
  15. How do you calculate Local Sidereal Time from Universal Time?
  16. During the Summer, where will the sunniest part of a yard be located?
  17. Why do we have to add an extra day in February every 4 years?
  18. How is Daylight Savings Time established, internationally?
  19. Can you explain what Local Sidereal Time is all about?
  20. What exactly is twilight, and how long does it last in Houston Texas?
  21. What is the difference between Greenwich Mean Time, GMT, and Universal Time, UT?
  22. What are the dates in March for equal day/night durations from pole to pole?
  23. Why isn't the day of equal day/night the same day as the Vernal Equinox in 1997 from New York?
  24. Why doesn't noon come exactly half way between sunrise and sunset?
  25. Exactly when did spring arrive in 1996?
  26. Why is there more than 12 hours of daylight on the Equinoxes?
  27. What is the vernal equinox?
  28. What are the dates for Easter from 1959 to 2000?
  29. Do the perihelion and aphelion times for the Earth correspond to the solstice dates?
  30. If the day is 23 hours and 56 minutes long and we use 24-hour clocks, where do the extra 4 minutes go?
  31. How does the Earth spin?
  32. Why does the first day of summer arrive on December 1 and not December 21 in the southern hemisphere?
  33. In which direction is the Earth's axis tilted by 23.5 degrees?
  34. Will there be a February 29th in the year 2000AD?
  35. Why is the rotation velocity of the Earth faster at the equator than the poles?
  36. Why does the Earth spin?
  37. If the Earth stopped spinning would gravity stop?
  38. Are there any alternative theories about what causes the seasons on the Earth?
  39. Will the equinoxes and solstices switch places in 13,000 years because of the precession of the Earth's rotation axis?
  40. Why does the Earth rotate on its axis at all?
  41. What measurements were made thousands of years ago to show that the rotation period of the Earth was different then?
  42. Did the Earth rotate faster in the past?
  43. How do astronomers know the Earth had a different rotation period long ago?
  44. Why is the tilt of the Earth's axis 23 1/2 degrees?
  45. What is the relationship between universal Time, and Eastern Standard Time?
  46. Is there a place on the Earth where the Sun would appear to rise in the west?
  47. What is the difference between 'ephemeris 1950' and 'ephemeris 2000'?
  48. Why is the '18 degree' limit used to define the end of twilight?
  49. At what location will it be perpetual twilight in the summer in the northern hemisphere?
  50. Can you slow Earth's rotation artificially?
  51. Will the direction the Earth rotates ever change?
  52. Why does the Earth rotate in the direction that it does?
  53. Does the northern hemisphere have milder seasons than the southern hemisphere?

 

Basic Properties etc:

  1. How do I find the exact latitude and longitude of my house?
  2. Where can I get the latitude and longitude of my city?
  3. How old is the Earth?
  4. Is the Earth's pole shifting?
  5. What is the current distance of the Earth from the Sun?
  6. How many different directions does the Earth move in space?
  7. What is the Earth's elongation from the Sun?
  8. How much ozone is there in the Standard Atmosphere for purposes of determining the visual magnitudes of stars?
  9. Where does the atmosphere end and outer space begin?
  10. Is there a crater called Playfair in the southern hemisphere named in 1973?
  11. How do we know the speed of the Earth?
  12. Why is the sky blue?
  13. What is the mass of the Earth?
  14. How quickly does the Earth move through space?
  15. How is the mass of the Earth determined?
  16. What is the equatorial speed of the Earth?
  17. What is the distance from the Sun to the Earth for each month of the year?
  18. How much energy would it take to explode the Earth?
  19. Are there differences in gravity from one place on the Earth to another?
  20. Why is the Earth tectonically active and not Mars or Venus?
  21. What are the biggest factors that affect the amount of sunlight reaching the Earth's surface ( solar insolation)?
  22. How do we know the Earth orbits in an ellipse and not a circle?
  23. Over a 10 kilometer run, how high is the Earth's curvature at the mid- point?
  24. If I wanted to face the direction the Earth is moving in its orbit, where in the sky should I look?
  25. How do you actually prove the Earth is not at the center of the solar system?
  26. Is there any gravity at the center of the Earth?
  27. How is the Earth-Sun distance determined?
  28. If the universe is mostly hydrogen and helium, why isn't the Earth composed the same way?
  29. Is the Moon helping the Earth avoid a Venus-like state by bleeding off surplus air produced by vulcanism?
  30. Is the Earth's atmosphere thicker at the equator due to rotation?

 

Magnetic field, aurora

  1. What causes auroras to have different colors?
  2. Are there places on the WWW that give aurora forecasts?
  4. Why haven't we seen any aurorae in Minnesota lately?
  5. When the Earth's magnetic field reverses, does its rotation also switch?
  6. Is it true that the Earth's magnetosphere is expanding?
  7. Where can I get information about the Earth's magnetosphere?
  8. Does the reversal of the Sun's magnetic field have any effect on the Earth?
  9. Is the Earth's magnetic field changing?
  10. Is the Earth about to reverse its magnetic field?
  11. When is the best time of the year to see aurorae from Scotland?
  12. What is the average density of solar wind particles that produce the aurora?
  13. Recently astronomers spotted a 'Coronal Projection' which affected the Earth. What was it?
  14. What will happen to digital transmission technology during the next sunspot cycle?
  15. What is the South Atlantic Anomaly?
  16. Are auroras seen on other planets?
  17. Why don't auroras happen near the equator?
  18. Can you hear an aurora?
  19. How often are aurorae seen in the continental United States?
  20. Do aurora produce radio waves?
  21. What are some of the early theories about auroras?
  22. How long have auroras been observed?
  23. How do auroras affect the Earth?
  24. How are auroras produced?
  25. Is there a greater risk for solar radiation when taking the polar route by jet plane?
  26. Is plasma present during an aurora?
  27. If auroras didn't exist how would the Earth be affected?
  28. Do aurora give off heat?
  29. Why does the Earth have radiation belts?
  30. Will there be a 'restructuring' of the Earth's magnetic field in the year 2013 that will end the Earth?
  31. How much mass does the Earth gain from the solar wind?
  32. What effects do sunspots have on the Earth?
  33. Where can I get the exact time?
  34. Can the Aurora Borealis be seen from Rhode Island?

 

Past, present, future; evolution

  1. What is the maximum and minimum distance for the Earth that is compatible with life?
  2. Are we currently in an ice age that has lasted millions of years?
  3. What conditions are required for starting life on Earth?
  4. What is your opinion about how life started on the Earth?
  5. What happened to the carbon dioxide in the Earth's early atmosphere?
  6. When the Earth's crust solidified, is this when it got its current non-spherical shape?
  7. Did the asteroid that hit the Earth 65 million years ago affect the Earth's orbit?
  8. Could intelligent life have existed on Earth a billion years ago?
  9. Why did the dinosaurs have to go extinct before humans could evolve?
  10. How did the Earth's atmosphere get to be so rich in nitrogen and not carbon dioxide?
  11. Is the Earth really shrinking?
  12. How did life get started on the Earth?
  13. What effect did the Moon have on the Earth 900 million years ago when it was 21,250 miles closer?
  14. If two neutron stars 1000 light years away collided, would life on Earth be wiped out?
  15. How do you think the Earth will finally come to an end?
  16. Will the Earth ever fall into the Sun?
  17. I once heard that the Earth could end in 10 different ways at any moment. What are they?
  18. What will happen to the Earth when there is no sun?
  19. How long will the Earth remain habitable?

 

Miscellaneous

  1. What causes the 'sprites' seen in certain weather phenomena?
  2. Why is the pressure at the center of the Earth not zero since the gravitational force vanishes there?
  3. What is the 'Tree of Life' and how many species of life are there on Earth?
  4. Where can I get a picture of the Earth and Moon as seen from millions of miles away?
  5. Where can I find a picture of the Earth seen from a very large distance in the solar system?
  6. What is a Schumann Resonance?
  7. Are there more stars in the sky in the north or south hemispheres?
  8. Why does the wavelength response of the human eye match the atmospheric transmission window in the visual range so well?
  9. Can the Earth be destroyed by a neutrino belt or a photon storm?
  10. If the Moon vanished, what would happen to the Earth?
  11. What portion of the stars are visible from any spot on the Earth?
  12. Is it true the Earth and Moon could not have condensed from the same material?
  13. What aspects of astronomy influence the weather?
  14. Are the Earth's Lagrange points stable or does the Moon perturb them?
  15. From the Moon, what would libration do to the position of the Earth in the sky?
  16. What is the first star that you see in the Northern and Southern Hemispheres?
  17. What is the current value for the moment of inertia of the Earth?
  18. Which produces the most seismic activity the Sun or the Moon?
  19. What causes weather systems to come from opposite directions in the northern and southern hemispheres?
  20. Could you answer some questions about the Earth for me?
  21. Does the motion of the Earth around its barycenter cause the core of the Earth to slosh around?
  22. Do the hydrogen nuclei from the solar wind combine with oxygen to produce water in the Earth's atmosphere?
  23. An Austrian astronomer, Hoeberger, has proposed the Earth once had 2 moons and one collided with the Earth to produce the Great Flood. Is this true?
  24. What is the difference between the 1971 atmosphere model by Jacchia, and the later one by Jacchia and Roberts?
  25. If a star at declination +50 is seen 30 degrees above the horizon, how far above the horizon will a star with a declination of +70 degrees be?
  26. What is the nature of the boundary between the Earth's atmosphere and outer space?
  27. Where does oil come from?
  28. How did the Earth get its name?
  29. How fast does the Earth spin, orbit the Sun, and move through the universe?
  30. What is earthshine and when can it be observed?"
  31. Why are the tides higher in some places on the Earth than others?
  32. Where can I get information about the Earth's relationship to the Sun and Moon?
  33. Do planetary conjunctions have any effect on the Earth?

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