 Earth's Aurora from Space. This image of the Aurora Australis, or Southern Lights, was taken from the Space Shuttle. Auroras are formed when charged particles streaming from the sun impact the Earth's magnetic field. Some of the particles are trapped by the field and follow along field lines until they hit the top of Earth's atmosphere. When the particles impact atoms in the air, they cause the atoms to glow.
 Credit: Brian Kent
The Aurora from Ithaca, NY. On October 28, 2003, one of the largest solar flares ever recorded sent a stream of high energy particles directly toward Earth, resulting in auroras that could be seen at low latitudes. A second flare led to auroras on the night of the 30th. This picture of the aurora was taken on Oct. 30, 2003 by Brian Kent, one of the Ask the Astronomer team members, at the Hartung-Boothroyd Observatory outside Ithaca. The Space Weather website has information about recent solar activity and can give you advance notice on when the aurora might be visible at your location.
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The Earth
At first it might not seem like the study of Earth would be an important part of astronomy. However, Earth is part of our solar system neighborhood, and many things happening on Earth are directly related to other objects in the solar system.
For example, auroras, tides, and seasons are all caused by Earth's interaction with the Sun or Moon. Comet and asteroid impacts change the surface of the Earth and can influence the evolution of life. Even topics in geology, such as volcanism, tectonics, and the study of rocks and minerals are useful in astronomy because they help us interpret what we see on other planets.
For instance, we know that on Earth the mineral hematite is often formed in hot-spring type environments, and so when Mars Global Surveyor detected hematite on the surface of Mars, it was evidence that there might once have been liquid water there.
Comparing Earth to other solar system objects can also teach us a lot about Earth's history. The early history of Earth is a good example of how this can work. Because Earth's rocks are recycled by plate tectonics, we have very few rocks dating back to Earth's beginning.
The oldest Earth rocks are about 3.8 billion years old, although some small, very old grains found in sandstone have been dated at 4.1 billion years. The solar system is believed to be about 4.6 billion years old. Therefore, there is little evidence left on Earth about the very early solar system. Some asteroids and comets, however, have not been altered much since their formation, and studying them can provide information about what the solar system was like when Earth was first forming.
Looking at old surfaces of larger objects, like our Moon, can also help us discern Earth's distant past. Studying craters on the Moon has shown us that our part of the solar system went through a period of "heavy bombardment" when large numbers of asteroids or comets impacted planets, moons, and each other. If the Moon was impacted many times, the Earth probably was too, even though the craters from this event have been destroyed by erosion and tectonics.
Many people find Earth facts and phenomena especially interesting because they relate to things we see every day. Please explore our archive of Earth science questions and our favorite links about Earth before writing in with your question.
The Ask an Astronomer team's favorite links about The Earth:
- Google Earth: Downloadable program that lets you explore anywhere on the earth. Easy to use and fascinating!
- The Earth: Wikipedia article about the earth. Loads of great information!
- Nine Planets: Earth: Earth information and facts from the Nine Planets Solar System Tour.
- NASA Earth Science
- The Aurora Page: Lots of information and pictures about the aurora, including sighting reports and forcasts.
- Earth Science Picture of the Day: Lots of great images of Earth are here with accompanying descriptions.
Previously asked questions about The Earth:
General questions:
- How many Earths fit into the Sun? (Beginner)
- How does night and day work? (Beginner)
- What are the names of the earth, moon, sun, and solar system? (Beginner)
- Is the Earth slowly getting larger? (Beginner)
- Where did the name 'Earth' come from? (Beginner)
- How much longer will the Earth last? (Beginner)
- What is the significance of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle and Antarctic Circle? (Beginner)
- Can we feel the Earth spin? (Beginner)
- What if the Earth rotated twice as fast? (Beginner)
- What causes the aurora? (Beginner)
- How do we know the age of the Universe and the Earth? (Intermediate)
- Why is twilight short near the equator? (Intermediate)
- Do the Sun's or Earth's magnetic field reverse? (Intermediate)
- What makes the Earth rotate? (Intermediate)
- How can we estimate the number of Earth-like planets in the Galaxy? (Intermediate)
- Did the Sumerians measure precession? (Intermediate)
- How long has there been water on Earth? (Intermediate)
- How does melting a material reset its radioactive clock? (Intermediate)
- Do the Earth's magnetic poles ever change places? (Intermediate)
- How do we know the mass of the Earth and the Moon? (Advanced)
Earth and its Moon:
- Are Earth and the Moon "twin planets"? (Beginner)
- Did the Moon or planets form in a manner similar to that of Earth? (Beginner)
- Are there solar tides? (Beginner)
- Why are there both high and low tides? (Intermediate)
- Why does the Earth have only one moon? (Intermediate)
- What would happen if Earth had more than one moon? (Intermediate)
- What would happen if the Moon fell out of its orbit around Earth? (Intermediate)
- What is Earthrise over the Moon? (Intermediate)
- Have astronomers discovered Earth's second moon? (Intermediate)
- Does Mt. Everest cast a shadow on the moon? (Intermediate)
- Does the Mediterranean sea have tides? (Intermediate)
- When can I see the Moon through the hole in the Pantheon? (Intermediate)
- How close was the Moon to the Earth when it formed? (Intermediate)
- Is Earth-moon tidal friction causing global warming? (Intermediate)
- Can other terrestrial moons be (or have been) stable? (Advanced)
Impacts:
- What would happen if an impact caused Earth to stop rotating? (Beginner)
- Are there any asteroids on a collision course with Earth? (Beginner)
- What would happen if an asteroid 10 kilometers across hit the Earth? (Beginner)
- Why are there no craters on Earth? Did all the meteorites miss us? (Beginner)
- Did a giant impact cause the Dark Ages? (Beginner)
- What is the biggest crater recorded on Earth? (Beginner)
- Why are craters round? (Beginner)
- How dangerous are the asteroids? (Intermediate)
- Would the biggest airplanes cause tsunamis if they crashed? (Intermediate)
- Can planets collide with one another? (Intermediate)
- Will Comet Elenin (C/2010 X1) affect the Earth on its close approach in Fall 2011? (Intermediate)
Other catastrophes:
- What will happen to life on Earth when the Sun becomes a red giant? (Beginner)
- What would happen if the gravity on Earth was suddenly turned off? (Beginner)
- How will the two black holes that are going to collide affect Earth? (Beginner)
- What would happen to us if the sun went out for an hour? (Beginner)
- How long could life on Earth survive if the Sun stopped shining? (Beginner)
- How close does a supernova need to be to damage the Earth's environment? (Intermediate)
- Will the sun go supernova in six years and destroy Earth (as seen on Yahoo)? (Intermediate)
- How big a change in the Earth's orbit would be required to destroy all life? (Intermediate)
- How long would it take the Earth to fall into the Sun? (Intermediate)
- What's going to happen on December 21st 2012? (Intermediate)
- Do the Earth's magnetic poles ever change places? (Intermediate)
- Will Comet Elenin (C/2010 X1) affect the Earth on its close approach in Fall 2011? (Intermediate)
- What would happen if a supermassive black hole came close to the Earth? (Advanced)
- Will the magnetic field of the Earth reverse its direction in the future? Will this cause problems? (Advanced)
- How long would it take for a mini-black hole to eat the Earth? (Advanced)
Climate and weather:
- Why isn't the summer solstice the hottest day of the year? (Beginner)
- What causes seasons? (Beginner)
- Did I see the Aurora Borealis as a child? (Beginner)
- What is the hottest time of day? (Beginner)
- How long could life on Earth survive if the Sun stopped shining? (Beginner)
- Why does the Earth tilt back and forward once a year? (Beginner)
- Will the seasons change due to precession? (Intermediate)
- What are the "dog days of summer"? (Intermediate)
- How critical is the Earth-Sun distance in maintaining our average temperatures on Earth? (Intermediate)
- Can any comparison be made between spiral galaxies and hurricanes? (Intermediate)
- How would the weather on Earth be different if it were a cube? (Intermediate)
- What makes the wind? (Intermediate)
- Why do airplanes take longer to fly West than East? (Intermediate)
- Does the Mediterranean sea have tides? (Intermediate)
- How much can the location of sunset differ from due West? (Intermediate)
- If the sun went out and our atmosphere froze solid, what color would it be? (Intermediate)
- Is Earth-moon tidal friction causing global warming? (Intermediate)
- Why does Mars have a dusty atmosphere? (Intermediate)
Orbit:
- At what speed does the earth move around the sun? (Beginner)
- Does the Sun orbit the Earth as well as the Earth orbiting the Sun? (Beginner)
- Can the sun rise from the west on Mars? (Beginner)
- Is there a proof that Earth moves? (Intermediate)
- How do you measure the distance between Earth and the Sun? (Intermediate)
- Considering the motion of the Earth, the solar system, and the galaxy, how fast am I moving while lying in bed asleep? (Intermediate)
- How fast does the Earth go at perihelion and aphelion? (Intermediate)
- How long would it take the Earth to fall into the Sun? (Intermediate)
- Can the Sun be closer to the Earth than any planet is to Earth? (Intermediate)
- Is the distance from the Earth to the Sun changing? (Advanced)
- What is the difference between nutation and precession of the Earth? (Advanced)
- When the Sun converts mass to energy, do the orbits of the planets change? (Advanced)
- How can I find the distance to the Sun on any given day? (Advanced)
Gravity:
- Why don't people walk upside-down on the bottom of the Earth? (Beginner)
- Are there solar tides? (Beginner)
- Does your weight change between the poles and the equator? (Intermediate)
- Does gravity vary across the surface of the Earth? (Intermediate)
- Would your weight change as you go underground? (Advanced)
Geology:
- Why is sea water salty, and not lake water? (Beginner)
- How can water be chemically trapped in rocks? (Intermediate)
- Do the Earth's magnetic poles ever change places? (Intermediate)
How to ask a question:
If you have a question about The Earth which isn't answered above, submit it here. If you have a question about another area of astronomy, find the topic you're interested in from the archive on our site menu, or go here for help.
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