Earth and Space

We tend to think of the Earth as apart from the rest of the universe.  That is natural as astronomy is the science of looking away from our home planet.  While there are many things in space we do not experience in our daily lives such as relativistic effects and black holes, there are other phenomena in space that are closely related to our day-to-day lives.  Some introductory astronomy texts lump the Earth and Moon in a chapter with all the other inner planets.  I think this is a mistake.  A separate section should be dedicated to the Earth and Moon as a starting point to understanding space.

There are many Earth to space examples to pick from and below I’ll describe a few.

I’ll start on the ground level.  The Earth experiences plate tectonics along with resultant earthquake and volcanic activity.  Lets take a look at shield volcanoes.  These volcanoes vent liquid lava rather than explosive pyroclastic material we typically associate with such events as the Mount St. Helens eruption in 1981.  Shield volcanoes are gently sloping (Hence, they resemble shields) as liquid lave runs downhill quickly preventing the buildup of steep slopes.  A prominent example are the Hawaiian Island chain situated above the Hawaii hot spot.  Why is there a chain rather than just one island?  As the Earth’s tectonic plate slides over the hot spot, a chain of islands are formed.

Shield volcano of Mauna Kea in Hawaii where the Keck Observatory sits at the summit. Credit: Wiki Commons.
Shield volcano of Mauna Kea in Hawaii where the Keck Observatory sits at the summit. Credit: Wiki Commons.

The largest shield volcano in the Solar System is Olympus Mons on Mars.  This volcano stands 16 miles high (Mt. Everest is 5.5 miles high) and has a base the size of Arizona.  The low gravity of Mars, a third that of Earth, allows for the extreme height of Olympus Mons.  And why is Olympus Mons a single volcano rather than a chain like Hawaii?  Mars does not have plate tectonics as Earth does.  Hence, the crust of Mars never slid across the hot spot as the Hawaiian Islands did on Earth.  Understanding the nature of shield volcanoes on Earth can be integrated into an comprehension that Mars has smaller mass, thus, smaller gravity than Earth and no plate tectonic activity either.  Land features are not the only place to find planetary similarities.

Computer generated image of Olympus Mons using data from Mars Global Surveyor laser altimeter. Credit: NASA/MOLA Science Team/ O. de Goursac, Adrian Lark.
Computer generated image of Olympus Mons using data from Mars Global Surveyor laser altimeter. Credit: NASA/MOLA Science Team/ O. de Goursac, Adrian Lark.

The rotation of Earth affects air circulation via the Coriolis effect.  In the Northern Hemisphere, air movement is deflected to the right.  In the Southern Hemisphere, air movement is deflected to the left.  What this means is in the Northern Hemisphere, low pressure systems rotate in a counterclockwise pattern.  You can see this in radar shots of hurricane systems which are massive regions of low pressure.  High pressure systems rotate in a clockwise pattern.  The pattern is reversed in the Southern Hemisphere.

Hurricane Mathew circulating in a counterclockwise fashion. Credit: NOAA.
Hurricane Mathew circulating in a counterclockwise fashion. Credit: NOAA.

Now lets take a look at Jupiter’s Giant Red Spot from this time lapse video of the approach of Voyager I in 1979.

Jupiter rotates in the same fashion as Earth.  That is, counterclockwise if looking down from the North Pole.  At first glance, the Giant Red Spot seems to resemble a hurricane and it might be easy to assume it is an area of low pressure.  However, it is in the Southern Hemisphere and rotates counterclockwise.  By understanding how the Coriolis effect works on Earth, you can deduce the Giant Red Spot is actually an area of high pressure.  Beyond this raging centuries old storm, understanding the nature of Earth’s magnetic field will help one understand the space environment surrounding Jupiter.

Most of the matter we encounter is electrically neutral.  That is, their constituent atoms contain as many negatively charged electrons as positively charged protons.  In space, the Sun is hot enough to break the atomic bonds between electrons and protons.  The result is an electrified gas called plasma.  Neon lights are filled with plasma.  When plasma encounters a magnetic field, it’s electrically charged particles travel along the path of a magnetic field line in helix pattern seen below.

Credit: cnx.org
Credit: cnx.org

This can be visualized on the Sun which has a more complex magnetic field than the Earth.  The Solar Dynamics Observatory images plasma traveling along the solar magnetic field lines in formations referred to as coronal loops.

Credit: SDO/NASA
Coronal loops.  Credit: SDO/NASA

Back on Earth, these charged particles move along the magnetic field lines until they hit the upper atmosphere in the polar regions.  Nitrogen and oxygen atoms absorb the kinetic energy of the incoming particles causing electrons to jump to a higher energy orbit.  When the electron moves back to its usual lower energy orbit, the absorbed kinetic energy is converted and released as light.  This light is known as the aurora.  Earth is not the only planet with an aurora, the gas giants have strong magnetic fields that produce the same effect, albeit mostly in ultraviolet.  This presents a good opportunity to understand that light and ultraviolet are both electromagnetic radiation.  The difference is our eyes are not designed to detect ultraviolet rays, but our skin can in the form of sunburn.  The aurora of Saturn as imaged by the Hubble can be seen below.

Credit: NASA/ESA/J. Clarke (Boston University).
Credit: NASA/ESA/J. Clarke (Boston University).

Electrons, when accelerated, will emit radio waves.  This is the principle behind radio transmitters.  Electrons are accelerated up and down a radio tower causing the transmission of a radio broadcast.  The same thing happens in space when electrons are accelerated along the path of a magnetic field line.  Jupiter emits radio waves in this fashion that can be detected on Earth with ham radio sets.  This process plays itself out in the deepest regions of the universe.  For one such example, we’ll take a look a the galaxy Centaurus A located 12 million light years away.  Below is an optical image of the galaxy.

Credit: ESO
Credit: ESO

In 1949, it was discovered this galaxy was a strong emitter of radio waves.  Below is a radio image of Centaurus A.

Credit: NRAO/AUI
Credit: NRAO/AUI

The radio source emanates perpendicular to the mass of the galaxy.  Each lobe is a million light years long (10 times the width of the Milky Way) and would appear 20 times the size of a full Moon if we could see radio waves.  This suggests a massive stream of plasma being ejected from the galaxy.  What could cause this to happen?  In the core of Centaurus A resides a black hole 55 million times the mass of the Sun.

It seems counter-intuitive that a black hole could result in such a massive ejection of matter.  We think of black holes as objects that suck in everything, including light.  However, some of the matter in the accretion disk surrounding the black hole hits a magnetic field before crossing the event horizon.  So instead of continuing into the black hole, the plasma is accelerated and ejected violently along the magnetic field line exiting the galaxy.  Below is a composite image of Centaurus A with optical, radio, and x-ray imaging.

Credit: ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray)
Credit: ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray)

There is a tendency to think of Earth science and astronomy as separate fields of study, but as we live on Earth we are also living in space – under the protective cover of the atmosphere.  The first step in understanding space is to learn the science behind what we experience in our surroundings.  From there, we can explore and understand the universe.

*Image atop post – Earth and the Milky Way from the International Space Station.  Credit:  NASA.

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