Understanding our Place in the Universe - Part II

The Importance of Studying Earth

Image Credit: NASA/NOAA

The day is September 8, 1900. For the residents of Galveston, Texas, the weather at the start of the morning was far from unusual for a late summer day on the Gulf Coast - hot, humid, and partly cloudy. While there was chatter about a storm coming in from the east, few were particularly worried that it was anything they couldn't handle. By mid-afternoon, however, it became very apparent that this was no ordinary storm, but a category 4 hurricane striking the town directly. Winds exceeding 140 mph scattered debris across the island, and a powerful storm surge inundated the coastal community under several feet of water, destroying homes and drowning trapped residents. By the morning of September 9 when the storm had passed, an estimated 6,000 - 12,000 casualties were left behind. To this day, the 1900 Galveston Hurricane is known as the deadliest single-day disaster in the history of the United States (for comparison to a weather-related catastrophe in recent history, Hurricane Katrina in 2005 killed 1,245 - 1,836 people total).

Over the century that followed, weather forecasting has developed substantially, in large part due to data from satellites that have been put in orbit around Earth by public space programs. While the poor emergency response to Hurricane Katrina in 2005 left hundreds to thousands of preventable deaths in the aftermath of the tragedy, advanced notice of the storm's trajectory allowed for mandatory evacuation warnings that undoubtedly saved many more throughout the Gulf Coast. Had the residents of New Orleans been as oblivious to the storm as those in Galveston one hundred years prior, the casualties would have likely been incomprehensible. While many Americans are openly enthusiastic about NASA's space exploration and planetary science projects, comparatively few grasp the importance of studying the one planet that offers the easiest and most cost-effective research opportunities - Earth.

As a particularly politicized field of research, Earth-focused climate science in the United States has received inconsistent funding from one federal administration to the next. In a decision that sparked notable controversy within the scientific community, the current presidential administration was especially quick to propose cutting support for critical Earth-science programs across multiple federal agencies like NASA, choosing to instead direct the agency's research focus towards space exploration:

"The Budget increases cooperation with industry through the use of public-private partnerships, focuses the Nation’s efforts on deep space exploration rather than Earth-centric research, and develops technologies that would help achieve U.S. space goals and benefit the economy."

Regardless of one's political beliefs, however, it is crucial that governments allocate sufficient funding towards monitoring the one planet we all share as inhabitants; it is inarguable that we all depend on its finite resources and its capacity to support our growing civilizations. In addition to protecting vulnerable communities from weather-related disasters like the Galveston Hurricane, understanding our climate system through satellite data is vital for commercial agriculture, fishing, aviation, oceanic shipping, and other industries. Even militaries depend on high-quality weather forecasts to develop strategies for fighting enemy forces that threaten national security.  Remote sensing data from satellites benefits other fields of Earth science research, as well, allowing for monitoring of threatening forest fires and dust storms across the globe, plankton population changes in the oceans that provide insight on the health of marine ecosystems, and even changes in the planet's crust that can help us better understand the propagation of earthquakes. It is for these reasons that funding Earth science is a prerequisite for effective planetary science - in order to understand our place in the universe, it is important to first understand our place in the universe. 

Backyard Astronomy: Navigating the Celestial Sphere

In my first post, I briefly alluded to the celestial sphere - the imaginary sphere on which the stars appear to be fixed. Just like how cartographers use latitude and longitude to define all points on Earth's surface, astronomers use coordinates of declination (DEC) and right ascension (RA) to map the night sky for observation. The priority is to have a coordinate system for stars and constellations that is universal for any geographic location at any time of year; the north star, for example (a.k.a. Polaris, which is on the handle of the Little Dipper constellation) is near the north celestial pole at a declination of approximately 90°. The celestial equator is simply a projection of Earth's equator into space, and defines 0° declination. This means that for an observer on Earth, the declination of the zenith (the point directly overhead) is equal to their latitude. Given that the equator is defined based on the planet's rotation, it is not to be confused with the ecliptic, which is the plane of Earth's orbit around the Sun. Recalling the previous Backyard Astronomy post, the ecliptic and the celestial equator are separated by an angle of about 23.4° due to the tilt of the planet's spin axis. Like Earth, the celestial sphere has north and south poles at DEC = ±90°.

A depiction of the basic coordinates on the celestial sphere.
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To fully understand right ascension, it is important to grasp the distinction between solar time and sidereal time. Most of us recognize the length of a solar day, which is approximately 24 hours and is defined based on the position of the Sun in the sky; one solar day is the length of time it takes the Sun to make a single revolution around the sky before returning to a given point. When mapping distant stars on the celestial sphere, however, it is important to consider the effect of Earth's orbit around the Sun. From an observer's perspective on Earth, the celestial sphere makes one revolution four minutes more quickly than the Sun. Because of this effect, one sidereal day is actually about 23 hours and 56 minutes in length. This means that it takes slightly less than 24 hours for a given constellation like the Big Dipper to circle the sky and return to its original position. As a result, the celestial sphere appears slightly shifted from one midnight to the next. This is the reason why we see different constellations in the night sky from season to season. When defining the coordinates of right ascension, astronomers use units of hours (h) instead of degrees (°), with 24h defining one 360° circle. For a given point in the sky, the right ascension shifts by approximately 1h each hour. With Earth's rotation under consideration, as well as the distinction between solar and sidereal time, the prime meridian of the celestial sphere (RA = 0h) is defined as the projection of Earth's prime meridian into space at noon during the spring equinox. For an observer at any location, the right ascension of the zenith at a given time would shift by four minutes from night to night.

An exaggerated illustration of the difference between a sidereal and solar day.
Not to scale.
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