Earth Day was first celebrated on April 22, 1970. Wisconsin senator Gaylord Nelson proposed the official event to be a day of activities honoring the Earth and Peace. The movement was later inspired by the 1972 photo taken by Apollo 17 astronauts on their way to the Moon from a distance of 29,400 kilometers. That photo, known as the Blue Marble, became a banner for Earth Day and is one of the most famous NASA photos ever.
Almost 50 years to the minute, at 07.39 GMT on 7 December 2022, Blue Marble v.2 was captured by the DSCOVR (Deep Space Climate Observatory) satellite parked at the L1 Lagrange point between the Earth and Sun, some 1.5 million kilometers from Earth. The satellite’s position at L1 provides a continuous view of Earth’s fully illuminated hemisphere, so it was only a matter of timing to match DSCOVR’s view to that of Apollo 17’s. The image above shows Blue Marble v.1 (left) and v.2 at the same scale and (approximately) the same orientation. But careful inspection reveals things have changed over those 50 years.
Urbanization, deforestation, pollution, and greenhouse gas emissions are altering the way Earth looks. One of the most striking differences is the visible reduction in the size of the Antarctic ice sheet. You can also see the increase in desertified areas, primarily the Sahara Desert in this image, at the southern edge of which we see deforestation. This increase of “brown” and decrease of “green” is also happening in the Amazon, but there it is more from intentional burning than changed rainfall patterns.
It’s somewhat ironic that, 50 years after the first Earth Day, Blue Marble v.2 shows these troublesome changes. Still, DSCOVR is providing valuable data that can inform us about the impacts of climate change.
DSCOVR takes images in multiple wavelengths from UV to IR. From that data scientists can determine the amounts of ozone, clouds, water, ice crystals, and aerosols (as from wildfire smoke). They can also measure the height and location of clouds.
DSCOVR can also measure the amount of leaf cover on Earth, as it’s directly illuminated by the Sun. Along with observations of ocean surface color, which varies depending on plastic content and phytoplankton blooms, scientists can determine the rate of all photosynthetic activity on our planet.
DSCOVR hasn’t been running long enough to provide any definitive conclusions. That will take a few years. But over time it will provide valuable insights into how the world is changing.
The night side of our planet is not visible to DSCOVR. Other satellites monitor that region for additional data, including the expansion urban sprawl measured by light pollution, heat island effects, and the glow of wildfires.
Next Week in Sky Lights ⇒ Rivers vs. Estuaries