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Darkness at Mid Day

by Geoff Chester, USNO Public Affairs | 02 April 2024

by Geoff Chester, USNO Public Affairs | 02 April 2024

The total solar eclipse of August 21, 2017, imaged in HDR from Smith's Ferry, Idaho
with an Antares Sentinel 80mm (3-inch) f/6 refractor telescope, iOptron Cube Pro mounting
and a Canon EOS Rebel T2i DSLR

The Moon wanes in the morning sky this week, steadily tracking toward an encounter with the Sun on the 8th.  New Moon occurs on the 8th at 3:21 pm Eastern Daylight Time.  As most people know by now, this New Moon will produce the last total solar eclipse visible from much of the U.S. until August 12, 2045.  On the evening of the 9th, look for the slender crescent Moon in the western twilight sky.  The sighting of this crescent marks Eid al-Fitr, the end of the holy month of Ramadan in the Islamic world.

The total solar eclipse on the 8th is undoubtedly the astronomical event of the year.  If you have never seen one, you owe it to yourself to try to find a spot to view it within the path of totality.  I have been fortunate to see five of these events, and each one has left me nearly speechless.  My most recent experience in 2017, where I observed from central Idaho, was particularly special due to the effects on wildlife at our remote site.  The path of totality this year passes over a number of major cities, and millions of people will be traveling to the central track, so it’s a safe bet that this will be one of the most widely observed solar eclipses in history.

Here in Washington we will experience a significant partial eclipse.  The show begins at 2:04 pm EDT when the limb of the Moon first contacts the limb of the Sun.  Over the course of the next hour and 16 minutes Luna hides more of the Sun until mid-eclipse at 3:20 pm.  At this time just over 87 percent of the Sun’s disc will be covered by the Moon.  Last contact of the two bodies will occur at 4:33 pm. 

While viewing a partial eclipse pales compared to seeing the fully eclipsed Sun, there are still some subtle effects that can be seen during a deep partial one.  You may notice that the air cools as the eclipse progresses, and you may also be aware that the lighting looks a bit odd.  The latter is due to light from the Sun’s chromosphere, a thin layer just above the visible solar surface.  Normally overwhelmed by the intense light of the visible surface, more of the chromosphere’s red glow makes up the light from the partially obscured solar disc.  The result is a subtle, eerie pinkish tint on the surrounding landscape.  

If you are observing the eclipse during any of the partial phases, I cannot stress how important it is to wear proper eye protection.  If you are attending an eclipse-watch event, please follow the advice of the hosts.  They will ensure that you experience the eclipse safely.

This week is International Dark Sky Week, a world-wide celebration of the beauty of the night sky.  Begun in 2003 by high school student Jennifer Barlow, the principal aim of the project is to raise public awareness about light pollution and its impacts on the visibility of the night sky, energy conservation, and the health and habits of nocturnal plants, animals, and humans.  Events for IDSW are now coordinated by DarkSky International, which has nearly 200,000 members in 70 countries.  

Nighttime outdoor lighting has exploded over the past century to the point where some 80 percent of the people on the planet today have never seen the Milky Way.  Billions of migratory birds die each year by running into tall brightly lit buildings or not being able to see the stars that they navigate by.  Sea turtle hatchlings follow the Full Moon to reach the sea, but often bright lights inland lead them in the wrong direction.  Light pollution affects human circadian rhythms, often leading to serious medical issues.  The solution to these issues is relatively simple: put less light into the sky by using sensible night lighting.  We will regain the beauty of the night sky and save energy in the process.

To help you get into the dark sky spirit, this week is also the April campaign for the Globe at Night sky awareness program.  You can participate by locating the constellation of Leo, the Lion, in your local sky and comparing your view with star brightness charts on the Globe at Night’s web app.  Leo’s brightest star Regulus is high in the south at 10:00 pm local time.  It lies at the base of a semicircle of fainter stars that mark the Lion’s “head”.  His hindquarters are marked by a right triangle of stars about 15 degrees to the easy of Regulus.

Jupiter is now best seen in the fading twilight glow.  The giant planet is bright enough to shine in the west shortly after sunset.  An hour after the Sun goes down Old Jove will only be 20 degrees above the horizon, and he sets shortly after 10:00 pm 

Early risers have a chance to glimpse two planets in morning twilight.  Mars and Saturn are low in the southeastern sky, about 5 degrees above the horizon half an hour before sunrise.  Mars will close the gap with Saturn over the course of the week.  Viewers of the total solar eclipse will see the pair close to each other during totality.


Commander, Naval Meteorology and Oceanography Command | 1100 Balch Blvd. | Stennis Space Center, Mississippi 39529

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