2022, April 18: Baked Mercury, Morning Moon

April 18, 2022: Venus, Jupiter, Mars, and Saturn are in the eastern sky before sunrise, while the moon is in the southwest.  Mercury is in the west-northwest after sundown.

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by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 6:06 a.m. CDT; Sunset, 7:35 p.m. CDT.  Check local sources for sunrise and sunset times for your location.

Daylight increases to thirteen hours, 30 minutes.  The summer solstice is still two months away and about two hours to add to daily sunshine.

Morning Sky

The bright moon is in the southwest this morning in front of the stars of Libra.  On early star maps, the constellation was part of Scorpius, that is to its east (left) with its bright star Antares.  Libra’s brightest stars, Zubenelgenubi and Zubeneschamali, retain their association with the Scorpion.  The star names mean, the “northern claw” and the “southern claw,” respectively.

Farther eastward, brilliant Venus gleams from low in the east-southeast.  At forty-five minutes before sunrise, it is over 9° above the horizon.  Bright Jupiter is 11.1° to the lower left of the Morning Star.

Jupiter is emerging from bright morning twilight and appears low in the sky.  It is bright and easy to locate, if the horizon is unobstructed and cloud free.  This morning the Jovian Giant is nearly 5° above the eastern horizon.

Venus quickly steps toward Jupiter and passes it at month’s end.

Mars is dimmer than Venus and Jupiter, 11.5° to the upper right of Earth’s Twin Planet and 9.0° to the lower left of Saturn.  The planets span 31.8° from Jupiter to Saturn.

The four planets are lined up along the plane of the solar system, known as the ecliptic.

From our vantage point on Earth, we see the solar system’s massive features are near the ecliptic.  This morning you can estimate the ecliptic’s location by starting at Jupiter or Venus, if Jupiter is not visible at your location.

Extend your arm and point at the planet.  Slowly sweep your arm past the other planets and continue in an arc to the moon.  You’ve traced the plane of the solar system.  Note that Antares is a little below the ecliptic plane.

Evening Sky

Unlike slower moving Jupiter, Mercury is racing into the evening sky. At forty-five minutes after sunset, the speedy planet is nearly 7° up in the west-northwest.  It is easily located, but a binocular is helpful for easy identification.

From Earth, the planet is largely featureless because of its proximity to the sun.  The planet was first visited in 1974 by Mariner 10.  Photographs of the surface resemble our cratered-moon, including a large impact feature, the Caloris Basin, that is nearly 1,000 miles across. 

The surface has long, high cliffs that run hundreds of miles and may drop a mile.  This is hypothesized to be from the interior shrinking, making the surface crack and slip.

Temperatures can reach 800°F during the day and fall to hundreds of degrees below zero during the Mercurian night.  As the planet rotates every 59 earth-days, the surface is slowly broiled, then slowly frozen.

Other spacecraft from NASA and ESA (European Space Agency) have visited the planet during this century. 

In our evening sky, the planet is heading toward the Pleiades star cluster, 15.1° to Mercury’s upper left this evening.

Watch the planet appear higher in the sky each evening.

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