Category: Astronomy

2019, July 9: Saturn at Opposition

On July 9, Saturn is at opposition, nearly a month after Jupiter was in the opposite direction in the sky from the sun.

Saturn is near opposition for several nights before and after reaching this point opposite the sun.  To locate the planet step outside after the sky darkens.  The chart above shows the sky about 90 minutes after sunset; check your sources for the time of sunset at your location. (For example, in Chicago, Illinois, the time for the above chart is 10 p.m. CDT.  Near Omaha, Nebraska, 90 minutes after sunset is 10:30 p.m. CDT.)

Jupiter is the bright “star” that is almost south, but less than one-third of the way up in the sky.  Golden-orange Antares is to the lower right of Jupiter.  Saturn is farther left of Jupiter in the southeast, lower in the sky than Jupiter.  Saturn is among the stars of Sagittarius, brighter than those surrounding stars, but not as bright as Jupiter.  For perspective, the moon is outside the chart.  The gibbous moon is in the southwest, above the bluish star Spica.  On July 15, the nearly full moon is to the right of Saturn.

Through a telescope, the planet’s rings are revealed.  If you’re careful, you might see its a few of its moons, depending on the diameter of the lens or the mirror and the magnification that is used.  The large gap in the rings, Cassini’s Division, might be seen as well.

Viewing Saturn through a telescope is one of life’s memorable experiences.  If you view this spectacular ringed wonder through a telescope, you will certainly remember.  A child will remember this experience.

Opposition occurs when Earth passes between a planet farther from the sun than Earth (Mars, Jupiter, Saturn, Uranus, and Neptune) and the sun.  The planet rises at sunset, appears in the south around midnight, and sets in the west.  When at opposition, the outer planets are closest to Earth, at their brightest points in the sky, and provide the best telescopic views.

Saturn appears at opposition again on July 20, 2020, when it reaches that point just six days after Jupiter’s opposition.  Jupiter passes Saturn in December 2020 for a Great Conjunction that occurs about every 20 years.

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2019, June 10: Jupiter at Opposition

Jupiter (NASA Photo)

Jupiter reaches opposition on June 10, 2019.  On that evening, and for a few evenings around that date, Jupiter rises in the southeast at sunset. As the sky darkens further, Jupiter appears higher in the sky.

At this time the planet is about 450 million miles away, yet it looks like a bright star.  The planet is to the left of the golden-orange star Antares.

Jupiter’s oppositions occur about every 400 days, about 35 days longer than an Earth year.  The planet is slower moving than Earth. Jupiter revolves around the sun about every 11.8 (earth) years.

Jupiter moves on a longer track and at a slower speed than Earth.

Once Earth moves between Jupiter and the sun, it speeds away and catches up with Jupiter again in about a year and 35 days.

While we remark that Jupiter is at opposition, this description is related to the notion that earth is stationary and immobile.  While it is inaccurate, it relates to the apparent movement of the heavens, in the same way we use “sunrise” and “sunset.”  Both solar events are from Earth’s rotation.

When Jupiter, and other planets outside Earth’s orbit, appears at opposition, it is at its closest point to Earth.  The planet rises at sunset, appears at its highest in the south at midnight, and sets in the western sky at sunrise.

After opposition, Jupiter appears higher in the sky each night at the same time.  In several weeks it appears in the south at sunset.  It disappears into sun’s glare in December.

If you have access to a telescope, Jupiter is a spectacular sight in that telescopic view.  The colors of its cloud bands are revealed and sometimes the Great Red Spot is visible.  The Red Spot is sometimes described as a long-lived storm.  It’s been observed in the clouds for over 400 years!

Jupiter’s four largest moons appear in the telescope as well.  They look like stars.  The moons are lined up in the equatorial plane.  They are visible through a binocular as well, if you can hold the optics steady enough to see them.

Go outside and take a look for Jupiter in the early evening sky!

2019, June 5-30: Mercury and Mars in the Evening Sky

The chart above shows the evening positions of Mercury and Mars from June 5, 2019, to June 30, 2019. The moon is part of the scene on June 5 and June 6.

About 45 minutes after sunset, Mercury and Mars are visible in the west-northwest  beneath Pollux and Castor, the Gemini Twins.  Early in the month, the  stars are about one-third of the way up in the sky.

Mercury is beginning an evening appearance.  Early in the month, it is brighter, but closer to the horizon.

Twilight lasts longer this time of year, so it’s not visible in the latter sky glow as the sky darkens further.  So, the upcoming conjunction with Mars is better viewed with a binocular.  Both planets’ movements are easier viewed across several nights.

On June 5, the waxing crescent moon, the waxing crescent moon that is 2.7 days past the New phase and only 9% illuminated is 6.3° to the upper left of Mars, which sets at the end of evening twilight.  At this time the Red Planet is about 13° up in the west-northwest, a little over halfway between Castor and Pollux and the horizon.

Each evening until the conjunction, Mercury is closer to Mars.

On June 18, Mercury passes close to Mars, less than the moon’s apparent diameter.  The chart above shows them 45 minutes after sunset when they appear in the west-northwest.  Use a binocular to locate them.  Can you see them without a binocular?

As the month progresses, the planets appear lower and in a brighter sky. Continue to use a binocular to track the planets.

By month’s end, a dimmer Mercury appears to the upper left of Mars.

2019, May 19-21: Moon Passes Jupiter

As Jupiter approaches opposition, the event when our planet Earth is between Jupiter and the sun.  Jupiter and the sun are in opposite sides of the sky.  Jupiter rises when the sun sets and Jupiter sets when the sun rises.  Jupiter is in the south at midnight, when the sun is in the south at noon.

A few weeks before opposition, Jupiter appears in the evening and the morning sky.  Here’s what’s to see depending on when you step outside to see it.

Evening

  • May 19: At 10:30 p.m. CDT, the moon, 15.2 days past its New phase and 98% illuminated, is nearly 7° to the upper right of Jupiter and almost 9° to the left of Antares in the southeastern sky.

  • May 20: At 11 p.m. CDT, the moon, 16.2 days old and 94% illuminated, is nearly 7° up in the southeast and 6.5° to the lower left of Jupiter.

Morning

By morning , the moon appears in the southwest.

  • May 20:  At the beginning of morning twilight (about 4 a.m. CDT), the moon, 15.4 days old and 98% illuminated, is 4.6° to the right of Jupiter.  The Giant planet is 24° up in the south-southwest.

  • May 21:  At the beginning of morning twilight, the moon, 16.5 days old and 93% illuminated, is 25° up in the south and 8.2° to the left of Jupiter.

 

2019, May 17: Moon in Clasp of the Pincers

On Friday evening (May 17), look toward the southeast for a nearly full moon.  The moon appears between Zubenelgenubi and Zubeneschamali, the northern claw and the southern claw, respectively.  The stars are not overly bright, and the moon’s size is exaggerated in the image above.

Today the stars are the two brightest in Libra, the Scales.  This constellation is the only inanimate object in the zodiac, the constellations that the sun, moon, and planets appear to move through.

The two stars were once part of Scorpius, the Scorpion, that is now rising in the southeast below the moon.  The scorpion was divided into two constellations, but the two stars retained their original names.

So if you imagine that the scorpion is largely below the southeast horizon with its pincers up in the sky holding the moon on this evening.

2019, May 15-16: Moon Passes Spica

Step outside as the sky darkens on Wed (May 15) and Thurs (May 26).  The moon appears to pass the bluish star Spica on the two evenings.  Spica is the brightest star in the constellation Virgo.

On May 15, the moon, 11.1 days past its New phase and 90% illuminated, appears 8° above Spica.

On the next evening, the moon, one day older and 92% illuminated, is over 11° to the left of Spica.

Across these two evenings you can see the moon’s eastward movement compared to the starry background.

We notice several changes in the moon:

  • Phase:  The illuminated portion of the moon changes slightly each night, dramatically across a week.
  • Daily Rising and Setting:  On a warm spring evening, notice the moon’s position, relative to nearby trees and houses, for an hour.  You see it get farther west during that time.  Like the sun, it rises in the eastern sky, sometimes southeast and sometimes northeast, and sets later somewhere in the west that mirrors its rising spot.
  • Daily eastward orbital motion:  Each day, the moon moves slightly to the east.  In about 27 days appears near Spica again, but its phase is not quite the same as on these two nights.

2019: May 11-13: Moon and Leo in Evening Sky

Leo, the Lion, stands high in the southwest as the sky darkens in early to mid-May.  The shape is fairly easy to locate.  Six stars resemble a backwards question mark, also known as “The Sickle” for the farm implement.  A triangle trails farther east.  Regulus is the bottom star of the question mark and represents the lion’s heart.  Denebola marks the lion’s tail.  The celestial lion is majestically facing westward as we view its profile.  The moon moves through the region May 11-13, 2019.  Here’s what to look for:

  • May 11: The moon reaches its First Quarter phase at 8:12 p.m. CDT. One hour after sunset, the moon, 7.1 days past its New Phase and 50% illuminated, is high in the southwest, 8.9° to the right of Regulus.

The angular degree measurement is used in astronomy to determine the separations and sizes of objects.  Because objects have various actual sizes and distances from Earth, the degree is the way for us to communicate apparent sizes and apparent separations.  The full moon has an apparent diameter of about 1/2°.  The charts we use typically exaggerate the size of the moon, so the chart cannot be used for a scale with the moon.  The distance from Regulus to Denebola is about 24°.

  • May 12: One hour after sunset, the moon (8.1d, 62%) is 6.2° to the upper left of Regulus.
  • May 13: The moon is closest to Earth at 4:53 p.m. CDT. An hour after sunset, the moon (9.1d, 73%), nearly 60° up in the south, is 8.5° to the lower right of Denebola– the tail of Leo.