Posts by Bob Trembley

In the Sky This Week – August 15, 2017
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5:30 AM Aug 15, 2017 East

Eastern morning sky - 5:30 AM Aug 15, 2017. Venus' orbit is shown in red. Credit: Stellarium / Bob Trembley.

Venus is a bit lower and Orion a bit higher in the eastern morning sky. Venus orbits closer to the Sun than Earth, and is racing ahead-of and away-from the Earth; the planet will vanish from view in mid-November as the Sun comes between it and the Earth.

Position of the Moon Aug. 15-19, 2017

Position of the Moon Aug. 15-19, 2017. Credit: Stellarium / Bob Trembley.

The waning crescent Moon appears thinner and closer to the horizon each morning in the eastern sky. Note: I used Stellarium's new "Astronomical calculations" feature to generate the ephemeris for this image - I expect you'll be seeing more of this.

1:50 AM Aug. 16, 2017 Conjunction

Conjunction of the Moon and Aldebaran - 1:50 AM Aug. 16, 2017. Credit: Stellarium / Bob Trembley.

The Moon be in conjunction with the star Aldebaran on the Aug. 16th, appearing VERY close to each other, VERY early in the morning.

Aldebaran Compared to the Sun

Orange giant star Aldebaran compared to the Sun. Credit: Universe Sandbox ² / Bob Trembley

Aldebaran is a orange giant star about 44 times the size of the Sun, located about 65 light years away. Aldebaran is positioned close to the ecliptic plane, and is frequently occulted by the Moon... just not this month.

10 PM Aug. 15, 2017 Southwest

Southwestern sky after sunset - Aug. 15, 2017. Credit: Stellarium / Bob Trembley.

Jupiter is visible only for a short time after sunset very low in the western sky - atmospheric turbulence made it a poor observing target for me last weekend. Saturn is high in the southern sky, and is a great observing target; last weekend, I saw five of Saturn's moons in the Warren Astronomical Society's huge Dobsonian telescope!

Overhead - Aug. 15, 2017 10 PM

The Sky Overhead - Aug. 15, 2017 10 PM. Credit: Stellarium / Bob Trembley.

The Solar System - Aug 15, 2017

The Solar System - Aug 15, 2017. Credit: NASA Eyes on the Solar System / Bob Trembley.

Apps used for this post:

Stellarium: a free open source planetarium app for PC/MAC/Linux.
Universe Sandbox ²: a physics-based 3D space simulator.
NASA Eyes on the Solar System: an immersive 3D solar system and space mission app - free for the PC /MAC.

In the Sky This Week – August 8, 2017
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5 AM Aug 8, 2017 East

Eastern morning sky - Aug 8, 2017. Credit: Stellarium / Bob Trembley.

Venus is a bit lower in the eastern predawn sky, and Orion is fully visible now before sunrise. The waxing gibbous Moon, just days after full,  rises in the east with the sunset, and sets in the west with at dawn.

10 PM Aug 8, 2017 Southwest

Southwest sky after sunset - Aug. 8, 1027. Credit: Stellarium / Bob Trembley.

Jupiter is low in the western sky, and visible for only a short time. Saturn is high in the southern sky after sunset, and sets about 2:00 AM.

The Perseid Meteor shower peaks the evening of August 11-12th; the Moon will be at Third-Quarter on August 14th.

11 PM Aug 8, 2017 Overhead

The sky overhead - Aug 8, 2017 11 PM. Credit: Stellarium / Bob Trembley.

The Solar System - Aug 8, 2017

The Solar System - Aug 8, 2017. NASA Eyes on the Solar System / Bob Trembley.

Apps used for this post:

Stellarium: a free open source planetarium app for PC/MAC/Linux.
NASA Eyes on the Solar System: an immersive 3D solar system and space mission app - free for the PC /MAC.

Perseid Meteor Shower 2017: Aug. 11-12
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Perseid Meteor Shower Radiant

Perseid Meteor Shower Radiant - August 12, 2017 2 AM. Credit: Stellarium / Bob Trembley

The Perseid meteor shower is a very popular annual event, with Perseid parties being held around the globe each year. Best seen from the northern hemisphere, the meteors will appear to radiate from a point in the constellation Perseus - between the "W" of the constellation Cassiopeia, and the bright star Capella (see image above).

Moon to the East of the 2017 Perseid Meteor Shower Radiant

The Moon will be east of the 2017 Perseid meteor shower radiant. Credit: Stellarium / Bob Trembley.

Every year I see posts about this year's shower being the "shower of the century" or it will be the "brightest shower in the recorded human history!" I'm not so sure about that this year... although the Perseids typically puts on a pretty good show at about 100 per hour, the waning gibbous Moon will be bright, and just to the east of the radiant; this will obscure many of the dimmer meteors.

Waxing Gibbous Moon - 79 Percent

Waning Gibbous Moon - 79 %. Credit: Stellarium

Peak: August 11-12
Active from: July 13th to August 26th
Radiant: 03:12 +57.6° (see image above)
Hourly Rate: 100
Velocity: 37 miles/sec (swift - 60km/sec)
Parent Object: 109P/Swift-Tuttle

Source: American Meteor Society

Meteor. Credit: Creative Commons, CC BY 3.0

In the Sky This Week – August 1, 2017
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5 AM Aug 1, 2017 East

Venus in the eastern morning sky - 5 AM Aug 1, 2017. Credit: Stellarium / Bob Trembley.

Venus is still high in the eastern morning sky; the constellation Orion appears a bit higher each morning.

10 PM Aug 1, 2017 Southwest

Waxing gibbous Moon, Saturn and Jupiter in the south-southwest sky after sunset - Aug. 1, 2017. Credit: Stellarium / Bob Trembley.

The southern sky is filled with objects this week: the waxing gibbous Moon accompanies Jupiter and Saturn for several days.

10 PM Aug 2, 2017 South - Conjunction

Conjunction in the southern sky after sunset - Aug. 2, 2017. Credit: Stellarium / Bob Trembley.

The Moon will appear very close to Saturn on the evening on August 2nd.

5 AM Aug 1, 2017 Southeast Constellation Cetus

Constellation Cetus in the southeast morning sky. Credit: Stellarium / Bob Trembley.

The constellation Cetus appears in the predawn sky to the southeast.

5 AM Aug 1, 2017 Southeast Constellation Cetus Artwork

Constellation Cetus Artwork. Credit: Stellarium / Bob Trembley.

Cetus is depicted as a sea monster in Greek mythology, but is often referred to as "the whale" today.

H.A. Rey Starlore

Stellarium can show constellation lines from the H.A. Rey's book "The Stars." Credit: Stellarium / Bob Trembley.

I know several astronomers who had a copy of H.A. Rey's "The Stars: A New Way to See Them" when they were young - I still have my copy! I was overjoyed to see that Stellarium has a starlore set depicting constellations as drawn by H.A. Rey in his book.

5 AM Aug 1, 2017 Southeast Constellation Cetus - H.A. Rey

H. A. Rey's version of the constellation Cetus. Credit: Stellarium / Bob Trembley.

The constellation Cetus in Stellarium as drawn by H.A. Rey in his book "The Stars: A New Way to See Them."

11 PM Aug 1, 2017 Overhead

The sky overhead - Aug 1, 2017 11 PM. Credit: Stellarium / Bob Trembley.

The sky overhead - Aug 1, 2017 11:00 PM

Solar System - Aug 1, 2017

The Solar System - Aug 1, 2017. Credit: NASA Eyes on the Solar System / Bob Trembley.

The Solar System - Aug 1, 2017.

Mars on Other Side of the Sun - Aug 1, 2017

Mars is currently on the opposite side of the Sun from Earth - Aug 1, 2017. Credit: NASA Eyes on the Solar System / Bob Trembley.

Mars is not visible in the sky right now because it is on the opposite side of the Sun from the Earth. Mars will reappear in the eastern predawn sky in mid-September.

5 AM Aug 1, 2017 East - Perth

Eastern morning sky from Perth - 5 AM Aug 1, 2017. Credit: Stellarium / Bob Trembley.

I live in Michigan at 42° N latitude; almost 90% of all humans live in the northern hemisphere, so these "In the sky" posts are apply to most of the human population. I was asked by a friend if I ever posted anything about southern hemisphere skies. "No" I replied, "But I should..." So...

The skies of the southern hemisphere look quite different than those of the northern hemisphere, and offers some spectacular objects for observers. Some familiar constellations like: Orion, Taurus and others nearer the horizon are visible, but appear upside-down, as does the Moon!

11 PM Aug 1, 2017 Overhead - Perth

The sky overhead from Perth. Credit: Stellarium / Bob Trembley.

Farther from the horizon, and more toward southern latitudes, are constellations and objects that northern hemisphere observers will never be able to see - and I've been told some of them are "bucket-list" material.

Apps used for this post:

Stellarium: a free open source planetarium app for PC/MAC/Linux.
NASA Eyes on the Solar System: an immersive 3D solar system and space mission app - free for the PC /MAC.

What’s in the Sky July 25, 2017
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Eastern predawn Sky July 25, 2017 5 AM

Venus in the Predawn Eastern sky. Image credit: Stellarium / Bob Trembley

Venus is still bright in the eastern predawn sky, but a little bit lower each morning. The constellation Orion is rising with the dawn; a little more of the constellation visible each morning.

Crescent Moon at Sunset July 25, 2017 9 PM

Crescent Moon at Sunset on July 25th. Image credit: Stellarium / Bob Trembley

A wafer-thin waxing crescent Moon will be visible for a short time after sunset in the west on July 25th.

Southern Sky July 25, 2017 10 PM

Jupiter and Saturn in the Southern Sky after Sunset. Image credit: Stellarium / Bob Trembley

Jupiter is visible low in the southwestern sky, and will be a little lower in the sky each evening after sunset. Saturn is high in the southern sky, and is a great target for telescope observers.

Conjunction July 28, 2017 11 PM

Jupiter will be 3° South of the Moon - July 28th After Sunset. Image credit: Stellarium / Bob Trembley

Jupiter will be a scant 3° South of the Moon after sunset on July 28th.

First Quarter Moon July 30, 2017 10 PM

First Quarter Moon - July 30th. Image credit: Stellarium / Bob Trembley

The Moon will be at First Quarter on the evening of July 30th, surrounded by Jupiter and Saturn, and the Southern Delta Aquariids Meteor Shower peaks on July 29-30th; this would be a great evening to host an astronomy outreach event!

Overhead - July 25, 2017 11 PM

Overhead - July 25, 2017 11 PM. Image credit: Stellarium / Bob Trembley

The Solar System July 25, 2017

The Solar System on July 25, 2017. Image credit: NASA Eyes on the Solar System / Bob Trembley

Apps used for this post:

Stellarium: a free open source planetarium app for PC/MAC/Linux.
NASA Eyes on the Solar System: an immersive 3D solar system and space mission app - free for the PC /MAC.

Southern Delta Aquariids Meteor Shower 2017
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Southern Delta Aquariids Meteor Shower Radiant

Southern Delta Aquariids Meteor Shower Radiant. Credit: Stellarium / Bob Trembley

The Southern Delta Aquariids is a strong shower best seen from the southern tropics. North of the equator, the radiant is located low in the southern sky - rates will be less than if seen from further south. This shower produces good rates for about a week centered on the night of maximum. These meteors are usually faint and lack persistent trains; few fireballs can be expected.

Waxing Crescent Moon

Waxing Crescent Moon. Credit: Stellarium.

Peak: July 29-30
Active from: July 21st to August 23rd
Radiant: 22:40 -16.4° (see image above)
Hourly Rate: 16
Velocity: 26 miles/sec (medium - 42km/sec)
Parent Object: P/2008 Y12

The moon will be a waxing crescent, rising shortly after midnight.
Source: American Meteor Society

Meteor. Credit: Creative Commons, CC BY 3.0

What’s in the Sky July 18, 2017
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Eastern Sky - July 18 2017 4:30 AM

Eastern Sky - July 18 2017 4:30 AM; Venus orbit is shown in red. Image credit: Stellarium / Bob Trembley

Venus continues to dominate the morning sky in the east, but appears slightly lower in the sky each morning as it pulls ahead of us in its orbit.

Conjunction of the Moon, Venus and Aldebaran- July 19-20, 2017 4:30 AM

Conjunction of the Moon, Venus and Aldebaran - July 19-20, 2017 4:30 AM. Image credit: Stellarium / Bob Trembley

The waning crescent Moon will appear near Venus the the star Aldebaran on the mornings of July 19th and 20th. The New Moon will be on the 23rd.

Southwestern Sky - July 18, 2017 11 PM

Southwestern Sky - July 18, 2017 11 PM. Image credit: Stellarium / Bob Trembley

Jupiter and Saturn appear in the south-southwestern sky after sunset; Jupiter will appear slightly lower in the western sky each day as the Earth pulls ahead of Jupiter in its orbit.

Andromeda rising in the northeast -July 18, 2017 11 PM

Andromeda rising in the northeast - July 18, 2017 11 PM; position of M31 is highlighted. Image credit: Stellarium / Bob Trembley

The constellations Pegasus and Andromeda appear low in the northeast sky after sunset; the wispy cloud of M31, the Andromeda galaxy, makes a good target for telescope observers.

Andromeda Galaxy

Andromeda Galaxy. Credit: Wikimedia Commons

M31 is the nearest major galaxy to the Milky Way. It is 2.5 million light years distant, and heading straight at us; in a little over 4 billion years, it will collide with the Milky way, and the two galaxies will merge into a large elliptical galaxy.

Don't expect M31 to look like this time-exposure image in your backyard telescope tho - it typically appears as a circular blue-greenish cloud, surrounded by a larger and dimmer cigar-shaped cloud.

Sharpest ever view of the Andromeda Galaxy. Click to see ZOOMable 6000px image.
Image credit: NASA, ESA, J. Dalcanton (University of Washington, USA), B. F. Williams (University of Washington, USA), L. C. Johnson (University of Washington, USA), the PHAT team, and R. Gendler.

In January of 2015, the Hubble Space Telescope team released this GIANT mosaic image of the Andromeda galaxy. There is a clickable-version that lets you explore a 48,000-light-year-long swath of the Andromeda galaxy in exquisite detail.

The Sky Overhead - July 18, 2017 11 PM

The Sky Overhead - July 18, 2017 11 PM. Image credit: Stellarium / Bob Trembley

The Solar System July 18-24, 2017

Animation of the Solar System from July 18-24, 2017. Image credit: NASA Eyes on the Solar System / Bob Trembley

Apps used for this post:

Stellarium: a free open source planetarium app for PC/MAC/Linux.
NASA Eyes on the Solar System: an immersive 3D solar system and space mission app - free for the PC /MAC.

Jupiter’s Great Red Spot from Juno
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Juno over the Great Red Spot

Juno over the Great Red Spot on July 10, 2017 (simulation at 9.7x real-time). Credit: NASA Eyes on the Solar System / Bob Trembley

The Juno spacecraft made its seventh close approach (perijove) to Jupiter on July 10th, flying directly over the Great Red Spot. The raw images from the mission are publicly available, and have been post-processed by several different individuals. The results are as beautiful as they are varied.

This stunning image, processed by Seán Doran, was featured on the Astronomy Picture of the Day on July 15, 2017:

Great Red Spot [ 060 ] V1. Credit : NASA / SwRI / MSSS / Gerald Eichstädt / Seán Doran © PUBLIC DOMAIN


Here are some more examples of post-processing from the imaging community:

Great Red Spot Turbulence near Mortyland ROI. Credit : NASA/SwRI/MSSS/Shawn Handran © PUBLIC DOMAIN

Like and Impressionist's Painting.Credit: NASA/SwRI/MSSS/Hilana-69 © PUBLIC DOMAIN

Sleepy Eye. Credit : NASA / SwRI / MSSS /Tom Momary © CC NC SA

This image was processed by Jason Major, who runs the fantastic Lights in the Dark website; the image was used in this post by NASA.

Jupiter’s Great Red Spot

Jupiter’s Great Red Spot imaged by Juno on July 10, 2017. Credit: NASA/SwRI/MSSS/Jason Major

This video was created using the NASA's Eyes on the Solar System app shows the Juno spacecraft coming up on the Great Red Spot; I knew the storm was big, but I've never seen it from this perspective... it's BIG!

This video gives you a good idea of how close the Juno spacecraft gets to Jupiter during perijove:


Juno Raw Images: https://www.missionjuno.swri.edu/junocam/processing

In the Sky This Week – July 11, 2017
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Venus Aldebaran Conjunction July 10-18 2017

Venus-Aldebaran Conjunction July 10-18, 2017 5:00 AM. Image credit: Stellarium / Bob Trembley

Venus continues to be the "morning star" in the east, and will appear very close to the red giant star Aldebaran - the "eye of the bull" in the constellation Taurus. On the 11th, Venus will be 3 north of Aldebaran, over the course of the week, Venus' day to day change in position relative to Aldebaran will be very noticeable.

Vega and Altair at Dawn - July 12, 2017

Vega and Altair Fading with the Dawn - July 12, 2017 5:45 AM. Image credit: Stellarium / Bob Trembley

In the west, bright stars Vega and Altair are the last to fade in the oncoming dawn.

On the 11th, a waning gibbous Moon will be rise in the east before midnight, and set in the west around 9:00 AM. On the 18th, a waning crescent Moon will rise shortly after 2:00 AM, and be visible until it is lost in the glare of the rising sun after 6:00 AM. The Moon will be at third quarter on the 16th, and will be visible from about 1:00 AM - 1:00 PM.*

Southern Sky - July 11, 2017

Southern Sky - July 11, 2017 11:00 PM. Image credit: Stellarium / Bob Trembley

Jupiter and Saturn are visible in the southern sky after sunset; Jupiter sets shortly after midnight, and Saturn sets around 3:30 AM.

Northern Sky - July 11, 2017

Northern Sky - July 11, 2017 11:00 PM. Image credit: Stellarium / Bob Trembley

The constellation Cassiopeia, recognizable as a "big W," appears low on the horizon to the north shortly after sunset.

The Sky Overhead - July 11, 2017

The Sky Overhead - July 11, 2017 11:00 PM. Image credit: Stellarium / Bob Trembley

The Solar System - July 10, 2017

The Solar System - July 10, 2017. Image credit: NASA Eyes on the Solar System / Bob Trembley

* I was once asked by a very well educated adult relative: "Why can I see the Moon during the day?" The Moon orbits around the Earth - that orbit takes the Moon around both the sunlit and nighttime sides of the Earth. A new Moon, being "in front of the Earth" is lost in the glare of the Sun; first and third quarter Moons can be seen during both day and nighttime hours. The full Moon, being "behind the Earth" is visible from dusk to dawn.

Apps used for this post:

Stellarium: a free open source planetarium app for PC/MAC/Linux.
NASA Eyes on the Solar System: an immersive 3D solar system and space mission app - free for the PC /MAC.

In the Sky This Week – July 4, 2017
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Venus and Capella

Venus and bright star Capella in the eastern morning sky - 4 AM July 5 2017. Venus' orbit is shown in red. Image credit: Stellarium / Bob Trembley

Venus is the bright morning star in the eastern sky, attended by the Pleiades star cluster, and the bright star Capella to the northeast.

Southern sky July 4, 2017

Jupiter, Saturn and the Moon in the southern sky - 10 PM July 4, 2017. Image credit: Stellarium / Bob Trembley

The southern sky is adorned with several jewels this week: the Moon appears high in the southern sky before sunset as a waxing gibbous - a few days past first quarter. Jupiter and Saturn are both visible, as are the bright stars Antares and Spica. The full Moon will be on July 9th.

Southeast July 4, 2017

Bright star Altair and constellation Sagittarius rising in the East - 10 PM July 4, 2017. Image credit: Stellarium / Bob Trembley

The bright star Altair (featured in the classic SF film Forbidden Planet) rises in the east followed by the constellation Sagittarius to the southeast. Sagittarius is recognizable by "The Teapot" asterism low on the horizon.

Constellation Sagittarius

Constellation Sagittarius and the center of the Milky Way Galaxy. Image credit: Stellarium / Bob Trembley

Sagittarius has several interesting deep sky objects to observe using telescopes; something cool you can do with the public during nighttime observing sessions is point to the Teapot's spout and say "that's where center of our Milky Way galaxy is!"

Northwest - 4 AM July 5 2017

Hercules and Ursa Major on the northwestern horizon - 4 AM July 5, 2017. Image credit: Stellarium / Bob Trembley

Before dawn, the constellation Hercules sets in the west, and "The Big Dipper" asterism is very low on the northern horizon.

Conjunction Moon Saturn Antares

Conjunction of the Moon, Saturn and Antares - 10 PM July 5, 2017. Image credit: Stellarium / Bob Trembley

Conjunction Moon Saturn

Conjunction of the Moon, Saturn and Antares - 10 PM July 6, 2017. Image credit: Stellarium / Bob Trembley

Conjunction Moon Saturn Antares

Conjunction of the Moon, Saturn and Antares - 10 PM July 7, 2017. Image credit: Stellarium / Bob Trembley

There will be a conjunction of the Moon, Saturn and the star Antares three nights in a row between July 5-7, with the Moon very close to Saturn on July 6th.

Overhead 10 PM July 4, 2017

Overhead - 10 PM July 4, 2017. Image credit: Stellarium / Bob Trembley

Solar System

Solar System July 4, 2017. Image credit: NASA Eyes on the Solar System / Bob Trembley

In the Sky This Week – June 27, 2017
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Venus remains high in the eastern morning sky, the Pleiades star cluster appears between Venus and the star Capella.

Venus and the Pleiades

Venus and the Pleiades in the eastern pre-dawn sky at 5 AM on June 27, 2017. Image credit: Stellarium / Bob Trembley

The Moon is a waxing crescent, appearing in the west after sunset.

Waxing Crescent Moon

Waxing Crescent Moon in the western sky at 10 PM on June 27, 2017. Image credit: Stellarium / Bob Trembley

Jupiter is high in the southwest, and Saturn is low in the southeast sky after sunset.

Saturn and Jupiter

Saturn and Jupiter in the southern skies at 10 PM on June 27, 2017. Image credit: Stellarium / Bob Trembley

There will be a conjunction of the Moon, Jupiter and the star Spica on the evenings of June 30th and July 1st.

Conjunction of The Moon, Jupiter and Spica

Conjunction (Day 1) of The Moon, Jupiter and Spica at 10 PM on June 30, 2017. Image credit: Stellarium / Bob Trembley

Conjunction of The Moon, Jupiter and Spica

Conjunction (Day 2) of The Moon, Jupiter and Spica at 10 PM on July 1, 2017. Image credit: Stellarium / Bob Trembley

Here is the current positions of the planets in the solar system:

The Solar System June 27 2017

The Solar System June 27, 2017. Image credit: NASA Eyes on the Solar System / Bob Trembley

Could “Planet Nine” be Considered a Planet?
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Planet Nine Location

Possible location for hypothesized Planet Nine. Credit: Universe Sandbox ²/ Bob Trembley

I got to wondering: given the International Astronomical Union's (IAU) current definition of a planet, if a hypothesized "Planet Nine" were to be found in the outer reaches of our solar system, could it (or anything in that region) be considered "a planet?"

The IAU definition of a planet is a celestial body that:
(a) is in orbit around the Sun.
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape.
(c) has cleared the neighborhood around its orbit.

An astronomical units (AU) is a unit of measurement equal to the mean distance from the center of the earth to the center of the sun - 149.6 million kilometers.

The Kuiper belt is a disc-shaped region of icy bodies in the solar system - including dwarf planets such as Pluto - and comets beyond the orbit of Neptune. It extends from about 30 to 55 AU.

A trans-Neptunian object (TNO) is any minor planet in the Solar System that orbits the Sun at a greater average distance (semi-major axis) than Neptune - 30 AU.

The Oort cloud as a hypothesized bubble of icy debris that surrounds our solar system. This distant cloud may extend a third of the way from our sun to the next star - between 5,000 and 100,000 AU.

The hypothesized location of "Planet Nine" is around 500 and 1200 AU; images I've seen all place it in a highly elliptical orbit, pretty near to the ecliptic plane. That puts it out in the trans-Neptunian region, and well into the Kuiper belt. The hypothesized mass of "Planet Nine" is ten times that of Earth, making it much larger than the typical size of trans-Neptunian objects.

The question is: with the existence of the Kuiper Best, and the pretty good chance that the Oort cloud exists, can any object out past Neptune ever be classified as a planet, given the requirement that a planet clear its neighborhood?

Oort Cloud Illustration. Credit: laurinemoreau.com

A related issue is that under the current IAU definition of a planet, exoplanets and satellites in orbit of brown dwarfs cannot be considered planets; I'd suggest a slight rewording to state that a planet must be "planetary mass object in orbit of a stellar or sub-stellar mass parent body."

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