APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

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Expand view Topic review: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by neufer » Mon Sep 27, 2021 11:36 pm

Click to play embedded YouTube video.

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by Chris Peterson » Wed Apr 26, 2017 1:46 pm

Nitpicker wrote:
RocketRon wrote:If the coma was that big, and that close to earth, wouldn't it have been easily visible to the naked eye ?
I think this comet never quite made it brighter than mag 6 (to allow unaided observation in a dark sky). And diffuse objects appear much dimmer than point sources of the same mag, anyway.
Andromeda is a good example- a diffuse object larger in our sky than 6 full moons, but which the majority of people go through life never seeing.

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by Nitpicker » Wed Apr 26, 2017 5:09 am

RocketRon wrote:If the coma was that big, and that close to earth, wouldn't it have been easily visible to the naked eye ?
I think this comet never quite made it brighter than mag 6 (to allow unaided observation in a dark sky). And diffuse objects appear much dimmer than point sources of the same mag, anyway.

Edit: Doh, see, I knew I read it somewhere:
APOD Robot wrote:The comet reached visual magnitude 7 earlier this month, making it a good target for binoculars and long duration exposure cameras.

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by RocketRon » Wed Apr 26, 2017 4:51 am

If the coma was that big, and that close to earth, wouldn't it have been easily visible to the naked eye ?
Chris Peterson wrote: How big the gas coma actually gets is a complicated thing, determined by the speed of outflow (which can exceed 1 km/s) and the rate of photodissociation of the glowing species (mostly C2). Usually gas comas don't get this large; dust comas, however, can exceed the size of the Sun.
Nitpicker wrote:By my rough calculations, the visible coma in this image is about 240,000 km in diameter, or almost twice the size of Jupiter. It appeared more than 10 times bigger than Jupiter ever does from Earth.

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by Chris Peterson » Wed Apr 26, 2017 4:48 am

neufer wrote:
Chris Peterson wrote: Whether any body remains in the same orbit depends on how it interacts with other bodies. Shorter period comets that remain inside the outer planets, and which have fairly low inclinations, are quite susceptible to gravitational perturbations from planets, especially Jupiter. These comets usually have orbits that evolve over time.

A comet like C/2017 E4, however, is almost perpendicular to the ecliptic, and has an eccentricity very close to 1. That means it has an orbital period of many thousands of years (and could even be in an open orbit, meaning it will never return). Such a comet probably won't have its orbit changed much by a single passage through the inner system.
A comet with an eccentricity very close to 1 requires very little to go from an elliptical orbit to a hyperbolic orbit (or vice versa).
Exactly. Indeed, the error on the measurements makes it impossible to say for sure just which side of one the value currently stands at.
Periodic comets that don't stray too close or too far from the Sun ( like Halley) are generally more or less predictable.
Oh yes, they're very predictable. But their orbits are constantly changing. Every pass results in new orbital elements. They're predictable because of our ability to use numerical integration tools to propagate their orbits forwards or backwards in time, modeling all the gravitational perturbations they undergo. (Such modeling is an important part of my own work.)

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by neufer » Wed Apr 26, 2017 2:23 am

Chris Peterson wrote:
ta152h0 wrote:
Returning comets , do they stay in the same orbit or do the focal points rotate around the Sun ?
Whether any body remains in the same orbit depends on how it interacts with other bodies. Shorter period comets that remain inside the outer planets, and which have fairly low inclinations, are quite susceptible to gravitational perturbations from planets, especially Jupiter. These comets usually have orbits that evolve over time.

A comet like C/2017 E4, however, is almost perpendicular to the ecliptic, and has an eccentricity very close to 1. That means it has an orbital period of many thousands of years (and could even be in an open orbit, meaning it will never return). Such a comet probably won't have its orbit changed much by a single passage through the inner system.
A comet with an eccentricity very close to 1 requires very little to go from an elliptical orbit to a hyperbolic orbit (or vice versa).

Periodic comets that don't stray too close or too far from the Sun ( like Halley) are generally more or less predictable.

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by Chris Peterson » Tue Apr 25, 2017 9:08 pm

ta152h0 wrote:Returning comets , do they stay in the same orbit or do the focal points rotate around the Sun ?
Whether any body remains in the same orbit depends on how it interacts with other bodies. Shorter period comets that remain inside the outer planets, and which have fairly low inclinations, are quite susceptible to gravitational perturbations from planets, especially Jupiter. These comets usually have orbits that evolve over time.

A comet like C/2017 E4, however, is almost perpendicular to the ecliptic, and has an eccentricity very close to 1. That means it has an orbital period of many thousands of years (and could even be in an open orbit, meaning it will never return). Such a comet probably won't have its orbit changed much by a single passage through the inner system.

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by ta152h0 » Tue Apr 25, 2017 8:51 pm

Returning comets , do they stay in the same orbit or do the focal points rotate around the Sun ?

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by BDanielMayfield » Tue Apr 25, 2017 4:23 pm

Case wrote:
Image
The 3D Solar System Simulator with the orbit of E4 helps visualise the path the comet is/was taking in our neighbourhood. Almost perpendicular to the orbital plane of the planets.
Very nice Case. Thanks for sharing both the image and the link.

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by Chris Peterson » Tue Apr 25, 2017 2:20 pm

Nitpicker wrote:By my rough calculations, the visible coma in this image is about 240,000 km in diameter, or almost twice the size of Jupiter. It appeared more than 10 times bigger than Jupiter ever does from Earth.
How big the gas coma actually gets is a complicated thing, determined by the speed of outflow (which can exceed 1 km/s) and the rate of photodissociation of the glowing species (mostly C2). Usually gas comas don't get this large; dust comas, however, can exceed the size of the Sun.

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by Chris Peterson » Tue Apr 25, 2017 2:15 pm

videobear wrote:Why is the coma green, but the tail white?
It is common for relatively low activity comets to have a green coma because the gas they are ejecting has a lot of C2, which glows green when ionized by the Sun's UV radiation. (If the comet becomes very active, the coma gets dustier and the scattered white sunlight dominates, causing the color to be largely lost.)

The ion tail is mostly made up of CO+, which is of a size that preferentially scatters shorter wavelengths, and thus appears blue. There may also be some active emissions, but I think scatter is dominant. Were the activity higher, we'd probably also see a dust tail, which would be white or slightly yellow.

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by Nitpicker » Tue Apr 25, 2017 1:39 pm

By my rough calculations, the visible coma in this image is about 240,000 km in diameter, or almost twice the size of Jupiter. It appeared more than 10 times bigger than Jupiter ever does from Earth.

(This isn't in response to the "why is the coma green?" question, which I imagine has some electro-magnetic explanation [that ought to cover it].)

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by videobear » Tue Apr 25, 2017 1:33 pm

Why is the coma green, but the tail white?

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by Case » Tue Apr 25, 2017 12:24 pm

Image
The 3D Solar System Simulator with the orbit of E4 helps visualise the path the comet is/was taking in our neighbourhood. Almost perpendicular to the orbital plane of the planets.

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by heehaw » Tue Apr 25, 2017 11:39 am

A tale of a comet!

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by Nitpicker » Tue Apr 25, 2017 11:36 am

RocketRon wrote:A stunning photo - and processing.
Oh to have a camera/telescope like that.....

What is the estimated distance from the Earth / Sun here ?
Yes, I too am suffering a little scope envy.

At the time of the APOD, Stellarium tells me the comet was 0.63 AU from Earth and 0.67 AU from the Sun.

(And OY Peg is ~1000 light years away.)

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by Nitpicker » Tue Apr 25, 2017 11:20 am

Jeanne wrote:What is the bright orange star in the lower middle of the picture?
It is "OY Pegasi", slightly dimmer than magnitude 6.

RA/Dec (J2000): 22h07m29.95s/+18d00'02.8".

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by Jeanne » Tue Apr 25, 2017 9:21 am

What is the bright orange star in the lower middle of the picture?

Re: APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by RocketRon » Tue Apr 25, 2017 4:40 am

A stunning photo - and processing.
Oh to have a camera/telescope like that.....

What is the estimated distance from the Earth / Sun here ?

APOD: A Split Ion Tail for Comet Lovejoy E4 (2017 Apr 25)

by APOD Robot » Tue Apr 25, 2017 4:09 am

Image A Split Ion Tail for Comet Lovejoy E4

Explanation: What's happened to Comet Lovejoy? In the pictured image, a processed composite, the comet was captured early this month after brightening unexpectedly and sporting a long and intricate ion tail. Remarkably, the typically complex effect of the Sun's wind and magnetic field here caused the middle of Comet Lovejoy's ion tail to resemble the head of a needle. Comet C/2017 E4 (Lovejoy) was discovered only last month by noted comet discoverer Terry Lovejoy. The comet reached visual magnitude 7 earlier this month, making it a good target for binoculars and long duration exposure cameras. What's happened to Comet Lovejoy (E4) since this image was taken might be considered even more remarkable -- the comet's nucleus appeared to be disintegrating and fading as it neared its closest approach to the Sun two days ago.

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