APOD: Comet Tails and Star Trails (2015 Jul 21)

[APOD Robot]

Comet Tails and Star Trails

Explanation: After grazing the western horizon on northern summer evenings Comet PanSTARRS (also known as C/2014 Q1) climbed higher in southern winter skies. A visitor to the inner Solar System discovered in August 2014 by the prolific panSTARRS survey, the comet was captured here on July 17. Comet and colorful tails were imaged from Home Observatory in Mackay, Queensland, Australia. The field of view spans just over 1 degree. Sweeping quickly across a the sky this comet PanSTARRS was closest to planet Earth about 2 days later. Still, the faint stars of the constellation Cancer left short trails in the telescopic image aligned to track the comet's rapid motion. PanSTARRS' bluish ion tails stream away from the Sun, buffetted by the solar wind. Driven by the pressure of sunlight, its more diffuse yellowish dust tail is pushed outward and lags behind the comet's orbit. A good target for binoculars from southern latitudes, in the next few days the comet will sweep through skies near Venus, Jupiter, and bright star Regulus.

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[Ann]

I love the colors of the tails.

Ann

[stargene]

I noticed that the axis of both the gas and the dust V-shaped streams coming off the comet are off center, relative to
the comet's approximate center, and with the same chirality. Could this be related to the comet's spin rate and
direction?

[Javachip]

Driven by the pressure of sunlight, its more diffuse yellowish dust tail is pushed outward and lags behind the comet's orbit.

Is this correct? I thought the dust trail was material expelled from the nucleus and left behind, analogous to the smoke left behind a train. So the dust trail does lag behind the comet's orbit, but is not primarily shaped by sunlight pressure, or is it?

[bystander]

Is this correct? I thought the dust trail was material expelled from the nucleus and left behind, analogous to the smoke left behind a train. So the dust trail does lag behind the comet's orbit, but is not primarily shaped by sunlight pressure, or is it?

Smoke lags behind a train because of atmospheric drag. In the vacuum of space, the fine dust and gas expelled from the nucleus would remain in the coma without some other force acting upon it.

[Chris Peterson]

Driven by the pressure of sunlight, its more diffuse yellowish dust tail is pushed outward and lags behind the comet's orbit.

Is this correct? I thought the dust trail was material expelled from the nucleus and left behind, analogous to the smoke left behind a train. So the dust trail does lag behind the comet's orbit, but is not primarily shaped by sunlight pressure, or is it?

See Ann's and my comments about comet tails from yesterday.

[Ron-Astro Pharmacist]

Boy – Chuck Wood didn't hold back on his feelings eleven years ago on the 35th anniversary of Apollo 11 lunar landing.

Good for him. I mimic his feelings about what could have been if the public supported a continued exploration of the moon. I guess that's democracy for all of us on today's 46th anniversary.

Sorry if not on topic but it is a pretty important day in history. I can pretend I'm a 15 year old boy again - for the day.

[starsurfer]

I love the colors of the tails.

Ann

I also love the colours as well, it reminds me of the double star Albireo!

[Dad is watching]

I love the colors of the tails.

Ann

Can the chemical make-up of the comet be determined from the colors manifested by the two tails? We would assume so, but would the 'strength', 'power' and 'energy' of the solar wind and 'SME pressure waves' (?) make a difference to the colors seen? Or will a specific comets tails always look the same regardless of the inter-planetary environment?

It is a great photo....

[What??]

What happened to Pluto? I expected to see several days of photos.

[Boomer12k]

It is interesting the different colors of the tails....

And a good picture....

:---[===] *

[Chris Peterson]

Can the chemical make-up of the comet be determined from the colors manifested by the two tails? We would assume so, but would the 'strength', 'power' and 'energy' of the solar wind and 'SME pressure waves' (?) make a difference to the colors seen?

Visually, we can't tell much from the color of the dust tail (which is similar with all comets). Instrumentally, there is some compositional information in the reflectance spectrum, but most comets seem to have the same sort of dust. The ion tail tends to look about the same visually from comet to comet, as well. Spectroscopically, some differences can be noted, but the elements present are present in all comets, so this isn't particularly useful, either.

[Peter Smith]

Driven by the pressure of sunlight, its more diffuse yellowish dust tail is pushed outward and lags behind the comet's orbit.

Is this correct? I thought the dust trail was material expelled from the nucleus and left behind, analogous to the smoke left behind a train. So the dust trail does lag behind the comet's orbit, but is not primarily shaped by sunlight pressure, or is it?

See Ann's and my comments about comet tails from yesterday.

So if the star trails in this image are aligned with the comet's orbit, why does the dust tail appear approximately at right angles to them?

[Chris Peterson]

So if the star trails in this image are aligned with the comet's orbit, why does the dust tail appear approximately at right angles to them?

A good deal of the debris that a comet throws off remains in a similar orbit. The distinguishing feature of the dust trail is that it is composed of particles of a size such that they are strongly affected by solar radiation pressure. They are being pushed away from the comet. So depending on where the comet is on its orbit, the tail may be in quite a different direction. Add to that a 2D projection of a 3D structure, and it's difficult to say much of anything about the actual position of the tail with respect to the orbit (in a single image).