Starship Asterisk*

Another Tail for Comet Garradd

Explanation: Remarkable comet Garradd (C2009/P1) has come to be known for two distinctive tails. From the perspective of earthbound comet watchers the tails are visible on opposite sides of its greenish coma. Seen here in a telescopic view, the recognizable dust tail fans out to the right, trailing the comet nucleus in its orbit. Streaming away from the sunward direction, a familiar bluish ion tail sweeps to the left. But the comet also seems to have, at least temporarily, sprouted a second ion tail recorded in this image from February 24. Other comet imagers have recently captured changing structures in Garradd's ion tail created as the plasma is buffeted by the magnetic fields in the solar wind. Now moving more quickly through northern skies, on March 5th comet Garradd will reach its closest approach to planet Earth, about 10.5 light-minutes distant.

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Is it really two ion trails or one which has been split in two? Something like putting your finger over the end of a water hose in order to produce two streams of water, I mean.

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geckzilla wrote:
Is it really two ion trails or one which has been split in two? Something like putting your finger over the end of a water hose in order to produce two streams of water, I mean.

• . http://apod.nasa.gov/apod/ap090207.html

http://www.colbertnation.com/the-colber ... -babyccino

Fantastic to see how part of the tail was blown off by the solarwind

Nice photo! Image Credit & Copyright: "Olivier Sedan (Sirene Observatory);" Comet pictures usually are!

Can HUBBLE focus in on this thing or ist it too close ?

Wolf Kotenberg wrote:Can HUBBLE focus in on this thing or ist it too close ?

It's not too close to focus on, but it's massively larger than the field of view of any HST camera. If the HST were used to look at the comet, it would be useful only for looking at the nucleus, and right now the comet is still so close to the Sun that the nucleus is buried in the coma. So I don't know what scientific objectives might be met by using the HST that couldn't be achieved as well or better from the ground.

On Feb. 28, APOD showed Garradd's ion tail on the right; today it's shown on the left. Which one is correct for an observer in the Northern Hemisphere, and would the orientation change if viewed from the Southern? Thanks!

Roscoe Turner wrote:On Feb. 28, APOD showed Garradd's ion tail on the right; today it's shown on the left. Which one is correct for an observer in the Northern Hemisphere, and would the orientation change if viewed from the Southern? Thanks!

"Right" and "left" generally don't have any unambiguous meaning when referring to astronomical objects. With respect to the horizon, the orientation of objects changes over the evening- for instance, a Moon might rise illuminated on one side, and set with it on the other. The degree to which this is observed depends on your latitude, as well.

Astronomical objects are usually referenced to cardinal directions, where "north" is toward the celestial north pole (roughly, Polaris), and "west" is the direction that objects move in the sky because of the Earth's rotation (which in itself can be confusing; when you look at Polaris, stars above it are moving towards the western horizon, and stars below it are moving towards the eastern horizon, but astronomically they are all moving west).

At any given time, everybody on Earth will see the tail of Garradd pointing in the same direction astronomically (for instance, all would see it pointing towards the same stars). But everybody will see it differently with respect to their horizon, depending on local solar time and location.

When looking at astronomical images, it is best not to get too concerned about orientation, given both the natural variations that can occur because of the location of the imager, and the artificial ones stemming from choice of optics, orientation of the camera, processing choices, etc.