by Chris Peterson » Mon Mar 05, 2012 6:43 pm
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.
[quote="Roscoe Turner"]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![/quote]
"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.