APOD: Zodiacal Light and Milky Way (2012 Oct 20)

[APOD Robot]

Zodiacal Light and Milky Way

Explanation: Ghostly apparitions of two fundamental planes in planet Earth's sky span this October all-sky view. The scene was captured from a lakeside campsite under dark skies in northern Maine, USA. In it, the plane of our Milky Way Galaxy arcs above faint airglow along the horizon. Zodiacal light, a band of dust scattering sunlight along the solar system's ecliptic plane, stretches almost horizontally across the wide field and intersects the Milky way near a point marked by bright planet Jupiter. Right of Jupiter, past the Pleiades star cluster, is the brightening of the Zodiacal band known as the Gegenschein, also visible to the eye on that dark night. Begirt with many a blazing star and rising above the distant mountains, Orion the hunter is reflected in the lake's calm waters.

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[Ann]

It's always nice when one of the great astrophotographers who regurlarly grace the Recent Submissions thread at Starship Asterisk* with their superior images get his own APOD. Congratulations, Babak Tafreshi, it is well-deserved!

I love seeing the reflection of Orion in the lake. That poem by Longfellow was new to me, and fun to read. Did Longfellow talk about the imagined "battle" between the two bright red supergiants of the sky, Betelgeuse of Orion the Hunter and Antares of Scorpius the lion(?)? Surely he wasn't referring to Orion toppling blue Regulus the red Leo-lion? Anyway, it was fun to read, and full of references in the fashion of poems written two hundred years ago or so. I believe the description of the Moon in the poem refers to Virgin Mary, who is sometimes depicted as standing on the crescent Moon because of a description of such a scene in the Bible.

I found it hard to spot the Zodiacal light, but I could see the Gegenshein. And it is curiously funny, isn't it, that the plane of our solar system is so strongly inclined to the of the disk of the Milky Way.

Ann

[Chris Peterson]

And it is curiously funny, isn't it, that the plane of our solar system is so strongly inclined to the of the disk of the Milky Way.

Why? There's no galactic mechanism that dictates the orientation of planetary systems- that's determined by the local angular momentum of protostellar nebulas. So to me, there's nothing curious or surprising at all about the inclination of our own system.

[emc]

Beautiful capture! The lakeside dock offers the appearance of a ladder… a good metaphor for some of the recent SA* conversation.

[Ann]

And it is curiously funny, isn't it, that the plane of our solar system is so strongly inclined to the of the disk of the Milky Way.

Why? There's no galactic mechanism that dictates the orientation of planetary systems- that's determined by the local angular momentum of protostellar nebulas. So to me, there's nothing curious or surprising at all about the inclination of our own system.

There's nothing truly strange about it, of course. Like you said, the inclination of any solar system is just a consequence of the local angular momentum of the protostellar nebula that gave birth to it. These things must be totally random.

It's just counterintuitive that our solar system should be "doing a handstand" as it were. I think it is counterintuitive to most people.

Ann

[Chris Peterson]

It's just counterintuitive that our solar system should be "doing a handstand" as it were. I think it is counterintuitive to most people.

Why is it a leaning handstand, as opposed to a leaning footstand? While the technical definition of inclination which includes the direction of rotation, visually there are really just values between 0° (laying down?) and 90° (standing up?).

[FLPhotoCatcher]

Wouldn't the rotation of the Milky Way galaxy cause most large gas clouds that condense to rotate in the same direction, similar to how the Coriolis effect causes low pressure areas, such as hurricanes, to rotate in the same direction in the northern hemisphere?

[geckzilla]

Wouldn't the rotation of the Milky Way galaxy cause most large gas clouds that condense to rotate in the same direction, similar to how the Coriolis effect causes low pressure areas, such as hurricanes, to rotate in the same direction in the northern hemisphere?

Milky Way is not rotating. Everything within it is orbiting. So, no, it's not similar enough.

[starstruck]

Milky Way is not rotating.

How do you know?, 'cos now that does seem counterintuitive! I thought all galaxies were rotating about their own respective galactic centre, be it a black hole or whatever.

[Ann]

Good to see you here again, Starstruck!!

Why don't you check out http://asterisk.apod.com/viewtopic.php?f=31&t=29816. This topic says that over time, galaxies become more and more organized and "settled". "Settled" means that they become disk-shaped, or so I think. Do the disks rotate? No idea, but the stars inside them definitely orbit.

Take a look at the video that you can see if you follow the link. It shows you a simulation of how galaxies grow from small unsettled conglomerations into large flat disks.

Ann

[starstruck]

Thanks for the link Ann. I should qualify what I said by adding that I meant all disk galaxies. It seems counterintuitive to me that they should form into disk shapes without there being some rotation about a centre present. So, forgive me for asking again, but is the Milky Way rotating, or not? Do we know, or not?

[Chris Peterson]

Milky Way is not rotating.

How do you know?, 'cos now that does seem counterintuitive! I thought all galaxies were rotating about their own respective galactic centre, be it a black hole or whatever.

It sort of depends on how you define "rotate". Usually, that carries a physical meaning that all a body's components are interacting in a way leading to common circular motion. That isn't the case with galaxies, where each star in them is orbiting independently, and not attached in any way to other stars, or (outside minor perturbations) influencing the motion of other stars. However, the common inclination of the disc stars in a spiral galaxy do reflect the (true) rotation that the protogalactic hydrogen cloud had. The stars in the galactic bulge, however, orbit on random inclinations, so any residual motion tied to early rotation is no longer discernible. The same is true for elliptical galaxies.

[DavidLeodis]

I found it hard to spot the Zodiacal light, but I could see the Gegenshein.

Ann

Hi Ann.

I have the opposite in that I cannot make out the Gegenshein that is "Right of Jupiter, past the Pleiades star cluster, is the brightening of the Zodiacal band known as the Gegenschein" (I wonder how far to the right of Jupiter it is?). Assuming the Zodiacal Light is the light coloured band down the left side and across the bottom then that is obvious on my monitor. In not being able to make out the Gegenschein it may be that my monitor is not correctly colour calibrated. I think though that the gorgeous scene is one that is better seen by eye than in a photo.

[Ann]

Well, the Gegenshein would be at about three o'clock, close to the tree at right. It isn't colored at all, but just a slight diffuse brightening in the sky.

Ann

[DavidLeodis]

Well, the Gegenshein would be at about three o'clock, close to the tree at right. It isn't colored at all, but just a slight diffuse brightening in the sky.

Ann

Thanks Ann.

I think I can now make it out (just!). If there had been no mention of a gegenschein in the explanation I would never have had any thought that it was there (well at least on my monitor)!

[Anthony Barreiro]

And it is curiously funny, isn't it, that the plane of our solar system is so strongly inclined to the of the disk of the Milky Way.

Why? There's no galactic mechanism that dictates the orientation of planetary systems- that's determined by the local angular momentum of protostellar nebulas. So to me, there's nothing curious or surprising at all about the inclination of our own system.

Like most people, I unconsciously assume that I'm standing still on a flat plane at the center of the universe, with everything moving around me. For me, curiosity and surprise arise whenever that assumption is overturned and I'm able to get my head around a bigger reality. Even knowing that the Earth is a sphere orbiting the Sun, it's still surprising to truly understand that the plane of Earth's rotation is inclined relative to the plane of her orbit around the Sun. And it's a big step to understand that the ecliptic plane of our one small solar system is oriented essentially randomly relative to the plane of the Milky Way galaxy's disk. Gaining a rough comprehension of our local group, with the Milky Way and Andromeda galaxies being slowly drawn toward one another, blows my mind (by the way, Andromeda is visible in Babak's image, to the right of the Milky Way, about halfway from the center toward 1 o'clock). Looking through a telescope at the big galaxies in the middle of the Virgo galaxy cluster or the galaxies toward Ursa Major, trying to imagine light travelling through space for 50 million or 100 million years, is about the limit of my comprehension. When astrophysicists start talking about redshifts and cosmic expansion, I think of Wordsworth's Intimations of Immortality.

Perhaps our capacity for surprise and wonder is a personal quality, like a taste for spicy food, or long Romantic poems.

[jehoener]

The red California Nebula is clearly visible above and to the left of the Pleiades.