# What are angular sizes of thin and thick disks in our Galaxy?

What are diapasons of galactic coordinates for thin and thick disks of our Galaxy?

• Can you clarify your question? What's a diapason? – gargoylezoo Jan 31 '14 at 23:55

The sun is usually taken as the center of the galactic coordinate systems. Our solar system is well within the thin disk of our galaxy (population I stars). So taking the headline question literally, we see the thin disk as well as the surrounding thick disk in almost every direction, meaning any galactic latitude and longitude.

The radius interval, where we find mostly stars of the thin or thick disk, varies with angles. Along the galactic plane the radius interval is across the galaxy (up to about 30 kilo parsecs, varying a bit with direction, because we are not in the center of the galaxy) for the thin disk, containing the sun as origin; perpendicular to the galactic plane it's about 1 kilo parsec to both directions for the thin disk, followed by a respective radius interval from 1 to 3 kilo parsecs for the thick disk, if I follow the Wikipedia articles referenced in the question.

The region dominated by the thick disk is the farther away from us the closer we look along the galactic plane.

There are certainly no sharp boundaries between the star populations. Actually the thick disk penetrates the thin disk, but it's much sparser populated.

The Gaia project may give a much more detailed answer about the distribution of stars within our galaxy in the next 5 to 10 years.

• No, the thich disk is NOT farther away from us the closer we look along the galactic plan. The thick disk is not an outer layer of the disk but extends right through the galactic plane. Even at $z=0$ (where $z$ is the vertical distance from the galactic plane), there are thick disk stars. The thick disk is defined not by the distance from the plane but by the dynamics of the stars that belong to the thick disk. – Dieudonné Feb 1 '14 at 11:19
• I took the thick disk as the region mainly populated by intermediate population II stars, and the thin disk as the region mainly populated by population I stars, although not happy with those definitions at all, because I think it's too much an oversimplification of the actual distribution of the stars. The main purpose of the answer has been, that we live in midst of the thin disk, hence can see thin and thick disk regions in any direction, without relevant angular constraints. – Gerald Feb 1 '14 at 14:09
• I agree with your points. I just wanted to point out that we are also within the thick disk. Although, as you point out, most stars in our neighbourhood are part of the thin disk. – Dieudonné Feb 1 '14 at 20:54
• Thanks for pointing it out! I've modified the answer a bit a few hours ago with the hope, that this is indicated without making the answer too confusing. – Gerald Feb 1 '14 at 21:17