Digital Universe Guide - Hayden Planetarium

138 3. THE MILKY WAY ATLAS
1lmo The light-month grid extends to 4 light-weeks, or 1 light-month. Lines of constant
radius are drawn for the first 7 light-days, after which lines are drawn each light-
week. The overlying grid has increments every two light-weeks.
1ly Beyond the light-month grid is the light-year grid. It consists of lines of constant
radius for each light-month and an overlying grid in increments of 6 light-months.
Displaying the Oort cloud (oort) along with this grid provides a good measure for
the Oort cloud sphere (about 10.5 light-months).
10ly A 10-light-year grid with lines of constant radius every year. Viewing the grid face-
on along with the stars, one is able to see the locations of those nearby stars close
to the plane. While this is not an exact measuring tool, it’s easy to see that Al-
pha Centauri (Proxima) is just more than 4 light-years and Sirius is between 8 and
9 light-years.
100ly A 100-light-year grid with lines of constant radius every 10 light-years. Here we can
see the radio sphere’s edge (radec) at 72 light-years with many of the extrasolar
planetary systems (expl).
1kly A 1,000-light-year (1-kilo-light-year) grid with lines every 500 light-years and lines
of constant radius every 100 light-years. On this scale we see several of the local
OB associations (ob) that lie in the Orion Arm (the Sun is located on the inner edge
of the Orion Arm, sometimes called a spur), as well as a few of the nearest open
clusters (oc).
10kly The 10 kly (10,000-light-year) grid is large enough to view those nearby data sets
that are confined to the plane of the Galaxy, more or less. All the OB associations
(ob) are found within the grid, as are data from the open clusters (oc), supernova
remnants (snr), and H ii regions (h2).