Older Low-Metallicity Globular Clusters in the Milky Way Halo - August September - Star Party Presentations for 41N Latitude - Demonstration center RA19h 2°Dec - Southern Cygnus - 25° radius

K. Fisher fisherka@csolutions.net Rev. 9/15/2007C; Orig. 9/14/2007


Using a GOTO mount in a series of quick slews around Cygnus, show three of five older low-metallicity globular clusters and one younger high-metallicity globular cluster by increasing distance and compare their relative visual angular and physical sizes. Younger high-metallicity globulars surrounding the Milky Way's core will be the subject of another star party presentation sheet.

Low-metallicity globular clusters contain large numbers of short-period low-metallicity Population II RR Lyrae "cluster" variables. The RR Lyr variable stars have periods of less than one day. The April 15, 2007 Astronomy Picture of the Day (APOD) features a single night of time-lapse exposures of globular cluster M3. Speeded up by time-lapse photography, the numerous RR Lyrae cluster variables in M3 can be seen blinking on and off. Amazingly, these magnitude changes translate into the surface of these distance stars pulsating in and out at a rate between 10 and 170 kilometers/second.

Overview Finder

Overview finder Fig. 1

Observing List

Table 1 - August Halo Globular Cluster Tour
IDID_altDist kpcRad_vel kms-1 [1]CoordinatesConSync starSlew_degs approx2v_magMpsasDia. arcminSize kpc3Relative physical sizeSpecFe/H_logMsolNotes_____________
SgeAltair6.121.560.007100%G1-0.733.67x104Seen through the galactic disk. Exhibits extinction.
HerRastaban (bet Dra)5.5°6.319.680.019271%F2-2.293.64x105None
LyrAlberio19°8.920.150.014200%F5-1.941.89x105Also seen through galactic disk.
DelAltair; Enif25°9.819.120.009129%F7-1.542.51x105C42 and C47 are south of the galactic disk.
DelAltair; Enif11.420.110.011157%F1-1.682.52x105Dim and small. Needs larger aperture and non-urban skies.
RR LyrHD1829890.23-72.4J192528.80+424648.0
LyrVega; Alberio33.5°7.1-8.1 varN/aN/aN/aN/aF5N/a0.64Archetype for RR Lyr short-period globular cluster variables (0.56 days). Use eyepiece diffraction grating to view low-res spectrum,

1 - Radial heliocentric velocity. Apparent speed (kilometers per second) and direction (negative is moving toward) relative to Sol.
2 - Approximate slew degrees from last object to current object
3 - Computed using half-angle formula, distance and angular size.

Visualizations and finder charts

Table 2 - Visualizations - Globular Clusters
IDRelative angular dia. 1°-1.2° e.p.Relative physical dia. parsecs4Finder
M71 M71 1 deg ep view

Fig. 2

M71 physical size view

Fig. 3

M71 finder

Fig. 4

M13 M13 1 deg ep view

Fig. 5

M13 physical size view

Fig. 6

M13 and M92 finder

Fig. 7

M92 M92 1 deg ep view

Fig. 8

M92 physical size view

Fig. 9

M13 and M92 finder

Fig. 10

M56 M56 1 deg ep view

Fig. 11

M56 physical size view

Fig. 12

M56 finder

Fig. 13

C47 C47 1 deg ep view

Fig. 14

C47 physical size view

Fig. 15

C47 and C42 finder

Fig. 16

C42 C42 1 deg ep view

Fig. 17

C42 physical size view

Fig. 18

C47 and C42 finder

Fig. 19

4 - Scaled to relative physical size (M71=100%) based on Table 1, above

Table 3 Visualizations - Other
Ortho map x-y 16kpc Ortho map view in xy plane to 16kpc

Fig. 20

Ortho map z-x 16kpc Ortho map view in zx plane to 16kpc

Fig. 21

Ortho map x-y 100kpc Ortho map view in xy plane to 100kpc

Fig. 22

Ortho map z-x 100kpc Ortho map view in zx plane to 100kpc

Fig. 23

Globular Metallicity - Pop. Table Populations of Globular Clusters by Metallicity

Fig. 24

Glob Metallicity - 3D distrib. 3D Schematic of Milky Way Globulars - Light blue = younger metal-rich - Dark blue = older metal-poor

Light blue = younger metal-rich
Dark blue = older metal-poor

Fig. 25

RR Lyr variables in C47

External content:
Time lapse of RR Lyraes in M3 (APOD)
Plot of RR Lyrae variables in C47 (NGC6934)

Fig. 26

Pulsating variable types - HR diagram Pulsating variable star types and the H-R diagram

Fig. 27

RR Lyr Light curve RR Lyr period

Fig. 28

RR Lyr finder RR Lyr finder

Fig. 29

Earth orbit schematic Earth Orbit Schematic

Fig. 30


The observing list and discussion topics are intended for use by a single-scope participant-presenter at a local club star party. Multiple star-party telescope owners can divide the observing list objects (above) and discussion topics (below) and present a row of two or three scopes that show a non-duplicative set of discussion topics and of globulars by distance.

The observing list in Table 1 has been used at suburban transition zone star parties and, in part, at urban light-polluted star parties.

Discussion topics

Star party presenters can re-enforce observations at the eyepiece with the visualizations in Table 2 to discuss the following principles: