M34 (NGC 1039) & M71 (NGC 68382)

Observatory / Course Archives / ASTR 110 Fall 2018 / Anema and Ruba

Both of these objects, M34 and M71, are star clusters. A star cluster is a group of stars which are bound together by gravitational forces. There are two different types of star clusters: globular and open. The left picture, M34, is open. The right picture, M71, is globular. Since it is open, M34's stars are much less crowded and spread out than the cluttered M71.

M34 is an open star cluster that is located 1,500 light years from the Earth. It is a relatively young star cluster (200mil-250mil yrs old) located in the northern constellation Perseus. It has a magnitude of 5.5, and the cluster spans 14 light years from end to end. In good viewing conditions, M34 can be seen without the use of a telescope.

M71 is a globular star cluster. It is located 13,000 light years away from the Earth and possesses a magnitude of 6.1. It is in the northern constellation Sagitta. At first, M71 was thought to be an open star cluster as it has more metals than most ancient globular clusters and it also has no dense central compression. However, after closer examination, it was decided that M71 was a loosely concentrated globular cluster after discovering a horizontal branch in the H-R diagram of M71. This is a characteristic of being a globular cluster. In order to see M71, telescopic aid is required to view it clearly. From end to end, M71 spans about 90 light years.

Both of these are star clusters, and both can be found in the northern hemisphere. On top of that, they are both part of constellations. However, these two different clusters have far less in common than they do in contrast.

These clusters are about as different as night and day. To start, M71 is a little more than 8X further away. M71's age is about 9-10 billion years old, whereas M34 is only about 250 million years old. Based on magnitudes, it would seem that M34 would be the brighter cluster. However, the sheer volume of stars in M71 is much greater than the amount of stars found in M34. Therefore, M71 has a higher overall intrinsic brightness and the difference is visible. Also, M34 is about 1/6th the diameter of M71. Categorically, they differ as well. M34 is an open cluster while M71 is a globular cluster. When examing the picture, M34 contains more blue stars than M71. This could be in part because M34 is much younger, its stars havent had the time to move towards becoming red giants.

References:

Star cluster website https://www.universetoday.com/78112/star-cluster/

Nasa M34 https://apod.nasa.gov/apod/ap100211.html

Messier M34 http://www.messier-objects.com/messier-34/

Wikipedia M34 https://en.wikipedia.org/wiki/Messier_34

Nasa M71 https://www.nasa.gov/feature/goddard/2017/messier-71

Messier M71 http://www.messier-objects.com/messier-71/

Wikipedia M71 https://en.wikipedia.org/wiki/Messier_71

Object	Messier 34	Messier 71
Right Ascension (J2000)	2:42:00	19:53:46
Declination (J2000)	+42:46':00"	+18:46':45"
Filters used	B (Blue), R (Red), V (Green)	B (Blue), C (Clear), R (Red), V (Green)
Exposure time per filter	B=200s, R & V=100s.	B=50, V & R=25s; C (25s x 10)
Image dimension	943x476 pixels; 20.43x10.31 arcminutes	871x591 pixels; 18.87x12.81 arcminutes
Date/time observed	October 29, 2018 7:20:17 UT	October 20, 2018 3:12:41 UT