Thursday, October 8, 2009

Get Out Your Bandannas

Note: There will be no October 15 post. Enjoy the October 8 post or browse my older posts. I'll be back with a new post on October 22.

Let’s wrap up our exploration of Capricornus the Sea Goat with a telescopic look at one of my favorite deep-sky objects: the globular cluster Messier 30.

Globular clusters, or “globs” as they are called in the astronomy community, are dense balls of gravitationally bound stars. There are at least 150 known globs scattered about our home galaxy, the Milky Way. Globs contain tens of thousands to millions of stars.

A number of the brighter globs that can be spotted from the Northern Hemisphere are found in the Messier catalog (MESS-ee-yay). This is the catalog of 110 deep-sky objects compiled by the famed 18th century French astronomer Charles Messier, who observed from the rooftops of Paris. The Messier catalog contains some of the finest binocular and telescope objects in the night sky and is widely used by amateur astronomers as an observing list.

Globs are my favorite type of deep-sky object, and Messier 30— or M30 as it is commonly known— is one of my favorites because of its irregular shape. I find the globs that are a bit asymmetric, rather than perfectly spherical, to have the most visual appeal.

Use the star map below to locate M30, just to the left (east) of the Bandanna asterism. If you have a dark sky (Moon-free and light pollution-free), try spotting it with binoculars first. If successful, you’ll see a small fuzzy ball, something like the end of a Q-tip.

Messier 30 in Capricornus
Star maps created with
Your Sky

But honestly, M30 is one of those objects that is best examined in a telescope. Depending on your aperture (diameter of the primary optical element)— which dictates your telescope’s ability to collect light from faint celestial objects— you may begin to resolve the cluster. If so, the stars in the cluster will begin to separate into distinct points of light, and you’ll be able to truly appreciate M30’s endearing quirkiness.

Once you’ve located M30 with a low-power eyepiece (high mm number), switch to a high-power eyepiece (low mm number) and pump up the volume. This object warrants the most magnification you can muster.

Globular cluster M30
Source: NASA/ESA

Honk if you love globs. Or just wave your bandanna.

Astronomy Essential: Human eyes can adapt to the dark.

Seasoned night-sky observers typically go through a ritual called dark adaptation prior to embarking on an evening of stargazing. Dark adapting involves avoiding all white-light sources for 20 to 30 minutes, which prepares their eyes for enhanced seeing in the dark.

In a dark environment, first the human eye responds with pupil dilation. Next, chemical changes occur in our retinas’ receptors: the rods and cones. The rods become super-sensitized to light, thereby enabling us to see in low-light conditions.

As you can imagine, dark adapting— and then avoiding bright light once adapted— results in greater success seeing faint celestial objects through binoculars or telescopes, as well as with the naked eye. Astronomers maintain their dark adaptation by using red-light flashlights, since red light does not interfere with night vision.