Experimentation

I love the things that can come out of a little experimentation such as using a small LED flashlight. Credit: Sean McGrath from Saint John, NB, Canada.Template:Tlx

A little experimentation is at the heart of the scientific method. Template:Clear

Control groups

The components of a control group are often applied in the performance of experimentation.

Gathering data

To gather data, use "dominant group" in quotes and anthropology or ethnography as additional search terms to explore the internet using search engines listed under External links.

Laboratories

Los Alamos National Laboratory Credit: Los Alamos National Laboratory.

A laboratory is a construct you create so as to produce reproducible measurements.

Def. "a room, building or institution equipped for scientific research, experimentation or analysis" is called a laboratory. Template:Clear

Measurements

A typical tape measure with both metric and US units is shown to measure two US pennies. Credit: Stilfehler.

Def. any act of quantifying relative to a standard is called a measurement. Template:Clear

Theories

These can take the form of a formal theory such as the Hubble scheme, see Evaluation of nebula NGC 6946, Hypotheses, or reasoning.

Evaluation of nebula NGC 6946

The composite image shows a classification of galaxies. Credit: Ville Koistinen.

Although nebula NGC 6946 is not known to rotate during observation in the plane of view or vertical to it, its appearance in both images is assessed using the Hubble scheme:

Probably the earliest classification of galaxies "is based on the forms of the photographic images."

"About 3 per cent are irregular, but the remaining nebulae fall into a sequence of type forms characterized by rotational symmetry about dominating nuclei."

"The sequence is composed of two sections, the elliptical nebulae and the spirals, which merge into each other."

"The classification of these nebulae is based on structure, the individual members of a class differing only in apparent size and luminosity."

The "forms divide themselves naturally into two groups:

1. those [nebulae] found in or near the Milky Way and
2. those in moderate or high galactic latitudes."

For the elliptical nebulae [galaxies], the classification En, where "n=1, 2, .... , 7 indicates the ellipticity of the image without the decimal point".

For example, NGC 3379 is E0, NGC 221 is E2, NGC 4621 is E5 and NGC 2117 is E7.

The spirals are divided into two types:

1. Normal spirals (S) of Early (Sa), Intermediate (Sb), and Late (Sc) and
2. Barred spirals (SB) of Early (SBa), Intermediate (SBb), and Late (SBc).

The irregular galaxies are put into that structure form with "Irr".

Examples are

1. Sa - NGC 4594,
2. Sb - NGC 2841,
3. Sc - NGC 5457,
4. SBa - NGC 2859,
5. SBb - NGC 3351,
6. SBc - NGC 7479, and
7. Irr - NGC 4449.

and forms of rotational symmetry described as

1. one-fold -

   

   Template:Tlx

2. two-fold -

   

   Template:Tlx

3. three-fold -

   

   Template:Tlx

4. four-fold -

   

   Template:Tlx

5. five-fold -

   

   Template:Tlx

6. six-fold -

   

   Template:Tlx

Orientation is determined from image structure and symmetry: The composite image below at right does appear to conform to a face-on galaxy.

Additional individuals have recorded their opinions on morphology:

The primary source used by SIMBAD considers the nebula to be one of 30 nearby spiral galaxies.

"Targets span a wide range in Hubble type, star formation activity, morphology, and inclination."

and an assessment based on the Hubble scheme has been estimated:

This is a composite scanned spectral image of NGC 6946. Credit: NASA / CXC / MSSL / R.Soria et al, Optical: AURA / Gemini OBs.

As a visual guide and examining the multispectral image at the right, NGC 6946 appears to be close to type Sb (example, NGC 2841).

A distance calculation from 1978 based on secondary indicators has been made:

Distance moduli have been estimated for NGC 6946 using its brightest blue stars and its HII ring. Its distance modulus is estimated to be log D₀ = 4.434. The distance in parsecs is given by

$d=10^{\frac{{\mu }_0}{5}+1},$

where µ₀ = 29.25. NGC 6946 is at 10^6.85 (7.08 x 10⁶) parsecs, or approximately 23.1 x 10⁶ light years. While this is greater than the NASA number, it is not an order of magnitude greater or smaller. Template:Clear

Several primary sources are consulted regarding classification and special characteristics:

Looking up "NGC 6946" on SIMBAD, without the quotes, reveals that SIMBAD considers NGC 6946 to be an "HII Galaxy" of morphological type "SAB(rs)cd".

A more extensive classification scheme starting from the Hubble scheme indicates that an Sab galaxy is approximately in between Sa and Sb. Template:Clear

See also

• Stars/Galaxies/Laboratory