The Major Advantage of the Measurement of the 21-Cm Radio

question 104

Multiple Choice

The major advantage of the measurement of the 21-cm radio emission from hydrogen gas for investigating the spiral structure of our Galaxy is that

• A) Doppler shift of this narrow-wavelength line emission is caused by the temperature of the hot hydrogen gas and therefore can be used to measure the distribution and temperature of this important component of the Milky Way.
• B) it is relatively easily absorbed by hydrogen gas in the Milky Way so that measurements are not confused by emission of this radiation from other galaxies beyond the Milky Way.It originates only from cold hydrogen gas and can be used to map this important component.
• C) this emission can easily penetrate the Milky Way gas and dust and comes only from hot gas;hence,it can be used to map the distribution of hot hydrogen gas.
• D) radio waves easily penetrate the Milky Way dust and gas;it is a very narrow wavelength,thus its Doppler shift can be used to measure gas motions.

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Definitions:

Chitin

A long-chain polymer of N-acetylglucosamine, a derivative of glucose, and is a primary component of cell walls in fungi and exoskeletons of arthropods.

Cellulose

A complex carbohydrate that is composed of glucose units, forming the primary structural component of plant cell walls.

Mycorrhizal Partnership

A symbiotic association between a fungus and the roots of a plant, helping the plant absorb nutrients from the soil more efficiently.

Absorptive Surface Area

The total area through which absorption of nutrients and drugs can occur, increased by structures like villi in the intestinal tract.