Frequencies Used in Radio Astronomy To study electromagnetic radiation from astronomical objects, radio astronomers primarily use which part of the spectrum?

Introduction / Context:
Radio astronomy spans a broad range of frequencies, but practical observations from the ground cluster where the ionosphere and atmosphere are most transparent and antennas are feasible. Identifying the most commonly used region is helpful for system design and interference mitigation.

Given Data / Assumptions:

• Ground-based observations (not space telescopes).
• Typical atmospheric windows and ionospheric transparency.
• Desire for reasonable angular resolution with practical dish sizes.

Concept / Approach:

The lower HF range is significantly affected by ionospheric absorption and refraction, limiting ground-based astronomical use. Much radio astronomy occurs in the centimeter to millimeter bands (microwaves), including key spectral lines such as the 1.42 GHz neutral hydrogen line (L band, at the edge of microwaves) and many molecular lines in the tens to hundreds of GHz. Microwaves offer atmospheric windows and allow high-resolution imaging with dishes and interferometers.

Step-by-Step Solution:

Verification / Alternative check:

Major observatories (VLA, ALMA) operate predominantly in microwave and millimeter-wave bands, confirming practice.

Why Other Options Are Wrong:

Low/medium frequencies are constrained by the ionosphere and RFI; “either (a) or (b)” is too broad; infrared belongs to optical/IR astronomy, not radio astronomy.

Common Pitfalls:

Equating “radio” only with HF/VHF; modern radio astronomy spans up to hundreds of GHz.

Final Answer:

microwaves