A tag is a keyword or label that categorizes your question with other, similar questions. Using the right tags makes it easier for others to find and answer your question.

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Questions about observation performed in the radio frequency range of the electromagnetic spectrum (between 10 MHz and 1GHz).
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Question related to light or other electromagnetic radiation from an object moving away from the observer is increased in wavelength, or shifted to the red end of the spectrum.
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gravitationally linked and orbiting around their common center of mass.
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Questions regarding the universe shortly after it's formation
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Questions regarding Electro-Magnetic fields, which are generated by charged sub-atomic particles (ions).
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Questions about photography of celestrial objects by amateur astronomers.
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Questions related to the most massive examples of black holes that typically reside at the centers of galaxies.
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Questions regarding the planet Venus, the second planet from Earth's sun.
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mainly composed of neutrons.
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Questions about solar system planets/moons and exoplanets that exhibit similar features to the Earth.
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Questions regarding the material at or near the center of an astronomical object.
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Questions regarding Neptune, the 8th and furthest major planet orbiting Earth's sun.
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Questions regarding celestial objects which emit regular pulses of electromagnetic energy.
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Questions about the water molecule (composed of two atoms of hydrodgen and one atom of oxygen) and its detection in celestial objects.
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Questions regarding Uranus, the 7th planet from Earth's sun.
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a planet that has a compact rocky surface like the Earth's; the four innermost planets in the solar system.
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Questions about reflecting telescopes using a concave primary mirror and a flat diagonal secondary mirror.