How do we know that a hot main sequence star (and not some other kind of star) is embedded in a cloud of interstellar gas?
What will be an ideal response?
Except for white dwarfs, all hot stars are very luminous. The large amount of ultraviolet light produced by them will ionize any gas in their vicinity and produce an HII region. The visible light from the HII region's emission spectrum tells us of the presence of the gas.
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Which emits radiation of the highest frequency?
A) a red-hot star B) the Sun C) a blue-hot star D) all the same
Which moons of our solar system are sometimes called the Galilean moons?
A) the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto B) the two largest moons in the solar system: Ganymede and Titan C) the moons that orbit their planet "backward" compared to their planet's rotation, such as Neptune's moon Triton D) the moons orbiting Uranus, which was once named "planet Galileo"
How does the escape speed from Mars compare with that of the Earth? [ MEarth=9.31? MMars ; REarth=1.88 ? RMars ]
A) 222.% B) 22.5% C) 44.9% D) 66.2% E) 20.2%
Water is flowing in a drainage channel of rectangular cross-section
At one point, the width of the channel is 12 m, the depth of water is 6.0 m, and the speed of the flow is 2.5 m/s. At a point downstream, the width has narrowed to 9.0 m, and the depth of water is 8.0 m. What is the speed of the flow at the second point? A) 2.0 m/s B) 2.5 m/s C) 3.0 m/s D) 3.5 m/s E) 4.0 m/s