Please help with this problem.   Consider a spacecraft in a 500 km altitude circular orbit.  This spacecraft transits (via Hohmann transfer) to a 200 km altitude circular orbit for repair, then back to a 500 km circular orbit.  Did it require more delta-V to transfer from the higher to lower orbit, or from the lower to higher orbit?  (Circle one) It required more delta-V to transit from 500 km (circular) to 200 km (circular) It required more delta-V to transit from 200 km (circular) to 500 km (circular) It requires the same delta-V to transit from 500 km to 200 km as it would to return There is not enough information to answer this question (if so what other information is missing?)

At rest carbon emits a spectral line at 364.0 nm. If this line is observed at 410.0 nm from exoplanet host Helvetio's, how fast is Helvitios moving toward or away from us in km/s?

In a globular cluster, astronomers (someday) discover a star with the same mass as our Sun, but consisting entirely of hydrogen and helium. Is this star a good place to point our SETI antennas and search for radio signals from an advanced civilization? Group of answer choices   No, because such a star (and any planets around it) would not have the heavier elements (carbon, nitrogen, oxygen, etc.) that we believe are necessary to start life as we know it.   Yes, because globular clusters are among the closest star clusters to us, so that they would be easy to search for radio signals.   Yes, because we have already found radio signals from another civilization living near a star in a globular cluster.   No, because such a star would most likely not have a stable (main-sequence) stage that is long enough for a technological civilization to develop.   Yes, because such a star is probably old and a technological civilization will have had a long time to evolve and develop there.

why do dark streaks appear in visible light images of the Trifid nebula, but appear bright in an infared image

What is the temperature of the Sun (google for the answer)? What is the re-entry temperature of the Space Shuttle (google for the answer)? Why don’t you burn up at the reentry temperature of 17318.5K for this Mach 20 flow? Why do you think that the body should actually re-enter the Earth's atmosphere in the opposite direction. (ie.. blunt/flat surface first.)

Solution from part A: E=-KE = PE/2 Solution from part B: =3/2kt a. (NOTE: Treat the cloud as two equal masses interacting gravitationally across a distance equal to the radius of the cloud.) Use your result from part a to write down the condition for gravitational collapse in terms of the kinetic and potential energies (NOTE: This condition is an INEQUALITY)          b. Use your result from part b in order to replace the kinetic energy with its temperature equivalent in your expression for the collapse condition.          c. Solve the expression in ii above for the mass.

What kind of object is the Messier Object M42, and where is it in the sky?