Astronomy | Astrophysics Answers

In the late 19th century, Percival Lowell claimed he could see canals on the surface of Mars; long, dark, narrow features.  This question looks at the reasonableness of his claim.

a) What is Mars's angular diameter (in arcseconds, or 1/3600 of a degree) when it is at opposition (i.e., closest approach to Earth)? (Look up the distance Mars is from earth on average at opposition.)

b) The smallest angle that Lowell's telescope could resolve (meaning the smallest angle an observer could make out) was 1 arcsecond.  This means that Lowell's canals would have had to be at least this wide to have been detected.  What is the narrowest width (km) Lowell's putative canals could be and would these be anything like canals on Earth?

a) A core sample retrieved from the planet contained 4 grams of uranium and 7 grams of lead. Recalling that uranium decays into lead with a half-life of 4.5 billion years, determine the minimum age of the planet. 

b) Look up the half life of the carbon 14 isotope, used extensively to determine the age of human artifacts (pottery, etc.). After what period of time would this isotope no longer be useful in dating an artifact.? Why? 

all questions please

a)   Determine the total power (from solar energy) at the top of the Earth’s atmosphere

b)   What power would be absorbed by the Earth’s surface in the absence of an atmosphere? Hint: Think about our albedo.

c)    What would the surface temperature be assuming it radiated into space all the energy it absorbed?

 A galaxy has a visible mass of 10 M and a flat rotation curve extending to 25 kpc at the level of 150 km s-1 . What is the ratio of its dark-matter mass to its visible mass?

Compute the gravitational energy of a pair of colliding galaxies, each of mass 10 Mo. separated by a distance of ῀ 10 kpc and compare it with the energy requirements of a powerful radio source. What conclusion do you arrive at from such a comparison?

Using a Hubble constant given by ho = 0.6, place an approximate upper limit on the angular size of a quasar of redshift z = 0.2 if it exhibits a time variability on the scale of I h. (Use the argument that no physical effect travels in a material object faster than light.)

Using a Hubble constant given by ho = 0.6, place an approximate upper limit on the angular size of a quasar of redshift z = 0.2 if it exhibits a time variability on the scale of I h. (Use the argument that no physical effect travels in a material object faster than light.)