Liquid water cannot exist for very long on the surface of Mars ...

[jilianpiloj]

Liquid water cannot exist for very long on the surface of Mars today because
 
  A) it gets rapidly destroyed by intense solar radiation
  B) its surface temperature is too high
  C) it rapidly reacts with the Martian surface to form peroxides
  D) its atmosphere is too thin

Question 2

Your Local Sky
 
  a. Where is the north (or south) celestial pole in your sky?
  b. Describe the meridian in your sky.
  c. Describe the celestial equator in your sky.
  d. What is the range of declinations that makes a star circumpolar in your sky? Explain.
  e. Describe the path of the Sun through your sky on the fall equinox.
  f. Describe the path of the Sun through your sky on the winter solstice.

[IAPPLET]

Answer to Question 1

D

Answer to Question 2

Answers will vary with latitude; the following is a sample answer for latitude 40N.

a. The north celestial pole appears in the sky at an altitude of 40, in the direction due north.
b. The meridian is a half-circle that stretches from the point due south on the horizon, through the zenith, to the point due north on the horizon.
c. The celestial equator is a half-circle that stretches from the point due east on the horizon, through an altitude of 50 due south, to the point due west on the horizon.
d. Because the north celestial pole appears due north at an altitude of 40, a star is circumpolar if it is within 40 of the north celestial pole. The north celestial pole has a declination of +90, so within 40 means declinations greater than +50.
e. On the fall equinox, the Sun rises due east, reaches an altitude of 50S on the meridian, and sets due west.
f. On the winter solstice, the Sun rises more than 23.5 south of due east, reaches an altitude of 50 - 23.5 = 26.5 on the meridian in the south, and sets more than 23.5 south of due west.

[jilianpiloj]

Excellent

[xiazhe]

Wow, this really help