Expert: Tom Whiting - 12/2/2007

Question
I am evaluating a children's book about the spring equinox. I believe and illustration contained in the book is incorrect, but would rest easier knowing I had a second opinion. Since I can't attach a picture, I'll have to describe it.

THe sun is in the center of the page, with four earth's surrounding it, one for each of the spring and fall equinox and the summer and winter solstice. In every earth picture, the axis of rotation is tilted to the left and the portion of the earth which is depicted shows a portion of North America, Central America, and a portion of South America. In the overall illustration, the winter solstice is on the right, the summer solstice on the left. This is meant to be a book for the Northern hemisphere. My issue is that it seems like the Northern hemisphere is tilted toward the sun in winter, and away from the sun in summer. Can this illustration be correct? I have a scan of the picture, if it helps and you can tell me where to send it. Thank you.

Answer
Hi Betsy,
No, you don't have to scan it...you are absolutely correct
as they have the summer and winter solstice reversed,
(or, they tilted the Earth's axis incorrectly; either way you are right- the diagram is incorrect).  But you
are correct, the northern hemisphere is tilted toward the
sun at the summer solstice on or about June 21, and away at the winter solstice, on or about December 22nd. Those are also the correct dates for the southern hemisphere position too, after you reverse it to make it read correctly. So simply swap the N. Hemisphere winter to the
left hand side of the diagram, and summer to on the right hand side, then it's correct. (Don't mess with the Earth's axis- just forget I even mentioned the axis of rotation)!
And since we revolve around the sun counter-clockwise as seen from above,the closest earth would depict our position on or about March 21 (spring equinox, or if you
want to keep the southern Hemisphere folk happy, call it
the Vernal Equinox), and the farthest Earth would represent the N. Hemisphere at the Autumn Equinox.
Hope all this helps,
Clear Skies,
Tom Whiting
Erie, PA  
PS...Oh, By The Way....
make sure you call it rotation around it's axis (daily spin, if you will) BUT we revolve around the sun....In astronomy, rotation is ALWAYS movement around an axis, and revolution is ALWAYS one body orbiting around another.
Please don't ever mix them up, or worse yet, substitute one for the other. That's a definite NO - NO in astronomy!
;-)
Because those two terms represent specific movements of all astronomical bodies. And since I am a retired teacher,
feel free to contact me directly for any more assistance
if you need it, at bwhiting@velocity.net
or if you want further assurance, feel free to scan the
diagram to me.