That's going to depend on where you are on Earth (your latitude), and on what
date you decide to look, and on what time of day or night. You may not have
noticed that everything in the sky rotates, and every star rises, crosses the sky,
and sets, just like the sun and the moon do, and each star rises about 4 minutes
earlier every night than it did the night before. Whatever is directly overhead now,
won't be in a half hour from now.
This is called the "equinox", or "equal nights" - when the night and day are approximately the same duration.
In the Northern Hemisphere, Leo the Lion is directly overhead around April-May so Springtime. It's in the east in winter and in the west in early summer, before it disappears behind the sun mid summer.
The equinoxes (vernal, or spring, and autumnal, or fall) are when the Sun appears to travel directly overhead at the equator. Shortly thereafter, the intertropical convergence belt (ITCZ) will align most directly along the equator.
at the December solstice
Because they're ignorant, whoever "they" are. The term "New Moon" does not mean the Moon is directly overhead, it means that the Moon is (approximately) between the Earth and the Sun.
Not always. The sun is directly overhead at the equator at the spring and fall equinoxes.
a spring constellation the lion
It is a reference to three bright stars that can be seen in northern hemisphere. Altair in the constellation Aquila, forms the top of the triangle. Vega in the constellation Lyra is the brightest star and is almost directly overhead. Deneb in the constellation Cygnus is the third star.
Most easily? The Winter cause it will be directly overhead around midnight - although you can see it in the Fall, Winter & Spring as it makes it's way from east to west across the sky.
In the Northern Hemisphere, why is Virgo considered to be a spring constellation?
That varies minute to minute. It is currently 10:32 PM Pacific Time on Sunday, January 18, 2015. I live in Sacramento, CA. The constellation Auriga is the nearest to being directly overhead at this moment. In another 30 minutes, it will be something different.
Leo
Cancer.
It is Cancer.
It is Leo.
It depends on your location
If you live in the northern hemisphere, Cygnus the Swan is best visible during the late fall, winter and early spring almost directly overhead.