Betula pendula scales. The foliage is a pale to medium green and turns yellow early in the autumn before the leaves fall. In mid-summer, the female catkins mature and the male catkins expand and release pollen, and wind pollination takes place. The small 1 to 2 mm winged seeds ripen in late summer on pendulous, cylindrical catkins long and broad. The seeds are very numerous and are separated by scales, and when ripe, the whole catkin disintegrates and the seeds are spread widely by the wind. Silver birch can easily be confused with the similar downy birch ("Betula pubescens"). Yet, downy birch
Northern celestial hemisphere referred to as the Northern Hemisphere. For the purpose of celestial mapping, astronomers may conceive the sky as the inside of a sphere divided into two halves by the celestial equator. The Northern Sky or Northern Hemisphere is therefore the half of the celestial sphere that is north of the celestial equator. Even if this geocentric model is the ideal projection of the terrestrial equator onto the imaginary celestial sphere, the northern and southern celestial hemispheres is not to be confused with descriptions of the terrestrial hemispheres of Earth itself. Northern celestial hemisphere The northern celestial hemisphere, also called the