The constellations that are visible in the night sky in the evening change from season to season because stars appear to move by 90 degrees across the sky every three months. Even though some constellations are circumpolar to northern or southern latitudes and can be seen year round, the sky offers different sights from different locations at different times of year.
The stars appear to move about 15 degrees per hour on average, completing a full circle (360 degrees) every 24 hours. Some rise directly east and set directly west, taking longer to cross the sky, but most of them follow shorter arcs, staying closer to the horizon before setting. As they move across the sky, the stars stay in the same patterns. These patterns, which we know as constellations, may appear larger or smaller at different times of the night or sideways or upside down at different times of year, but their shape never changes, at least not in our lifetime.
Summer and winter constellations are different because stars in fact take a little less than an hour to move by 15 degrees, and they complete an entire circle in 23 hours and 56 minutes. In other words, they rise and set four minutes earlier each night. The distance they cross in those remaining 4 minutes is a little less than 1 degree, which means that they move about 361 degrees per day. These extra degrees eventually add up and, as a result, the stars rise and set an hour earlier every two weeks, two hours earlier each month and, after a full year, we see them in the same position as before. As the seasons pass, different constellations of stars are visible in different areas of the sky because the stars move by about 90 degrees from one season to the next.
The term “seasonal constellations” usually refers to the constellations that are visible in the sky at around 9 pm in the evening or to constellations that are best observed during a particular season. These, however, are not the only constellations that can be seen in the sky on any given evening. For instance, Andromeda, a prominent autumn constellation, can be seen high overhead on summer evenings around midnight. Orion, which dominates the winter sky in the evening, can also be seen in the late summer, when it rises just before dawn. The list of seasonal constellations is provided below.
Northern spring/southern autumn constellations (late March to late June):
|Chamaeleon||Leo Minor||Ursa Minor|
Northern summer/southern winter constellations (late June to late September):
Northern autumn/southern spring constellations (late September to late December):
Northern winter/southern summer constellations (late December to late March):
Not all constellations are visible from every location on Earth. The southern constellations Crux, Carina and Centaurus, for instance, are circumpolar to observers in the southern hemisphere, but are invisible to most, if not all, northern observers. Similarly, the northern constellations Ursa Major, Ursa Minor, Cassiopeia, Cepheus and Draco are visible in the northern hemisphere throughout the year, but cannot be seen from most locations south of the equator. Nevertheless, there is a best time of year to observe each of the constellations, even the least conspicuous ones. The table below shows the best months to observe the constellations in the evening (9 pm) and the latitudes (northern and southern) between which they are visible.
|Constellation||Month||Northern latitude||Southern latitude|