The night sky is full of fascinating features to observe. From the Moon, to our neighboring planets, to the stars. There are an abundance of views to take in by just simply looking up.
However, each time you gaze at the night sky it appears a bit differently. Depending on the time, day or season, the world above us displays a different perspective. Why? Well, because our universe is constantly in motion.
In this guide, we will help you navigate the night sky by giving you a better understanding of:
You can navigate directly to a particular section by clicking the topic above. Otherwise, let's jump right in.
What is the Celestial Sphere?
Within an astronomical context, the celestial sphere is represented as the sky's appearance concentric to Earth. In other words, if you were to imagine the sky as a static projected screen speckled with stars, this perceived starry dome around the Earth would be considered the celestial sphere.
However, this static screen illusion is solely used for the purpose of imaginary reference. In actuality, the stars, planets and other celestial objects in the sky are not fixed on an imaginary screen. They are positioned in various distances away from our location on Earth.
Since the Earth is not transparent, we're unable to see this entire celestial sphere when we go outside and look around. Instead, you will only be able to see half of this sphere as a hemispherical dome ending at the horizon.
The horizon is simply the point at which the sky and and Earth appear to intersect. It is much easier to see the horizon when looking out at the ocean or gazing across a desert. Otherwise hills, buildings and trees often block our clear view of the horizon.
Two additional important points to note on the celestial sphere are the zenith and nadir. 90° above the horizon, on the celestial sphere, is known as the zenith point. In contrast, the point 90° below the horizon is called the nadir.
Finally, along the horizon, the helpful directional references are known as the cardinal points. You may be more familiar with these cardinal points as North, South, East and West.
You're probably already familiar with the north pole and the south pole. Those two reference points will make it easy for you to understand the north celestial pole and the south celestial pole.
The north celestial pole lies directly above the north pole on the celestial sphere and the south celestial pole is located directly above the south pole on the celestial sphere.
Similarly, the celestial equator is represented as the Earth's equator extended out to the celestial sphere. This line separates the northern and southern halves of the celestial sphere.
What is the Ecliptic?
The ecliptic, like the celestial equator, is represented as a path that completely circumvents the Earth. However, with respect to the equator, it is tilted at a 23.5° angle. The Sun, Moon and planets appear along the ecliptic as Earth rotates.
Additionally, the 12 constellations of the zodiac connect along the ecliptic. This group of constellations include: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, and Pisces.
The 1st constellation on the ecliptic is Aries. Out of the 88 constellations, it is ranked 39th in overall size at 441 square degrees. Its symbol is "the Ram" and its brightest star is named Hamal (Alpha Arietis). The three other bright stars that make up the constellation include Sheratan, Mesarthim, and 41 Arietis.
The 2nd constellation on the ecliptic is Taurus. The Taurus constellation is represented by "the Bull" symbol. It is the 17th largest of the 88 constellations with an area of 797 square degrees. Taurus is comprised of 19 main stars with its brightest being Aldebaran. It is also known for its two major star clusters, the Pleidaes and the Hyades.
The 3rd constellation on the ecliptic is Gemini. In Latin, the name means "twins" referencing Castor and Pollux, its two brightest stars. With an area of 514 square degrees, Gemini is the 30th largest constellation.
The 4th constellation on the ecliptic is Cancer. It is symbolized with "the Crab". Out of the 88 constellations it is ranked 31st in size at 506 square degrees. Cancer is made up of 5 main stars, with its brightest being Beta Cancri.
The 5th constellation on the ecliptic is Leo. It is the 12th largest constellation with an area of 947 square degrees. "The Lion" is its represented symbol.
The 6th constellation on the ecliptic is Virgo. It is the largest constellation out of the 12 zodiacs and the second largest out of the 88 constellations with an area of 1294 square degrees. Virgo's brightest star is Spica and the constellation is symbolized by "the Maiden".
The 7th constellation on the ecliptic is Libra. Its symbol and Latin name represents the Weighing Scales. With an area of 538 square degrees, it is the 29th largest constellation.
The 8th constellation on the ecliptic is Scorpius. Its symbol is "the Scorpion". Scorpius has an area of 497 square degrees, which makes it the 33rd largest constellation. Antares is the brightest star in Scorpius.
The 9th constellation on the ecliptic is Sagittarius. Its symbol is "the Archer". Sagittarius is the 15th largest constellation with an area of 867 square degrees. Epsilon Sagittarii is the constellation's brightest star.
The 10th constellation on the ecliptic is Capricornus. Its symbol is "the Sea Goat". The brightest star in Capricornus is Denib Algedi. Capricornus is the 40th largest constellation with an area of 414 square degrees.
The 11th constellation on the ecliptic is Aquarius. It is the 10th largest constellation with an area of 980 square degrees. Its symbol is "the Water Bearer". The brightest star in Aquarius is Sadalsuud (Beta Aquarii).
The 12th constellation on the ecliptic is Pisces. It is symbolized by "the Fishes". With an area of 889 square degrees it is the 14th largest constellation. The brightest star in Pisces is Alpherg (Eta Piscium).
How does the Sky move?
Using the Sun as an initial starting point when it is highest above the horizon, you will notice that it takes 24 hours for it to reappear at the highest point. This is why one "day", or one "solar day", is calculated as 24 hours. It is referencing the Sun's apparent motion around the celestial sphere.
The stars, however, are slightly different. If you measure a specific star's position in the night sky, you will notice it takes 23 hours and 56 minutes for it to return the same position the following night. Thus, stars actually appear to rise 4 minutes earlier each night which helps explain why you cannot find the exact same star layout in the sky each month or season.
As Earth rotates in an eastward direction, the sky appears to move in an westward direction. This is most clearly observed by the Sun rising above the eastern horizon, appearing to move westward throughout the day and setting below the western horizon. Similarly, the stars in the night sky follow that same trajectory.
Now that you have a better understanding of the night sky and how to more easily navigate it, it's time to begin exploring the world above.
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