One of the things that makes astronomy such a great hobby is that everybody can join in. You don’t need to board a rocket to see space, just walk outside on a clear night and look up. The constellations are easy to see with our bare eyes, however with a pair of binoculars we can see more, from the moons of Jupiter to star-birth nebulae and even galaxies.
THE CELESTIAL SPHERE
The celestial sphere is an imaginary sphere around the Earth on which celestial objects in the sky can be precisely mapped, just as locations on Earth can be mapped on a globe. Different parts of the sphere are visible from different areas of the Earth, and because our planet is continuously rotating, different areas of the sphere come into view over the course of a night.
THE SPINNING SKY
It is impossible to see the entire celestial sphere at once because Earth comes in the way. However, due to Earth’s rotation about its axis and revolution around the Sun, different parts of the celestial sphere come into view at different times. How much we can see and how the stars move depends on where on Earth we live.
View from the North Pole
From here only the northern hemisphere of the sphere can be seen, the other half is never visible. The stars move in Circles around the Celestial pole, which is directly overhead.
View from the equator
From the equator, we can see the whole of the celestial sphere, but over the course of a year. The north and south celestial poles lie on the horizons making polar constellations hard to see.
View from mid-latitudes
From the mid-latitude regions, we can always see the constellations around the celestial poles but the other constellations change during the night and over the year.
PRACTICAL STARGAZING
On a typical dark night, a person with good vision can see upto 3,000 stars, so there are plenty of interesting features to find with our bare eyes and learn about them.
SIZING UP THE SKY
Astronomers treat the sky as if it were a huge sphere surrounding Earth. Distances between objects are measured in degrees. There are 360 degrees in a circle, so the distance around the whole sky is 360 degrees. The Moon is about half a degree wide.
We can use different hand gestures to map out stars and constellations in the night sky.
FINGER WIDTH
The tip of a finger pointing upwards at arm’s length is about 1 degree wide and can completely cover a full moon.
HANDSPAN
The distance between the thumb and little finger when the hand is held at arm’s length is approximately 25 degrees.
FIST
A fist when held upright at arm’s length is about 10 degrees wide.
Likewise different hand gestures cover different degrees helping us to map constellations and stars without requiring special equipments.
MAPPING THE STARS
We can measure the exact position of a star at any moment with two numbers. One is altitude: the star’s height above the horizon measured in degrees. The other is azimuth: the angle from due north measured clockwise around the observer’s horizon and the star.
THE CHANGING SKY
After watching the sky for a few minutes it will be noticed that the stars move slowly, rising in the east and setting in the west. This is an illusion caused by Earth’s rotation. The pattern of movement varies between different parts of the world.
MOVEMENT AT THE EQUATOR
At the equator, all the stars rise in the east, cross the sky and then set in the west. The constellations visible by night change gradually over the course of a year.
MOVEMENT AT THE NORTH POLE
At the North Pole no stars would ever rise or set. Instead, they would simply move in circles around the pole star, which never moves.
MOVEMENT AT MID-LATITUDES
From most parts of the world, some stars stay visible throughout the night, travelling in a circle, while other stars rise and set.
OPTICAL INSTRUMENTS
Binoculars and telescopes boost stargazing. Their big lenses or mirrors collect more light than the human eye can and reveal very faint objects visible from Earth such as nebulae or galaxies. Their eye pieces, meanwhile, create a magnified image of a small part of the sky, enabling stargazers to separate closely spaced celestial bodies like double stars and see more details on the Moon and planets.
The essentials for a night’s stargazing are warm clothes and a star chart (generally a planisphere). One can download apps on smartphones and tablets that will show the night sky visible from their location at any time and any date.
HAPPY STARGAZING!
Rajanya Poddar(Batch 21)