celestial sphere with constellations

celestial sphere with constellations插图

Constellation mapsdivide the celestial sphere into 88 parts, known as constellations, helping astronomers locate stars and deep sky objects. The star constellations that can be seen in the night sky depend on the observer’s location and season, and they change throughout the year.

How do we locate objects on the celestial sphere?

The use of RA and Dec to locate objects in the celestial sphere There are two coordinates that allow to locate an object in the sky: Azimuth and Altitude. Their value depends in the location of the observer Azimuth: Use as reference the north direction (close to Polaris) and the range of

What are the constellations in modern astronomy?

In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms (which themselves are generally referred to in non-technical language as “constellations”), which are patterns formed by prominent stars within apparent proximity to one another on Earth’s night sky.

How can objects of the celestial sphere are measured?

Units of the Celestial Sphere. Astronomers can use the Right Ascension and Declination to locate or track any object in the night sky, regardless of the observer’s position on Earth. Declination is measured in degrees north or south of the celestial equator, with negative numbers indicating south.

What are the coordinates of the celestial sphere?

?Celestial Coordinate System: ?Declination (0-90): The north/south positions of points on the celestial sphere. “Latitude” ?Right Ascension (0-24 hrs): The east/west positions of points on the celestial sphere. “Longitude” ? These two give the location of any object on the sky Dec=90 Dec=0

How to measure right ascension?

Right ascension (symbol α, abbreviated RA) measures the angular distance of an object eastward along the celestial equator from the vernal equinox to the hour circle passing through the object. The vernal equinox point is one of the two where the ecliptic intersects the celestial equator. Analogous to terrestrial longitude, right ascension is usually measured in sidereal hours, minutes and seconds instead of degrees, a result of the method of measuring right ascensions by timing the passage of objects across the meridian as the Earth rotates. There are (360° / 24h) = 15° in one hour of right ascension, 24h of right ascension around the entire celestial equator.

What is the equatorial coordinate system?

The equatorial coordinate system is a widely-used celestial coordinate system used to specify the positions of celestial objects.

What is the celestial sphere?

In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with Earth. All objects in the observer’s sky can be thought of as projected upon the inside surface of the celestial sphere, as if it were the underside of a dome. The celestial sphere is a practical tool for spherical astronomy, …

How does parallax work?

This effect, known as parallax, can be represented as a small offset from a mean position. The celestial sphere can be considered to be centered at the Earth’s center, The Sun’s center, or any other convenient location, and offsets from positions referred to these centers can be calculated. In this way, astronomers can predict geocentric or heliocentric positions of objects on the celestial sphere, without the need to calculate the individual geometry of any particular observer, and the utility of the celestial sphere is maintained. Individual observers can work out their own small offsets from the mean positions, if necessary. In many cases in astronomy, the offsets are insignificant.

How do stars coordinate?

A star’s spherical coordinates are often expressed as a pair, right ascension and declination, without a distance coordinate. Because of the great distances to most celestial objects, astronomers often have little or no information on their exact distances, and hence use only the direction. The direction of sufficiently distant objects is the same for all observers, and it is convenient to specify this direction with the same coordinates for all. In contrast, in the horizontal coordinate system, a star’s position differs from observer to observer based on their positions on the Earth’s surface, and is continuously changing with the Earth’s rotation. Telescopes equipped with equatorial mounts and setting circles employ the equatorial coordinate system to find objects. Setting circles in conjunction with a star chart or ephemeris allow the telescope to be easily pointed at known objects on the celestial sphere.

Why does the sky seem to be standing still?

Because astronomical objects are at such remote distances, casual observation of the sky offers no information on the actual distances. All objects seem equally far away, as if fixed to the inside of a sphere of large but unknown radius, which rotates from east to west overhead while underfoot, the Earth seems to stand still. For purposes of spherical astronomy, which is concerned only with the directions to objects, it makes no difference whether this is actually the case, or if it is the Earth which rotates while the celestial sphere stands still.

What color is the right ascension?

Right ascension (blue) and declination (green) as seen from outside the celestial sphere. (Image Courtesy of Wikipedia)

What is the Celestial Sphere?

The celestial sphere definition in astronomy is an imaginary sphere surrounding the Earth. Another way of imagining the celestial sphere is to picture the Earth inside a transparent, celestial dome on which the Sun, Moon, planets, and stars are fixed. In this conception of the celestial sphere, the Earth is at the center of the universe.

North Celestial Pole

Several important points, also imaginary, are associated with the celestial sphere. One of them is the north celestial pole, an imaginary extension of the Earth’s North Pole into space. It is a point on the celestial sphere directly above the Earth’s North Pole. At night, the stars seem to turn around the north celestial pole.

South Celestial Pole

The other significant point on the celestial sphere is the south celestial pole. Like its counterpart in the north, the south celestial pole is the point on the celestial sphere directly above Earth’s South Pole.

Celestial Sphere : Related Terminology

Other significant points on the celestial sphere include the celestial equator, the celestial meridian, zenith and nadir, and the celestial horizon. It is important to distinguish these points because they are terms used to describe events and objects in astronomy.

How many constellations can you see from a single location?

Observers can never see all 88 constellations from a single location on Earth. While some of the southern constellations can be seen from northern latitudes at certain times of year – Scorpius, for instance, is visible over the southern horizon in the summer – others never rise over the horizon. Crux, also known as the Southern Cross, which is prominent enough in the southern sky to be featured on several national flags in the southern hemisphere, can never be seen from most locations north of the equator. Similarly, the constellation Ursa Minor, which contains Polaris, the closest bright star to the north celestial pole, cannot be seen from most places south of the equator.

Why do we see different constellations at different times of the year?

As the Earth orbits around the Sun, constellations move slowly to the west over the course of a year and we see different parts of the sky at night because, as the seasons change, we are looking in a different direction in space. This means that different constellations are viewable at different times of year.

Which constellation is closest to the north pole?

Similarly, the constellation Ursa Minor, which contains Polaris, the closest bright star to the north celestial pole, cannot be seen from most places south of the equator. The position of all stars and deep sky objects on the celestial sphere is mapped relative to the celestial equator and poles, just as different locations on Earth are mapped …

What is the northern hemisphere?

Northern hemisphere map, image: Roberto Mura. The celestial sphere, an imaginary sphere surrounding Earth, is divided into the northern and southern hemispheres by the line of the Earth’s equator, extended into space.

How many constellations are there in the sky?

Out of the 88 constellations recognized by the International Astronomical Union (IAU), 36 are found predominantly in the northern sky, while the remaining 52 are located in the southern sky.

Where are circumpolar stars located?

Near the equator, there are no circumpolar stars. With the celestial poles on the horizon, all stars appear to rise in the east and set in the west for observers at the equator. Observers can never see all 88 constellations from a single location on Earth.

Do stars move farther from the celestial poles?

Polaris and other stars lying near the celestial poles appear to move across a smaller area than stars lying closer to the equator. The farther they are from the poles, the wider the circle the stars make across the night sky. The stars that are close to the poles never set below the horizon for observers in locations where the stars are visible: they are circumpolar. Near the equator, there are no circumpolar stars. With the celestial poles on the horizon, all stars appear to rise in the east and set in the west for observers at the equator.

How long does it take for the Sun to return to the same constellation?

The sun returns to the same constellation in 1-year intervals. Moon. E to W in about 12 hours, 25 minutes from moonrise to moonset. Moonrise is about 50 minutes later each day. Like the sun, this timing is modulated by the season and your latitude on Earth.

What is the red ecliptic?

The red "Ecliptic" is the sun’s path. The sun is at the vernal equinox around March 21 and travels eastward (increasing right ascension). Just the celestial sphere plus the ecliptic, with solstices and equinoxes marked. Drawn for northern latitudes, these are the paths the sun takes across the sky on the equinoxes and solstices.

Why don’t we get eclipses every month?

Note that eclipses don’t happen every month because the moon’s orbit is tilted 5 degrees out of the earth-sun plane. So we really only get eclipse seasons twice a year (when the sun is on the "line of nodes" in the diagram below).

How long does it take for a planet to travel 360 degrees?

It takes 27.3 days to travel 360 degrees with respect to the stars, but phases repeat on a 29.5-day cycle. Planets. E to W in about 12 from rising to setting (again modulated by season and latitude). Additional, very small variations are caused by the planets’s own motions against the background stars.

How long does it take for a star to rise?

E to W in about 12 hours (modulated by season, by latitude, and by where the star is on the sky: circumpolar stars, for instance, do not rise and set, but they will travel in a circle around the pole, 180 degrees in 12 hours minus about 4 minutes.) Star rise is about 4 minutes (3m 56s) earlier each day.

How many years does the Earth’s pole wobble?

The earth’s pole describes a circular wobble of 23.5 degree amplitude centered on a point in the constellation of Draco every 26,000 years (often called "precession of the equinoxes").

Does latitude work south of the equator?

This works south of the equator also, but you have to switch all of the "norths" with the "souths". The final point to make about this is that these latitude/de clination/altitude correspondences are always true, but that longitude/right ascension correspondences depend on the hour of the day and also the season.

What is the Big Dipper?

An example: the Big Dipper is an asterism inside of the Ursa Major constellation. Seasons listed are for mid-northern latitudes. For southern latitudes, flip the season listed. For example, if a constellation is listed as best viewed in the summer, in the southern hemisphere the constellation would be best viewed in the winter …

What is a constellation?

A constellation is a grouping of stars that represents one of the 88 divisions of the celestial sphere as defined by the International Astronomical Union. Many constellations are derived from old traditional asterisms, which are star patterns within a constellation. An example: the Big Dipper is an asterism inside of the Ursa Major constellation.

Who said "I’m not sure about the universe"?

and I’m not sure about the universe. — Albert Einstein