Precession is caused by the gravitational influence of the Sun and the Moon acting on Earth’s equatorial bulge . ... The projection onto the sky of Earth’s axis of rotation results in two notable points at opposite directions: the north and south celestial poles.
Do celestial poles change?
Despite their apparently fixed positions, the celestial poles in the long term do not actually remain permanently fixed against the background of the stars. Because of a phenomenon known as the precession of the equinoxes, the poles trace out circles on the celestial sphere, with a period of about 25,700 years.
Does the celestial equator change?
Due to Earth’s axial tilt, the celestial equator is currently inclined by about 23.44° with respect to the ecliptic (the plane of Earth’s orbit), but has varied from about 22.0° to 24.5° over the past 5 million years due to perturbation from other planets.
Why does the Sun’s position relative to the celestial equator change?
The apparent yearly path of the Sun through the stars is called the ecliptic. This circular path is tilted 23.5 degrees with respect to the celestial equator because the Earth’s rotation axis is tilted by 23.5 degrees with respect to its orbital plane .
What causes precession and why does it move the celestial equator among the stars?
The cause of the precession is the equatorial bulge of the Earth, caused by the centrifugal force of the Earth’s rotation (the centrifugal force is discussed in a later section). That rotation changes the Earth from a perfect sphere to a slightly flattened one, thicker across the equator.
How many hours of declination exist on earth?
The total range of right ascension is 24 hrs = 360 deg / 15 deg/hr . The 15 deg/hr conversion factor arises from the rotation rate of the Earth. Declination is analogous to latitude and is measured as north or south of the celestial equator.
Is the celestial equator different for every observer?
At the Earth’s equator, the celestial equator passes through the zenith . ... This means that for observers at the Earth’s poles, all of the stars are circumpolar and the observers never see any of stars in the opposite hemisphere.
What star does the celestial pole point to?
Polaris is located quite close to the point in the sky where the north rotational axis points – a spot called the north celestial pole. As our planet rotates through the night, the stars around the pole appear to rotate around the sky. Over the hours, these stars each sweep out a circle around the celestial pole.
Why is Pole Star fixed?
The sky above Earth appears to rotate due to the rotation of the world . The apparent fixed stars go east to west because the Earth rotates west to east. But since the axis of rotation of Earth passes through the pole star, it’s that time about which the sky rotates and hence the pole star appears fixed.
Will Polaris ever be the North Star again?
Because of precession, different stars will serve as north stars and the constellations arrayed along the ecliptic (zodiac) will gradually change positions. Their move about one degree every 73 years. Polaris will remain the North Star throughout the rest of our lives and for a few centuries later .
How many times each year does the Sun pass through your zenith if you live on the equator?
Once or twice each year , people who live at lower latitudes (within 23.5 degrees of the equator) can see the sun reach the zenith, an imaginary point directly overhead.
Is the zenith always 90 degrees?
The point straight overhead on the celestial sphere for any observer is called the zenith and is always 90 degrees from the horizon . The arc that goes through the north point on the horizon, zenith, and south point on the horizon is called the meridian.
Why are there no circumpolar stars at the equator?
At the Earth’s equator, no star is circumpolar because all the stars rise and set daily in that part of the world . ... In short, the closer you are to the North or South Pole, the greater the circle of circumpolar stars; the closer you are to the Earth’s equator, the smaller the circle of circumpolar stars.
What happens every 72 years?
During the precession, the Earth’s axis traces out an imaginary conical surface in space and a circle on the celestial sphere. The Celestial North Pole or CNP (i.e., the projection of the Earth’s axis onto the northern sky) moves about 1° along this circle every 72 years (360×72 = 26,000).
Why would a catalog not use altitude and azimuth?
Because the altitude and azimuth of a star are constantly changing , it is not possible to use them in a catalog of positions. ... The declination of a star is its angular distance in degrees measured from the celestial equator along the meridian through the star.
What is Earth’s wobble called?
When the Earth rotates on its spin axis — an imaginary line that passes through the North and South Poles — it drifts and wobbles. These spin-axis movements are called “ polar motion” in scientific parlance.
