Astronomy chapter 1

when is the next leap year?

2016

at what angle is the earth is tilted?

23.5 degree

date of winter equinoxes

December 20

date of autumnal equinoxes

September 23

all leap years from starting from 2000

2004 2008 2012 2016

What is the length of time the earth completes on orbit around the sun?

365 days

How many constellations are there?

88

Why does the tilt of earth's axis relative to its orbit cause the seasons as earth revolves around the sun?

As the Earth orbits the Sun the 23.5 degree tilt faces the same way, throughout the entire year. This means that for half the year the Northern hemisphere is tilted towards the sun, and the other half the Southern tip is facing the sun. When the North directly faces the sun it is summer - and when the South takes that position (it's summer) it is the North's winter. Spring and Fall are simply the intermediate periods in the orbit.

why is it warmer in the summer than in the winter?

During the days with longer periods of daylight, more light and heat from the Sun strike that hemisphere. So, when the Sun is higher in the sky, its energy is more concentrated on Earth's surface. Thus, during these days more energy is deposited on each square meter of the surface, thereby warming them more, than when the Sun is lower in the sky. The temperature and hence the seasons are determined by the duration of daylight at any place and the height of the Sun in the sky there.

What is the celestial equator and how is it related to the earth's equator?

If we expand Earth's equator onto the celestial sphere, we obtain the celestial equator, which divides the sky into northern and southern hemispheres.

date of summer equinoxes

June 21

date of vernal equinoxes

March 20

total solar eclipse

an eclipse of the sun in which the moon completely hides the solar surface or photosphere and thereby cuts off all direct rays of sunlight from the observer.

what is the ecliptic and why is it tilted with the respect to the celestial equator?

The ecliptic is the Sun's annual path around the celestial sphere. This occurs because Earth's rotation axis is tilted away from a line perpendicular to the ecliptic.

how is an annular eclipse of the sun different from a solar eclipse?

The moon completely covers the sun in a total eclipse, whereas in an annular eclipse a ring of sunlight can be seen around the moon.

why does the moon exhibit phases?

The moon is a sphere that travels once around the Earth every 29.5 days. As it does so, it is illuminated from varying angles by the sun.

how does the daily path of the sun across the sky change with the seasons?

The path is curved due to Earth's tilted axis. The path is long because the Earth makes an oblong orbit around the Sun.

what is the difference between a sidereal month and synodic month?

The sidereal month is the time it takes the Moon to complete one revolution with respect to the background stars. However, because Earth is constantly moving in its orbit about the Sun, the Moon must travel through more than 360° to get from one new Moon to the next.

what is the difference between umbra and penumbra?

The umbra is the part where it's completely black nothing can be seen, the penumbra is the part where Earth blocks only some of the sunlight.

What are the vernal and autumnal equinoxes and the winter and summer solstices?

There are only two times of the year when the Earth's axis is tilted neither toward nor away from the sun, resulting in a "nearly" equal amount of daylight and darkness at all latitudes.he summer solstice occurs at the moment the earth's tilt toward from the sun is at a maximum.

How are constellations useful to astronomers?

They're a guide to help generalize the layout of the known universe and make it easier to understand.

what is the ecliptic?

a plane, a great circle on the celestial sphere representing the sun's apparent path during the year, so called because lunar and solar eclipses can occur only when the moon crosses it.

What is the celestial sphere?

an imaginary sphere of which the observer is the center and on which all celestial objects are considered to lie.

circumpolar stars

as viewed from a given latitude on Earth, never sets (that is, never disappears below the horizon), due to its proximity to one of the celestial poles.

precession

change in the orientation of the rotational axis of a rotating body.

constellations

group of stars forming a recognizable pattern that is traditionally named after its apparent form or identified with a mythological figure.

what is precession?

he slow movement of the axis of a spinning body around another axis due to a torque (such as gravitational influence) acting to change the direction of the first axis.

annular eclipse

occurs when the Sun and Moon are exactly in line, but the apparent size of the Moon is smaller than that of the Sun. .earth,moon,sun