The Sky

Question 1

Why are astronomical coordinates important?

Answer 1

Fundamental importance to know where a source is in the sky at any time, a coordinate system.

Question 2

Why are circles so important to astronomical coordinates?

Answer 2

is a system for specifying positions of celestial objects: satellites, planets, stars, galaxies and so on

Question 3

What are Coordinate Systems?

Answer 3

Can specify a positions in 3 dimensional space, merely the directions of the object on the celestial sphere, if it’s distance is not known or not important

Question 4

What is the right ascension?

Answer 4

Is the angular distance measured eastward along the celestial equator from the vernal equinox to the hour circle of the point in question.

Question 5

What is the declination?

Answer 5

the angular distance of a point north or south of the celestial equator

Question 6

What is right ascension measured?

Answer 6

Measured eastward from the vernal equinox along the celestial equator to the hour circle of the body or point and expressed in degrees or hours

Question 7

What is the declination measured?

Answer 7

Measured from 0-90 Degrees in the northern hemisphere as we go away from the celestial equator and from 0–90 degrees as we head south from the equator

Question 8

What do we mean by diurnal motion?

Answer 8

Earth rotates around it’s axis once in 24 hours

Question 9

What is a Solar day?

Answer 9

An average over the entire year, since the time from sunrise to sunrise varies slightly over a year.

Question 10

What effect does diurnal motion have on viewing the sky?

Answer 10

Fundamental motion we see for objects in the sky over a single day-they are seen to move from east to west in the sky(although it is us who are rotating in the opposite direction

Question 11

What is the ecliptic?

Answer 11

The sun moves through the celestial sphere in a circle called the ecliptic

Question 12

How does the ecliptic compare to the celestial equator?

Answer 12

This circle is offset from the celestial equator by 23.5 degrees

Question 13

What causes the seasons?

Answer 13

Conversation of angular momentum- any freely spinning body tends to maintain it’s orientation. As a consequence of this and the offset of the ecliptic from the celestial equator we have the seasons.

Question 14

What is conservation of angular momentum?

Answer 14

Any freely spinning body tends to maintain it’s orientation. The principle that, in the absence of net torque( twisting force), the total angular momentum of a system remains constant.

Question 15

How does it effect earth’s rotation?

Answer 15

Earth loses angular momentum as it’s rotation rate is slowed by the moon

Question 16

What is a Equinox?

Answer 16

Points where the celestial equator and ecliptic cross- Vernal&Autumnal

Question 17

What is a solstice?

Answer 17

Points at which the ecliptic is as far north (summer) or south (winter) of the celestial

Question 18

What is the vernal equinox?

Answer 18

The sun crosses the celestial equator heading northward (March 21, first day of spring). Also forms the origin of right ascension increased eastward from the equinox

Question 19

What is summer solstice?

Answer 19

The sun is at it’s northern most position and days are longest in the north (June 21, first day of summer)

Question 20

What is autumnal equinox?

Answer 20

The sun is crossing the celestial equator heading south (Sept. 22, first day of fall)

Question 21

What is winter solstice?

Answer 21

The sun is at it’s southern most position (first day of winter- Dec. 21)

Question 22

What is precession?

Answer 22

The gradual wobble of the axis of a rotating object around a vertical line.

Question 23

How does precession effect the earth and over what period of time?

Answer 23

Gravitational forces from the sun and moon act on the bulge to try to re-orient the earth, causing the earth to precess (gradually change orientation) much like a gyroscope or top.

Question 24

Where is the north celestial pole over time?

Answer 24

The earth spin axis maintains the 23.5 degrees offset from the ecliptic and traces out a circle in the sky with a 23.5 degree radius over 26000 year period.
(The equinox will shift as well since the entire ecliptic changes)

Question 25

What is the difference between a mean solar day and a sidereal day?

Answer 25

Sidereal day is about 4 min shorter than the mean solar day due to the orbit of the earth.
Sidereal time does not depends on our orbital position.