# A Trouble visualizing and understanding the celestial sphere

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1. Jan 9, 2018

### starstruck_

Hi!

So it's been a while since I've done this and uh I also haven't slept well over the past few days so literally nothing is clicking. I have so many questions about this celestial sphere business. Please bear with me. It also doesn't help that our notes have like 5 different diagrams of the same thing.

So the celestial sphere is infinite, it stretches out around the Earth.
The zenith and Nadir tilt depending on the person's location, right? If you're right in the middle of the equatorial plane, would your zenith align with the celestial poles (which align with the earth's poles apparently)?

What if you're not a the center of the plane, then what happens? Does the sphere shift? I don't understand.
Or does it stay expanded along earth's poles and equator but now you have to account for the tilt of the zenith/nadir when describing the location of the stars? I dont get this at all - some images have the poles of the earth and poles of the celestial sphere aligned and some don't . I don't know how else to explain what I'm having trouble with,I'm sorry.

EDIT:

So I found this site http://www.astronomynotes.com/nakedeye/s4.htm

Basically, the celestial sphere is the extension of Earth, however the part of the celestial sphere that the observer sees changes because of their horizon at their latitude and their zenith? or no ? All of those have the observer at the center again - my professor said that the zenith and nadir go through the center of the earth and through the person so ?

2. Jan 9, 2018

### phyzguy

It's hard to do these things when you haven't slept well. Get some sleep and try again in the morning.
If you're on the equator, then your zenith (the point directly overhead) would be some point on the celestial equator. If you're standing on the north pole, then the north celestial pole will be directly overhead (your zenith).

The celestial sphere doesn't change, but as the Earth rotates and if you move around, then the part of the celestial sphere you see will change. Perhaps this figure helps.

3. Jan 10, 2018 at 10:51 PM

### stefan r

The distance from Earth's equator to 45° north (Montana/Wyoming border) is very small compared to distances to the stars. The floor is at a 45 degree angle (22° summer and 68° winter in Wyoming). The angle between Polaris and Orion will be the same. If you have a dancer pole you can hang at an angle to make the celestial equator directly overhead. Point your grip hand toward Polaris.

4. Jan 10, 2018 at 11:08 PM

### phyzguy

What do you mean by this statement? I think you are confusing things. The Earth's axis points in the same direction in summer and winter. The angle between your floor and a line to Polaris is always 45 degrees, regardless of the time of day or time of year.

5. Jan 10, 2018 at 11:26 PM

### stefan r

The ecliptic plane +/- 23°. sun, planets, and moon.

6. Jan 10, 2018 at 11:30 PM

### phyzguy

First, since the OP is just trying to figure out the Celestial Sphere, I think you're muddying the water by bringing in the Ecliptic plane. Second, it's true that the ecliptic plane is tilted 23 degrees relative to the Earth's equator, but it is always tilted by the same 23 degrees relative to the equator. It doesn't change between summer and winter.

7. Jan 15, 2018 at 7:51 PM

### starstruck_

sooo after staring at different diagrams of the celestial sphere for a while this is what I understood:

It's just an extension of the earth's poles and equator, the part of the celestial sphere that a person sees depends on where they are located, as well as the rotation of the celestial sphere around the Earth.

The azimuth and nadir are observer specific - perpendicular to the horizon which is tangent to the observer's location on the earth (which explains why time lapse photos of stars at the equator look vertical, as well as the rotation of the circumpolar stars). The eliptical plane is the path that the sun follows on the celestial plane or from the sun's pov, that the earth follows during the year(?) - it is 23.5 degrees to the equator - the tilt of the earth's axis essentially.

The celestial meridian is also observer specific (?) looking south, the meridian divides the observer's sky into the east (left) and west (right).

This is pretty much what I got, the diagrams helped me pick up what I was misunderstanding, hoping I got it right this time?

8. Jan 15, 2018 at 8:05 PM

### phyzguy

I think you have the right idea. A few comments below.

This is basically correct, but I would state it differently. Rather than say that the celestial sphere rotates around the Earth, I think it's better to think of the celestial sphere as fixed while the Earth rotates underneath it.

Correct, but it is ecliptic, not eliptic. It's called that because eclipses happen on this plane.

Correct.

Last edited: Jan 15, 2018 at 8:19 PM