# How Do You Calculate Star Rise and Set Times for Different Declinations?

• SpY]
In summary, the conversation discussed coordinate systems on the celestial sphere, including the celestial meridian and celestial equator. It also touched on determining the rising and setting times for stars with a declination north of the celestial equator. A PowerPoint presentation was suggested as a potential resource for further understanding.
SpY]
Hi everyone, I just started an introductory course in astronomy and we've covered co-ordinate systems on the celestial sphere. I haven't seen any threads like these so I apologize if it's in the wrong section.

In this very crude drawing of the northern celestial sphere, the observer is situated at a latitude θ North, corresponding to the altitude of the North celestial pole. Running from North to South is the celestial meridian, and perpendicular to that running from East to West is the celestial equator.

Now for a star that was on the celestial equator (declination zero), the total visible hour angle would be 12 hours - if the sidereal time was 0:00 then it would be 6:00 on the East point and 18:00 on the West point of the horizon. These are the times of starrise/starset (or sunrise/sunset for the sun).

My question is that if a star (or the sun at a time of the year) had a declination δ North of the celestial equator, how can you find the rising and setting times? All I have is that for δ=0, the the visible hour angle of the star is 12h; and for δ=90-θ North the star becomes circumpolar and 24h are visible.

Might this PPT presentation help?

physics.gmu.edu/~hgeller/astr402/StarTimeExample.ppt

I remember doing this question in math although I do not remember the formula. You can determine hours many hours and minutes there is for day and night, for any latitude, on any day of the year. I was not a fan of those questions

## What is the difference between sun and star rise/set?

The sun rise/set refers to the daily event of the sun appearing and disappearing on the horizon. Star rise/set, on the other hand, refers to the daily event of a particular star becoming visible and disappearing from view as the Earth rotates.

## How do scientists determine the exact time of sun/star rise/set?

Scientists use mathematical calculations based on the Earth's rotation and the position of the sun or star in the sky to determine the exact time of rise/set. This can also be done using specialized instruments such as a theodolite or a sextant.

## What factors can affect the time of sun/star rise/set?

The time of sun/star rise/set can be affected by factors such as geographical location, the time of year, and atmospheric conditions. For example, the time of sunrise may be slightly earlier in the summer due to the Earth's tilt, and cloudy or hazy conditions may delay the visibility of stars.

## Why is it important to accurately determine sun/star rise/set?

Determining the exact time of sun/star rise/set is important for a variety of reasons. It helps us plan our daily activities, such as farming and travel, and also plays a crucial role in navigation and astronomy. Additionally, changes in the timing of sun/star rise/set can indicate shifts in the Earth's rotation or other astronomical events.

## Can sun/star rise/set be predicted for future dates?

Yes, scientists can use their understanding of the Earth's rotation and the position of celestial bodies to predict the time of sun/star rise/set for future dates. However, this prediction may not be 100% accurate due to factors such as weather conditions and minor changes in the Earth's rotation.

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