Is the time of the sunrise?

Question

the time the top of the sun starts to become visible, or the time that the sun is completely visible on the horizon?

Answer 1

According to the US Naval Observatory web site, sunrise and sunset are the times when the top of the sun just touches the horizon... going up at sunrise and sinking out of sight at sunset. Try this website... http://aa.usno.navy.mil/faq/docs/RST_defs.html#top

Answer 2

Depends on what you are doing.

In mathematics, it is the time when the centre of the Sun is exactly 90 degrees from the zenith. The theoretical horizon is defined as being 90 degrees from the horizon, therefore sunrise is when the Sun is exactly half visible.

In reality, when the Sun is in that (theoretical) position, the air refraction makes it appear approximately one degree higher. Sailors observe the compass error at sunrise or sunset when the bottom of the sun is half a sun-diameter ABOVE the horizon (the whole sun is above the horizon, with some space between the sun's limb and the horizon). This gives them the best approximation of the mathematical sunrise or sunset, making all calculations a lot easier.

With the mathematical definition, the theoretical times of sunrise and sunset are exactly 12 hours apart when the sun's declination is exactly zero, making the day equal to the night at 12 hours each. This occurs twice every year on days we call equinox (latin for "equal night").

However, in practice, sunrise and sunset table usually correct for the refraction and give the time at which the top of the apparent, refracted sun (the one we actually see) is exactly on the theoretical horizon. In other words: sunrise is the very first second at which the top of the sun becomes visible. Sunset is the very lst second when the top of the sun finally disappears. This is the definition astronomers use for practical work.

Of course, your real horizon is rarely the same as the theoretical horizon. Even at sea, if your eyes are higher than the water surface (and hopefully, they are) then the visible horizon is more than 90 degrees from the zenith and sunrise would be a bit sooner (a few seconds) than what the sunrise table tells you.

Answer 3

Wow, you ask a tough question! Thinking about it, the moment the sun becomes visible also depends on how high above the ground you are. For example, an observer looking out a second story window will see the tip of the sun at least ten seconds earlier than a second observer standing on the ground. To make this even more confusing, the further from the equator the two observers are, the greater the difference will be.

My guess is, there is some precise scientific definition based on the sun's rays being tangent to the Earth at the point you are standing. I know that sounds abstruse, but it would at least resolve the ambiguity caused by vantage points being different.

Answer 4

This is a very good question. I always considered it the moment the sun became visible, but I have no real reason for that belief.

Answer 5

ill just stick with the old saying, the sun rises when some b*tch decides to wake up, pull her pants down to her ankles and hold on tight.... oh wait, i guess i coulda said when dawn shows her crack, aka, the crack of dawn.... lol

honestly i think it is the moment it becomes visible, not all the way up over the horizon....

Answer 6

top its sunsetting and same as it coming down only visable fully at dinnertime even after a few mins the sun is not completley viseable due to hiding behind cloud even if it looks round u cant see the sun only half a bun thats what i learned from that maths poem and it shows tht it can only be visable at dinnertime cuz its higher than all the clouds and remmeber its in space so at 12:)0 am u can see it all as its high as high in space but u cant after a few mins cuz its hiding behind the moon if ecilpse and other things stars coments in space dinnertime where it allows things to past through space cuz the sun is not blocking their travel

Answer 7

starts to become visible

Answer 8

try a on line weather desk they usually tell also my local news channel tells you may have to watch a few times im sure you'll find it on both of those i don t know if the news says it every day i know they do though they may have it on the screen (why cant remember it) go to the local news web site ill bet it their they told me 2 days ago i forgot sorry you ll find it trust me

Answer 9

top becomes visible

Answer 10

yes let me see ooh i dont get it