Is there a word for the highest point a star reaches above the horizon? I’m trying to find some sort of calculator online that could tell me when, for a particular night and latitude and longitude, a particular object would be at its highest point. Knowing the specific word for this point would be very helpful in my searches.
Sadly, this isn’t too urgent–it looks like it’s going to be cloudy for the next three days.
Zenith.
I think the closest term is transit.
Zenith is the highest point in the sky, period, and most stars won’t hit it. A star’s highest point is its meridian crossing.
Note that this is the origin of “AM” and “PM”: “Ante Meridian” is before the Sun reaches its highest point, and “Post Meridian” is after it reaches that point.
“Transit”, in the second sense noted at the top of scr4’s linked article, is correct, although it refers to the event of the crossing rather than the point of the crossing. “Meridian transit” will help you weed out all the results referring to Venus and Mercury moving in front of the Sun.
“Zenith” always refers to the highest point in the sky; a given astronomical object won’t necessarily get anywhere near the zenith (it will if the declination of the object equals the observer’s latitude.)
By the way, your latitude doesn’t matter to find the time of meridian transit; all observers on a given longitude see a given astronomical object cross their meridian at the same time (assuming it gets above their horizon, of course.)
Thank you MikeS! I found a calculator that does exactly what I was looking for by searching “meridian transit”.
I think the time when an object reaches its highest point in the sky would be the siderial time minus the object’s right ascension, or something pretty close to that.
Doesn’t “apogee” work pretty well here? I realize it’s not measuring quite the same thing, but from our point of view it’s similar.
“Apogee” only applies to an object orbiting around the earth. It’s the highest point of the orbit, but here, “highest” refers to altitude (distance from the earth), not the angle from the horizon as seen from a certain location on earth.
Not quite: The object’s right ascension is the sidereal time when it reaches its highest point. The object’s Right Ascension minus the sidereal time at solar midnight would be the solar time when the object reaches the meridian.
Not at all the same thing, and using the same word for both would only serve to confuse matters.
Showoff. But yes.*
A star is said to culminate at its upper transit. (Some stars, if your latitude is high enough, will not sink below the horizon, and they will cross the local meridian twice, at upper and lower transit.)
ETA: LST-RA = the length of sidereal time since culmination. I possibly have the signs wrong.
You mean I didn’t drop something or other? Thanks!
What’s the asterisk for? Or is it a star?
Originally, it went along with my ETA, which refined your statement. LST-RA does not equal transit time, it equals the time since transit.
Transit occurs when the local apparent sidereal time equals the body’s right ascension. Unfortunately, converting from local time (which is based on mean solar time and then further adjusted into stepwise time zones) to LAST is not at all easy.