You are the only person I have found on the net who has thoroughly explained right ascension in not just lay mans terms but any terms. Thank you very much.
Thank you! Thank you! Thank you! For the first time in well over a decade of staring at "explanations," you have made crystal clear and cognitively manageable (did I just concoct a term?) the meaning of right ascension. And you did it in under ten minutes! I am absolutely delighted. Thank you!
Whenever I'm doing throughout the day, I know that soon I proceed watching these series. They are so encouraging to learn the world by telling about complex things in simple stories, so empowering! Thank you!
Bravo, Professor. Finally I understand the celestial sky. I've watching a lot of videos and they have confused me, rather than illuminate this concept. Thank you. Keep up the good work.
This is such a great course and your explanations are clear and concise Michel. I never took the time to understand Declination and RA. Now I understand. Thank you, I am taking notes of each video episode in a composition grid notebook where my Book Cover Subject is: Astronomy, my School is: Hard Knocks and my Grade Is: 62nd Grade. You never stop learning through life, ever...
That is correct. A lot of joy and satisfaction can be gained by learning new concepts or finally understanding concepts we couldn't get before. I still learn things I couldn't understand as a student. 🙂
In 3 months I begin my Astrophysics degree after many years of dreaming. I have absolutely aced my entry course through my local college and hold the highest confidence, all bar my knowledge of RA. I have been trying to wrap my head around this for a long time, and not to echo too many people here but I have never found such a clear explanation. Not only do I now have the confidence to use my telescope properly, I feel like I have just crushed a major hurdle on my path to my future career. Thank you for this video, you have just made my day sir.
I wish you all the best with your studies. Based on your success so far, you are a disciplined student and a hard worker. Keep it up. Glad we were able to help.
I've been an ameteur astronomer for many years but embarrassingly I could not understand Right Ascension...you are the only one who explained it in such a way that finally made sense! Im still a little iffy about finding a star using the declination at any given time, but now i understand it much better, thank you so much! One question, how do you determine the hours behind during each date listed?
Glad it was helpful. 🙂 On March 21, Orion is 6 hours behind the Sun. On Aprl 21, Orion is 4 hours behind the Sun. On May 21, Orion is 2 hours behind the Sun. That is the best way to think about it.
I learned from this video especially those stars that are part of the zodiac constellation the moment they are with the sun ( O hrs) it means that the sun travelling along the ecliptic points towards the zodiac constellation assigned on that particular month.... Very detailed discussion in this video....Thanks alot sir❤❤❤❤❤❤❤❤❤❤
I'm studying celestial navigation for sailing class and started playing around with Stellarium to practice locating stars. However, what we look up as GHA in nautical almanacs shows up as RA in Stellarium and I had no idea what it meant. This video really cleared things up. Thank you!
Both this video and the previous one on Declination were extremely informative and helpful to me. Thank you very much for an excellent job of explaining an initially daunting-to-me concept clearly, and with the perfect combination of conciseness and detail.
Thank you for explaining this clearly and concisely. I was having trouble understanding right ascension, but now I understand it. If you don't mind though, I have a couple of questions I hope you can answer: 1. Are the RA numbers listed only based when viewed from the equator? Reason I ask is because I live about 40 degrees North, so some stars I see to the north never set. Also, even for stars that do set where I live, such as Vega, are noticeably off of when they should set, and I'm assuming this is also because I don't live at the equator. So, I'm assuming that a star's right ascension is based on when viewed from the equator, since those stars more to the north actually "set" when viewed from the equator, right? And Is there a way to convert the right ascension for different latitudes? 2. Polaris has a RA of about 2 hours, since it's not exactly 90 degrees north. However, if it was exactly 90, would it's RA be undefined, as it technically would always stay right on the horizon when viewed from the equator?
1. The RA does not depend on where you are, but that will affect when and where you will see the star / constellation based on your field of vision from your vantage point. 2. Technically RA would be undefined if Polaris was perfectly at 90 degrees. However that said, any star exactly at 90 degrees wouldn't be there very long because of the precession of the Earth.
Thanks, you made me understand RA much better now. There is one point that I missed out or don't quite get, that is why subtract 2hrs going forward every month. Add ?
Since RA is in terms of hours BEHIND the Sun, and all heavenly bodies (except for the planets) catch up to the Sun 2 hours every month. The time behind the Sun reduces by 2 hours every month. After the star passes the Sun in the sky, then the Star will get further and further ahead (2 hours per monht) and then you must add the 2 hours each month, untill the star gets close to the Sun again and it will be behind the Sun catching up........
Thank you for your videos. They are really helpful. From my first year in campus, there's always a video of yours that really helps me in a particular unit. Now I'm almost joining my 4th year. Wow time flies!
Sir you are a fantastic teacher , you make the material so easy to understand . I am an astronomy afficionado myself and I have been observing the night sky through binocular and with naked eye for 5 years. I understand the night sky to a fair degree too. Hope to learn a lot more from your videos . Hopefully one day I will be able to meet you 🙏
Hi, I've learned a lot of you professor. Thanks a bunch. I have a question; How to apply this table method of R.A for circumpolar stars? I mean, what does it mean for a star to be 1 hour behind the sun if it's circumpolar and doesn't set at all? Also, how to apply the same thing for higher altitudes where the sun stays in the sky for most of the day? and thank you for all your efforts
For example, the big dipper can be seen from most of North America and Europe for most if not all of the year. If you keep spotting it throughout the year, you can see it move around Polaris. The RA will help you determine on which side it will be when you go looking for it. During the summer of course the time window for observation does become a lot smaller.
Perhaps a more technical understanding of what RA is might be useful here: 1) An object is at 0 hours RA when on the Vernal equinox it crosses with the ecliptic and the celestial equator (this point is called the First Point of Aries-perhaps not the most useful of names because procession means this point is no longer in Aries) 2) The RA is then measured in hours, minutes and seconds along the celestial equator from this point. Note that 24 hours = 360 degrees. Astronomers use hours and minutes because they are really measuring the time that the star is moving through the sky 3) So when we say that Sirius has a RA of 6 hours we are saying that if it was the Vernal equinox then it would be a quarter of the way around the equator(Eastwards from the view of looking onto the Earth) which is why it appears in the sky 6 hours behind the Sun. 4) If we then wait a month until April 21st the Earth has moved 30 degrees around in its orbit so its further away from Sirius (imagining it in 2D helps here) so the apparent distance between the Sun and Sirius is smaller (of course the actual distance hasn't changed) which is why it appears in the sky as being 2 hours closer each month I don't know if any of this is right but it is my best understanding of what the Professor is explaining here. I try and visualise the orbits and rotations in my mind from different perspectives and also simplify to 2D before I think of it in 3D because I find that easiest. Interesting stuff :)
@@superwelshgandalf could be because of the difference between solar and sidereal time. 4 minutes delay per day times 30 is 120 minutes, which is to say, 2 hours
This really very helpful by using this its easy to locate everything i have seen the RA video more than 10 times bcoz iam a slow learner but now iam confident thank you so much for sharing your knowledge to everyone with this principle i was able to locate stars but when i look for saturn iam not able to locate may be my calculation is wrong saturn on wiki says Northpole RA and NP DEC is it different from normal RA AND DEC
Thank you for this video. I have struggled with this concept and you have made it much clearer!! But would you need to take into account your location on the Earth's surface when determining when to view an object? So, say for example I am situated in Beunos Aires, and I want to view Arcturus (RA=14hr), would I need to adjust my viewing time accordingly? Thanks
Falling in love with the way u teach us.. One question from where we get to know the information... About the basic time difference of all the stars with sun, such as Sirius is 6hr45mins difference with sun at march 21,from where we get this information?
There are many of them on the market. They are all good and it becomes a personal preference. I neve found a "perfect" text book while teaching astronomy.
Thank you for the very clear explanation ..I am trying to watch Betelgeuse ..It has a right ascension of 6hrs..I calculated it according to what you did..Can you show a full chart from one vernal equinox to another and how we get back to the same RA for the next Mar 21.? Does it reverse at some point of time ?
Great series. Thank you. When working the table for RA, I understand that 30 degrees, the rotation around the sun every month, equals two hours but it is not clear why you subtract versus add the 2 hours. Can you help clarify why we subtract the 2 hours instead of add the 2 hours. Would appreciate and context on this. Thank you.
Excellent Presentation ! I do have a question What happens on Sept 21 when we're at the Autumnal Equinox when Sirius would be -6hrs (Sept) behind the Sun? Do we now the hours that it is behind sunrise as -4hrs (Oct), -2hrs (Nov) , 0 (Dec), -2(Jan), -4 (Feb), 6 (Mar)?
On march 21 Sirius is 6 hours behind the Sun (+6) which means that when the Sun sets, Sirius will set 6 hours later. On April 21 Sirius is 4 hours behinds the Sun thus when the Sun sets, Sirius will set 4 hours later. On May 21, Sirius is 2 hours behind the Sun which means that...........
Wow thank you so much! Looks like I'm gonna have to wake up at 4am to get a glimpse of my favorite star (: I never took astronomy in school so you are blowing my mind right now and teaching me so much. Thank you
Interesting video. Think I almost understand. In the example of Sirius in the video before this in the example you said to look South at about 50 degrees How does that work with this example? Suppose the sun rises at 6am, would that mean at 2 AM at 50 degrees I should see Sirius? Then that poses another question of which compass direction, I know you said 090°. Or am I missing something here?
Fantastic series of lectures, thank you very much ! A comic moment : you have written "latitude" as "lattidude" - it seems that this is one of those letter exchanges that nobody seems to notice....
It seems that the declension of the star is not playing any role in pinpointing the star at all and all you need is the RA to locate the star in the sky!! Could you explain a bit more regarding how the declension works together with RA and not separetly as you have done in the earlier lecture?
The right ascension will tell you if the star is visible in the sky at all at any time of the year and the time of night. The angle of declination will tell you what angle (relative to the horizon or relative to the zenith) you must look to see the star (of if the star is not visible at all from your location on the Earth at any time of the year if it is always below the horizon).
You are right I was thinking the same, since stars are changing the position so what's the use of declination it might tell us about whether the star is visible or not but we can't figure out the exact position at "any" time .
Love this video! Finally makes sense, but one question. Polaris apparently has a right ascension of 2hrs. Meaning it is 2 hrs behind the sun on March 21st and 0 hrs behind on April 21st. I don't get how that is possible as Polaris won't set or rise. How do I reconcile this? Is Polaris just an exception, but then why have a right ascension?
Actually, Polaris is not exactly at the North Celestial Pole and thus makes small circles around the polar axis. It therefore still has a right ascension.
So is there a rule governing when to use negative numbers and positive ones? In your example of Vega on March 21 you show the RA at 18 hours. This would be equivalent to -6 hours correct? Is it all the same to the field of experts or is there a preferred method for usage?
So my star chart from the IAU show Castor around 7:40 RH. I'm surmising the chart is based on the object's position at the Vernal Equinox, right? According to the lecture material, the RH meridian is fixed and the objects change coordinates as the year goes by. Correct?
The position is relative to where the Sun is at the Vernal Equinox. You then have to adjust that position throughout the year to find its new location relative to the Sun's position for that time of year. It changes 2 hours per month.
The right ascension of Sagittarius is 19 hour, but Sun enters constellation Sagittarius on Dec. 18, 2020. Why is that? According to my calculations (based on yours), it must have entered at the beginning of January, right? 10-day deviation seems a lot. I need this information for my astronomy homework not for some sort of astrological oracle:) Thanks in advance.
Mr Michel , One more doubt .Vega was setting on March 21 rst in 2022 at 13 hrs 42 minutes.So it set nearly 20 hours later than the previous day's Sun set i.e at 18 hrs 12 minutes.Even on 22-03-22 Vega was setting at 13 hrs 38 minutes. As you said setting time of Vega after sun set was not 18 hrs , as it's RA indicates , but nearly 20 hours .Could you kindly clarify how to account for this ? Regards G S Kumar.
Vega is listed as having a right ascension of of 18h36, which means that its right ascension could also be listed as - 5h24. We also know that Vega is close to being directly overhead after sundown during the summer (July-August) So to find Vega on July 21 (4 months after March 21) : 18 h 36 - (4 x (-2)) = 10 h 36 which places it about 10 hours after the Sun at sundown and thus after it is dark, you will find it about directly overhead.
a very clarifying series (channel 1 & 2) of lectures indeed. Sometimes I have to watch a lecture a 2nd (or 3rd ;-)) time to fully understand it. Although I understand this lecture about Right Ascension quite well, I'm puzzled and disoriented about your 'position' in this video; as mentioned in your previous video (about the angle of declination), you live near LA (34° LAT), and your facing almost north while watching the camera... In this video (at minute 1) you show the movement of the sun, from your RIGHT to your LEFT, so from the east to the west,,, So far so good, BUT you show this motion IN FRONT OF YOU???? If I try repeat the exact same thing (I live near Brussels: 55°51' N, 4°21' E) while also facing north, the movement of the sun is BEHIND ME! So for me, in order to see the motion of the sun IN FRONT OF ME, I would have to face SOUTH, and the motion of the sun is from the LEFT to the RIGHT (still from the east to the west, obviously...). What's wrong in my reasoning, or what am I missing?
It is due inclined axis of earth. If you want you can stand at a particular point at a particula point on earth and jot down the position of sun. Do this again after half a year you'll see the differnce.
awesome!!!! There are not many stars in the nyc night sky due to all the light pollution. I always see this very bright star west of my northern facing window and have wondered for a while what star it is. I can faintly see one of the dippers to the east and from it's pot i follow that edge and see a star but it is much dimmer. at my 40 degree latitude, i have to look dead north what feels like 45 degrees. Perhaps that is polaris. the bright one i thought was siris but not if it's at -16. I'm going to figure this out !
Neither has priority, and you will need both in order to know where to find something in the sky at any time of the year. It depends on what you are trying to do.
@@MichelvanBiezen .Ok, let see I want to locate polaris. Declination was clear for me, , I am located at 26 degree north polaris has 90, then I have to go outside face to north and from zenit to north direction measure 64 degree. Now right ascension, polaris has 2 hr and 30 min +/-, it is April 5th after sun set I will have a short time to see polaris, but where to look; facing north close to horizon because it is catching up the sun or following the 64 degree above. Thank you so much.
sir, do we only can see any stars on these particular days as you mentioned like mar 21, apr 21 like cant we see sirius on march 10th if yes how we need to calculate should we need to assume march 10 as near to 21
I am a little confused here. From what I understand, Right Ascension (RA) and Declination (Dec) are the two coordinates that specify the location of stars and planets (and other extra-terrestrial objects) on the celestial sphere and their coordinates (except planets, Moon, comets, asteroids and the Sun) remain fixed with respect to the First Point of Aries (The position of which is also fixed) along the celestial equator. The First Point of Aries, I understand is the where the celestial equator cuts the plane of ecliptic, usually at Vernal Equinox. From the video I gather that RA is actually all about an object's position (rising, culmination, setting) how many hours ahead or behind the Sun's own and it is changing every month. Even the Star atlases how the declination and right ascension coordinates. If RA changed every month then star atlases would use a different coordinate to plot the position of the stars on the celestial sphere. I would be very grateful, if you could clarify this for me. Thank you.
Thank you very much for this series! I am still very confused though about the RA and zenith. Does this mean all stars pass through the Zenith at some point or another? I thought the RA will tell me when to see the star after the sun rises or sets (and the angle of declination shows me where to look), not necessarily at the zenith point. Is that correct? Thank you so much again :)
@@MichelvanBiezen Thanks a lot, sir. But you said in the video that, for Sirius, for instance, it would be directly overhead in March 21 (because it has an RA of 6 hours). Did I misunderstand, or are you just giving an example? Once again, thank you very much! I find your videos as brilliant as they are helpful, sir.
@@MrRasalgethi He did say Zenith, but I think he mispoke. At the end he mentioned to use Declination to find how high in the sky to look. RA just helps you determine where on the arc the object would be (Longitude). Declination will show you where on the meridian it would be.
Excellent video, but I'm still not quite clear on the 2 hour rule. In your demo, Sirius is +6 on March 21st, losing 2 hours every month, when it gets to September, it is -6 hours, from then on, do the numbers star to fall again? e.g. October -4, November -2, December 0 and so on until it gets back to +6 on March 21st of the following year.
I am in Indonesia. But on July 21, isn't Sirius is ahead of the sun? I watch it rise heliacally in mid-July every year for the first time in the pre-dawn light.
Firstly, thanks a lot for these videos they are fantastic! I was wondering, how do you find the RA zero starting point in the night sky at a given time of year or could you explain more regarding the two hour rule per month? Everything makes sense on the date of the vernal equinox but on say April 21st why is Sirius appearing two hours earlier? I know it's going to be obvious when it hits me :D
I have the same question. What I understand is on the meridian noon (12:00 PM GMT) March 21when the RA of each Celeste body is related to the Sun which is 0h:0m:0s. The sun rise and set is changing on the seasons but should all reference to the noon time gmt March 21. If you keep a watch and then compensate the time on the watch and the months, days passed vernal equinox to figure out the RA. Not sure this is right, please comment.
I'm trying to build an application that shows you a picture of the night sky as it would be on a specified date and time from a specific location. Any idea where I could learn the math required to generate these pictures dynamically? (assuming I know the location of all of the stars in the night sky)
It's good to know how Right Ascension works. But even I have to admit it's a pretty old fashioned way of dealing with star locations in these modern times.
So this makes sense for equinoxes, but how about solstices and other times of the year when the sun is above the horizon for different times not just 12 hours?
I don't get it, let's take Sirus as an example, if this is March 21st, by RA I need to wait for sunset then I should find Sirus 6 hrs behind the sun which means right above me (in the Zineth) so what do I do now with the A of D? Shouldn't I be looking at ( 34 - 16= +18 degrees) as per the previous video?
No, Sirius will not go through the zenith unless you are much farther south than let's say Los Angeles. If you are in Los Angeles which is 34 degrees north of the equator, then to find Sirius you have to look 34 - ( - 16) = 50 degrees south of the zenith.
This video has gone someway to explain to me R.A. and DEC but especially R.A. because I have a Telescope myself but always had trouble trying to figure this out so if I understand him correctly DEC tells you where in the sky the star you want to observe is and R.A. tells you when that is what time you should expect to see it but since I still have trouble figuring this out I would appreciate it if anyone replies to this post of mine to confirm I have got this correct
The angle of declination tells you how high or how low in the sky to look when facing south or north. The right ascension tells you at what time during the night the object will cross the line from north to south, although the added complication is that the time changes by 2 hours every month.
So since we round to the nearest even hour, would we consider Pollux to be 8 hrs behind the sun on March 21st and Capella to be 6 hrs behind the sun on March 21st? Why is it that we do this?
Do I need to add or subtract time depending on what latitude I am at and what time of year it is? I am thinking of the sun setting later in the summers and earlier in winters.
Dear Michael , Iam very much grateful to your explanation. This holds good for stars that have rising to setting time equal to 12 hours.But how to calculate the rising to setting time of stars with higher positive or negative declinations.Kindly shed light on this aspect. Regards G S Kumar.
Could you send me a file with many exercises about "how to find and identify stars", special for southern hemisphere, please? And something about the same way using azimuth and elevation?
I guess I'm obtuse, but how is it determined where a star is for a particular time? I understand how it appears on any given point on the Celestial Equator and I understand declination, but aren't they both dependent on time? The earth is constantly in motion and the stars are rising and setting..
The angle of declination is constant for every star. But the right ascension requires one to know the time of day and the day of the year in order to find each star at any time.
@@MichelvanBiezen Thank you so much for your reply! I just had a "eureka!" moment. The earth moves relative to the Celestial Sphere, not vice versa, and that's what was giving me fits. I couldn't grasp how you could know the position of a star without knowing the date and time, also. Great series! Thanks again!
Is it possible to see the stars: Aldebaran, Dubhe and Mizar at 23.5 degrees South? Which are mean circumpolar stars at 23.5 degrees south? Is it correct say: Alpha Centauri has a declination (-60 degrees) and my position is 23.5 degrees south. I have to look at -83.5 degrees (83.5 degrees south)?
If your position is 23.5 degrees south ( = - 23.5 degrees) and you want to look for Alpha Centauri, then you need to look 37.5 degrees south of the zenith. You should be able to see Aldeberan no problem, but Mizar will be more difficult as it will be close to the horizon for you.
You are the only person I have found on the net who has thoroughly explained right ascension in not just lay mans terms but any terms. Thank you very much.
How can somebody explain so good with just a white board and a marker. I mean no animations nothing but an absolute gem. Thank you sir!
i agreed, he explained really good, bur i fell bad for the ones who didn't found this channel, because this channel is great
You are my hero. Finally, for the first time in my life i found the "real" explanation about RA. Well explained. Thank you
Thank you! Thank you! Thank you! For the first time in well over a decade of staring at "explanations," you have made crystal clear and cognitively manageable (did I just concoct a term?) the meaning of right ascension. And you did it in under ten minutes! I am absolutely delighted. Thank you!
i've been studying astronomy for 3 years, and this is the first time i've ever heard such a beautiful explanation! amaznig job.
Wow, thank you!
Best explanation of celestial coordinates ever! I deeply appreciate this video
Whenever I'm doing throughout the day, I know that soon I proceed watching these series. They are so encouraging to learn the world by telling about complex things in simple stories, so empowering! Thank you!
Glad you like them! 🙂
This man just saved my entire term.
Bravo, Professor. Finally I understand the celestial sky. I've watching a lot of videos and they have confused me, rather than illuminate this concept. Thank you. Keep up the good work.
Incredibly helpful video. No one has explained it as well as you have
Thank you. Glad you found our videos! 🙂
This is by far the best explanation I jave come across
This is such a great course and your explanations are clear and concise Michel. I never took the time to understand Declination and RA. Now I understand. Thank you, I am taking notes of each video episode in a composition grid notebook where my Book Cover Subject is: Astronomy, my School is: Hard Knocks and my Grade Is: 62nd Grade. You never stop learning through life, ever...
That is correct. A lot of joy and satisfaction can be gained by learning new concepts or finally understanding concepts we couldn't get before. I still learn things I couldn't understand as a student. 🙂
This was very lucid and easy to comprehend. Ultimate explanation.
In 3 months I begin my Astrophysics degree after many years of dreaming. I have absolutely aced my entry course through my local college and hold the highest confidence, all bar my knowledge of RA. I have been trying to wrap my head around this for a long time, and not to echo too many people here but I have never found such a clear explanation. Not only do I now have the confidence to use my telescope properly, I feel like I have just crushed a major hurdle on my path to my future career. Thank you for this video, you have just made my day sir.
I wish you all the best with your studies. Based on your success so far, you are a disciplined student and a hard worker. Keep it up. Glad we were able to help.
@@MichelvanBiezen Thank you very much for the kind words and the response!
I just jumped in the middle here (videos 8 and 9) and the content is completely understandable; thank you very much for having this online.
Glad you found our videos. 🙂
You've made this concept so much clearer to me. Thank you
I've been an ameteur astronomer for many years but embarrassingly I could not understand Right Ascension...you are the only one who explained it in such a way that finally made sense! Im still a little iffy about finding a star using the declination at any given time, but now i understand it much better, thank you so much!
One question, how do you determine the hours behind during each date listed?
Glad it was helpful. 🙂
On March 21, Orion is 6 hours behind the Sun. On Aprl 21, Orion is 4 hours behind the Sun. On May 21, Orion is 2 hours behind the Sun. That is the best way to think about it.
I have been struggling so long to understand this, but thanks to your wonderful video I have better understanding. Thank you very much.
Glad it was helpful!
I learned from this video especially those stars that are part of the zodiac constellation the moment they are with the sun ( O hrs) it means that the sun travelling along the ecliptic points towards the zodiac constellation assigned on that particular month.... Very detailed discussion in this video....Thanks alot sir❤❤❤❤❤❤❤❤❤❤
Thank you. You are correct.
This is very well delivered. Thank you,i am just enthusiastic about astronomy and u make it more fun and a lot easier to learn.
You're very welcome
Thanks for this wonderful lecture. It saved a lot of time and efforts for me.
Keep doing the excellent work you do at dispensing knowledge and understanding to people.
Beautifully explained! Bravo sir!!
Many thanks!
I'm studying celestial navigation for sailing class and started playing around with Stellarium to practice locating stars. However, what we look up as GHA in nautical almanacs shows up as RA in Stellarium and I had no idea what it meant. This video really cleared things up. Thank you!
Both this video and the previous one on Declination were extremely informative and helpful to me. Thank you very much for an excellent job of explaining an initially daunting-to-me concept clearly, and with the perfect combination of conciseness and detail.
Thank you for your nice comment.
Your explanation is awesome. Thank you so much. It's a long time I've questioned about right ascension.
Glad it was helpful!
Thank you for explaining this clearly and concisely. I was having trouble understanding right ascension, but now I understand it. If you don't mind though, I have a couple of questions I hope you can answer:
1. Are the RA numbers listed only based when viewed from the equator? Reason I ask is because I live about 40 degrees North, so some stars I see to the north never set. Also, even for stars that do set where I live, such as Vega, are noticeably off of when they should set, and I'm assuming this is also because I don't live at the equator. So, I'm assuming that a star's right ascension is based on when viewed from the equator, since those stars more to the north actually "set" when viewed from the equator, right? And Is there a way to convert the right ascension for different latitudes?
2. Polaris has a RA of about 2 hours, since it's not exactly 90 degrees north. However, if it was exactly 90, would it's RA be undefined, as it technically would always stay right on the horizon when viewed from the equator?
1. The RA does not depend on where you are, but that will affect when and where you will see the star / constellation based on your field of vision from your vantage point. 2. Technically RA would be undefined if Polaris was perfectly at 90 degrees. However that said, any star exactly at 90 degrees wouldn't be there very long because of the precession of the Earth.
@@MichelvanBiezen Thank you!
Thanks, you made me understand RA much better now. There is one point that I missed out or don't quite get, that is why subtract 2hrs going forward every month. Add ?
Since RA is in terms of hours BEHIND the Sun, and all heavenly bodies (except for the planets) catch up to the Sun 2 hours every month. The time behind the Sun reduces by 2 hours every month. After the star passes the Sun in the sky, then the Star will get further and further ahead (2 hours per monht) and then you must add the 2 hours each month, untill the star gets close to the Sun again and it will be behind the Sun catching up........
Thank you for your videos. They are really helpful. From my first year in campus, there's always a video of yours that really helps me in a particular unit. Now I'm almost joining my 4th year. Wow time flies!
Sir you are a fantastic teacher , you make the material so easy to understand . I am an astronomy afficionado myself and I have been observing the night sky through binocular and with naked eye for 5 years. I understand the night sky to a fair degree too.
Hope to learn a lot more from your videos . Hopefully one day I will be able to meet you 🙏
That would be great. Enjoy the night sky!
@@MichelvanBiezen thank you sir . Hope to interact with you more and learn
a very good video series Michel, great service to science and mankind. Kindly keep these coming. god bless.
best explanation I've heard
Cristal clear explanation, thank you Professor van Biezen!
Thanks for the explanation! Very clear and concise.
Hi, I've learned a lot of you professor. Thanks a bunch. I have a question; How to apply this table method of R.A for circumpolar stars? I mean, what does it mean for a star to be 1 hour behind the sun if it's circumpolar and doesn't set at all? Also, how to apply the same thing for higher altitudes where the sun stays in the sky for most of the day? and thank you for all your efforts
For example, the big dipper can be seen from most of North America and Europe for most if not all of the year. If you keep spotting it throughout the year, you can see it move around Polaris. The RA will help you determine on which side it will be when you go looking for it. During the summer of course the time window for observation does become a lot smaller.
Perhaps a more technical understanding of what RA is might be useful here:
1) An object is at 0 hours RA when on the Vernal equinox it crosses with the ecliptic and the celestial equator (this point is called the First Point of Aries-perhaps not the most useful of names because procession means this point is no longer in Aries)
2) The RA is then measured in hours, minutes and seconds along the celestial equator from this point. Note that 24 hours = 360 degrees. Astronomers use hours and minutes because they are really measuring the time that the star is moving through the sky
3) So when we say that Sirius has a RA of 6 hours we are saying that if it was the Vernal equinox then it would be a quarter of the way around the equator(Eastwards from the view of looking onto the Earth) which is why it appears in the sky 6 hours behind the Sun.
4) If we then wait a month until April 21st the Earth has moved 30 degrees around in its orbit so its further away from Sirius (imagining it in 2D helps here) so the apparent distance between the Sun and Sirius is smaller (of course the actual distance hasn't changed) which is why it appears in the sky as being 2 hours closer each month
I don't know if any of this is right but it is my best understanding of what the Professor is explaining here. I try and visualise the orbits and rotations in my mind from different perspectives and also simplify to 2D before I think of it in 3D because I find that easiest.
Interesting stuff :)
Thanks for this - can you elaborate on your fourth point (if possible) it's bending my brain the two hours less per month thing!
@@superwelshgandalf could be because of the difference between solar and sidereal time. 4 minutes delay per day times 30 is 120 minutes, which is to say, 2 hours
greatest explainter of all time
This really very helpful by using this its easy to locate everything i have seen the RA video more than 10 times bcoz iam a slow learner but now iam confident thank you so much for sharing your knowledge to everyone with this principle i was able to locate stars but when i look for saturn iam not able to locate may be my calculation is wrong saturn on wiki says
Northpole RA and NP DEC is it different from normal RA AND DEC
Thanks Michel for the lovely clear explanations.
You explain astronomy the best.
Thank you for this video. I have struggled with this concept and you have made it much clearer!!
But would you need to take into account your location on the Earth's surface when determining when to view an object? So, say for example I am situated in Beunos Aires, and I want to view Arcturus (RA=14hr), would I need to adjust my viewing time accordingly?
Thanks
Marcus,
Not for the right ascension, but yes for the angle of declination.
Falling in love with the way u teach us..
One question from where we get to know the information... About the basic time difference of all the stars with sun, such as Sirius is 6hr45mins difference with sun at march 21,from where we get this information?
Most astronomy text books will have that information in tables in the back of the book. Otherwise the internet is a good source for that informtion.
Thanks a lot sir. Can you please suggest some basic astronomy books.
There are many of them on the market. They are all good and it becomes a personal preference. I neve found a "perfect" text book while teaching astronomy.
This series is the best!
Superb lecture explaining RA. Many many thanks for uploading this. Have a lovely day.
Thank you and your are welcome.
Yes! Thank you so much . This was so well explained!
So what is the right ascension for January and February? Will we add 2, for example in Sirius Jan = 10, Feb = 8?
That is correct.
@@MichelvanBiezen ok thanks
THANK YOU SO MUCH FOR THIS. You have no idea how crazy I was going trying to understand this from my textbook over and over TToTT
We are glad the video was helpful Thank you for the feedback.
Thank you for the very clear explanation ..I am trying to watch Betelgeuse ..It has a right ascension of 6hrs..I calculated it according to what you did..Can you show a full chart from one vernal equinox to another and how we get back to the same RA for the next Mar 21.? Does it reverse at some point of time ?
I dont know about this stuff...Trying to understand it would be very helpful to know.
Very wonderfully explained
Glad you liked it 🙂
Great series. Thank you. When working the table for RA, I understand that 30 degrees, the rotation around the sun every month, equals two hours but it is not clear why you subtract versus add the 2 hours. Can you help clarify why we subtract the 2 hours instead of add the 2 hours. Would appreciate and context on this. Thank you.
If Orion is 5 hours behind the Sun on March 21, it will be 3 hours behind the Sun on April 21, and 1 hour behind the Sun on May 21.
Thank you for your reply, but it does not really answer my question or at least how it answers my question.
Beautiful lecture. Thank you.
Excellent Presentation !
I do have a question What happens on Sept 21 when we're at the Autumnal Equinox when Sirius would be -6hrs (Sept) behind the Sun? Do we now the hours that it is behind sunrise as -4hrs (Oct), -2hrs (Nov) , 0 (Dec), -2(Jan), -4 (Feb), 6 (Mar)?
On march 21 Sirius is 6 hours behind the Sun (+6) which means that when the Sun sets, Sirius will set 6 hours later. On April 21 Sirius is 4 hours behinds the Sun thus when the Sun sets, Sirius will set 4 hours later. On May 21, Sirius is 2 hours behind the Sun which means that...........
Wow thank you so much! Looks like I'm gonna have to wake up at 4am to get a glimpse of my favorite star (: I never took astronomy in school so you are blowing my mind right now and teaching me so much. Thank you
really helpful and ...easy to understand
Interesting video. Think I almost understand. In the example of Sirius in the video before this in the example you said to look South at about 50 degrees How does that work with this example? Suppose the sun rises at 6am, would that mean at 2 AM at 50 degrees I should see Sirius? Then that poses another question of which compass direction, I know you said 090°. Or am I missing something here?
Amazing series of lectures
Fantastic series of lectures, thank you very much !
A comic moment : you have written "latitude" as "lattidude" - it seems that this is one of those letter exchanges that nobody seems to notice....
That is funny indeed
It seems that the declension of the star is not playing any role in pinpointing the star at all and all you need is the RA to locate the star in the sky!! Could you explain a bit more regarding how the declension works together with RA and not separetly as you have done in the earlier lecture?
The right ascension will tell you if the star is visible in the sky at all at any time of the year and the time of night. The angle of declination will tell you what angle (relative to the horizon or relative to the zenith) you must look to see the star (of if the star is not visible at all from your location on the Earth at any time of the year if it is always below the horizon).
You are right I was thinking the same, since stars are changing the position so what's the use of declination it might tell us about whether the star is visible or not but we can't figure out the exact position at "any" time .
IIUC, Aldebaran wouldn't go through your local zenith, but it's highest point would be 16 - 34 = -18 (= 18 degree to the south), right?
That looks about right.
Love this video! Finally makes sense, but one question. Polaris apparently has a right ascension of 2hrs. Meaning it is 2 hrs behind the sun on March 21st and 0 hrs behind on April 21st. I don't get how that is possible as Polaris won't set or rise. How do I reconcile this? Is Polaris just an exception, but then why have a right ascension?
Actually, Polaris is not exactly at the North Celestial Pole and thus makes small circles around the polar axis. It therefore still has a right ascension.
Very glad to have viewed this so clear .
Sir can you suggest good book for celestial mechanics 🙏🙏🙏 and super explained as always loved that💖💖💖
I haven't seen a book that does a good job explaining that. It appears that they already assume you know how to do that.
So is there a rule governing when to use negative numbers and positive ones? In your example of Vega on March 21 you show the RA at 18 hours. This would be equivalent to -6 hours correct? Is it all the same to the field of experts or is there a preferred method for usage?
It is all the same and I have seen it used both ways.
So my star chart from the IAU show Castor around 7:40 RH. I'm surmising the chart is based on the object's position at the Vernal Equinox, right? According to the lecture material, the RH meridian is fixed and the objects change coordinates as the year goes by. Correct?
The position is relative to where the Sun is at the Vernal Equinox. You then have to adjust that position throughout the year to find its new location relative to the Sun's position for that time of year. It changes 2 hours per month.
The right ascension of Sagittarius is 19 hour, but Sun enters constellation Sagittarius on Dec. 18, 2020. Why is that? According to my calculations (based on yours), it must have entered at the beginning of January, right? 10-day deviation seems a lot. I need this information for my astronomy homework not for some sort of astrological oracle:) Thanks in advance.
Mr Michel , One more doubt .Vega was setting on March 21 rst in 2022 at 13 hrs 42 minutes.So it set nearly 20 hours later than the previous day's Sun set i.e at 18 hrs 12 minutes.Even on 22-03-22 Vega was setting at 13 hrs 38 minutes. As you said setting time of Vega after sun set was not 18 hrs , as it's RA indicates , but nearly 20 hours .Could you kindly clarify how to account for this ?
Regards G S Kumar.
Vega is listed as having a right ascension of of 18h36, which means that its right ascension could also be listed as - 5h24. We also know that Vega is close to being directly overhead after sundown during the summer (July-August) So to find Vega on July 21 (4 months after March 21) : 18 h 36 - (4 x (-2)) = 10 h 36 which places it about 10 hours after the Sun at sundown and thus after it is dark, you will find it about directly overhead.
Mr Michel.Thanks a lot.
a very clarifying series (channel 1 & 2) of lectures indeed. Sometimes I have to watch a lecture a 2nd (or 3rd ;-)) time to fully understand it. Although I understand this lecture about Right Ascension quite well, I'm puzzled and disoriented about your 'position' in this video; as mentioned in your previous video (about the angle of declination), you live near LA (34° LAT), and your facing almost north while watching the camera... In this video (at minute 1) you show the movement of the sun, from your RIGHT to your LEFT, so from the east to the west,,, So far so good, BUT you show this motion IN FRONT OF YOU???? If I try repeat the exact same thing (I live near Brussels: 55°51' N, 4°21' E) while also facing north, the movement of the sun is BEHIND ME! So for me, in order to see the motion of the sun IN FRONT OF ME, I would have to face SOUTH, and the motion of the sun is from the LEFT to the RIGHT (still from the east to the west, obviously...). What's wrong in my reasoning, or what am I missing?
It is due inclined axis of earth. If you want you can stand at a particular point at a particula point on earth and jot down the position of sun. Do this again after half a year you'll see the differnce.
Thank you! So easy to understand
awesome!!!! There are not many stars in the nyc night sky due to all the light pollution. I always see this very bright star west of my northern facing window and have wondered for a while what star it is. I can faintly see one of the dippers to the east and from it's pot i follow that edge and see a star but it is much dimmer. at my 40 degree latitude, i have to look dead north what feels like 45 degrees. Perhaps that is polaris. the bright one i thought was siris but not if it's at -16. I'm going to figure this out !
Ok, very good lesson, but how we combine angle of declination and right ascension, which one have priority. Thanks
Neither has priority, and you will need both in order to know where to find something in the sky at any time of the year. It depends on what you are trying to do.
@@MichelvanBiezen .Ok, let see I want to locate polaris. Declination was clear for me, , I am located at 26 degree north polaris has 90, then I have to go outside face to north and from zenit to north direction measure 64 degree.
Now right ascension, polaris has 2 hr and 30 min +/-, it is April 5th after sun set I will have a short time to see polaris, but where to look; facing north close to horizon because it is catching up the sun or following the 64 degree above.
Thank you so much.
sir, do we only can see any stars on these particular days as you mentioned like mar 21, apr 21 like cant we see sirius on march 10th if yes how we need to calculate should we need to assume march 10 as near to 21
Yes, we use interpolation. The stars move about 30 degrees per month or about 1 degree per day from night to night.
Wonderful! Thank you for your lectures :)
I am a little confused here. From what I understand, Right Ascension (RA) and Declination (Dec) are the two coordinates that specify the location of stars and planets (and other extra-terrestrial objects) on the celestial sphere and their coordinates (except planets, Moon, comets, asteroids and the Sun) remain fixed with respect to the First Point of Aries (The position of which is also fixed) along the celestial equator. The First Point of Aries, I understand is the where the celestial equator cuts the plane of ecliptic, usually at Vernal Equinox. From the video I gather that RA is actually all about an object's position (rising, culmination, setting) how many hours ahead or behind the Sun's own and it is changing every month.
Even the Star atlases how the declination and right ascension coordinates. If RA changed every month then star atlases would use a different coordinate to plot the position of the stars on the celestial sphere. I would be very grateful, if you could clarify this for me. Thank you.
Nice explanation sir
Thank you. Glad you liked it. 🙂
Thank you very much for this series! I am still very confused though about the RA and zenith. Does this mean all stars pass through the Zenith at some point or another? I thought the RA will tell me when to see the star after the sun rises or sets (and the angle of declination shows me where to look), not necessarily at the zenith point. Is that correct?
Thank you so much again :)
No, only few stars pass through the zenith. All stars pass through the line connecting the northern horizon to the zenith and to the southern horizon.
@@MichelvanBiezen Thanks a lot, sir. But you said in the video that, for Sirius, for instance, it would be directly overhead in March 21 (because it has an RA of 6 hours). Did I misunderstand, or are you just giving an example?
Once again, thank you very much! I find your videos as brilliant as they are helpful, sir.
Basically u need to understand why RA term comes in
@@MrRasalgethi He did say Zenith, but I think he mispoke. At the end he mentioned to use Declination to find how high in the sky to look. RA just helps you determine where on the arc the object would be (Longitude). Declination will show you where on the meridian it would be.
Sir,
Is there any CATALOGUE of 'RA & Dec' of main (Easily identifiable) stars which is AVAILABLE TO GENERAL PEOPLE. If yes, please share the link.
I don't have a link readily available, but there are many such lists to be found on the internet.
Great lecturer
Glad you think so!
Excellent. Thankyou. 👍
You are welcome! 🙂
Thank you, so informative
Glad it was helpful!
BTW the year is 12 months, so what happens the next six months (Sep to Dec) which is missing from your informative lecture?
The pattern continues with a shift of 2 hours for every month, (Not enough board space).
Excellent video, but I'm still not quite clear on the 2 hour rule. In your demo, Sirius is +6 on March 21st, losing 2 hours every month, when it gets to September, it is -6 hours, from then on, do the numbers star to fall again? e.g. October -4, November -2, December 0 and so on until it gets back to +6 on March 21st of the following year.
On March 21st, Sirius rises 6 hours after the Sun rises. On September 21st, Sirius rises 6 hours before the Sun rises.
Thanks Michel.
I am in Indonesia. But on July 21, isn't Sirius is ahead of the sun? I watch it rise heliacally in mid-July every year for the first time in the pre-dawn light.
Since the RA of Sirius is 6 hrs 45 min, on July 21, Sirius should be slightly ahead of the Sun by 1 hour and 45 minutes.
@ 6:10 Why Vega will be moving through Zenith, if it's A of D is +38* ( +34* in your location) ?
I should have more properly said (When Vega crosses the line connecting north and south to the zenith
@@MichelvanBiezen Thank you! Very good material, easy to follow and understand!
Firstly, thanks a lot for these videos they are fantastic! I was wondering, how do you find the RA zero starting point in the night sky at a given time of year or could you explain more regarding the two hour rule per month? Everything makes sense on the date of the vernal equinox but on say April 21st why is Sirius appearing two hours earlier? I know it's going to be obvious when it hits me :D
I have the same question. What I understand is on the meridian noon (12:00 PM GMT) March 21when the RA of each Celeste body is related to the Sun which is 0h:0m:0s. The sun rise and set is changing on the seasons but should all reference to the noon time gmt March 21. If you keep a watch and then compensate the time on the watch and the months, days passed vernal equinox to figure out the RA. Not sure this is right, please comment.
I'm trying to build an application that shows you a picture of the night sky as it would be on a specified date and time from a specific location. Any idea where I could learn the math required to generate these pictures dynamically? (assuming I know the location of all of the stars in the night sky)
It's good to know how Right Ascension works. But even I have to admit it's a pretty old fashioned way of dealing with star locations in these modern times.
So this makes sense for equinoxes, but how about solstices and other times of the year when the sun is above the horizon for different times not just 12 hours?
I don't get it, let's take Sirus as an example, if this is March 21st, by RA I need to wait for sunset then I should find Sirus 6 hrs behind the sun which means right above me (in the Zineth) so what do I do now with the A of D? Shouldn't I be looking at ( 34 - 16= +18 degrees) as per the previous video?
No, Sirius will not go through the zenith unless you are much farther south than let's say Los Angeles. If you are in Los Angeles which is 34 degrees north of the equator, then to find Sirius you have to look 34 - ( - 16) = 50 degrees south of the zenith.
This video has gone someway to explain to me R.A. and DEC but especially R.A. because I have a Telescope myself but always had trouble trying to figure this out so if I understand him correctly DEC tells you where in the sky the star you want to observe is and R.A. tells you when that is what time you should expect to see it but since I still have trouble figuring this out I would appreciate it if anyone replies to this post of mine to confirm I have got this correct
The angle of declination tells you how high or how low in the sky to look when facing south or north. The right ascension tells you at what time during the night the object will cross the line from north to south, although the added complication is that the time changes by 2 hours every month.
i thought i had to cram without understanding cz i couldnt understand . but now, i understand it. yoyo
So since we round to the nearest even hour, would we consider Pollux to be 8 hrs behind the sun on March 21st and Capella to be 6 hrs behind the sun on March 21st? Why is it that we do this?
For the purpose of casual viewing, rounding works. But computerized tracking devices on telescopes use much higher precision.
Do I need to add or subtract time depending on what latitude I am at and what time of year it is? I am thinking of the sun setting later in the summers and earlier in winters.
The stars and constellations are fixed relative to the celestial sphere. The Sun, Moon, and planets do move through the sphere.
Excellent lecture.
Dear Michael , Iam very much grateful to your explanation. This holds good for stars that have rising to setting time equal to 12 hours.But how to calculate the rising to setting time of stars with higher positive or negative declinations.Kindly shed light on this aspect.
Regards G S Kumar.
who knew a man with bow tie that's not bill Nye could steal my heart
Glad you like out videos. 🙂
Thanks! Very well done!
Our pleasure!
Could you send me a file with many exercises about "how to find and identify stars", special for southern hemisphere, please? And something about the same way using azimuth and elevation?
How does this apply if you are in the Southern Hemisphere? Do we use March 21st as well ? Thanks
+David Lam
Yes, March 21 is a universal date for the right ascension. The angle of declination is negative south of the equator.
Thank you!
David Lam n
excellent teaching！！！
I guess I'm obtuse, but how is it determined where a star is for a particular time? I understand how it appears on any given point on the Celestial Equator and I understand declination, but aren't they both dependent on time? The earth is constantly in motion and the stars are rising and setting..
The angle of declination is constant for every star. But the right ascension requires one to know the time of day and the day of the year in order to find each star at any time.
@@MichelvanBiezen Thank you so much for your reply! I just had a "eureka!" moment. The earth moves relative to the Celestial Sphere, not vice versa, and that's what was giving me fits. I couldn't grasp how you could know the position of a star without knowing the date and time, also. Great series! Thanks again!
Is it possible to see the stars: Aldebaran, Dubhe and Mizar at 23.5 degrees South? Which are mean circumpolar stars at 23.5 degrees south?
Is it correct say: Alpha Centauri has a declination (-60 degrees) and my position is 23.5 degrees south. I have to look at -83.5 degrees (83.5 degrees south)?
If your position is 23.5 degrees south ( = - 23.5 degrees) and you want to look for Alpha Centauri, then you need to look 37.5 degrees south of the zenith. You should be able to see Aldeberan no problem, but Mizar will be more difficult as it will be close to the horizon for you.
+Michel van Biezen dec of alpha cent - my latitude?
+Michel van Biezen Can we use the same table - about RA and Dec for Southern Hemisphere?