We can't say for sure when planetary hours started being used, but it seems that the practice started around the first century BCE.
Of course, back then, we didn't know as much about space and the planets. That said, people did still know quite a bit! Planetary hours use what we call the seven classical planets, which are:
These planets each have a dedicated weekday and specified hours throughout the different weekdays. Check out the Planetary Hour Calculator to see how these hours are laid out.
Meanings of the Planets
The sun is a symbol of success and happiness.
It has an intense nature.
It rules Sunday.
Mercury is a symbol of quick change and versatility.
It has a neutral nature.
It rules Wednesday.
Saturn is a symbol of diligence, study, and work.
It rules Saturday.
The moon is a symbol of reflection and intuition.
It has a gentle nature.
It rules Monday.
Jupiter is a symbol of wealth and protection.
It rules Thursday.
Mars is a symbol of courage and competition.
It has an intense nature.
It rules Tuesday.
Venus is a symbol of love, sex, and beauty.
It has a gentle nature.
It rules Friday.
So what do I do with this information?
That's really up to you. It depends on your goals, your energy reserves, your resources, etc.
If you like to do magic spells or rituals, a little planning can help you time your activities to coincide with the proper planetary days and hours. It's believed by many people that this can give your workings a boost. Alternatively, the day and hour could potentially get in the way of your goals. Don't do a spell for reconciliation during the day and hour of Mars, for example.
If you don't do spells, this information can still be used in slightly more passive ways. Wearing the colors or metals associated with certain days might help you to use the energy of the day. Is it Friday and you have a date tonight? Maybe wear a cute green top and a copper bracelet.
Some people plan their week based on the planetary days. Monday's energy would be good for divination or meditation. Tuesday would be a good day to tackle a difficult task. Wednesday would be a good day to have an important conversation.
It's also just kinda cool to know, you know?
Wait, so how do I know which days are which planet...?
Okay, it's gonna sound complicated, but bear with me.
Sun = Sunday
Moon = Monday
Mars = Tuesday
Mercury = Wednesday
Jupiter = Thursday
Venus = Friday
Saturn = Saturday
This is how the planets fall during the week. This is what planet rules each day, regardless of the hour. It can be important to pay attention to this, because, for example, you might not want to do a love spell during the hour of Venus (sex, love) on a Tuesday (Mars, competition, battle).
Here are some tips to help you remember which planets fall on which days:
Sunday has "sun" in it. Easy.
Monday almost has "moon" in it. Still easy.
Tuesday is named for Tiw, Norse god of combat. Mars is the Roman god of war.
Wednesday is Mercury. Mercury is the most versatile/neutral of the planets, and Wednesday is right in the middle of the week.
Thursday is named for Thor, Norse god of thunder. Jupiter is the Roman god of thunder.
Friday is named for Frigg/Freya, the Norse goddess of marriage. Venus is the Roman goddess of love and sex. (Plus Friday is a good night for a date.)
Saturday is Saturn. Almost as easy to remember as Sunday and Monday!
Okay, but how does that translate to hours...?
The planetary hours are not actually one hour long. They will change depending on the date. This is because the daytime hours and nighttime hours are separate groups. So please keep in mind that, outside of calculations, "hour" does not actually mean 60 minutes.
To calculate the daytime hours, you want to find out how many minutes are between sunrise and sunset. Then divide that into twelve. For example, today, where I am (because your location will change the times), sunrise is at 6:51 AM. Sunset will be at 20:47 (8:47 PM). That's 13 hours and 56 minutes, which is 836 minutes. (13 x 60 + 56 = 836. Remember PEMDAS? And we thought we'd never use it!) Divide that into 12 to get 69.6, so each daytime planetary hour will be 69 minutes and 40 seconds. (Personally, I don't sweat the seconds, but it is technically the best way to do it since it'll throw your minutes off a tiny bit if you don't take them into account.)
To make that into simple formulas, for anyone who might want them, it's:
sunset time - sunrise time = X hours and Y minutes
X x 60 + Y = minutes
minutes / 12 = planetary hour duration
(Remember to use military time format to make this work more easily.)
Now! To figure out the planets for those hours, you will first need to memorize which planets rule which days. Done? Cool.
So the first hour of sunrise will always be ruled by that weekday's ruling planet. If it's Sunday, the first hour is the Sun. Always. Monday is the Moon, Tuesday is Mars, etc. Got it? Good.
Now, to get the second hour, go back two days and use that day's ruling planet. To get the third hour, go back two more days. The fourth hour, two more days. Just keep doing that.
Today is Saturday, so the first planetary hour is ruled by Saturn. The second hour will be the planet that rules two days before Saturn. Saturday, Friday, Thursday, so it'll be Jupiter. Two days before Thursday is Tuesday, so the third hour is Mars.
The nighttime hours... are done exactly the same way. The only difference is that you'll calculate the minutes between sunset and sunrise of the next day. Everything else is exactly the same.
To get the minutes between sunset and sunrise is a bit trickier, since we can't do simple subtraction like the other. The easiest way to do it is probably like this, using military hours:
(sunrise + 24 hours) - sunset = minutes
So let's say sunset tonight is 20:47 and sunrise is at 6:50 tomorrow. If we add 24 hours, now we have 30:50 for sunrise.
30:50 - 20:47 = 10 hours and 3 minutes.
Everything else will be the same as the daytime formulas.
Or you could use the planetary hour calculator below to do all that pesky math for you! I just wanted to give an explanation so that you can figure it out on your own if you ever want or need to.
PLANETARY HOUR CALCULATOR
Skip the math!
By entering the day of the week and a few times, you can easily find out when the planetary hours of day and night begin and even what the ruling planets for those times are. This can be very helpful in ritual planning.
How to use this calculator:
Replace everything blue.
Type the day of the week (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday).
Type the blue times in this format:
mm/dd hh:mm a or p
7/18 06:35 p
All times are converted into 24-hour military time to avoid confusion about AM and PM.
Military time can be tricky if you're not used to it. Here are the basics. (Tip: just subtract 12 from the hour if the number is 1300 or above.)
0000 = 12:00am (Midnight)
0100 = 1:00am
0200 = 2:00am
0300 = 3:00am
0400 = 4:00am
0500 = 5:00am
0600 = 6:00am
0700 = 7:00am
0800 = 8:00am
0900 = 9:00am
1000 = 10:00am
1100 = 11:00am
1200 = 12:00pm (Noon)
1300 = 1:00pm
1400 = 2:00pm
1500 = 3:00pm
1600 = 4:00pm
1700 = 5:00pm
1800 = 6:00pm
1900 = 7:00pm
2000 = 8:00pm
2100 = 9:00pm
2200 = 10:00pm
2300 = 11:00pm