The light that left the year you were born
Light takes a year to cover a light year. So somewhere up there is a star far enough away that the light reaching your eye tonight set off the year you did. Put in your birth year and where you are, and this finds it, then tells you what time to go outside and which way to face.
Your star
Denebola
36 light years away, in Leo
The light reaching your eye tonight left Denebola the year you were born.
It happens to sit in Leo. That’s a coincidence of direction, not anything about you, but it does give you a name people know to point with.
Near misses
Tap one to see where it is instead.
Tonight from Denver
Working out tonight’s sky…
Your light’s trip
The light you’ll see from Denebola tonight has been travelling your whole life. Here’s the trip, at a few decades a second.
1990
You’re born. The light is 0 light years out, 0% of the way here.
How it works
A light year is a distance
It’s how far light gets in a year, a little under six trillion miles. A star 36 light years away is showing you light that left it 36 years ago. Pick the right star and the light you see tonight is exactly as old as you are.
The distances are measured
Every distance here comes from parallax: astronomers measure how much a close star shifts against the far background as the Earth goes round the sun, and the size of the shift gives the distance. They’re rounded to a tenth of a light year, so treat the year as good to about a year.
Only stars you can see
The list only includes stars bright enough to find without a telescope, and it only offers you one that actually rises where you are. That rules out some closer ones. Alpha Centauri is the nearest star to the sun and never clears the horizon from most of the United States.
The times are worked out on your device
Your star’s position, the sun’s and your place on the globe go into the same sums an astronomy app uses. Nothing is looked up online and nothing about you leaves the page.
Questions people ask
What is my birth star?
Here, it’s the star whose light set off toward Earth the year you were born, so the light you see from it tonight is as old as you are. Put in your birth year and the tool finds the closest match that you can actually see from where you live.
Is this the same as the birth star in Vedic astrology?
No. In Vedic astrology your birth star, or nakshatra, is the part of the sky the moon was in when you were born. This is a different idea: a real star, a measured distance, and light that has been travelling for exactly your lifetime.
How accurate is it?
The distances are published parallax measurements, so the year is good to about a year for the nearer stars and can be a year or two out for the farther ones. The times are good to a few minutes. Your horizon, the weather and the streetlights are the bigger variables.
What if I was born after about 2017?
Then no star you can see is close enough. The nearest one visible from most of the northern hemisphere is Sirius, about 8.6 light years away, so its light is always at least eight years old. The tool shows you the closest there is instead.
Why isn’t my star in my zodiac sign?
Because the zodiac is twelve constellations out of eighty-eight, picked because the sun passes in front of them. Most stars are somewhere else. When yours does land in a sign, it’s a coincidence of direction.
Why can’t I see it tonight?
Every star spends part of the year in the daytime sky, lost in the sun’s glare. The month-by-month chart shows when yours comes back after dark, and the tool gives the next good night.
There’s a whole course like this
The birth star is one lesson from Star Signs, an astronomy course that starts with your star sign and ends with you outside, finding the real thing. It’s being built now.