A thoroughly sporadic column from astronomer Mike Brown on space and science, planets and dwarf planets, the sun, the moon, the stars, and the joys and frustrations of search, discovery, and life. With a family in tow. Or towing. Or perhaps in mutual orbit.

Tiny Bunnies

This morning my 2 ½ year old daughter Lilah opened the front door to find the tiniest Easter basket I have ever seen, filled with candy, bubbles, and stickers. My suspicion, as yet unconfirmed, is that Easter baskets everywhere were equally tiny today, and that it is all the fault of the moon.
This is the third Easter Diane, Lilah, and I have spent in our house up in the foothills above Pasadena. After last year’s record low rainfall, Easter – and springtime in general – was marked by an intensifying of the brown in the canyon in our backyard. That same brown all over southern California contributed greatly to the intense wildfires that swept the region last fall. The small-scale wildlife that was abundant in our backyard two years ago – rabbits, squirrels, even the occasional bobcat and [once] black bear – generally disappeared.
This year the occasional torrential rains typical of southern California winters returned and gave everything a nice soaking. The canyon in our backyard is awash in green and is about to explode into a sea of yellow mustard flowers. Even the great canyon oaks which dominate the canyon and are designed for long term droughts have a fresh sheen from the first set of new leaves in two years. Squirrels have been running around chasing the droppings of the bird food we keep out for the finches and sparrows and blue jays and titmice. Some as-yet-unknown small animal sneaks through the fence around my garden and has been nibbling on the leaves of the artichokes. The first sweet pea pods are forming. Lilah has a small box with caterpillars waiting to change into butterflies and a small bucket with tadpoles waiting to change into frogs. With the equinox passing just two days ago, it certainly feels like spring has come.
But the bunnies? Two year ago, our first Easter, the connection between Easter and bunnies was obvious. They were everywhere. You couldn’t open a curtain or door in the morning without stumbling on a new set of bunnies nibbling on the bushes, hopping down the street, playing in the grass. It was easy to explain to Lilah that the Easter bunny was certainly on his way. This year, though, the bunnies are almost unseen. One or two tiny babies have been spotted, but not the abundance of two Easters ago. What is going on?
I think the fault is not with the bunnies, but with Easter. Easter is awfully early this year, and it is likely that no one told the bunnies to start earlier. Two years ago Easter was on April 16th, a full three weeks later.
The bunnies should, of course, be watching the sun and the moon to know when Easter is. This year, in particular, with Easter so early, the method of choosing the date of Easter has been much in the news. Easter falls on the first Sunday after the first full moon after the Spring Equinox. The Spring Equinox is, of course, the precise midpoint between the long night of the Winter Solstice, back in December, and the eternal twilight of Summer Solstice, in June. On the Equinox, the day and night are of equal duration (the origin of the name) all around the planet. Also, the sun rises and sets directly east and west. Thus, one way to know that the equinox is near is if, like me, you live in a town where most streets are on a north-south-east-west grid, you will start to notice that the sun is always setting (or rising) precisely in your eyes as you head westward to go home at night (or eastward to leave home in the morning). That means the equinox.
Even the equinox occurred a little early this year. The precise moment when the sun was precisely over the equator (another way to define the equinox) was 5:48AM GMT on March 20th, which translates to 10:48PM PDT on March 19th here in Pasadena. Last year it was 5:07PM PDT on March 20th. In reality the equinox didn’t change, just our calendar. With leap year this year our calendar is behind by almost a day. It will catch up again over the next 4 years.
The full moon, which could come at any time over the next four weeks, happened to follow closely this year, occurring at 10:40am on March 21st. And it was a Friday, so the next Sunday was only 2 days later. Today is March 23rd, and it is Easter. The bunnies could have gotten it right by watching to see when night and day were equal lengths, looking for the next full moon, and watching driveways everywhere for an extra fat morning newspaper to know it was Sunday and thus Easter.
Except that this is not really correct. I used to imagine teams of astronomers sitting around with precise measuring tools to declare when the equinox had occurred to set everything in motion. I used to smugly explain all about astronomy’s role in determining the date of Easter to anyone who would listen. I used to wonder if it ever happened that the full moon followed the solstice by minutes and made for instant Easter. But, this year, I finally looked up who really decides. The answer is a bit disappointing, at least to me. For the purposes of Easter-determining, the equinox is on March 21st. No astronomer needs to track the sky; we can all just look at the calendar. The precise moment of the full moon? Not actually important either. Officially, centuries old calculations are used, which differ from the actual date of the full moon by up to two days.
Still, I could at least be smug in my amusement that yet again a major Christian holiday had clear ties to early astronomy and astrology and was designed to co-opt some sort of Pagan equinox celebration. Except, when I read more, I realized even that was not true. The timing was an actual attempt to figure out an actual date of the Last Supper, for which there is some indication that it was slightly before Passover. Passover, in the Hebrew calendar, occurs on the 15th day of Nisan. The first day of a moon was originally declared to occur when credible witnesses had seen a crescent moon. Nisan, which approximately translates in Babylonian as “until the barley is ripe,” was declared based on the critical springtime crop. It occurred around the time of the equinox. Fifteen days after the start of Nisan the moon would be full. And Passover would begin, on the day of the first full moon after the equinox.
So my smug amusement is totally misguided. Instead I should have understood and respected the observational, agricultural, and astronomical aspects of the much older Hebrew calendar. It is quite amazing that such a calendar designed thousands of years ago still underpins the basis of the day of one of the larger religious holidays of the year. But even with my newfound respect I can see the problems. The bunnies, even if they knew the astronomical rules, could never read all of the ancient tables. They will never know ahead of time when Easter is here. And occasionally, when the moon is right (and the tables are right too), Easter will show up weeks too early and then bunnies will not have grown. Easter baskets everywhere will have to be downsized so the tiny bunnies can carry them to front doors.
Luckily for me, at 2 ½ Lilah doesn’t yet know what she is missing. But next year, as a 3 ½ year old, she may catch on. Happily, next year, Easter is not until April 12th, and, once again, the bunnies will be running all around the yard, hiding candy and eggs as they go.


  1. You wrote: "The timing was an actual attempt to figure out an actual date of the Last Supper, for which there is some indication that it was slightly before Passover. Passover, in the Hebrew calendar, occurs on the 15th day of Nisan."

    The Last Supper was a Passover seder -- the celebratory dinner at the beginning of Passover. Passover does, indeed, begin on Nisan 15. The seder is celebrated after sundown on Nisan 14. Why? Because of a quirk of the Hebrew calendar: each day is considered to start at sundown. So Nisan 15 actually commences as the sun sets on Nisan 14. The seder, by being held after the sun sets on Nisan 14, is being held just as Nisan 15 begins by the Hebrew calendar.

    By tradition, Jews in North America celebrate two seders -- one on the evening of Nisan 14 and one on the evening of Nisan 15. Why? Because they wanted to hold the seder on the same day it was being held in Israel, and they couldn't decide which evening, North American time, was closer to the time of the seder in Israel. This predates such modernities as standardized time zones. And math was apparently not much of a rabbinical specialty.



  2. Thanks for the clarification/expansion!