Astronomical mind blower!
The Universe Has 10 Times More Galaxies Than Scientists Thought
Aloha astronomy lovers!
This Friday 9/30/16 is a Black Moon and Friday 10/7/16 is IfA Open House!
No reason to fear Friday’s “black moon”
On Friday a relatively rarewill take place – a shadowy phenomenon known as the “black moon.” Yes, it sounds apocalyptic, but a “black moon” is nothing bad.
And while it will rise above the Western Hemisphere, there won’t really be anything to see.
What is it? A “black moon” is simply a spooky nickname for the secondto fall in a calendar month. A “black moon” occurs about once every 32 months.
While a full moon happens when the moon’s Earth-facing side is fully illuminated by the sun, a new moon is when the side we see is fully covered in shadow. As a result, the new moon is basically invisible to Earthlings looking up at the sky.
This “black moon” officially occurs at 8:11 p.m. EST on Sept. 30, 2016. (3:11 p.m. Hawaii Time)
For those in the, it will already be after midnight on Oct. 1. To make things a little complicated, since it won’t be the second new moon in a calendar month on that side of the globe, it doesn’t qualify as a “black moon” there. However, the Eastern Hemisphere will get one at the end of October.
The appearance of a crescent moon a few days after this new moon will usher in the Jewish New Year, Rosh Hashanah, beginning Sunday evening Oct. 2, and the Islamic New Year, Muharram, on Monday, Oct. 3 – two holidays guided by the lunar calendar.
IT’S THAT TIME AGAIN! INSTITUTE FOR ASTRONOMY OPEN HOUSE!!!
JD Armstrong want to invite you all to the 10th annual IfA Maui Open House. Many of you have been to previous Open Houses, and know how much fun they are. We will have an Infrared camera demonstration, student science displays, short talks about science on Haleakalā, and more.
Friday October 7, 2016 6pm to 8 pm
Look through a telescope
Talks about Science on Haleakalā
The Institute for Astronomy is located in Pukalani, between Longs and Kamehameha Schools. Please park on the street.
The Open House will be held rain or shine, but some activities will be weather permitting.
Awesome article by Phil Plait.
On Monday at 22:34 UTC (6:34 pm Eastern U.S. time), the Sun will reach its highest declination in the sky, its farthest point north for the year. That is the moment of the June solstice.
This means that, in the Northern hemisphere, we have the longest day of the year, and the shortest night. If you live your life standing on your head in the Southern hemisphere, it means you have the shortest day, and the longest night.
I enjoy writing about the solstices and equinoctes* when they happen, so you can read all about how and why they occur in past articles. I’ll note that Monday is notthe date of the earliest sunrise and latest sunset though; that has to do with the Earth’s orbit being slightly elliptical, so I’ll make a special point of linking to this article last year where I explain why that happens. I’ll also note that some people call this the first day of summer (or winter for those in the south), but I disagree; I tend to think of it as actually the midpoint. You can read about that to your brain’s delight as well.
No, instead of spending time on that here, I’d prefer to point out something rather special that led to me wandering down a rabbit hole Sunday night as I researched it: Not only is the solstice Monday, but the Moon is full on Monday as well. That moment occurred at 11:02 UTC (07:02 Eastern; I’ll note it’ll look full all day and probably even Tuesday as well).
A full Moon on the same day as the June solstice (or the December one, for that matter) is relatively rare. As I thought about this Sunday night, I wondered just howrare it was. My first thought was that it probably happens once every 30 years or so, since the full Moon can occur on any day, and there are 30 in June.
But then I realized it’s not that simple. Sometimes in astronomy two cycles can beat together in unusual ways, throwing off what you might expect. So I dug into it. I found a list of solstice full Moon dates on the Farmer’s Almanac website, and perusing the numbers it appears that we get a full Moon on the June solstice roughly every 19 years or so … or multiples thereof.
Nineteen years? That sounded familiar. It took me a few minutes, but then it clicked: That’s the Metonic cycle! Let me explain.
The Moon goes through a full phase of cycles (from full to new and full again) in about 29.53 days. That all by itself is interesting.
One Earth year is, on average, about 365.24 days long. But there’s a funny coincidence here: 19 years is 6,939.56 days, and that is almost a perfect multiple of 29.53! Nineteen years is almost exactly 235 lunar phase cycles. That means that when you have a full Moon on a given date, 19 years later it’ll be on that same date once again. That’s what’s called the Metonic cycle. This fact has been known for about 2,500 years, which is pretty amazing.
But looking at the Farmer’s Almanac, you see it doesn’t seem to happen every 19 years. Why not?
This is where I really started to dig deep. I looked at leap years, and fractional leftovers between the lunar phase month (called the synodic month) and the Earth’s year, and on and on. That can account for some of the reason the full Moon doesn’t always fall on the same calendar date every 19 years.
Then I realized something: time zones.
Astronomical sites list the times of the solstices and full Moons in Coordinated Universal Time (UTC, similar to Greenwich time). That makes it easy for everyone, since you can just look up how far off your time zone is from that (for example, right now the East Coast of the U.S. is on Eastern Daylight Time, UTC – 4 hours).
But that can mess up the full Moon June solstice cycle. Why? Because the exact moment of the solstice changes year to year, and can even occur on different days! It can be on June 20, 21, or sometimes even 22. If the solstice occurs on June 21 at 23:59, and the full Moon two minutes later, technically they’re on different days!
Worse, that’s UTC. In the U.S., where it’s four to seven hours earlier than UTC, both would occur on the same calendar day. So it’s possible (and even likely) that one place in the world would see a full Moon on the same calendar day as the solstice, and another part of the world wouldn’t. What a mess!
Look at Monday’s solstice: It occurs at 22:34 UTC. For someone a couple of time zones east of the U.K., that means it happens on June 21. For them, they don’t get a full Moon on the day of the solstice. The exact moments of the solstice and full Moon are independent of time on Earth (the solstice occurs at the same moment for everyone on the planet, for example), but because we bin time up into days, that can throw off the days on which we say those events happened. Weird.
Going back to the Farmer’s Almanac, you may notice that while the solstice full Moon doesn’t happen every 19 years, it does appear to have a cycle of multiples of 19. For example, there was one in 1796, then the next in 1834, a gap of 38 years, 2 x 19. Other such gaps can be found. The gaps happen because the full Moon missed the calendarday of the solstice by some hours. Not only that, but that table is for the U.S. East Coast, so it doesn’t work for the whole world.
The root of this problem is using calendar days, which are arbitrary to some extent. There’s an overall 19-year cycle, but because of time zones it can get thrown off. A better way to do this would be to ask, “How often does a full Moon occur within a day of the solstice?,” or better yet within 12 hours before to 12 hours after the moment of the solstice.
In that case, I’d expect the 19-year Metonic cycle to be more obvious. However, looking that up using calendars for the full Moon (like this one) and the solstices (like this one) is difficult and tedious. The best way would be to run the calculations specifically looking for that, which I thought of too late to ask anyone to do for Monday’s events. I’ll leave that as an exercise for the reader.
Anyway, my point is … well, I guess I don’t have a point except that numbers are fun to play with and the cycles in the sky are neither always obvious nor simple to grasp.
But they’re there, and if a full Moon falling on the solstice is interesting enough to people that they go outside and take a look for themselves, then I’m all for it.
So happy full Moon June solstice! Enjoy it, because the next one won’t be for a while—June 21, 2062, in fact … if you use UTC.
*Equinoctes is the actual plural for equinox. Some dictionaries say that’s a bit old-fashioned, and equinoxes is now used, which is fine by me. Languages change over time. But I rather like the way equinoctes sounds, and I like using it. So I do.
Look outside after sunset. Face west and see if you can catch a glimpse of cute and quick Mercury! It will be low in the sky with a beautiful crescent Moon above it. On May 9, Mercury will pass directly in front of the Sun, called a transit. In Hawaii, the transit will be in progress at SUNRISE.
Such a quick moving planet, the ancient people depicted Mercury as the messenger god with winged shoes and a winged helmet!
Also, tonight’s Moon will display “Earth Shine”……the dimly lit part of the Moon revealing the entire orb. This is caused by sunshine bouncing off Earth onto the Moon.
A beautiful sight! Go see it tonight!
Eclipse begins: 4:35 pm (Sun Altitude – 26 deg)
Max eclipse: 5:37 pm (Sun Altitude – 12 deg)
Eclipse ends: 6:31 pm (Sun Altitude – 0 deg)
Sunset: 6:33 pm