Iris: goddess of rainbows
Let's imagine that a Greek god or goddess who, after having been relegated to the status of mythological figure since the 5th century AD, was so desperate for worshippers that he/she approaches you and swears by the River Styx to do anything you wanted him/her to do. In response you say something like, "Apollo, stand on your head," or "Zeus, join the MeToo movement," or "Athena, well, I don't know, smile or something." Provided that the desperate deity swore by the River Styx to fulfill your request, you could be well assured that he/she would do so. Were a god/goddess to break such a vow, he/she would be cast into Tarturus for seven times seventy years. During that (let me fetch a calculator....) During that 490 year stay, the doomed deity would not only be deprived of all divine powers, he/she would be enfeebled to the point of paralysis, tormented by harpies, and rendered miserable beyond all description. After his/her confinement period ended, of course, he/she would be released back to Olympus, his/her godhead would be restored and all would be well, except, of course, when he/she realized that -ha ha ha- he's/she's still just a mythological figure. So, in this circumstance, if you commanded Apollo to stand on his head, then you'd soon be admiring his upturned feet.
The River Styx is the meandering river that originates from Mount Chelmus in Arcadia and descends into the underworld where it wraps around Hades' death kingdom nine times (the inspiration of Dante's nine circles.) The ferryman Charon conveys the spirits of the recently deceased across this river. When a god swears by the River Styx, Iris, the goddess of rainbows, gathers some of its waters in a jar and pours it over the god's hands, thereby sealing the compact. Delivering this water is Iris's secondary function in the mythological Universe. Iris serves first and foremost as a messenger. Unlike the winged Hermes who communicates principally between the gods, Iris conveys messages from Olympus to Earth by descending along the rainbow arcs: the only conduit connecting them. Being both intangible and inaccessible, rainbows were the perfect bridge along which Iris could travel. No flesh-bound mortal was capable of even reaching it, let alone standing or walking on it. Being the daughter of the ocean deity Thaumas and oceanid Electra, Iris is one of the older deities and so rarely becomes embroiled in the fights waged between the other deities. She is, instead, a serene sort of goddess who often naps in the shadow of Hera's throne until summoned to deliver a message by one of the Olympians. How appropriate that she chose Zephyrus, the west wind, as her husband. He is known for being the gentlest of all the winds, a counterpoise to Boreas, the assailing north wind harsh enough to kill even the heartiest mortal. Western zephyrs, like afternoon rainbows, are the insinuations of Olympian beauty into our mortal realm and as such delight the senses as much as they enliven the spirit. The rainbow bridges that extend between the highest climes and lowest tiers still appear from time to time and shall forever remain in our sights but well beyond our reach.
THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
207-780-4249 www.usm.maine.edu/planet
70 Falmouth Street Portland, Maine 04103
43.6667° N 70.2667° W
Altitude: 10 feet below sea level
Founded January 1970
Julian Date: 2459024.16
2019-2020: CLXVII
THE DAILY ASTRONOMER
Tuesday, June 30, 2020
Tuesday, June 30, 2020
Remote Planetarium 55: The "Invisible" Lunar Eclipse
Current circumstances compel us to deviate slightly from our itinerary. We progressed beyond the solar system's bounds around mid-May and are preparing to begin an exploration of variable stars. Before we proceed, however, we return to lunar eclipses. The impending "Independence Day Penumbral Lunar Eclipse!!" necessitates this rapid revistiation of lunar eclipses. (Tomorrow we start the variable star sequence.)
As the catchy name implies, this eclipse occurs on July 4th. Well, technically, it begins on July 4th and concludes on July 5th. Fortunately, as indicated in the map below, observers in our region will see the entire eclipse.
Unfortunately, there is nothing much to see. This upcoming event is actually a "partial penumbral eclipse," meaning that the only a section of the moon will move through the penumbra, the outer region of Earth's shadow. Those eager skywatchers hoping to behold a celestial spectacle will instead experience a crashing disappointment. Whereas a total penumbral eclipse subtly darkens the entire moon, a partial penumbral eclipse casts a very faint shadow only on one part of it. Even at "maximum" eclipse, that shadow is imperceptibly faint.
So, why bother to devote an entire class to it?
Well, in the first place, this eclipse has garnered unexpected media coverage. Many people are hoping to see a gorgeous lunar eclipse after watching the fireworks display. Realize that municipal authorities might put the kibosh on the pyrotechnics due to social distancing requirements and the current condition of the landscape which is so parched a hostile glance could inflame it. It is our task to be wet blankets and tell you that the follow up eclipse will prove to be a non-event, as well.
Secondly, this eclipse does give us another opportunity to discuss the Saros cycle. Every solar and lunar eclipse is part of Saros cycle of eclipses. Each eclipse within a given Saros shares a similar geometry and position with all the others in the same cycle. Each successive eclipse within the Saros is separated by 18 years and 11 days.
This impending eclipse is the 3rd of 71 lunar eclipses within Lunar Saros Cycle 149. What we will be witnessing (though not seeing) on July 4th/5th is the beginning of a Saros cycle that started in 1984 and will finally end in the year 3246.
The first Saros 149 eclipse occurred on June 13, 1984. [In that same month, Cirque du Soleil was founded; and, quite importantly, the final episode of the Britcom "The Young Ones" was broadcast on BBC 2.] This was a partial penumbral eclipse during which only a small part of the moon's upper regions passed through the penumbra.
The second Saros 149 event happened on June 24, 2002. [Earlier that year, the 2001 Mars Odyssey Space Probe began mapping the Martian surface.] The image below shows the moon's path during that partial penumbral eclipse. Only a small section of the moon glided through the outer shadow.
The third 149 Saros cycle eclipse occurs on July 4/5th. Notice the moon's path during that event:
The moon's path is slightly higher than the one it followed in 2002. Consequently, more of the moon will pass through the penumbra. Still, the resultant darkening will be negligible.
When will the next Saros 149 lunar eclipse occur?
18 years and 11 days later: July 16, 2038
What can we conclude about this eclipse?
First, we know the moon's path will be higher during this eclipse than it was in 2020. It will still be a partial penumbral eclipse, meaning that it won't prove to be a dazzling event.
We can see that the moon's path is higher and more of it passes through the penumbra. Each Saros Cycle 149 eclipse happens at the moon's descending node, the intersection point between Earth's orbit and the moon's. Each successive 149 eclipse moves the moon northward.
____________________________________
Remember that lunar eclipses that are part of even numbered Saros cycles occur at the ascending note. Lunar eclipses that are part of an odd number Saros cycles occur at the descending node.
____________________________________
Can you predict the dates of the next three 149 Saros cycle eclipses?
- July 16, 2056
- August 7, 2074
- August 17, 2092
The first total lunar eclipse in this Saros cycle will occur on April 16, 2489. We see in the image below that the entire moon will move through the umbra.
By studying the world map below we see that observers within our throat of the forest will be enthralled by the eclipse which will be in progress at moon rise. Assuming, of course, that our descendants will not have evolved to the level of demi-god and won't consider such trivial celestial events worthy of notice.
Using our knowledge of Saros cycles, we can expect the following 149 lunar eclipse to occur on April 28, 2507! Yes, that total lunar eclipse will be of longer duration because the moon's path through the umbra will be higher.
The last total lunar eclipse in 149 will happen on September 17, 2741.
The last lunar eclipse -also a partial penumbral- occurs on July 20, 3246.
While the upcoming eclipse event won't scintillate the senses, it does allow us the opportunity to contemplate the power of mathematical astronomy to make accurate predictions about the remote future.
_____________________________
Today's skywatching tip:
Don't bother venturing out to observe the July 4th/5th penumbral lunar eclipse. Wait for the beautiful lunar eclipse on November 19, 2021. Although technically partial, this eclipse will appear nearly total.
______________________________
Tomorrow, back out into deep space with extrinsic variable stars.
To subscribe or unsubscribe from the Daily Astronomer: