This month's full moon -- known as the Flower Moon -- will undergo a entire eclipse early on Wednesday morning (May 26), when it becomes completely immersed for a short while in Earth's shadow. But it also so happens that in the exact same time our normal satellite will be close that point in its orbit closest to Earth, so we will see a"supermoon" as well.
The total phase of the eclipse, once the moon is covered in Earth's blood-red shadow, begins at 7:25 a.m. EDT (1125 GMT) and lasts 14 minutes 30 seconds.
Though the eclipse happens at the same time for everybody, whether you can view it -- and just how much of it you can view -- depends on exactly what time the moon rises and puts in your place (and, clearly, the weather). The eastern U.S. will only find the beginning stages of the eclipse before moonset, but the West Coast will see all totality, with the moon setting until the eclipse ends.
Check out the map and timetable below to find out as soon as the eclipse is visible from where you are, or attempt this interactive map by Time and Date. Furthermore, make certain to check out Space.com's comprehensive guide to the stages of the lunar eclipse.
Tuesday night (May 25) at 9:55 p.m. EDT (0155 May 26 GMT), the moon will arrive in perigee -- that point in its orbit bringing it closest to Earth -- a distance of 222,022 kilometers (357,311 kilometers) away.
While circling Earth within an ellipse-shaped path, the moon comes to perigee after, occasionally twice a month, and the Earth-moon distance during these approaches vary by 3%. On Wednesday morning, a little over nine hours following the moon reaches perigee, at 7:14 a.m. EDT (1114 GMT), the moon will officially turn complete and will also experience an eclipse.
It will, in fact, be the biggest full moon in clear size this season, popularly defined by many as a"supermoon." In contrast, on Dec. 18, the complete moon will closely coincide with apogee, its farthest point from the ground. On that night the moon will appear 13.7% smaller than it will appear Wednesday morning.
Many websites are putting a particular emphasis on the fact that this supermoon coincides with a entire lunar eclipse -- as if this makes the conditions of this eclipse extra special. But actually, as much as a total eclipse is worried, having a complete moon so big and so close works against audiences by multiplying the length of totality, when the whole disk of the moon has been covered with the planet's dark inner shadow, called the umbra.
When the moon is closer to Earth, it moves into its orbit more rapidly than ordinary. Thus, it's moving through the Earth's shadow at a quicker pace.
And since this eclipse barely qualifies as a total one -- that the moon is tucked completely into the umbra with hardly any room to spare -- totality will be remarkably short: lasting less than 15 minutes.
Conversely, if the moon had been near the apogee point of its orbit -- colloquially known as a "micromoon" -- it would seem smaller and move more slowly, thus helping to expand the duration of overall phase of the battle by maybe up to 45 minutes!
Large tides
In addition, the near winner of Wednesday's full moon with perigee will end in a dramatically large range of low and high ocean tides.
The greatest tides will not, however, coincide with the perigee moon but may actually lag by up to a day or so depending on the particular coastal location. For instance, for New York City, higher water (6.3 ft, or 1.9 meters) at The Battery comes in 9:02 p.m. EDT on Wednesday. By Cape Fear, North Carolina, the maximum tide (5.5 feet, or 1.7 m) happens at 10:42 p.m. EDT on Wednesday, while in Boston Harbor a peak tide height of 12.2 feet (3.7 m) comes in 11:56 p.m. EDT on Wednesday. All three of these high tides occur 23 to 25 hours after perigee.
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Any aquatic storm at sea round this time would almost surely aggravate coastal flooding issues. Such an extreme wave is called a perigean spring tide, the word spring has been derived from the German"springen" -- to"spring up," and is not, as is frequently mistaken, a reference to the spring season. Spring tides occur when the moon is either at new or full stage. Sometimes the moon and sun form a line with the Earth, so their tidal effects include together (the sun exerts a bit less than half of the tidal force of the moon.) At these times tides are feeble.
Tidal force varies as the inverse cube of a person's distance. We've already noted that this month that the moon is nearly 14% nearer at perigee than at apogee. Therefore, it is going to exert 48 percent more tidal force at this full moon compared to the spring tides for the complete apogee moon in December.
Massive moon at moonrise and moonset
Many astronomy books show comparison images of a full moon at perigee compared to a complete moon at apogee. Placed side by side, the difference in apparent size is quite clear. However, normally the variant of the moon's space is not easily apparent to observers viewing the moon straight in the actual sky.
Or is it?
When the perigee moon lies near the horizon it can appear absolutely enormous. That's if the famous"moon illusion" combines with reality to produce a truly stunning view. For reasons not fully understood by astronomers or psychologists, a low-hanging moon appears unbelievably large when hovering near to trees, buildings and other foreground objects. The fact that the moon will be a lot nearer than usual this week will only amplify this strange effect.
Even a perigee moon, either rising from the east at sunset or falling down at the west at sunrise, might seem to make the moon look so snug it almost appears that you could touch it. You may see it for yourself by noting the times for moonrise and moonset to your area.
Happy mooning -- also for people who will see it, appreciate the eclipse!
