Here we go, with showers, heavy rains, thunderstorms; temperatures in the 40s and 50s and blasting icy winds.
I guess we missed out on a real period of spring-like weather, so just like in Monty Python and the Holy Grail, perhaps we’ll give summer a complete miss as well as spring.
We have a strong upper air low pressure system over us. When we get systems like this, the low pressure aloft gives us colder temperatures aloft which makes the air below unstable, rising rapidly to produce heavy showers.
Here’s the upper air chart for the jet stream at 18,000 feet. The white lines making a circle just to our east show the upper air low pressure system. (NYC is in out on the right side of the map – look for the outline of the coastline and the state boundaries in black – hard to see sometimes).
This map shows the white lines of the winds about 1 mile up and the colors show temperature, which is related to our temperatures here at the surface. Notice the white lines dragging down the blue color into the eastern United States, bringing the colder temperatures we are having.
Warmer air arrives early next week, making for a nice Memorial Day and warmest later in the week. See the orange color over us on Saturday morning’s map – 16 to 18 degrees C a mile up, which can mean 32 to 36 degrees C here on the ground – in the upper 80s/lower 90s F.
If you are flying west across the United States this summer, leaving just at or after sunset, find Venus bright and low in the northwestern sky and see how long it takes to set.
I had the good fortune once to notice the planet Venus just above the western horizon out my window. Normally, Venus would have set in an hour or so, but I was able to watch it set over several hours. Why?
As the aircraft flies westward at 500 mph, it is almost as fast as the earth’s rotation of about 700 mph at mid-latitudes. If you think about it, if the plane flew at the same speed as the earth’s rotation, the sun and stars would appear not to move in the sky. You can use this effect to watch the planet Venus, and around Memorial Day weekend the planets Jupiter and Mercury, very slowly set. In May, Jupiter is low in the west after sunset, sinking out of sight in early June, leaving Venus and Mercury together through mid-June. Venus is a solo show low in the west through fall.
So, if you are flying westward, you are lucky because time, as measured by the sun and stars, appears to slow down (a supersonic jet would land “before” it took off, based on local time at the departure and arrival cities). You would be doubly fortunate to see the planets hang out for a long time if you are flying westward after sunset.
We’ve had quite a string of sunny days with deep blue skies here in the northeast! Have you noticed that something is missing? Usually on sunny, warm days we get those puffy cumulus clouds later in the afternoon. But we’ve mostly had just blue skies with a trace of high cirrus clouds.
That’s because we’ve been sandwiched between two strong low pressure systems in the jet stream, with a resulting strong high pressure over us. When that happens, the weather patterns stall and we get a long string of whatever weather we are having at the moment.
At this moment, we are having weather more typical of the dry, clear coastal desert of southern California. We are stuck on the eastern side of the jet stream ridge and so we have a steady easterly wind at the surface, which brings in some low clouds at night and temperatures drop to the water temperature and below into the 40s. During the day, the strong upper air high pressure system keeps us sunny and its sinking air suppresses the puffy clouds.
So, it looks like California weather until the jet stream traffic jams unblock!
[An expanded discussion will be in the Almanac column in the upcoming Westchester Astronomers newsletter for May.]
In May, you can stay up all night with Saturn! Not that you would, but it’s nice to know that Saturn, the ringed planet, is there for you. Saturn rises in the east as the Sun is setting. While Saturn is brighter than all but seven stars in our sky, it is not as obvious as outstandingly brilliant Jupiter, in the western sky at sunset. Follow Jupiter this month as it falls down into the twilight brightness, leading us to a three-planet-pile-up low in the west-northwest just after sunset this Memorial Day weekend. Don’t forget to spend some time looking for its brightest moons and the dark cloud bands on the planet.
I often say…..
“Binoculars will help you find [fill in the blank with a great astronomical sight!] low in the twilight sky”
….This time, take my advice over the Memorial Day weekend. About 40 to 45 minutes after sunset, look for the pile-up of bright planets low in the part of the sky just above where the Sun sets. Spying Venus, Jupiter and Mercury, all together in the wide view that binoculars provide, will be worth the need to find a clear western horizon so you can look low in the west northwest. Many popular space websites will show charts with directions.
Saturn is just past opposition, rising at sunset, getting higher in the evening sky this month. A good spotting scope or most telescopes will show the ring that makes Saturn different from the other bright lights in the sky. Saturn is still tiny, even in a telescope, but if you get a steady sky and increase the magnification, Saturn’s rings will show some details and the subtle cloud bands and moons will be visible. Saturn’s Titan is the second largest moon in the Solar System, smaller than the champion, Jupiter’s Ganymede. Titan should be visible in a telescope, and other moons in a larger telescope.
Strange two-faced moon Iapetus is visible to the south of Saturn around May 10th. It moves west of Saturn, brightening to magnitude +10, as it approaches greatest elongation on the 30th. Iapetus’ orbit is tilted compared to the rings, so future Iapetians will have a great view of Saturn’s rings for much of the moon’s 79-day trip around Saturn.
The Moon will have a weak penumbral eclipse near midnight on May 24/25. It will not be noticeable to our eyes. Even on the Moon, it would only be a partial eclipse of the Sun by the Earth, and only visible from the Moon’s South Pole. Of more significance, the Moon is closest to the Earth for May on the 25th, 21 hours after full Moon. The lining up of the Earth, Moon and Sun in a straight line, augmented by a closer than usual Moon, will make tides higher than normal. Also, an annular eclipse of the Sun – not a total eclipse – is not visible here, on the 10th at sunrise in Australia and later in the South Pacific Ocean. While we’re on the subject of things you can’t see, our best meteor shower in May peaks on the 5th. While you might see a few meteors at any time, almost all of the meteors from this shower are visible only south of 40 degrees north latitude.
The crescent Moon makes a nice photo op with Jupiter on the 11th and 12th. The Moon just misses Spica on the 22nd.
Twilight lasts longer as we get closer to the summer solstice on June 21st, more and more earth-orbiting satellites are visible each night, some as late as midnight. The International Space Station is not visible here for the first half of the month; after that, it is seen in the morning sky. In early June, the ISS is visible as often as five times a night, every 96 minutes.
Abrams Planetarium is offering a sky calendar and chart of bright stars in the sky for May at http://www.pa.msu.edu/abrams/. I love their great diagrams of where to find bright objects in the sky. For May, it’s free and you can make copies, this month only! Or you can download a copy, below….
Overexposure can be a problem for photos for a family-friendly web site, but not in this case as Jupiter and the Moon patiently pose together while I fumble with exposures and other camera settings on my wonderful Canon Rebel XS on a sturdy tripod (thanks, kids for that great Christmas present!).
Here’s a 1/2 second exposure, ISO 400, f8 that gives an idea of the scene as seen by the human eye.
Here a close up of the Moon, zooming in with a 250 mm variable lens; f8, 1/80 second, ISO 400, cropped from larger photo…
And the same moon, overexposed (!) to show a lunar mountain as a dot on the left (south) end of the crescent. (Cropped from a larger photo.)
Settings: f8 ISO 400 1/10 second exposure.
Jupiter’s moons are barely visible, even at the 250 mm setting. This is cropped from a larger scene to show the four moons to the lower right of the planet. (Look carefully for the faintest moon, farthest to the right. 1 second exposure at ISO 400.
The ISS (Is Someone Singing?) will be very bright as it passes over the northeastern US on Tuesday evening. The ISS will come from the southwest, passing to the left of Orion, just skimming in front of Jupiter and between the two Dippers.
It will be brighter than Jupiter and easy to see if the clouds stay away.
Here’s a finder chart that may be helpful for the overflight that will last from 8:35 to 8:45 pm give or take five minutes.
If you are observing tonight with us, the Westchester Astronomers (see
), it’ll be a race to see if the high clouds get there first. But some models hold off the clouds until after midnight, so we are go for viewing tonight, unless the clouds come in ahead of schedule this afternoon.
Here’s a pdf of the star chart for this evening, from Sky and Telescope….
skychartPDF ap 06 2013
Astronomical Twilight ends (Sun 12 degrees below the horizon): 9:05pm
We should be able to get Comet PanSTARRS in our telescopes by 8:30. Bring binoculars for a good view!
PanSTARRS sets just after 10pm. It rises again after 2:30am, in case you want to see it in the morning sky as well
Jupiter will be high up in the sky, visible even as the sky is getting dark. Here’s a chart of where it’s four brightest moons will be as seen in a telescope….
Saturn will rise after 9:10pm. It may look a bit fuzzy, so low in the sky, but this chart shows its moons and rings as they might look in a telescope (at high magnification, to show details)…
The sky chart will be good for a week or so for evening skies from locations near latitude 40 degrees north.
Jupiter’s moons move enough to be noticeable even over several hours, so the chart with Jupiter’s moons is best for this evening and will change, as Saturn’s moons, each night. Sky and Telescope and other web sites have maps of the moons’ positions for other times.