The next solar eclipse visible in the US occurs on Sunday, May 20, 2012. In a solar eclipse, the Moon passes directly between the Sun and the Earth and, if you are in the Moon’s shadow, appears to block out the Sun. Normally, if you are able to view a solar eclipse at totality, the Moon appears to completely block out the disk of the Sun. Sunday’s eclipse occurs near apogee, or the Moon’s furthest distance from the Earth. Therefore, the disk of the Sun won’t be completely blocked out and, at totality, a bright ring (called the annulus, hence annular eclipse) will appear around the Moon. In the continental US, only people in a narrow band from northern California to northern Texas will be able to view the annular ring. Most of the rest of the US will see a partial solar eclipse. For those of us in Iowa it will begin around 7:20 CST and will last until sunset.
Please bear in mind that special precautions must be taken when viewing a solar eclipse. Looking directly at the Sun is extremely dangerous and is to be avoided. The safest way is to use pinhole projection to view a projected image of the eclipse. #14 welders glass also offers sufficient eye protection. Sunglasses do NOT offer sufficient eye protection. Telescopes and binoculars are not safe unless properly filtered with a solar filter accessory. Enjoy the eclipse, but please do it safely. Please see the following NASA link for more on eye safety:
The bright star above the west-southwest horizon around twilight is the star Procyon. It is the last visible vestige of the winter triangle, most of which has slipped below the horizon by twilight these days. The bright star above the east-northeast horizon at twilight is the star Vega. It is the first visible member of the summer triangle which completely rises later in the evening. If we didn’t have modern calendars to tell us the season, this is how we might know it’s spring.
The next full Moon occurs on the evening of Saturday, May 5th. This full Moon, out of all in 2012, occurs nearest to the Moon being at perigee, or its closest approach to Earth. Therefore, the Moon will appear slightly larger than an average full Moon. You may have heard this event referred to as a “supermoon” in popular media, but that term is not preferred by astronomers. See an actual size comparison here:
http://en.wikipedia.org/wiki/File:Supermoon_comparison.jpg
One effect that is more pronounced is the effect on tides. Tides, as we talked about a couple weeks ago, are influenced primarily by the gravity of the Moon because it is so close and secondarily by the gravity of the Sun because it is so massive (but further away). At new and full Moon, the Moon and Sun line up and work together to produce larger tides – the spring tides. This month, these tides will be even larger due to the overlap of the full Moon with perigee - the perigean spring tides.
If you look at Venus through a telescope these days it looks like a thin crescent Moon. It is catching up to us in its orbit and most of the shadowed side is oriented towards us. Its brightness is therefore a balance between how close it is to us and how much of the lit side we see. That peak balance was reached on April 30th. The distance gap will continue to close through early June, but the crescent will get thinner and thinner so the brightness will diminish. However, the closing of this particular appearance will be spectacular in that Venus will pass directly between Earth and the Sun on June 5th/6th.
April 15th saw Saturn reach opposition. Saturn now rises at sunset, is visible the whole night, and is also at its brightest. Great telescopic views await us in the coming weeks. Of course, Saturn is famous for its rings and people expect to see them when looking through a telescope. However, the orientation of the rings changes due the tilt of Saturn’s rotation axis and its travel around the Sun relative to the Earth. Occasionally the rings seem to disappear as we see them perfectly edge on. Fortunately, from our perspective the orientation is currently tilted and the next few years promise great views of the rings.
On April 15th, 2012 we mark the 100th anniversary of the sinking of Titanic. There is a fascinating article on astronomical connections to this event in Sky & Telescope magazine which you can read here:
http://media.skyandtelescope.com/documents/Titanic+layout.pdf
The article discusses two connections in particular. It points out that there was no Moon in the sky the night the ship struck the iceberg. If there had been, water breaking around the base of the iceberg would have been easier to spot. The second is even more interesting in that it suggests the sinking may be related to a rare confluence. Ocean tides are due to the gravitational influence of the Moon and Sun. When the Moon and Sun line up at new and full Moon we have the so-called spring tides (completely unrelated to the season) which are larger than normal tides. During certain times of the year, the spring tides coincide with the Moon being at perigee, or its closest approach to the Earth, resulting in even larger tides called perigean spring tides. In January of 1912, the perigean spring tides also coincided with the Earth being at perihelion, or its closest approach to the Sun. This ideal gravitational alignment for producing large tides may have contributed to an unusually large number of icebergs in the north Atlantic in April by helping to float grounded icebergs along the coasts of Labrador and Newfoundland which would then have continued their journey southward.
Orion is easy to find above the west-southwest horizon after sunset this time of year. That it is so instantly recognizable makes it a useful guide for other night sky features. Follow Orion’s belt eastward and you will find the bright star Sirius in the constellation Canis Major (from the Latin for greater dog – can you spot the dog?). The upper two stars of Orion (Betelguese and Bellatrix) that form his right and left shoulders point eastward to another bright star, Procyon in the constellation Canis Minor (from the Latin for lesser dog – with only two stars in this constellation, you’ll have to use your imagination to see the dog). Sirius, Betelguese and Procyon form a nice equilateral triangle of stars called the Winter Triangle. Above the Winter Triangle you should easily spot the two brightest stars in the constellation Gemini (the twins): Castor and Pollux.
Elongation, in astronomy, refers to the angle between the Sun and a planet as viewed from Earth. We’ve been talking about certain planets and the Moon being at opposition, meaning they appear to us to be opposite the Sun, or that their elongation is 180 degrees. This is possible for the Moon because it orbits the Earth. It is also possible for Mars, Jupiter, and Saturn (and the other outer planets) because they are farther from the Sun than the Earth. Planets closer to the Sun like Venus and Mercury cannot be at opposition. Their greatest elongation is substantially smaller due to our perspective. Today Venus reaches its greatest elongation: 46 degrees. This angle will start to shrink in the coming weeks.
In the telescope, Venus appears half lit like the first quarter Moon. The lit side will shrink to a crescent as it continues to move in its orbit to a position between us and the Sun. In early June a very rare and special event will occur: a transit of Venus across the face of the Sun. Since the following transit won’t occur until December 2117, we will be talking about the 2012 transit a lot more as it approaches.
The waxing crescent Moon will be near Jupiter and Venus in the western sky at sunset the next few nights. This show has been repeating approximately once a month for several months now. The Moon traces nearly the same path across the sky from month to month and passes by several planets as it does so – it will pass by Mars in a few days. This is a testament to the near perfect flatness of our Solar System. Jupiter is now nearly right below Venus and they keep pulling farther apart. Soon Jupiter will dip below the horizon and we won’t see it again in the evening until late fall. But, don’t fret – Saturn is approaching opposition and we should have great views through the summer.
You wouldn’t know it from the weather in the Midwest recently, but the first day of spring for the northern hemisphere is March 20th. This is the March equinox – also called the vernal or spring equinox, but we must remember that it also marks the first day of fall for the southern hemisphere. Equinox comes from the Latin for “equal night” and, indeed we have approximately the same number of daylight and night hours this time of year. We can give an exact time for this event (12:14 AM CST) because this is the moment the Sun is at the intersection of its path on the celestial sphere with the celestial equator. On December 21st we talked about the Sun being as far south of the celestial equator as it could be and its apparent path has been taking it farther north since. On Tuesday morning it crosses the celestial equator and continues north. In June we’ll talk about the northern solstice.
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This is a weekly blog updated by Jeff Butikofer.