December 23, 2009

Ursid meteors, Mars in Reverse, the Moon and Pleiades

Here’s a little Holiday treat you might want to stay up late (or get up early) for. The Ursid meteor shower peaks on the morning of Tuesday, 22 December. As you may have guessed by the name, the Ursid shower’s radiant is circumpolar, near Kochab, the “front” star in the bowl of Ursa Minor, the little dipper. Ursids are the dusty debris of comet 8P/Tuttle and tend to be faint and relatively slow moving.

The American Meteor Society offers these Ursid observing tips:

Most of the Ursid meteors are faint therefore it is important to observe from rural areas away from city lights. Since the radiant lies in the northern half of the sky it would be best to face this general direction to see the most activity. There is no need to stare directly at the radiant, rather it is advised simply to place the radiant somewhere within your field of view so that it will to easy to trace which meteors line up with Kochab (Ursids) and those that don’t (non-Ursids or sporadics). From dark skies one should also be able to count 10-15 sporadic (random) meteors per hour.

Mars in Reverse

I don’t think you’ll hear a backup warning beeper but Mars began retrograde or apparent westward motion on 21 December. What this means in practical, observable, terms is that as Earth overtakes Mars as we approach opposition in late January the Red Planet will appear to move westward against background stars. Mars will retrograde more than 10 degrees from western Leo into central Cancer during January, 2010. You might consider observing Mars at least once a week for the next month. I suggest you use the star Regulus, Leo’s “front paw” as a reference point. Measure the angular separation between Mars and Regulus by fully extending your arm and using your fist as a reference. Remember when your arm is fully extended your fist subtends 10 degrees, an open palm with outstretched fingers about 20 degrees. I’ll venture a guess that as I write this Mars is about 13 or 14 degrees west of Regulus, or “a fist and a couple of fingers”. If you’d like to know more about using using fingers, hands and fists to measure angular distances in the sky contact me here.

Mr. Moon and the Seven Sisters

The Moon will glide by the Pleiades on the evening of Tuesday, 29 December. You can observe this one naked eye but the Moon will be two days away from full and very bright. Binoculars will show a very nice view of the Moon less than a degree west (to the right) of the Seven Sisters.

Finally I should mention what will likely be the last celestial event of note during 2009 and the IYA. There will be a penumbral lunar eclipse on 31 December which will be visible in the Eastern Hemisphere. If it happens to be dark where you are at 19:23 UT (2:23 pm EST) on New Year’s Eve you’ll have to look carefully for this one. The umbral magnitude of this eclipse will be 0.082. In other words only a very tiny fraction of the Moon’s disc will fall under the Earth’s shadow.

Skies have been overcast here in southern Indiana for over a week so we’ve missed the Geminids, Mercury and the Ursids. Hope your New Year will be great and your Skies Clear!

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December 14, 2009

A new Moon, Mercury, Jupiter and Neptune dance and the Winter Solstice

As we discussed last week, the Moon will be “new” on Wednesday, December 16th. Look for a very slender crescent Moon on the western horizon after sunset on succeding evenings. As I’ve mentioned before I really enjoy chasing very old waning crescent and young waxing crescent Moons. Try spotting the very old Moon 47 hours before “new” on the morning of the 14th or 23 hours before new on the 15th. The 33 hour young Moon on the evening of the 17th will be a real challenge or the 57 hour young Moon on the 18th will be an easier target.

Some observers enjoy the challenge of seeing opposing crescent Moons, that is an Old crescent Moon and Young crescent Moon with the shortest period between. If you are interested in trying this and reporting your results, positive or negative, message me here.

Mercury

While you’re out watching the young Moon during evenings this week try spotting the elusive Mercury. Mercury and Venus are “inferior” planets, they orbit the Sun inside Earth’s orbit. They appear relatively near the Sun as “evening stars”  or “morning stars” from our vantage point here on the “third stone”.

18-dec-09-mercury.JPG

Mercury will reach maximum eastern elongation, 20.3 degrees from the Sun, on 18 December. For observers in the northern hemisphere it will peak at 16.3 degrees above your western horizon at sunset on Tuesday, 15 December. This elongation does not favor observers in the southern hemisphere as Mercury will peak at 12.5 degrees above your western horizon on 22 December. Mercury is coming around toward us from the far side of the Sun and, early on in this apparition, will appear as a tiny gibbous moon half lit on the date of maximum elongation. As Mercury approaches inferior conjunction with the Sun (on 4 January) it will increase in angular size while it’s illuminated portion shrinks to a thin crescent. Use binoculars or a telescope with a low power eyepiece if you have one to view the tiny planet. See the finder chart with the view looking southwest at 5:30 pm local time on Friday, 18 December. An added treat will be the passing of the waxing crescent Moon which will appear just to the west (lower right) of Mercury on the 17th and just east (above left) of him on the 18th. Click on the chart which was generated using the Stellarium planetarium program to enlarge.

Jupiter, Neptune and the Gallilean moons

You’ll need a telescope for this exercise. This week after Mercury has set and darkness is falling look for the other bright “evening star” to the southwest. This is Jupiter. This week Jupiter and Neptune meet for their third conjunction of 2009. Jove will serve as a locator beacon for Neptune which is 6 times further away and much more difficult to spot. Compare Jupiter at magnitude -2.2 and angular size of 36 arc seconds to Neptune at +7.9 and 2.2″ wide. Observing Neptune is a challenge because of its distance. I have observed the planets of our solar system out to Uranus but never seen Neptune. On Sunday, 20 December, Jupiter will appear lass than half a degree south-southeast of Neptune. I suggest that you try to observe them over several evenings and make a sketch of their changing positions from evening to evening. Neptune will glide north to south to the west of Jupiter against the background of fixed stars. Dress warmly and give this a try.

Mars

 240px-Mars_Hubble.jpgWe’re catching up with and will pass Mars in January. The red planet is rising at about 10:30 pm now and rises out of the atmospheric turbulence around local midnight. Look for Mars at this hour above your eastern horizon east of (below and left of) Cancer near the Sickle of Leo. I think the rusty red disc of this planetary interloper stands out very obviously below and to the left of Orion and Gemini. Can you spot it?

Mars will reach opposition on 29 January, 2010, at a distance of 61.7 million miles or nearly twice the distance of the 2003 opposition. This time around its magnitude will be -1.3 and angular size 14.1″ compared to -2.9 and 25.1″ in 2003. I suggest you try observing Mars at least once a week. We’re close enough now that surface details will be revealed when viewed with telescopes of 4 inch aperature or greater. It is also interesting to observe Mars naked eye and watch it as it grows brighter as opposition approaches.

Winter Solstice

21 December is the winter solstice, the start of winter in the northern hemisphere, summer in the southern. Remember Earth is tilted 23.4 degrees to the plane of its orbit around the Sun. At the December solstice Earth’s south pole is most tilted toward the Sun. On the 21st the northern hemisphere will have the fewest hours of daylight (”shortest” day) and the southern hemisphere the longest. This tilt of Earth’s axis is the reason we have seasons, it has nothing to do with our distance from the Sun. Earth will be at perihelion (nearest the Sun) on 3 January, 2010 at about 0.983 Astronomical Unit or about 2% nearer than average. The most significant influence on our seasonal temperatures is the angle at which sunlight strikes Earth. Seasons are more extreme in the north because more of the southern hemisphere is covered by oceans. Large bodies of water smooth temperature averages.

Intuitively you may think the days are already getting longer. This is because the earliest sunset for the northern hemisphere occurred on 7 December. Because more people see the sunset than sunrise this is a popular misconception. Although the 21st is the “shortest” day in the north, earliest sunset was 7 December and the latest sunrise will be 4 January, 2010

You can get a sense of why the days are shorter by observing where the Sun rises or sets and comparing this position to a sunrise or sunset at the spring equinox next March or the summer solstice in June. Simply go outside at sunrise or sunset and make note of the position of the Sun along your horizon. Compare this to your observations in Spring and Summer. You can also see how low the Sun is above the southern horizon during the early afternoon hours.

 panorama-3.JPG

 This panoramic image is a composite of three pictures I took looking west at sunsets in November, September and June. See how the position of the Sun changes?

The most significant astronomy, science and spaceflight stories of 2009?

I’ll post my annual poll the last week of the month. If you have a suggestion for this list please email me with it and participate in our poll. 2009 has been a year filled with changes, joy and sadness for me. I was reunited with my daughters after more than 30 years without them and lost 3 of my wonderful feline companions, Shelby age 17, Missy 16 and Dianna age 15. I miss them terribly.

I hope your 2010 will be filled with wonderful days and Clear Skies!

Mark, the StarGeezer

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December 7, 2009

Observer’s Guide for December 2009

Here’s a short list of what I consider to be the most interesting stargazing “highlights” for December, 2009. The cold weather is here for those of us who live in the Northern Hemisphere so if you plan on spending an evening outdoors to take in any of these celestial treats be sure to wear several layers of warm clothing.

December 6-12 ISS and morning Moon watch

The International Space Station will be visible before dawn over many North American cities and towns this week. Most of these visible passes will occur between 5:45 and 7am local standard time. The ISS is a naked eye object, binoculars or a telescope is not necessary. Click the Heavens-Above link to the right to find the best days and times at your location.

Here’s another morning exercise for this week! I thought of this one to explain to our daughter, Sasheen, “how the Moon grows old and becomes new again”. It takes just a moment and you can do it while you’re on the way to work or school. You’ll need a clear view to the east and west. Once outside, look for the Moon above the western horizon (where the Sun sets). The earlier in the week you do this for the first time the better.

waning-crescent-moon-etx-20-sept-06-009.jpg Once you’ve found the Moon make a mental note of its position relative to the Sun and its “phase” which is the amount of the Moon’s disc that’s lit by sunlight. The Moon’s western limb (the left side in your view) will be in sunlight and its eastern limb (to your right) in an ever widening shadow. Each day the Moon will appear about 15 degrees east, nearer the Sun, and a smaller part of its disc will be in sunlight. Make mental note of the Moon’s changing position relative to the Sun and phase from day to day. Try to make your observations at or about the same time each morning.

After watching this celestial dance for two or three days I hope you will have a sense of how the Moon’s orbit brings her apparent position closer to the Sun and the start of a “new” lunation.  On the mornings of the 13th through 15th the Moon will be west of (rising before) the Sun at dawn. “New” Moon on the 16th will find our Moon with her back to the Sun. From the 17th on she’ll be east of (setting after) sunset. My favorite days for moon watching are very thin crescent waning (old) or waxing (new) phases. So go out and watch her naked eye or better yet with your binoculars or telescope mornings just before or evenings just after “new” on the 16th.

Geminid meteors

No matter where you live December provides some of the best meteor activity of the year. The Geminid meteor shower is active for about a week centered on the peak which is Sunday night/Monday morning December 13-14. This shower is one of the most dependable, observable showers of the year. Peak rates of 60 to 70 meteors per hour may be observed from dark locations away from light pollution. The best time to observe will be from 2am local standard time Monday morning.

 geminids-13-dec-09.JPG

According to Robert Lunsford of the American Meteor Society “you can count on strong activity from the Geminids”. Watching meteors does NOT require optical aid such as binoculars or a telescope. All you need are “tu dos ojos” (your two eyes). Find a comfortable spot (a hammock?) out of the direct glare of neighboring lights. Dress warmly; lay back while watching the darkest area of your sky. The “radiant”, the point from which all meteors from this shower will appear to emanate is northwest of Castor, one of the “head” stars in the constellation Gemini. See the chart which I created using the Stellarium planetarium software. The red lines simulate the Geminid radiant and meteor activity. Click on the thumbnail chart to enlarge.

Coming attractions

Coming up: An evening appearance of Mercury, Jupiter and Neptune convene, the Winter Solstice and a New Year’s Eve lunar eclipse over Asia.

I am preparing our 2009 Poll of what you think the most significant astronomy/spaceflight event was for the year. If you have any suggestions for this list or a comment or question about my observer’s guide email me here.

Clear Skies,

The Geezer

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