July 16, 2010

Watch as the Moon glides past our “Parade of Planets”

w-horizon-10-pm-15-july-10.gifOver the next few nights enjoy the view as the waxing crescent Moon glides past our evening “parade of planets” at dusk

Wednesday night the three day old Moon will appear just below glistening Venus. Thursday night the Moon will appear near fading Mars and Friday night it visits Saturn.

As I’ve mentioned many times before, slender crescent Moons are my favorite lunar phase. If you have binoculars or a telescope use them for great views of the Moon and, especially, Saturn. The Moon will help you locate each planet. Can you see the “earthglow” on the Moon’s disc? Earthglow is sunlight reflecting off Earth.

The chart above shows the Moon’s position on July 15th and was produced using Your Sky.

Click on the image to enlarge

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July 9, 2010

A “Parade of Planets” adorns the evening sky


While you’re out on the deck enjoying the sunsets on these warm summer evenings linger awhile and enjoy a “Planet Parade” in the west after sunset. Over the next few weeks planets Venus, Mars and Saturn will dominate the early evening sky above the western horizon. Even tiny, speedy Mercury will join the party for a few brief evenings in late July. The chart above is for 10pm on the evening of July 7th. Click image to enlarge.
In early August the three planets will appear to join each other within a circle of a diameter of less than 5 degrees. You won’t need a telescope to enjoy the show but if you have one Saturn is the most interesting telescopic target of the trio. Use the charts I’ve prepared using John Walker’s neat planetarium tool Your Sky.
The motions of Mercury and Venus in their orbits are mostly responsible for their relative positions in our sky. As for Mars and Saturn our line of sight out to their orbits is the primary reason we will see this “conjunction” of heavenly bodies this summer. The best evenings to catch Mercury will be around July 26th as he joins the quartet of planets at the western (right hand) side of the arc of a line which stretches roughly 30 degrees across the sky through Virgo and Leo.

west-horizon-26-july-0130-ut.gifBeginning this weekend (July 10-11) east to west (left to right) the order of appearances will be Saturn, Mars, the star Regulus (Leo) and Venus. Venus and Regulus will have a rendezvous of their own July 7-10, then Venus will continue moving east of the star. The chart at the left shows the sky on evenings around July 26th as Mercury joins the party

Observe the changing positions of the planets from night to night. I think you’ll enjoy the show.
Have a question or comment? Click here to contact me.

The International Space Station will be visible orbiting overhead nearly every evening over the next few days. For a list of the dates and times click the Heaven’s-Above link at the right or use the above link to request one.

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July 6, 2010

Morning Moonwatch as the “Old” Moon becomes “New”


Here’s a morning exercise for this week! I thought of this one to demonstrate to our daughters “how the Moon grows old and becomes new again”.

You can try this late at night if you’re a nightowl or mornings as you’re on the way out to start your day.

The Moon reached last quarter on July 4th and will be ”new” on July 11th

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.

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 rise and set about 25 minutes later and appear about 15 degrees further east, nearer the Sun, and a smaller part of its disc will be sunlit. 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.

The line separating the lit and dark areas of the Moon is called the “terminator”. As the Moon wanes the terminator is where the Sun is setting. The terminator is the place to point your telescope or binoculars as the Moon waxes or wanes because this is the area where surface features like craters and mountain peaks stand out in shadowed relief. Consider how the shadows are longest at sunrise and sunset here on Earth and you’ll get the idea.

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 or lunar cycle.  On the mornings of the 8th through 10th the Moon will be just west of (rising before) the Sun at dawn. “New” Moon on the 11th will find our Moon with her back to the Sun. In other words, the far side of the Moon will be “full” as the side facing Earth is “new”. From the 12th 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” July 8th through 12th.

There will be a total solar eclipse coincident with the new Moon on July 11th but it will be visible only in the South Pacific. This eclipse compliments the partial Lunar eclipse which took place June 26th at the last Full Moon. As the Moon begins the next Lunation she will pass just 7 degrees below and left of Venus on the 14th and approximately the same distance from Mars on the 15th.

I took the above image one morning at about 4am in September, 2004. It shows the waning crescent Moon and one of my favorite craters, Gassendi. Click on the image to enlarge it and look closely and you can see shadows cast by the peaks on the eastern rim of the crater. When this image was taken it was late afternoon in that area of the Moon.

Here’s a quiz for you:

How long is a “day” on the Moon? Meaning sunrise to sunset.

a)one day, b)28 days, c)one month, d)28 hours.

To assist your moonwatching activities here is a list of Moonrise/set times based on Louisville, KY for the week of July 4-11. Times are listed in 24 hour “military” format. Example: July 5 moonrise was 1:16am, moonset 3:11pm EDT

July 05 0116 1511
July 06 0146 1614
July 07 0222 1719

July 08 0305 1823
July 09 0357 1925
July 10 0459 2021
July 11 0610 2109

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