Friday, December 12, 2014

December 2014 Constellation of the Month: Triangulum

To the west of the great square of Pegasus, which we described last month, near the wishbone-shaped Perseus  is Triangulum.  It is a compact triangle with somewhat faint stars, so it will be a little challenging to find.  Some consider it an especially attractive constellation.
The big item of interest in Triangulum is the Triangulum Galaxy, M33.  It is the 3rd largest galaxy in our little Local Group of galaxies – after the Andromeda Galaxy (see Nov. 2012), and our own Milky Way.  When seen through binoculars or a small telescope, like the Discovery Center's, it is about the size of the full moon. 
Which brings us to the question we posed last month:  How many full moons, side-by-side, would it take to stretch across the sky in a line (arc) from the eastern horizon to the western horizon?  The answer is about 360 – which is a lot more than most people guess.  That, coincidentally, is the number of degrees in a circle.  Since the arc we're talking about is a half-circle, the Moon is about ½ degrees in diameter, as it appears to us in the sky.  This, in an extremely unlikely coincidence, is the same size as the disk of the Sun.  That is why, in a full eclipse of the sun, the Moon will almost exactly cover the disk Sun. 

You can prove this half-degree figure for yourself – and maybe win a bet or two, at sunset (or moonset).  When the bottom of the circle of the sun touches the horizon in the West, how long will it take for the Sun to completely set?  The answer is 2 minutes, which is a lot quicker than most people would guess.

Here's how you can use that information to calculate with width of the Sun or Moon in degrees of a circle.  The Sun or Moon traverse across the half-circle (180 degrees) of the sky in 12 hours, which is 720 minutes.  2 minutes is 1/360th of 720 minutes.  1/360th of 180 degrees (the arc of the sky) is ½ degree.

Friday, December 5, 2014

The DC Women's Hiking Group will meet Tues., Dec. 9th and Thurs., 11th at Michael Ciaiola Conservation Area in Patterson, NY.

Take I-84 West to exit 20 for I-684 toward NY-22/White Plains/Pawling.
Keep right at the fork, follow signs for NY 22/Brewster/Pawling and merge onto I-684N.
Continue on NY-22N.
Turn right onto Haviland Hollow Rd.
The Conservation Area will be on the left.
Meet at 8:30am.

Sunday, November 23, 2014

The DC Women's Hiking Group will hike at Quarry Head in Wilton, CT on Tues., Nov. 25th.  No hike Thursday, Nov. 27th.  Happy Thanksgiving!

 Take Rt. 35 past the fountain and follow onto Rt. 33 into Wilton.
There will be a State of CT brown sign on the left hand side between mailboxes #760 and #764.
Turn left into the road and follow up the hill.
There will be a sign for parking up ahead.
Meet at 8:30am.

Sunday, November 16, 2014

The DC Womens Hiking Group will meet at Lewisboro Park in NY this week, Tues., Nov. 18th and Thurs., Nov. 20th.
Located on the south side of Rt. 35 between Mead Street and Bouton Road in South Salem.
Turn at white sign for Lewisboro Park off of Rt. 35 and follow up hill to upper parking area.
Meet at 8:30am.

Monday, November 3, 2014

The DC Women's Hiking Group will hike Thurs., Nov. 13th at Florida Refuge in Ridgefield, CT.
No school on Tues., Nov. 11th, so no hike planned.
Take Rt. 7 and turn onto Florida Hill Road. Make a right onto High Valley Road.
Park along the side of High Valley Road closest to Florida Hill Road.
Meet at 8:30am.
The DC  Women's Hiking Group will hike Thursday, Nov. 6th at Weir Farm.
No school on Tuesday, Nov. 4th, so no hike planned.

 Take Branchville Road and follow National Park signs to Weir Farm.

 Meet in parking lot on Nod Hill Rd. across from historic buildings at 8:30am.

Friday, October 31, 2014

November 2014 Constellations of the Month: Pegasus and Andromeda

High in the sky and a little to the West are our November 2014 constellations of the month, Pegasus and Andromeda.  They are east of July's constellation of the month, the Summer Triangle.

They look like a big square, with some appendages.  This is called the Great Square of Pegasus, even though the northeast star in the square belongs to Andromeda (which is why we needed to have 2 constellations this month).  Can you guess how many side-by-side Full Moons it would take to stretch across one side of the square? 

At the end of one of the appendages is the globular star cluster M15, which has about 100,000 stars.  Globular clusters, unlike other stars and clusters we see in our Milky Way galaxy, are not located in the disk of the galaxy.  They are found "above" and "below" (there is no direction which is "up" or "down" in space) the central part of the disk.  They formed before the rest of the galaxy took shape. 

Andromeda's stars are relatively faint, and they don't form a recognizable shape.  But the constellation has one major attraction – M 31, the Andromeda Galaxy.   It is a huge spiral galaxy which looks much like our own Milky Way.  It is bigger than the Milky Way and contains about a trillion stars, which is at least twice as many as the Milky Way.  It is bright enough to be seen with the naked eye.   It appears so bright, because it is so close -- only 2.5 million light years (16 trillion miles) away.  With the naked eye, it looks about as wide as 3 Full Moons.

... which brings us to the earlier question of how many Full Moons would stretch across a side of the Great Square – Answer: about 30.  That's a lot more than most of us would guess.  The Moon appears to us as about half a degree wide, and a semicircle across the sky from one horizon to the opposite horizon is 180 degrees.  So, about 360 Full Moons side-by-side would be required to traverse the sky from horizon to  horizon.