Archive
09/18/2012 – Ephemeris – The center of the Milky Way
Ephemeris for Tuesday, September 18th. The sun will rise at 7:25. It’ll be up for 12 hours and 21 minutes, setting at 7:46. The moon, 3 days past new, will set at 8:58 this evening.
Look to the south southwest at 10 p.m. At the constellation of Sagittarius, which looks like a teapot. It’s located at the south end of the Milky Way. Just off the spout of the teapot lies, beyond the clouds of stars, gas and dust, at a distance of about 27,000 light years, the center of the Milky Way. The center contains a 4 million sun mass black hole with a bevy of stars orbiting around it like planets orbit the sun. Black holes are so massive that, nothing, not even light can escape their gravity. Lots of energy is released by matter falling in to a black hole. Currently our Milky Way’s black hole is quiet, nothing of note is falling in. However there is a cloud of gas and dust approaching the black hole, so its quiet phase may end next year.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Location of the center of the Milky Way and the Teapot of Sagittarius.
While the actual center of the galaxy cannot be seen in optical wavelengths it is visible in radio, infrared and x-rays. The black hole at the center of the Milky Way is designated Sagittarius A* (pronounced Sagittarius A Star). Check it out in Wikipedia and other sources.
02/21/2012 – Ephemeris – The winter Milky Way
Ephemeris for Fat Tuesday, Tuesday, February 21st. The sun will rise at 7:34. It’ll be up for 10 hours and 44 minutes, setting at 6:18. The moon is new today, and won’t be visible.
The winter Milky Way doesn’t seem as bright as the summer part. That’s mainly because we are looking away from the center of the Milky Way Galaxy. The galaxy appears to us as a band encircling the sky because we are within it, and our galaxy is a flat spiral galaxy. Our galaxy has the mass of maybe 200 billion suns and has a diameter of about 100 thousand light years. We are approximately 25 thousand light years from the center, which lies in the summer constellation of Sagittarius. There is a star forming region in the constellation of Orion, and part of it shows up as the Great Orion Nebula. There are more of these regions south of Orion, which we can’t see from Michigan. It’s said that the southern Milky Way is brighter than the one we see.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Artist's conception of the Milky Way. From NASA/JPL/Spitzer/Cal Tech
08/25/11 – Ephemeris – The Great Rift
Thursday, August 25th. The sun rises at 6:56. It’ll be up for 13 hours and 35 minutes, setting at 8:31. The moon, 3 days before new, will rise at 3:57 tomorrow morning.
High overhead the Milky Way is seen passing through the Summer Triangle of three bright stars. Here we find the Milky Way split into two sections. The split starts in the constellation of Cygnus the Swan or Northern Cross very high in the east. The western part of the Milky Way ends southwest of the Aquila the eagle. This dark dividing feature is called the Great Rift. Despite the lack of stars seen there, it doesn’t mean that there are fewer stars there than in the brighter patches of the Milky Way. The rift is a great dark cloud that obscures the light of the stars behind it. Sometimes binoculars can be used to find the edges of the clouds of the rift, as stars numbers drop off suddenly. This is especially easy in Aquila.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The Great Rift in the Milky Way. Created using Stellarium.
08/23/11 – Ephemeris – The wonders found in the constellation Scutum
Tuesday, August 23rd. The sun rises at 6:54. It’ll be up for 13 hours and 41 minutes, setting at 8:35. The moon, 2 days past last quarter, will rise at 1:45 tomorrow morning.
The teapot pattern of stars that is the constellation of Sagittarius lies at the southern end of the Milky Way this evening. It appears that the Milky Way is steam rising from the spout. The area above Sagittarius in the brightest part of the Milky Way is the dim constellation of Scutum the shield. Don’t bother looking for the stars that make up the constellation; what’s important is the star clouds of the Milky Way. Scan this area with binoculars or small telescope for star clusters and nebulae or clouds of gas. In binoculars both clusters and nebulae will appear fuzzy, but a small telescope will tell most of them apart. Even if you’ve never been able to find anything in your telescope, put on the lowest power eyepiece you have and scan back and forth for these wonders.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The constellations Sagittarius and Scutum. Created using Stellarium.
08/22/11 – Ephemeris – The constellation Sagittarius
Monday, August 22nd. The sun rises at 6:52. It’ll be up for 13 hours and 44 minutes, setting at 8:36. The moon, 1 day past last quarter, will rise at 12:50 tomorrow morning.
The Milky Way runs from north to south through the heavens at 11 p.m. You’ll notice that the Milky Way is brighter and broader just above the horizon in the south. In that glow in the south is a star pattern that looks like a stout little teapot, with a the Milky way like steam rising from the spout, which faces the west. This pattern of stars is the major part of the constellation called Sagittarius. According to Greek mythology Sagittarius is a centaur with a bow and arrow poised to shoot Scorpius the scorpion to the right. This centaur is called Chiron, the most learned of the breed, centaurs usually being a rowdy bunch. The center of the pinwheel of our galaxy lies hidden beyond the stars above the spout of the teapot.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The constellations Sagittarius and Scutum. Created using Stellarium.
07/26/11 – Ephemeris – The Milky Way
Tuesday, July 26th. The sun rises at 6:22. It’ll be up for 14 hours and 53 minutes, setting at 9:15. The moon, 3 days past last quarter, will rise at 3:01 tomorrow morning.
The Milky Way, which is rising to pass overhead later in the evening is what we see of a huge structure of stars of which we are a part. We call it the Milky Way galaxy. It’s a spiral galaxy with a straight bar of stars through the center, a barred spiral galaxy about a hundred thousand light years across. It’s part of a small cluster of galaxies called the Local Group. Besides these three dozen galaxies, the Milky Way has small satellite galaxies orbiting it. The largest of these are the two Magellanic clouds seen from the southern hemisphere of earth. Even now a tiny galaxy is colliding with our galaxy. We can penetrate to the center of our own galaxy in infrared light, but not visible light from our location 26,000 light years away.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The Milky Way 360 degrees - Wikipedia
This is a mosaic of photographs showing the Milky Way as seen from the earth. The summer Milky Way we see is from just right of center to the left edge.
04/08/11 – Ephemeris – Looking out the thin side of the Milky Way
Friday, April 8th. The sun will rise at 7:11. It’ll be up for 13 hours and 7 minutes, setting at 8:18. The moon, 3 days before first quarter, will set at 1:39 tomorrow morning.
In winter and summer we see the Milky Way crossing the sky from north to south. In the autumn we see it cross nearly overhead from east to west. In the spring, especially next month the Milky way is barely visible low in the north. The Milky Way circles the sky as a great circle. It is what we see of our own galaxy. It is a spiral galaxy 100,000 light years in diameter and less than 5,000 light years thick where we are. So in the spring we look out the thin side of our galaxy. The stars are sparser than in other parts of the sky, the constellations generally are larger. The really cool part is that in telescopes we can see other galaxies, other Milky Ways beyond. In the spring we have a huge cluster of thousands of galaxies out there about 50 million light years away.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Looking out the thin side of the Milky Way. Created using Cartes duCiel
This is the entire dome of the sky on May 15th at 11 p.m. Note the Milky Way ringing the horizon. The red dots are galaxies, the blue and gray dots are star clusters in our galaxy, the green ones are nebulae, also in our galaxy.
Bob Moler's Ephemeris Blog 