Archive
10/24/2016 – Ephemeris – Fomalhaut, the loneliest star in the sky
Ephemeris for Monday, October 24th. The Sun will rise at 8:10. It’ll be up for 10 hours and 31 minutes, setting at 6:42. The Moon, 2 days past last quarter, will rise at 3:01 tomorrow morning.
There’s a bright star that appears for only seven and a half hours on autumn evenings. It’s appearance, low in the south at 10 p.m., is a clear indication of the autumn season. The star’s name is Fomalhaut, which means fish’s mouth. That’s fitting because it’s in the constellation of Piscis Austrinus, the southern fish. At our latitude it’s kind of the fish that got away, because Fomalhaut appears to be quite alone low in the sky. The dimness of the constellation’s other stars and location close to the horizon make the faint stars hard to spot. The earth’s thick atmosphere near the horizon reduces their brightness by a factor of two or more, so Fomalhaut, one of the brightest stars in the sky, keeps a lonely vigil in the south.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Aquarius and Fomalhaut as visualized by Stellarium.
05/27/2016 – Ephemeris – Alkaid, the star at the end of the Big Dipper
Ephemeris for Friday, May 27th. Today the Sun will be up for 15 hours and 14 minutes, setting at 9:17, and will rise tomorrow at 6:02. The Moon, 2 days before last quarter, will rise at 1:40 tomorrow morning.
The star at the end of the handle of the Big Dipper is named Alkaid. It is the bright star that’s closest to the zenith at 11 p.m. It is a rare blue-white star. Alkaid and Dubhe, at the other end of the Big Dipper are stars that do not belong to the Ursa Major Association. And thousands of years from now these two stars will leave the central stars of the dipper behind, and deform the Big Dipper. Over the millennia the Big Dipper would look like a tin cup. Near Alkaid are two popular deep sky objects. And being this far from the hazy band of the Milky Way one would guess that they would be galaxies. And they are. The Whirlpool Galaxy and the Pinwheel Galaxy. Two gorgeous spiral galaxies.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The change in the Big Dipper over time. Source: stargazerslounge.com. Ultimate source: Stellarium.
The Big Dipper and Alkaid with the Whirlpool (M51) and Pinwheel (M101) galaxies. Created using Stellarium.
The Whirlpool Galaxy, M51. Credit Scott Anttila.
The Pinwheel Galaxy, M101. Credit Scott Anttila.
05/26/2016 – Ephemeris – Polaris the North Star
Ephemeris for Thursday, May 26th. Today the Sun will be up for 15 hours and 12 minutes, setting at 9:16, and will rise tomorrow at 6:03. The Moon, 3 days before last quarter, will rise at 1:02 tomorrow morning.
The star Polaris is perhaps the most important star in the northern hemisphere sky. That’s because it is nearly over the Earth’s north pole. It’s also called the North Star or the Pole Star. Polaris can be found by using the two stars at the front of the bowl of the Big Dipper, These two stars, we call Pointer Stars do point very accurately to Polaris. It is not the brightest star as some think, but a brighter than average star in a most unique position in the sky. During the lifetimes of those now living Polaris will be getting slowly closer to the pole. It won’t reach it, but in 100 years will begin to recede from the pole. The altitude of Polaris in degrees approximately equals ones latitude.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Looking North at the Big Dipper pointing at Polaris. Created using my Looking Up program.
Closeup of Polaris and the Celestial North Pole. The declination lines are 1 degree apart. Created using Cartes du Ciel (Sky Charts).
05/24/2016 – Ephemeris – Follow the spike to Spica
Ephemeris for Tuesday, May 24th. Today the Sun will be up for 15 hours and 9 minutes, setting at 9:14, and will rise tomorrow at 6:04. The Moon, 3 days past full, will rise at 11:35 this evening.
Just about due south at 11 p.m. is the bright star Spica which can be found from all the way back overhead to the Big Dipper. Follow the arc of the handle of the Big Dipper to the bright star Arcturus high in the south, southeast. Then straighten the curve of the arc to a straight spike which points to Spica. Arcturus is much brighter than Spica and has an orange tint to Spica’s bluish hue. In fact Spica is the bluest of the 21 first magnitude stars. That means that it is hot. Actually Spica is really two blue stars orbiting each other in 4 days. Spica is 250 light years away, which is reasonably close. Spica was an important star to the ancients. One temple was built, and aligned to its setting point.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The evening sky to the south. All the finder stars are there, so follow the arc of the Big Dipper’s handle to Arcturus. Straighten it to a spike that points to Spica. Created using Stellarium.
04/26/2016 – Ephemeris – Arcturus, just passing through
Ephemeris for Tuesday, April 26th. The Sun rises at 6:39. It’ll be up for 14 hours and 2 minutes, setting at 8:42. The Moon, 3 days before last quarter, will rise at 12:48 tomorrow morning.
Arcturus is an orange-colored giant star, 37 light years away. We see it high in the east and pointed to by following the arc of the handle of the Big Dipper. Arcturus is a rapidly moving star. It’s velocity is about 76 miles per second (122 km/s). It’s almost at its nearest to the Sun now. In the next 2,000 years it will move about one degree, twice the width of the Moon toward Spica. Arcturus may be part of a dwarf galaxy being assimilated by the Milky Way which may account to its odd motion. Arcturus is thought to be close to 8% more massive than the Sun and about 6 to 8 ½ billion years old. It has entered its red giant stage after running out of hydrogen in its core. It may be a glimpse of what the sun will look like in 5 billion years.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The constellation Bootes and the 4th brightest star in the night sky. The thin line extending to the right from Arcturus is the distance it will travel in the next 2,000 years. That line is nearly one degree ling, or 2 Mon diameters. Created using Cartes du Ciel (Sky Charts)
03/29/2016 – Ephemeris – The Little King Star, Regulus
Ephemeris for Tuesday, March 29th. The Sun will rise at 7:28. It’ll be up for 12 hours and 39 minutes, setting at 8:07. The Moon, 2 days before last quarter, will rise at 2:00 tomorrow morning.
Regulus is the brightest star in the constellation of Leo the lion at the bottom of the backward question mark that is the head and mane of Leo. It’s in the southeast at 9 p.m. above the much brighter Planet Jupiter. Alluding to the lion’s status in the animal kingdom, Regulus is the little king star. It is dead last in order of brightness of the 21 brightest first magnitude stars, 1/13th the brightness of Sirius the brightest star low in the southwest at the same time. To the Babylonians it was the king, the 15th of their constellations that marked the passage of the sun. Regulus is about 79 light years away, and 288 times the brightness of the sun. It is a rapidly spinning ellipsoid 3 times the sun’s diameter, rotating in just under 16 hours.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Regulus and Jupiter in the constellation of Leo at 10 p.m., March 29, 2016. Created using Cartes du Ciel (Sky Charts).
03/28/2016 – Ephemeris – The brightest spring star is now rising in the east
Ephemeris for Monday, March 28th. The Sun will rise at 7:30. It’ll be up for 12 hours and 35 minutes, setting at 8:06. The Moon, 3 days before last quarter, will rise at 1:07 tomorrow morning.
Rising in the eastern sky at 10 p.m. is the 4th brightest night-time star. It’s found off the curve of the handle of the Big Dipper above it in the northeast. It’s the tail end of a kite shaped constellation of Boötes the herdsman. Arcturus is an orange-colored giant star, 37 light years away. Its light was used open the 1933 Chicago Worlds Fair believing its light left the star in 1893 the year of the previous Chicago Worlds Fair. It turns out that Arcturus is 3 light years closer than what they thought. Arcturus is a rapidly moving star. It’s velocity is about 76 miles (122 km) per second. It’s at its nearest to the sun now. Arcturus is thought to be close to the sun’s mass, and much older. It may be a glimpse of what the sun will look like in 5 billion years.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Arcturus off the handle of the Big Dipper rising. Created using Stellarium.
03/17/16 – Ephemeris – Why are there no green stars?
Ephemeris for St. Patrick’s Day, Thursday, March 17th. The Sun will rise at 7:50. It’ll be up for 12 hours and 1 minute, setting at 7:52. The Moon, 2 days past first quarter, will set at 5:10 tomorrow morning.
Today we celebrate the patron saint of the Emerald Isle. And green is the color of the day. When we look to the skies we don’t see a lot of green. Well, maybe in the Hubble Space Telescope’s false color photographs like the original Pillars of Creation, where green represents hydrogen, and in the northern lights. The colors we see in stars are red or orange if they are cooler than the Sun, yellow if they are the same temperature as the Sun, and white or bluish if hotter than the Sun. In the spectrum of light we can see, green is in the middle, between yellow and blue. As a matter of fact the Sun radiates its energy most heavily in the green. So if you got rid of those other colors the Sun itself would be green.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Star cluster showing star colors, probably enhanced. Source uncredited image from planetsforkids.org.
“Black body” Radiation Curves by temperatures. The Sun’s surface temperature is around 5800 Kelvin. Note the peak radiation besides increasing in amplitude slides from red to blue with increasing temperature.
Aurora looking north at 10/24/2011 at 10:52 p.m. The first color visible in an aurora or northern lights is green. More active aurorae give off other colors. Credit: Bob Moler.
Looking overhead in an active aurora, and the variety of colors, even green. Credit: Bob Moler.
Pillars of Creation in false color by the Hubble Telescope. Sometimes the colors are given to specific elemental emissions, of shifted because the colors represent radiation that is invisible to the human eye. Credit: NASA/ESA/HST.
02/18/2016 – Ephemeris – Castor and Pollux
Ephemeris for Thursday, February 18th. The Sun will rise at 7:39. It’ll be up for 10 hours and 35 minutes, setting at 6:14. The Moon, 3 days past first quarter, will set at 5:28 tomorrow morning.
The star Pollux is at the head of the same named brother of Gemini the twins. Castor is the slightly dimmer star right above it. Pollux is about 34 light years away. It’s twice as massive as the Sun, and has run out of hydrogen in its core and is in the process of evolving into a red giant star. One planet, twice as massive as Jupiter has been detected around it. Castor is at 51 light years away. There are 6 stars in its system. The brightest three are visible in telescopes. Each is a spectroscopic binary, meaning that the companion stars are detected by the Doppler shifts of the lines in their spectra as the stars orbit each other. The Doppler shift is just one of the many pieces of information revealed by the spectroscope.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Castro and Pollux with the bright Moon and other bright stars and constellations of winter. 9 p.m. February 18, 2016. Created using Stellarium.
The Castor star system exploded in this JPL/NASA infographic.
The entire infographic is here.
02/16/2015 – Ephemeris – The little Dog Star
Ephemeris for Tuesday, February 16th. The Sun will rise at 7:42. It’ll be up for 10 hours and 29 minutes, setting at 6:12. The Moon, 1 day past first quarter, will set at 3:45 tomorrow morning.
Procyon is the bright star to the east or left of Betelgeuse in the sky tonight, which puts it in the east-southeast at 9 tonight. Procyon is the brightest of the two stars in Canis Minor, Orion’s little hunting dog. Procyon is sometimes called the Little Dog Star for that reason. The Dog Star Sirius is a ways below and right of it. The name Procyon means “Before the Dog”, because Procyon, though east of Sirius, rises before it due to its more northerly position. This only works if one is north of 30 degrees north latitude. South of that, Sirius rises first. Procyon is a white star 11 and a half light years away, 3 light years farther than Sirius, and like Sirius it has a faint white dwarf companion. It’s a bit less than half the Sun’s age.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Procyon, Sirius and the stars of winter. Created using Stellarium
Note that at their rising Procyon is higher in the sky than Sirius.
There are some grid lines on the chart. The ones running from lower left to upper right are lines of declination, which are like latitude lines on the Earth. On this chart they are 10º apart. The line that intersects the horizon at the east compass point is the celestial equator. It will meet the western compass point at the horizon. As the Earth rotates the stars and planets will move westward in the direction of these declination lines. The lines that run from upper left to lower right are hour lines of right ascension. Here they are 15 degrees or one hour apart, The Earth rotates 360º in a sidereal* day. 360 divided by 24 hours gives 15º an hour. So the celestial sphere of stars and planets will slide 15º westward in a sidereal hour.
* A sidereal day, rotation with respect to the stars, is about 4 minutes shorter that the solar day, the day and time we keep based on the Sun. The Sun moves about one degree eastward each day, so the rotation has to catch up that one degree each day. The rotation of one degree takes 4 minutes. I’ll let you work that one out for yourself.
Bob Moler's Ephemeris Blog 