Archive
10/05/2015 – Ephemeris – The loneliest star
Ephemeris for Monday, October 5th. The Sun will rise at 7:45. It’ll be up for 11 hours and 31 minutes, setting at 7:16. The Moon, 1 day past last quarter, will rise at 1:38 tomorrow morning.
There’s a bright and lonely star that appears low in the south for only seven and a half hours a night on autumn evenings. It’s appearance is a sign as sure as the falling leaves that autumn is here At 10 p.m. tonight it’s low in the south-southeast. The star’s name is Fomalhaut, which means fish’s mouth. This is appropriate because it’s in the constellation of Piscis Austrinus, the southern fish. At our latitude it’s the fish that got away, because Fomalhaut appears to be quite alone. The dimness of the constellation’s other stars and location close to the horizon make the fainter stars hard to spot. The earth’s thick atmosphere near the horizon reduces the stars brightness by a factor of two or more, so Fomalhaut appears to keep a lonely vigil in the south.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Fomalhaut appears quite alone in the south-southeast at about 10 p.m. Created using Stellarium.
Actually Fomalhaut isn’t all that alone, It apparently has a companion planet.
Fomalhaut b and it’s path around its star. Credit: NASA, ESA, and P. Kalas (University of California, Berkeley and SETI Institute)
07/27/2015 – Ephemeris – Deneb, the dimmest of the Summer Triangle stars. But is it really?
Ephemeris for Monday, July 27th. The Sun rises at 6:23. It’ll be up for 14 hours and 51 minutes, setting at 9:14. The Moon, 3 days past first quarter, will set at 3:36 tomorrow morning.
This evening when it gets dark the bright star Deneb in Cygnus the swan will be high in the east northeast. Deneb is the dimmest star of the summer triangle. Of the other stars of the triangle, Vega is very high in the east, while Altair is lower in the southeast. While Deneb’s apparent magnitude, or brightness as seen from earth, makes it the dimmest of the three bright stars, Deneb’s vast distance of possibly 2,600 light years makes it over 100 times the distance of Vega. If brought as close as Vega, Deneb would be almost as bright as the full moon. It is as bright as two hundred thousand suns. It apparently has run out of hydrogen in its core. Once a blue super giant star, it’s currently evolving through the white supergiant stage.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The Summer Triangle. Created using Stellarium and The Gimp.
One of my old photographs of Deneb and the North American Nebula digitized from a slide.
The Hertzsprung-Russell diagram of star luminosity vs. surface temperature. Note that Deneb is at the top center, while the Sun is lower on the main sequence. Credit: European Southern Observatory (ESO).
07/23/2015 – Ephemeris – Altair, the nearest star of the Summer Triangle
Thursday, July 23rd. Today the Sun will be up for 14 hours and 59 minutes, setting at 9:18. The Moon, 1 day before first quarter, will set at 12:57 tomorrow morning. Tomorrow the Sun will rise at 6:20.
The southernmost star of the Summer Triangle is Altair, high in the south. The other two stars of the triangle are Vega nearly overhead, and Deneb high in the east. Altair is the closest of the three at a distance of 16.7 light years away. One light year is nearly 6 trillion miles. Altair is 10 times the brightness of the sun. If seen at Altair’s distance, the sun would only be as bright as one of the two stars that flank it. What is rather different about Altair is its rapid rotation. While it’s almost twice the sun’s diameter, it rotates once in only 8.9 hours, The CHARA Interferometer at Mt. Wilson has actually imaged its squashed disk in the infrared. Our sun’s a slow poke, taking nearly a month to rotate once.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The Summer Triangle. Created using Stellarium and The Gimp.
Aquila the Eagle in the southeastern sky. Created using Stellarium.
Credit: Zina Deretsky, National Science Foundation
07/21/2015 – Ephemeris – Vega, the brightest star of the Summer Triangle
Ephemeris for Tuesday, July 21st. Today the Sun will be up for 15 hours and 3 minutes, setting at 9:20. The Moon, 3 days before first quarter, will set at 12:01 tomorrow morning. Tomorrow the Sun will rise at 6:17.
The bright star high in the east is Vega, one of the stars of the Summer Triangle an informal constellation called an asterism. Vega belongs to the official constellation Lyra the harp, which includes a narrow parallelogram of stars to its south. Vega was regarded by astronomers as a standard calibration star. Though a first magnitude star, its actual magnitude is 0.03 and slightly variable. It is a type A0 (A-zero) pure white star, and is 25 light years away. Astronomers however got a shock in 1983 when calibrating the Infrared Astronomy Satellite (IRAS) on it: Vega showed an excess of Infrared radiation that means the star is orbited by a disk of dust, perhaps the beginnings of a planetary system. Due to the slow wobble of the earth’s axis Vega will be our pole star in 14 thousand years.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The Summer Triangle. Created using Stellarium and The Gimp.
Magnified view of Lyra. Created using Stellarium.
Vega in the mid-infrared from the Spitzer Infrared Satellite. Credit: NASA/JPL-Caltech/University of Arizona
07/09/2015 – Ephemeris – The first stars to appear at night
Ephemeris for Thursday, July 9th. Today the Sun will be up for 15 hours and 23 minutes, setting at 9:29. The Moon, 1 day past last quarter, will rise at 2:05 tomorrow morning, and tomorrow the Sun will rise at 6:07.
Let’s check out all the bright stars in the evening sky, as it gets dark tonight. Low in the west are the planets Venus and Jupiter. High in the west is the bright yellow-orange star Arcturus. In the northwest is the Big Dipper, whose curved handle points to Arcturus. Straightening that curve to a spike will point to Spica a blue-white star low in the southwest. The planet Saturn is located in the south. Below and left of it is the red star Antares which usually twinkles merrily. High in the east is the bright white star Vega. To its lower right is Altair, and to its lower left the star Deneb. Vega, Altair and Deneb make the Summer Triangle, whose rising in the east signals the coming of summer.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
I talked about seeing the first stars a month ago. It seems that in holding star parties this time of year we spend a lot of time watching the first stars appear. I wanted to discuss the Summer Triangle, but it wandered off to what you see above. I’ll get there next week, I promise.
The first stars and planets to appear. See if you can located them from the text. Created using Stellarium for about 10 p.m., July 9, 2015.
06/12/2015 – Ephemeris – The first stars to appear at night
Ephemeris for Friday, June 12th. Today the Sun will be up for 15 hours and 31 minutes, setting at 9:28. The Moon, 3 days past last quarter, will rise at 4:03 tomorrow morning. Tomorrow the Sun will rise at 5:56.
Evening twilight lasts a very long time this time of year, so the stars will come out slowly. By about a half hour after sunset the planets Venus and Jupiter should be visible in the west. Probably the first actual star to appear is very high in the east, the orange star Arcturus in the constellation of Boötes, which is the 4th brightest night-time star. Next, lower in the northeast, is the 5th brightest star the white Vega in Lyra the harp. By this time Saturn should appear low in the southeast as a yellowish star. Soon many more stars will become visible with the Big Dipper overhead pointing to Polaris in the north, blue-white Spica in the south, Regulus, left of Jupiter and Capella low in the northwest.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The first stars to appear after sunset. This is created from Stellarium for a half hour after sunset. It’s a bit optimistic, in my view, though my eyes aren’t the best. Try your eyes. Click on image to enlarge.
05/12/2015 – Ephemeris – Arcturus, a look at the Sun’s future
Ephemeris for Tuesday, May 12th. Today the Sun will be up for 14 hours and 42 minutes, setting at 9:00. The Moon, 1 day past last quarter, will rise at 3:43 tomorrow morning. Tomorrow the Sun will rise at 6:17.
Arcturus, a red giant star is about midway up the sky in the southeast at 10 p.m. It’s visible earlier, being the 4th brightest night-time star and the third brightest star-like object out at that time after Venus and Mars. A pointer to it is the handle of the Big Dipper, following the arc of the handle to Arcturus. Though only 37 light years away, it’s not from around here. It’s passing through the galactic disk from north to south. Arcturus is about 7 billion years old, and is about 8% more massive than our Sun. It appears to be starting its red giant phase, after running out of hydrogen to fuse to helium in its core and is beginning to fuse helium. It’s a preview of coming attractions for our Sun when it gets that old.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Finding Arcturus. Orientation for 11 p.m. on May 12, 2015. Created using Stellarium.
Evolution of a sun-like star. Note the sizes of the star at the various stages are compressed, also the time line. In the red giant stage the star is possibly a hundred times larger than at the main sequence stage. The white dwarf stage is a hundred times smaller than the main sequence stage. Click to enlarge. Credit: From a NASA/Chandra poster.
04/06/2015 – Ephemeris – Arcturus the 4th brightest star
Ephemeris for Monday, April 6th. The Sun will rise at 7:14. It’ll be up for 13 hours and 1 minute, setting at 8:16. The Moon, 2 days past full, will rise at 10:37 this evening.
One of the stars that stays up most of the year, except late autumn and most of winter is Arcturus. Now in the evening Arcturus is low in the east. It’s a bright star, officially the 4th brightest star in the night sky, and the 4th brightest star-like object in our night sky after Venus, Jupiter, and Sirius. Arcturus can be found by following the arc of the handle of the Big Dipper to it. Remember, follow the arc to Arcturus. Arcturus belongs to the kite shaped constellation of Boötes, which we’ll visit in greater detail when it’s higher in the sky. Arcturus is an interesting star. It’s 37 light years away, and moving quite rapidly at 75 miles per second (122km/s), mostly across the sky. Some astronomers think that it
Arcturus off the handle of the Big Dipper at 9:30 p.m. April 6, 2015. Created using Stellarium.
may be part of a captured dwarf galaxy.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
03/27/2015 – Ephemeris – The North Star, Polaris
Ephemeris for Friday, March 27th. The Sun will rise at 7:33. It’ll be up for 12 hours and 30 minutes, setting at 8:03. The Moon, at first quarter today, will set at 3:49 tomorrow morning.
Tonight we turn our eyes northward to Polaris, the North Star. It is the closest bright star to the north pole of the sky. It appears nearly stationary as all the other stars appear to revolve around it as the Earth rotates. Some folks, think that Polaris is the brightest star in the sky. It’s not. It is a good solid second magnitude star, about the brightness of a Big Dipper star. The Big Dipper can be used to point to it, by using the two stars at the front of the bowl. Polaris is at the end of the handle of the Little Dipper. The Little Dipper has four dim stars in its rather oddly bent handle and back of its bowl. The two stars at the front of the bowl of the Little Dipper are Kochab and the dimmer Pherkad, which are also called the Guard Stars or the Guardians of the Pole.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
How to find Polaris. The grid is the equatorial grid showing the proximity to the pole. Created using Stellarium.
02/16/2015 – Ephemeris – The Winter Circle
Feb 16. This is Bob Moler with Ephemeris for President’s Day, Monday, February 16th. The sun will rise at 7:42. It’ll be up for 10 hours and 30 minutes, setting at 6:12. The moon, 2 days before new, will rise at 6:25 tomorrow morning.
The winter skies are blessed with more first magnitude stars than any other season. That’s a full one-third of the total are seen is a relatively small area. Six of these stars lie in a large circle centered on the seventh. This circle is up at 9 p.m. Starting high overhead is Capella in Auriga the charioteer. Moving down clockwise is Aldebaran in the face of Taurus the Bull. Then down to Orion’s knee we find Rigel. Down and left is the brightest star of all Sirius the Dog Star in Canis Major, lowest of these stars in the south-southeast. Moving up and left is Procyon in Canis Minor, Above Procyon is Pollux in Gemini the twins. All these are centered on Betelgeuse the bright red star in Orion’s shoulder.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The Winter Circle of 1st magnitude stars
Bob Moler's Ephemeris Blog 