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09/07/2017 – Ephemeris – Capella rising

September 7, 2017 1 comment

Ephemeris for Thursday, September 7th. The Sun will rise at 7:12. It’ll be up for 12 hours and 55 minutes, setting at 8:07. The Moon, 1 day past full, will rise at 9:08 this evening.

For those with the advantage of a low northern horizon, will see a bright star moving nearly parallel above the horizon over the evening hours or notice its change in position from night to night, moving to the northeast. The star is Capella, northernmost of the bright winter stars. It never quite sets for locations north of the latitude of Ludington (44° N), meaning it’s circumpolar like the Big Dipper. It’s slow motion, due to its position close to the north pole of the sky sometimes makes it seem odd. I’ve gotten several calls about it over the years. Capella is the brightest star in the constellation Auriga the charioteer, a constellation I see as a pentagon, with a small triangle of three stars on one side. I’ll wait until the winter season to talk further about them.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Capella rising

Capella appearing to rise like an aircraft taking off. Shown here at hourly intervals from 9 p.m. to midnight. Created using Stellarium and GIMP.

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08/28/2017 – Ephemeris – Polaris the North Star

August 28, 2017 1 comment

Ephemeris for Monday, August 28th. The Sun will rise at 7:00. It’ll be up for 13 hours and 25 minutes, setting at 8:25. The Moon, 1 day before first quarter, will set at 12:19 tomorrow morning.

The bright star Polaris is a very important star. It is also known as the North Star and the Pole Star. Its unique position is nearly directly at the zenith at the Earth’s north pole, making it a very important navigational star. It’s about 40 minutes of arc, or about one and a third Moon diameters away from the extension of the Earth’s axis into the sky. As a rule of thumb, it’s angular altitude above the northern horizon is approximately one’s latitude, and it stands about at the due north compass point. Polaris is found using the Big Dipper, using the two stars at the front of the dipper bowl to point to it. It’s located at the tip of the handle of the very dim Little Dipper, which this time of year in the evening appears to standing on its handle.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Polaris Finder Chart

Polaris finder chart for 10 p.m., August 28th. Created using my LookingUp program

Rotation of the sky around Polaris

Animation of the rotation of the sky around Polaris on the night of August 28/29, 2017. Created using Stellarium and Filmora.

I’ve left the constellation lines off.  The Big Dipper is seen easily as is Cassiopeia’s “W” opposite it around the stationary Polaris.

 

 

07/10/2017 – Ephemeris – Deneb, a super bright star

July 10, 2017 1 comment

Ephemeris for Monday, July 10th. Today the Sun will be up for 15 hours and 20 minutes, setting at 9:27, and it will rise tomorrow at 6:08. The Moon, 1 day past full, will rise at 10:24 this evening.

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 higher 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 1,400 light years* makes it over 50 times the distance of Vega. If brought as close as Vega, Deneb would be as bright at least as the quarter moon. It is possibly as bright as 200 thousand Suns; and a huge star, possibly as large in diameter as the orbit of the Earth. For all this it is only 20 to 25 times the mass of the sun.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

* Deneb’s distance is not well known.  Over the years with the Ephemeris program and this blog I’ve given various distances to the star.  Having no companion and being beyond the distance where trigonometric parallax is used, at least from the ground, makes distance measurement difficult.  Hipparcos  satellite measurements give a distance about twice as great.  Estimates of the true brightness of a star are based on its known distance.  An error in distance by a factor of two gives an error in terms of intrinsic luminosity by a factor of 4, due to the inverse square law of brightness with distance.

Addendum

The constellations Lyra, Cygnus and Aquila

Deneb with the other stars and constellations in the Summer Triangle. Created using Stellarium.

Deneb & North American Nebula

One of my old photographs of Deneb and the North American Nebula digitized from a slide. Deneb’s ultraviolet emissions cause the North American and unnamed here Pelican Nebulae to glow.  The red color is due to hydrogen.

06/29/2017 – Ephemeris – A closer look at the star Vega

June 29, 2017 1 comment

Ephemeris for Thursday, June 29th. Today the Sun will be up for 15 hours and 31 minutes, setting at 9:31, and it will rise tomorrow at 6:00. The Moon, 1 day before first quarter, will set at 1:21 tomorrow morning.

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 is regarded by astronomers as a standard calibration star. Though a first magnitude star, its actual magnitude is 0.03. It is a type A0 pure white star, and is 27 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 a Kuiper belt of its own. Due to the slow wobble of the earth’s axis Vega will be our pole star in 14 thousand years.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Lyra

Magnified view of Lyra. Created using Stellarium.

Vega

Vega in the mid-infrared from the Spitzer Infrared Satellite. Credit: NASA/JPL-Caltech/University of Arizona.

Categories: Ephemeris Program, stars Tags: ,

06/27/2017 – Ephemeris – Arcturus as a look at the Sun’s future

June 27, 2017 1 comment

Ephemeris for Tuesday, June 27th. Today the Sun will be up for 15 hours and 32 minutes, setting at 9:31, and it will rise tomorrow at 5:59. The Moon, 3 days before first quarter, will set at 12:18 tomorrow morning.

With the Moon brightening the night sky, let’s take a look at the star Arcturus, which with its pointer, the curve of the Big Dipper’s handle is slipping into the high western sky. Arcturus is the 4th brightest night time star, though some think the star Vega, high in the east is brighter. They are different colors because Arcturus is orange, while Vega is whiter than the Sun. Arcturus is a preview of what the Sun will become in four or five billion years from now. It is only 10% more massive than the Sun and is that much older than the Sun, so it is turning into its red giant stage, after running out of hydrogen to turn into helium in its core to produce energy. The helium is now compressing and heating to begin its reaction.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Arcturus finder chart

Arcturus finder chart with the Big Dipper and Vega as guide posts. Created using Stellarium.

Here’s one of my prior posts about Arcturus, about its great space velocity:  https://bobmoler.wordpress.com/2016/04/26/04262016-ephemeris-arcturus-just-passing-through/

06/26/2017 – Ephemeris – Latest sunset and the apparent positions of the Summer Triangle stars

June 26, 2017 1 comment

Ephemeris for Monday, June 26th. Today the Sun will be up for 15 hours and 32 minutes, setting at 9:31, and it will rise tomorrow at 5:59. The Moon, 3 days past new, will set at 11:40 this evening.

Tonight we have the latest sunset of the year. From now on until December sunsets will become earlier. Other than the sunrise and sunset numbers, we’ll begin to notice it for real in a few weeks. At first that realization strikes me a sad note that summer is beginning to end. However the astronomer in me realizes that means more night-time hours, and that the summer Milky Way is coming. Of the three bright stars of the Summer Triangle overhead and in the east, two of its stars are in the milky band. They are Deneb to the north and Altair to the south. Vega, closest to the zenith is not in the band. Actually all the stars we see with the naked eye or small telescopes belong to the Milky Way galaxy.
The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

The constellations Lyra, Cygnus and Aquila

Looking at the stars of the Summer Triangle and their location in and near the Milky Way band. Created using Stellarium.

06/22/2017 – Ephemeris – Now that it’s summer, lets check out the Summer Triangle

June 22, 2017 1 comment

Ephemeris for Thursday, June 22nd. Today the Sun will be up for 15 hours and 33 minutes, setting at 9:31, and it will rise tomorrow at 5:57. The Moon, 1 day before new, will rise at 5:45 tomorrow morning.

We’re a day into summer, and the asterism or informal constellation called the Summer Triangle can be seen rising in the east as it gets dark. Highest of the three bright stars is Vega in the constellation Lyra the harp, whose body is seen in a narrow parallelogram nearby. The second star of the triangle is Deneb lower and left of Vega, It appears dimmer than Vega because it is by far the most distant of the three. The third star of the Summer Triangle is seen farther below and a right of Vega. It is Altair in Aquila the eagle, and the closest. Altair is 16.5 light years away, Vega is 27 light years while Deneb may be a whopping 2600 light years away. One light year is 6 trillion miles (9 trillion km).

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

The Summer Triangle July 5, 2012 at 11 p.m. Created using Stellaruim and The Gimp.

The Summer Triangle. Created using Stellarium and The Gimp.