07/08/2022 – Ephemeris – Polaris the North Star

This is Ephemeris for Friday, July 8th. Today the Sun will be up for 15 hours and 24 minutes, setting at 9:29, and it will rise tomorrow at 6:06. The Moon, 2 days past first quarter, will set at 2:17 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, its 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 be standing on its handle.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hours). They may be different for your location.

Addendum

Polaris finder and location animation. Three frames: visual appearance in the sky, lines of the asterisms of the Big and Little Dippers, addition of the equatorial grid of celestial coordinates analogous to longitude and latitude on the Earth. The right ascension (like longitude) lines converge over the Earth’s North Pole, with Polaris close by. Created using Stellarium and GIMP.

The two stars at the front of the Big Dipper’s bowl, at the bottom of the dipper as it appears now in the evening, point to Polaris near the 11-hour right ascension line. Right ascension, though the same as earthly longitude, is measured in hours, rather than degrees. An hour equals 15 degrees, making 24 hours equal 360 degrees.

08/30/2021 – Ephemeris – “W”

This is Bob Moler with Ephemeris for Monday, August 30th. Today the Sun will be up for 13 hours and 19 minutes, setting at 8:22, and it will rise tomorrow at 7:04. The Moon, at last quarter today, will rise at 12:26 tomorrow morning.

Rising higher each evening in the northeastern sky is a group of stars that make the pattern of the letter W. It is the constellation of Cassiopeia the queen. It is one of the more recognizable star patterns. From our latitude here in Northern Michigan, it is circumpolar, meaning that it never sets. Though, the best time to see it is in the autumn and winter, when it’s highest in the sky. It is opposite the Big Dipper from Polaris, the north star. In fact, a line drawn from any of the handle stars of the Big Dipper through Polaris will reach Cassiopeia. So as the Big Dipper descends in the northwestern sky now, Cassiopeia ascends in the northeast. They change places in winter and spring as the Big Dipper ascends in the northeast.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hr). They may be different for your location.

Addendum

Animation showing the juxtaposition of Cassiopeia and the Big Dipper from Polaris, the North Star. Click on the image to enlarge it. Created using Stellarium and GIMP.

01/18/2021 – Ephemeris – The Drinking Gourd

This is Bob Moler with Ephemeris for Martin Luther King Jr. Day, Monday, January 18th. Today the Sun will be up for 9 hours and 18 minutes, setting at 5:32, and it will rise tomorrow at 8:13. The Moon, 2 days before first quarter, will set at 11:34 this evening.

This day is set aside to honor the Reverend Dr. Martin Luther King Jr. who gave his life for the struggle for equality for blacks and other minorities and to end segregation. A struggle that continues to this day. In the decades before the Civil War runaway slaves would travel, often at night, northward from the slave states of the south to the northern free states and Canada over the metaphorical Underground Railroad following the Drinking Gourd, the Big Dipper as their compass. Over the last several millennia the Great Bear, Ursa Major has been that northward pointer. For much of that time the North Pole of the sky had been passing near the handle of the Big Dipper or bear’s tail.

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

Addendum

An animation showing the Big Dipper, also known as the Drinking Gourd pointing to Polaris, the North Star which is just about due north. This is for 9 pm January 18th, about 3 1/2 hours after sunset. Created using Stellarium with additional annotations.

04/24/2020 – Ephemeris – The Big Dipper can be used to point to other stars and constellations

This is Bob Moler with Ephemeris for Arbor Day, Friday, April 24th. Today the Sun will be up for 13 hours and 57 minutes, setting at 8:39, and it will rise tomorrow at 6:41. The Moon, 2 days past new, will set at 10:21 this evening.

The Big Dipper can be used to point to other stars and constellations. Right now the Big Dipper is nearly overhead. The front bowl stars point to Polaris, the North Star which never seems to move in the sky. The handle can be used to find two stars. First follow the arc of the handle away from the bowl to find the fourth brightest night-time star Arcturus in the base of the kite shaped constellation of Boötes. Straighten the arc to a spike and continue to the south and you will come to the bright blue-white star Spica in Virgo the virgin. You can remember these stars with the phrase “Follow the arc of the handle to Arcturus and then spike to Spica” or if you prefer the alternate pronunciation of the latter star “Speak to Speeka”.

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

Addendum

Finding stars and constellations using the Big Dipper. Click on the image to enlarge. Created using my LookingUp program for Windows.

09/24/2019 – Ephemeris – Cassiopeia the “W” shaped constellation

Ephemeris for Tuesday, September 24th. Today the Sun will be up for 12 hours and 4 minutes, setting at 7:36, and it will rise tomorrow at 7:33. The Moon, 3 days past last quarter, will rise at 3:13 tomorrow morning.

The stars of the autumn skies slowly are replacing the summer stars from the east. Look in the northeastern sky by 9 p.m. and you can find the W shaped constellation of Cassiopeia the queen. Cassiopeia is so far north that it never sets for us in Michigan. It is opposite the pole star Polaris from the Big Dipper. There’s a dim star that appears above the middle star of the W which turns the W into a very crooked backed chair. Cassiopeia, in Greek mythology, represents a queen of ancient Ethiopia, the W represents the profile of her throne. She enters in to the great autumn story whose other characters are also seen in the stars as the constellations Andromeda, Pegasus, Perseus, Cetus and her husband Cepheus.

For my retelling of the Greek myth that links these autumn constellations click here.

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

Addendum

Cassiopeia, in the northeast is opposite Polaris from the Big Dipper. For 9 p.m. in late September. Created using Stellarium. Artistic credit: Johan Meuris.

04/08/2019 – Ephemeris – How to find Polaris, the North Star

Ephemeris for Monday, April 8th. Today the Sun will be up for 13 hours and 7 minutes, setting at 8:18, and it will rise tomorrow at 7:09. The Moon, 3 days past new, will set at 11:54 this evening.

The most useful of the navigation stars for the average person is Polaris, the North Star or Pole Star. It is very close to the point in the sky that the Earth’s axis points to in the north. Currently it is about three-quarters of a degree from the pole, about one and a half moon diameters. In 2110 or thereabouts it will approach to slightly less than a moon diameter from the pole before slowly heading away. Polaris is always closer to true north than a magnetic compass in Michigan. To find it use the two stars in front of the Big Dipper’s bowl to point to it. This time of year the Big Dipper is above Polaris, so the pointer stars, that’s what they are called, point down to it. Polaris is at the end of the handle of the faint Little Dipper.  The reason for Polaris’ motion is the slow 26,000 year wobbling of the Earth’s axis, called precession.

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

Addendum

Ursa Major and Minor, the Big and Little Dippers. See how the two stars at the front of the bowl point to Polaris. It happens that the pointer stars are close to the 11th hour of right ascension (longitude in the sky). The right ascension lines converge at the north celestial pole, just as the longitude lines converge at the Earth’s north pole. Created using Stellarium.

The year I was born, 1941, Polaris was a whole degree from the celestial north pole.

If you’ve ever wondered why right ascension is in hours instead of degrees it’s because the Earth rotates within the celestial sphere, so it’s easier to keep track of the east-west position in the sky by using a clock that set to gain 3 minutes and 56 seconds a day.  Such a clock keeps sidereal (star) time rather than solar (sun) time.  One hour equals 15 angular degrees or 4 minutes a degree.

 

05/14/2018 – Ephemeris – Big Dipper: Pointer to the Stars

Ephemeris for Monday, May 14th. Today the Sun will be up for 14 hours and 47 minutes, setting at 9:03, and it will rise tomorrow at 6:14. The Moon, 1 day before new, will rise at 6:45 tomorrow morning.

The Big Dipper points to other stars and constellations. Right now the Big Dipper is nearly overhead. The front bowl stars point to Polaris, the North Star which never seems to move in the sky. The handle can be used to find two stars. First follow the arc of the handle away from the bowl to find the fourth brightest night-time star Arcturus in the base of the kite shaped constellation of Boötes. Straighten the arc to a spike and continue to the south and you will come to the bright blue-white star Spica in Virgo the virgin. You can remember these stars with the phrase “Follow the arc of the handle to Arcturus and then spike to Spica” or if you prefer the alternate pronunciation of the latter star “Speak to Speeka”.

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

Addendum

As can be seen below, there was one pointer function that didn’t make it into the program:  A leaky dipper drips on Leo.

Using the Big Dipper as a pointer to other stars. The pointers to Polaris could be life saving, since it is always north. The view is southward. The cross displayed near the center is the zenith. One might want to lay down to take all this in. Created using my LookingUp program.

02/13/2018 – Ephemeris – The Big Dipper as a pointer to other stars and constellations

Ephemeris for Tuesday, March 13th. The Sun will rise at 7:58. It’ll be up for 11 hours and 47 minutes, setting at 7:46. The Moon, 4 days before new, will rise at 6:42 tomorrow morning.

With the Big Dipper up in the northeastern sky it is a sign that spring is coming. At 9 p.m. The Big Dipper can be used to find other stars and constellations. The Big Dipper’s most famous function is in locating Polaris the North Star. It’s a good way of finding directions at night. The altitude of Polaris, that is angle above the horizon, will give one’s approximate latitude north of the equator. Another constellation that can be found is Leo the lion. It is rising in the east in the evening, but it can also be found from the Big Dipper by imagining that a hole were drilled in the bottom of the bowl to let the water leak out. It would fall on Leo’s back. The Big Dipper can be used to find two more stars, but they have not yet risen.

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

Addendum

The Big Dipper points to Polaris, the, North Star, and to Leo the lion at 9 p.m., March 13th. In another hour the 4th brightest night-time star Arcturus will appear above the eastern horizon pointed to by the arc of the handle of the Big Dipper. We’ll revisit the Big Dipper next month when Arcturus and Spica will also be found by the use of the Big Dipper. Created using Stellarium and Libre Office.

11/09/2017 – Ephemeris – Cassiopeia the queen and her husband

Ephemeris for Thursday, November 9th. The Sun will rise at 7:31. It’ll be up for 9 hours and 49 minutes, setting at 5:20. The Moon, 1 day before last quarter, will rise at 10:59 this evening.

The stars of the autumn skies hold forth now, but one prominent autumn constellation never leaves us, here in northern Michigan. Look high in the northeastern sky by 8 p.m. and you can find the W shaped constellation of Cassiopeia the queen. It is opposite the pole star Polaris from the Big Dipper, slinking low in the north-northwest. There’s a dim star that appears above the middle star of the W which turns the W into a very crooked backed chair. Above and left of Cassiopeia is a dim upside down church steeple shaped constellation of Cepheus the king. The Milky Way flows through a corner of Cepheus and Cassiopeia toward the northeastern horizon and through the constellation of Perseus the hero, and the bright star Capella in Auriga the Charioteer.

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

Addendum

Cassiopeia and constellations along the Milky Way in the northeast these autumn evenings. (8 p.m. November 9, 2017). Click on image to enlarge. Created using Stellarium and GIMP.

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

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

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.