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Archive for April, 2018

04/30/2018 – Ephemeris – Venus-Earth resonances, and Jupiter & the Moon tonight

April 30, 2018 Comments off

Ephemeris for Monday, April 30th. The Sun rises at 6:34. It’ll be up for 14 hours and 12 minutes, setting at 8:46. The Moon, 1 day past full, will rise at 9:30 this evening.

Jupiter will be near the moon tonight. The gravitational force between the planets produces some interesting resonances in their orbital periods. Venus has three different kinds with the Earth. First, Venus orbits the Sun 13 times in the same time it takes the Earth to orbit the Sun 8 times. This is a 13 to 8 resonance. This sets up the 5 Venus Cycles equaling 8 years resonance the Mayan’s discovered. A Venus cycle of 584 days takes Venus to go from Morning Star to Evening Star and back again. The next one wasn’t discovered until we started to bounce radar signals off Venus. We found it rotates backwards, and very slowly at that. Its rotation with respect to the stars is longer than its year. And it so happens that every passage near the Earth the same side of Venus is facing us.

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

Addendum

The Moon and Jupiter

The Moon and Jupiter at 10 p.m. tonight, April 30, 2018. Created using Stellarium.

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04/27/2018 – Ephemeris – The Mayan special relationship to Venus

April 27, 2018 Comments off

Ephemeris for Arbor Day, Friday, April 27th. The Sun rises at 6:38. It’ll be up for 14 hours and 4 minutes, setting at 8:42. The Moon, 2 days before full, will set at 6:20 tomorrow morning.

The Mayans of Mesoamerica a thousand years ago diligently observed Venus and discovered Venus’ unique cycles that they used to correct their calendars. The first was the Venus Cycle, the period we’d say that Venus passes between the Earth and the Sun to enter the morning sky to the next time it does it. That was 584 days. Its appearance in the morning sky would last 263 days, Then it would disappear near the Sun, actually behind it for 50 days. It would reappear in the evening sky for another 263 days before again disappearing near the Sun, this time for only 8 days. These are the 4 phases of a Venus cycle. Five of these cycles equals almost exactly 8 years, called a sequence. 13 sequences equal 104 years, a Venus Round.

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

Addendum

Venus Cycle

Venus Cycle derived from John P Pratt who has another purpose for the diagram and annotated by me to include the number of days in each phase. For my purposes ignore points 1 and 4. The Mayan cycle starts with 7, the first appearance of Venus during the morning. Points 8 and 5 are the points where Venus is at greatest elongation from the Sun. Credit John P Pratt.

04/26/2018 – Ephemeris – When the Greeks thought Venus was two separate planets

April 26, 2018 Comments off

Ephemeris for Thursday, April 26th. The Sun rises at 6:40. It’ll be up for 14 hours and 1 minute, setting at 8:41. The Moon, 3 days before full, will set at 5:52 tomorrow morning.

For the next three programs I’m going to take a look at Venus through the eyes of the ancient, or pre-telescopic cultures. It’s a teaser for the program I’m presenting at the NMC Observatory May 4th. Venus from the mists of time to today. We call Venus’ appearance in the morning the Morning Star and its evening appearance, the Evening Star. The very ancient Greeks thought they were two separate planets. The morning planet was Phosphorus, and the evening planet was Hesperus. Somewhere around the 4th or 3rd century BC someone figured the when Hesperus was out in the evening Phosphorus was not out the next morning, and vice versa. The then single planet was named Aphrodite, by whose Roman name, Venus, we still call it by today.

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

Addendum

Venus (Hesperus) at its evening eastern greatest elongation

Venus (Hesperus) at its evening eastern greatest elongation on August 18, 2018 showing the part of its orbit that’s above the horizon. Created using Stellarium and GIMP.

Venus (Phosphorus) at its morning western greatest elongation

Venus (Phosphorus) at its morning western greatest elongation on January 6, 2019 showing the part of its orbit that’s above the horizon. Jupiter is the other planet visible. Created using Stellarium and GIMP.

Venus at inferior conjunction

Venus at inferior conjunction on October 27, 2018 showing its entire orbit on a smaller scale than the images above from the Earth’s perspective.  The far part of the orbit goes behind the Sun. The planets Mercury and Jupiter are seen left of the Sun. Created using Stellarium.

04/25/2018 – Ephemeris – It’s bright planet Wednesday

April 25, 2018 Comments off

Ephemeris for Wednesday, April 25th. The Sun rises at 6:41. It’ll be up for 13 hours and 58 minutes, setting at 8:40. The Moon, 3 days past first quarter, will set at 5:22 tomorrow morning.

It’s Wednesday again and time to look for the bright planets. One bright planet is in the evening sky, the brightest, Venus. It will be visible low in the western twilight from about 9:10 p.m. until it sets at 10:58. Venus is blindingly bright in binoculars or a small telescope. Jupiter will rise this evening at 9:42 p.m. That doesn’t make it an evening planet. It has to rise before sunset to be an evening planet. Give it a couple of weeks. Saturn will rise at 1:37 a.m., while Mars will rise at 2:33 a.m.

At 6 tomorrow morning these three planets will be strung across the southern sky. Bright Jupiter will be in the southwest, dimmer Mars and Saturn will be in the south, with Mars to the left of Saturn in the morning twilight.

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

Addendum

Venus in evening twilight

Venus in evening twilight at 9 p.m, tonight April 25, 2018. Created using Stellarium.

The Gibbous Moon

The Gibbous Moon tonight at 10 p.m., April 25, 2018. Created using Stellarium.

The morning planets

The morning planets at 6 a.m. April 26, 2018. Click on the image to enlarge. Created using Stellarium.

Telescopic morning planets

The morning planets as seen in a telescope using the same magnification. A magnified image of Mars is inset showing some of the features that may be visible under higher magnification. Created using Cartes du Ciel (Sky Charts).

Planets and the Moon at sunset and sunrise of a single night

Planets and the Moon at sunset and sunrise of a single night starting with sunset on the right on April 25, 2018. The night ends on the left with sunrise on the 26th. Click on the image to enlarge. Created using my LookingUp program.

04/24/2018 – Ephemeris – Venus will be south of the Pleiades tonight

April 24, 2018 Comments off

Ephemeris for Tuesday, April 24th. The Sun rises at 6:43. It’ll be up for 13 hours and 55 minutes, setting at 8:39. The Moon, 2 days past first quarter, will set at 4:51 tomorrow morning.

Tonight the brilliant planet Venus will be just south of the Pleiades, also known as the Seven Sisters star cluster. From our cockeyed position on the Earth about half way from the equator and the North Pole. The sky in the east and west, low in the sky, is tilted about the same angle, namely about 45 degrees. If you’re listening to this program from other than Northern Michigan the angle will be the same as your latitude. So instead of south being down, as one would expect when looking to the south, south is to the lower left when looking to the west. On this program Thursday, Friday and Monday I’ll be talking about Venus and what the ancients found out about the planet in the days before the telescope was invented.

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

Addendum

The sky low in the west

Venus, Pleiades, Aldebaran with the Hyades star cluster and Orion are seen in the west at 9:45 p.m. April 24, 2018. Venus is south of the Pleiades. Created using Stellarium.

Venus and the Pleiades with grid

A closer look at Venus and the Pleiades with the coordinate grid added. The lines that run from upper right to lower left are lines of right ascension, analogous to longitude lines on the Earth. To the upper right is north and lower left is south. The other lines are those of declination. Like latitude lines on the Earth, they run east and west. Created using Stellarium.

04/23/2018 – Ephemeris – The Ursa Major Association

April 23, 2018 Comments off

Ephemeris for Monday, April 23rd. The Sun rises at 6:45. It’ll be up for 13 hours and 52 minutes, setting at 8:37. The Moon, 1 day past first quarter, will set at 4:15 tomorrow morning.

The usual impression is to think that the stars of a constellation are actually located close together. This is usually not true. The stars of a constellation can be at vastly different distances. The Big Dipper is different. The five stars, excepting the two end stars of the dipper and 12 other dimmer stars in the general area are of similar distance and have the same motion through space. The group is called the Ursa Major Moving Cluster or Ursa Major Association, and is moving about 9 miles per second relative to the solar system to the east and south. An association is a rather loose, sparse star cluster. This association lies about 75 light years away. If it were five times farther away, it would be the same distance as the Pleiades.

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

Addendum

The Big Dipper

Craig Brown’s drawing of where the stars of the Big Dipper are and are heading. Click on the image to go to Craig’s WordPress post.

04/20/2018 – Ephemeris – Astronomy Day and the Lyrid meteor shower this weekend

April 20, 2018 Comments off

Ephemeris for Friday, April 20th. The Sun rises at 6:50. It’ll be up for 13 hours and 44 minutes, setting at 8:34. The Moon, 2 days before first quarter, will set at 1:50 tomorrow morning.

Tomorrow is Astronomy Day. The Grand Traverse Astronomical Society will celebrate with a star party at Northwestern Michigan College’s Rogers Observatory. Tomorrow April 21st, from 9 p.m. to 11 p.m. There will also be activities inside the observatory, so clear or cloudy there will be something to see or do for all ages. The Lyrid Meteor Shower will be active this weekend and reach a peak Sunday. The meteors from this shower will seem to come from near the constellation of Lyra the harp, a small and narrow parallelogram of stars with the bright star Vega near it. The best viewing will be for a few hours in the wee morning hours after the Moon sets Sunday or Monday mornings.

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

Addendum

Lyrid meteor shower radiant

All sky view at 4 a.m. Sunday or Monday morning with the Lyrid radiant. Created using Stellarium.

The additional radiants showing in the image above are the (sigma) σ-Scorpids which will reach peak on April 28th, a minor shower and (eta) η-Auqariids which will reach peak on May 6th.  Both these meteor showers have severe interference by the Moon.