04/17/2017 – Ephemeris – How to find the stars Arcturus and Spica from the Big Dipper

April 17, 2017 Comments off

Ephemeris for Monday, April 17th.  The Sun rises at 6:54.  It’ll be up for 13 hours and 35 minutes, setting at 8:30.  The Moon, 2 days before last quarter, will rise at 2:21 tomorrow morning.

The Big Dipper, now nearing the zenith at 10 p.m. points to several stars and constellations.  It’s handle points to two bright stars.  First we follow the arc of the handle to the bright orange star Arcturus, the 4th brightest night-time star.  The reason I say night-time is that the sun is a star also but by definition is not out at night.  The arc to Arcturus is a how to find Arcturus and a clue to its name.  Arcturus, midway up the sky in the east, lies at the base point of the kite shaped constellation of Boötes the herdsman.  From Arcturus, straighten out the arc to a spike and one soon arrives at Spica a blue-white star in Virgo the virgin, now low in the southeast.  It is below Jupiter this year.  Spica is also sometimes pronounced ‘Speeka’.

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

Addendum

Finding Arcturus and Spica

How to find the stars Arcturus and Spica from the Big Dipper in April 2017. Created using my LookingUp program.

04/14/2014 – Ephemeris – Why does Easter occur on a different Sunday every year?

April 14, 2017 Comments off

The answer is astronomical!

Ephemeris for Good Friday, Friday, April 14th.  The Sun will rise at 6:59.  It’ll be up for 13 hours and 26 minutes, setting at 8:26.  The Moon, 3 days past full, will rise at 11:48 this evening.

Easter will be celebrated by western and eastern christian churches this Sunday.  Easter is a movable feast in that it falls on a different date each year following the first full moon of spring.  It’s an attempt to follow the Jewish Passover, which starts on the 15th of the month of Nisan.  Being a lunar calendar the 15th the generally the night of the full moon.  And since the Last Supper was a Seder, the Christian church wanted to follow Passover as closely as possible using the Roman solar based calendar where the year was 365.25 days long.  Passover started at sunset this past Monday night.  The western churches eventually adopted the Gregorian calendar to keep in sync with the seasons.  The Eastern churches did not, however Easter is late enough this year so they both fall on the same date.

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

Addendum

The seasonal, or officially the Tropical Year, from vernal equinox to vernal equinox is approximately 365.24220 days long, about 11 1/2 minutes shorter than the Julian (after Julius Caesar) Calendar year.  The Julian Calendar kept up with the year by having three 365 ordinary years and one leap year of 366 days.  It over corrects.  To make the calculation for Easter easier in the various dioceses of the far-flung church, the vernal equinox, the day the Sun crosses the celestial equator, heading northward was defined as March 21st.  The actual vernal equinox was falling behind the Julian Calendar by 0.8 days every century.

By 1582 the Roman Catholic Church under Pope Gregory XIII decided to correct the problem.  By then the real vernal equinox occurred on March 11th.  Easter is supposed to be a spring feast, and using March 21st as the vernal equinox would eventually push Easter into summer.  The Pope instituted a commission to look into the problem.  This commission headed by Christophorus Clavius* came up with what we know as the Gregorian Calendar.  First, eliminate 10 days from the calendar.  This was done in October 1582 between October 4th and 15th.  Then to keep the calendar in sync with the actual year it was decreed that leap years would continued for years divisible by 4; except that century years, those divisible by 100 be ordinary years, except those by also divisible by 400.  Thus the year 1900 was an ordinary year, but the year 2000 was a leap year, and the year 2100 will be an ordinary year.  Adoption of this as a civil calendar took 400 years to be universal.

The Greek Orthodox and other eastern churches kept the Julian Calendar, so on occasion their Easter is sometimes celebrated in May.  The Jewish Calendar is, as I alluded to in the program transcript, a lunar calendar.  It has a relationship to the Julian Calendar in that 19 Julian Years equals 235 lunar months almost exactly. This is called the Metonic Cycle.  Those 235 months equal 12 lunar years of 12 and 13 months.  So without correction Passover too will slowly head into summer in millennia to come.

* Clavius was honored by having a large, rather spectacular crater on the Moon named for him.  Search these posts for Clavius to find it.

 

 

 

04/13/2017 – Ephemeris – Venus is in the morning sky

April 13, 2017 Comments off

Ephemeris for Thursday, April 13th.  The Sun will rise at 7:01.  It’ll be up for 13 hours and 23 minutes, setting at 8:25.  The Moon, 2 days past full, will rise at 10:52 this evening.

Venus is beginning to make its morning appearance now, rising just before 6 a.m.  It’s north and west of the Sun, but it’s path away from the Sun is at a low angle to the horizon.  Venus is now in its crescent phase, which is getting fatter, as it separates from the Sun.  It is also getting smaller in our telescopes as it recedes from us. Venus has no natural satellites,  however it currently has a small robotic one.  It is Japan’s Akatsuki or Dawn spacecraft.  Launched in 2010, it failed to fire its rocket engine for the entire time needed to drop it into orbit of Venus.  The engineers devised a plan to chase Venus for 5 years and gently maneuver the spacecraft into orbit using only its attitude thrusters.  This they accomplished in December of 2015.

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

Addendum

Telescopic Venus

Telescopic Venus as created with Stellarium for early morning April 14, 2017. Stellarium is coloring Venus as it would be colored low in the sky.

Akatsuki

Artists drawing of Akatsuki orbiting Venus. Credit Japanese Institute of Space and Astronautical Science (ISAS)

Localized Vortex

A localized vortex in the clouds of Venus captured by Akatsuki. Credit ISAS.

Venus cloud animation.

An animation of the clouds rotating on Venus’ night side by Akatsuki. Credit ISAS

Categories: Ephemeris Program, Venus Tags:

04/12/2017 – Ephemeris – It’s Wednesday, do you know where your bright planets are?

April 12, 2017 Comments off

Ephemeris for Wednesday, April 12th.  The Sun will rise at 7:03.  It’ll be up for 13 hours and 20 minutes, setting at 8:23.  The Moon, 1 day past full, will rise at 9:53 this evening.

Tonight is Yuri’s Night the anniversary of Yuri Gagarin’s first human orbital flight in 1961.  Now celebrated around the world.  Mars is still in the west after sunset and fading.  It will set at 11:08 p.m.  Coming to dominate the evening sky low in the east in evening twilight is Jupiter.  It will rise to be low in the east-southeast at 10 p.m.   At 6 a.m. Jupiter is still hanging on in the western sky, and will be below and right of the Moon at that time.  At the same time Saturn be about due south.  It will rise in the east-southeast at 1:38 a.m. tomorrow.  Venus is beginning to make an appearance in the morning sky.  It will rise at 5:40 tomorrow morning but will have to compete with the ever brightening twilight in the morning, but each morning it will rise about 6 minutes earlier.

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

Addendum

Mras after sunset

Mars in the west with bright stars at 9 p.m. April 12, 2017. Created using Stellarium.

Jupiter

Jupiter in dark skies with some southern spring constellations on April 12, 2017. Created using Stellarium.

Telescopic Jupiter

Jupiter and moons at 10 p.m. April 12, 2017 The Great Red Spot is near the central meridian of the planet at that time.  Created using Cartes du Ciel (Sly Charts).

Morning planets

Jupiter, the Moon, Saturn and Venus at the eastern horizon at 6 a.m. April 13, 2017. Created using Stellarium.

Binocular Moon

The waning gibbous Moon as it might be seen in binoculars at 6 a.m. April 13, 2017. Created using Stellarium.

Saturn and its moons

Saturn and moons in telescopes at 6 a.m. April 13, 2017. Created using Cartes du Ciel (Sky Charts).

The planets and Moon on a single night

Planets and the Moon at sunset and sunrise of a single night starting with sunset on the right on April 12, 2017. The night ends on the left with sunrise on April 13. Click on the image to enlarge. Created using my LookingUp program.

 

 

04/11/2017 – Ephemeris – What’s under Jupiter’s cloud tops?

April 11, 2017 Comments off

Ephemeris for Tuesday, April 11th.  The Sun will rise at 7:04.  It’ll be up for 13 hours and 17 minutes, setting at 8:22.  The Moon, at full today, will rise at 8:54 this evening.

I made an error in yesterday’s on-air program which I fixed before posting this blog version.  The moon Io will be over the face of Jupiter from when it rises tonight until 8:58 p.m.*, thereafter it will be seen just to the west of the planet.  What we see of Jupiter are its cloud tops.  Planetary astronomers have some very educated guesses as to what lies beneath them.  An atmosphere of mainly hydrogen and helium, ending in a hot liquid ocean of hydrogen.  Beneath that a core of metallic hydrogen that generates the planet’s huge magnetic field.  Below that maybe a core of solid iron and other metals.  NASA’s Juno spacecraft now orbiting Jupiter is tasked with finding out the interior structure by measuring the velocity of the spacecraft as it flies just above the cloud tops of this giant planet.

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

* Observers in other locations around the world can check out the table from yesterday’s post of other Jovian satellite events after this entry is posted at 4:01 UT, April 11, 2017.

Addendum

Jupiter on two nights

Jupiter and its moons in a telescope at 10 p.m. both April 10th & 11th, 2017. Created using Cartes du Ciel (Sky Charts).

For a year’s worth of Jovian satellite events and when the Great Red Spot crosses Jupiter’s central meridian, go to: http://www.projectpluto.com/jevent.htm.

Juno Spacecraft

The Juno spacecraft. Credit: NASA.

Jupiter's south pole

A February 2, 2017 Juno image of Jupiter’s south pole and its chaotic storm clouds. I think I have a paisley tie that looks like that. Credit NASA/JPL-Caltech/SwRI/MSSS/John Landino.

04/10/2017 – Ephemeris – Jupiter takes over as king of the evening sky

April 10, 2017 Comments off

Ephemeris for Monday, April 10th.  The Sun will rise at 7:06.  It’ll be up for 13 hours and 14 minutes, setting at 8:21.  The Moon, 1 day before full, will set at 7:36 tomorrow morning.

By the time we see the Moon tonight it will be about 5 hours from officially being full.  However bright planet Jupiter should be easily visible about 5 moon diameters to the right and a bit above the Moon.  In a small telescope it is easy to see the disk of Jupiter, and possible see the cloud bands in the atmosphere,  due to the planet’s rapid rotation, of less than 10 hours.  Jupiter’s mass is over 300 times the Earth’s, while one could squeeze over a thousand Earth’s into its volume.  Jupiter has something like 67 satellites,  but only for are visible in small to medium telescopes.  Tonight they will be strung out all on one side of Jupiter, tomorrow night two will be on the other side of the planet, and another will be playing peek-a-boo in front of Jupiter.

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

Addendum

 

Jupiter on two nights

Jupiter and its moons in a telescope at 10 p.m. both April 10th & 11th, 2017. Created using Cartes du Ciel (Sky Charts).

Event Date & Time EDT Date & Time UT
Io Occultation Start 10 April 2017 10:31 p.m. 11 April 2017 2:31
Io Eclipse ends 11 April 2017 12:28 a.m. 11 April 2017 4:46
Ganymede Occultation start 11 April 2017 4:28 a.m. 11 April 2017 8:28
Ganymede Eclipse end Not visible 11 April 2017 11:02
Europa Occultation start Not visible 11 April 2017 18:44
Europa Eclipse ends Not visible 11 April 2017 21:19
Io Transit starts Not visible 11 April 2017 23:48
Io Shadow ingress Not visible 11 April 2017 23:54
Io Transit ends 11 April 2017 8:58 p.m. 12 April 2017 1:58
Io Shadow egress 11 April 2017 10:05 p.m. 12 April 2017 2:05

Where times EDT show as not visible, Jupiter is below the horizon.  Date and time UT are for observers in other locations.  UT is Universal Time, or Greenwich Mean Time.

Occultation = moon passes behind Jupiter
Eclipse = moon in Jupiter’s shadow
Transit = moon passes in front of Jupiter
Shadow = moon’s shadow is cast on the face of Jupiter

 

04/07/2017 – Ephemeris – Learn about light pollution tonight

April 7, 2017 Comments off

Ephemeris for Friday, April 7th.  The Sun will rise at 7:12.  It’ll be up for 13 hours and 5 minutes, setting at 8:17.  The Moon, half way from first quarter to full, will set at 6:11 tomorrow morning.

This evening at 8 p.m. the Grand Traverse Astronomical Society will hold its monthly meeting at Northwestern Michigan College’s Rogers Observatory featuring a talk by observatory director Jerry Dobek about light pollution and what can be done about it to help preserve our dark night skies.  I expect he will give us a progress report on the effort to make the Sleeping Bear Dunes National Lakeshore a Dark Sky Park.  Special emphasis will be LEDs, now that they are proliferating, the good the bad and the ugly.  At 9 p.m. there will be a star party with the gibbous Moon and Jupiter at opposition from the Sun and about at its closest to us at 414 million miles (666 million km) away.

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

Addendum

Jupiter and Moons

Jupiter and its moons as it should appear tonight at 10 p.m. April 7, 2017 (2 hr UT April 8). Note also the Great Red Spot, which may be paler than it appears here. I double checked the transit time of the red spot across Jupiter’s central meridian, which is predicted for 10:42 p.m. (2:42 UT, April 8) across Jupiter’s central meridian. The position of the Red Spot is correct for 10 p.m.

Times are from Project Pluto:  https://www.projectpluto.com/jeve_grs.htm