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06/05/2017 – Ephemeris – Why Venus is low in the eastern sky

June 5, 2017 1 comment

Ephemeris for Monday, June 5th. Today the Sun will be up for 15 hours and 25 minutes, setting at 9:23, and it will rise tomorrow at 5:58. The Moon, half way from first quarter to full, will set at 4:40 tomorrow morning.

Saturday the planet Venus was at greatest western elongation from the Sun, That is it is the farthest west it will appear from the Sun. It’s still not very high in our sky. However for those in the southern hemisphere Venus will appear very high in the east. There is a rule about this: Planets which are east of the Sun, like Mars is now are easiest seen on spring evenings. Planets which are west of the Sun, like Venus is now are easiest seen on autumn mornings. Since the southern hemisphere has the opposite seasons as the north, this is their autumn, and morning planets are easiest seen. This is especially true for Mercury, which is even closer to the Sun than Venus. Generally it’s only seen when it appears on spring evenings and autumn mornings.

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

Addendum

Low morning planets

Venus’ low morning appearance is due to the fact that on spring mornings the ecliptic (red line path of the Sun in the sky and nearly that of the planets) lies low to the horizon. Created using Stellarium.

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:

02/23/2017 – Ephemeris – The Evening Star’s days are numbered

February 23, 2017 Comments off

Ephemeris for Thursday, February 23rd.  The Sun will rise at 7:29.  It’ll be up for 10 hours and 53 minutes, setting at 6:22.  The Moon, 3 days before new, will rise at 6:15 tomorrow morning.

The brilliant Evening Star, the planet Venus entered our evening sky last June.  It seemed it took forever to move far enough away from the Sun to be easily seen after sunset.  The summer and autumn time is a hard time to spot a planet near the Sun after sunset, because they appear more to the left of the Sun than above it.  Now, in late winter Venus is high in the west after sunset.  But that won’t last.  It’s nearly 9 month’s reign as the Evening Star are about up. In 27 days it will be gone, out of the evening sky as it rapidly passes between the Earth and the Sun.  Venus will be only 26 million miles (42 million km) from the Earth.  Back is 2012 it crossed the face of the sun at conjunction, On March 25th it will be 16 Sun diameters north of our star.

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

Addendum

Venus' orbit in the evening sky.

Venus and Mars showing Venus’ orbit showing how far north it will get above the ecliptic, the yellow line, which is the path of the Sun. Created using Stellarium.

 

Categories: Ephemeris Program, Venus Tags:

01/12/17 – Ephemeris – Venus is at greatest eastern elongation today

January 12, 2017 2 comments

Ephemeris for Thursday, January 12th.  The Sun will rise at 8:17.  It’ll be up for 9 hours and 7 minutes, setting at 5:25.  The Moon, at full today, will rise at 6:04 this evening.

Today, around 8 a.m. the planet Venus will reach its greatest eastern elongation from the Sun. What that means in simple terms is that Venus will appear as far east of the Sun that it can get.  The angle between it and the Sun will be 47.1 degrees.  Venus, like Mercury orbits the Sun inside the Earth’s orbit, so is always seen close to the Sun.  In telescopes Venus will look like a tiny half illuminated orb, like a first quarter Moon.  That’s for the same reason.  The Sun is illuminating half of the side we can see.  Venus is  moving directly toward us now, at a distance of 63 million miles (102 million km).    As Venus approaches us, it will grow in size in telescopes, becoming larger in appearance than Jupiter the largest planet.  It will leave the evening sky, passing between the Earth and the Sun, only 26 million miles away on March 25th.

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

Addendum

Venus in our sky

Venus at 5:30 p.m. January 12, 2017 also displaying its orbit. Created using Stellarium.

Telescopic Venus

Venus in a telescope showing it half illuminated at greatest eastern elongation. Created using Stellarium.

There’s an odd phase effect called the “Venus Dichotomy” where at the instant of greatest elongation that Venus’ phase is not exactly half illuminated.  Half phase may differ by several hours.  The actual time of greatest eastern elongation according to NASA’s SKYCAL Calendar at https://eclipse.gsfc.nasa.gov/SKYCAL/SKYCAL.html is January 12 at 7:59 a.m. EST or 12:59 UT.

Inner solar system

Inner solar system showing the relationship of Venus and the Earth. At greatest elongation The angle between Venus-Sun line and Venus-Earth line is 90 degrees. which is why Venus shows as half illuminated. Created using the application NASA’s Eyes.

Note that the chart above also shows NASA’s inner solar system missions.  To download the app, created by the Jet Propulsion Laboratory (JPL), go to https://eyes.nasa.gov/.  Use it to follow the progress of NASA solar system missions.

10/25/2016 – Ephemeris – Venus is becoming more visible after sunset

October 25, 2016 Comments off

Ephemeris for Tuesday, October 25th.  The Sun will rise at 8:12.  It’ll be up for 10 hours and 28 minutes, setting at 6:40.  The Moon, 3 days past last quarter, will rise at 4:02 tomorrow morning.

Venus is becoming quite visible low in the southwest after sunset as the Evening Star.  As such it is a beautiful addition to our autumn and winter skies.  As seen in telescopes it is a tiny gibbous disc, 79% illuminated by the sun.  It’s beauty is only cloud-top deep.  For a planet that appears to be nearly Earth’s twin at 95% the Earth’s size, it can be said to be Earth’s evil twin.  Its bright white cloud-tops aren’t made of water but sulfuric acid, and it gets worse the farther down you go.  The farther one goes down in Venus’ carbon dioxide atmosphere, the hotter and higher the atmospheric pressure gets.  At the surface the temperature is over 850 degrees Fahrenheit (460º C) and the atmospheric pressure is nearly 100 times that of Earth.  Venus’ surface temperature is actually hotter than Mercury the closest planet to the Sun, a hellish runaway greenhouse effect.

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

Addendum

 

Evening planets

Venus and the other evening planets at 7:30 p.m. Created using Stellarium.

Telescopic Venus

Venus as it might appear in a telescope minus all the atmospheric effects of being close to the horizon. It is 13.6 ‘ in diameter. Created using Stellarium.

06/06/2016 – Ephemeris – Venus passes behind the Sun today

June 6, 2016 Comments off

Ephemeris for Monday, June 6th.  Today the Sun will be up for 15 hours and 27 minutes, setting at 9:25, and it will rise tomorrow at 5:57.  The Moon, 2 days past new, will set at 10:52 this evening.

Today the planet Venus will be in superior conjunction with the Sun, and indeed will pass directly behind the Sun.  That event will be completely unobservable due to the Sun’s brilliance.  Fours years ago we observed the transit of Venus across the Sun.  June 6, 2012.  It got me thinking.  Transits of Venus occur in pairs 8 years apart followed by a very long interval of over 100 years.  It turns out the Venus orbits the Sun 13 times in approximately the same time that the earth orbits the Sun 8 times.  In 4 years Venus goes around the Sun 6 ½ times and put’s Venus behind the Sun 4 years after 2012.  Today to be precise.  In another 4 years we’ll have Venus between the Earth and the Sun again, except Venus will be a bit too far north to transit the Sun.

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

Addendum

Venus approaches the Sun

SOlar and Heliospheric Observatory (SOHO) stationed at the Earth-Sun Lagrangian point 1 (L1) a million miles sunward of the Earth. Sent back this animated GIF of Venus approaching the Sun in the last few days. In the LASCO C2 coronagraph the large disk at the center blocks the brightest part of the Sun’s image. The white circle represents the Sun’s disk size. Credit ESA/NASA.

05/13/2016 – Ephemeris – GTAS Astronomy Day tomorrow

May 13, 2016 Comments off

Ephemeris for Friday, May 13th.  Today the Sun will be up for 14 hours and 46 minutes, setting at 9:02.   The Moon, at first quarter today, will set at 2:59 tomorrow morning.  Tomorrow the Sun will rise at 6:15.

The Grand Traverse Astronomical Society will host a public viewing night for Astronomy Day tomorrow night, that’s Saturday the 14th, starting at 9 p.m.  It will be at Northwestern Michigan College’s Joseph Rogers Observatory.  If its clear the slightly gibbous moon will be featured along with Jupiter, Mars and the ringed planet Saturn and other wonders of the spring sky.  The observatory is located south of Traverse City, on Birmley Road between Garfield and Keystone roads.  For the society these, twice monthly star parties at the observatory and sidewalk astronomy outings by members, to the Sleeping Bear Dunes National Lakeshore and other locations are what they do.

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

Other thoughts

I was checking out the Solar and Heliospheric Observatory (SOHO) LASCO C3 animation and Venus is making an entrance from the right as it heads for superior conjunction on June 6.  June 6?  Hmm. Wasn’t that last transit or Venus on June 5th 2012.  We and Venus should be near the line of nodes again, where the planes of our respective orbits cross.  I cranked up Stellarium, and sure enough the Sun will occult Venus that day… Not that we could see it.