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02/19/2019 – Ephemeris – The Moon ain’t just super near the horizon

February 19, 2019 Leave a comment

Ephemeris for Tuesday, February 19th. Today the Sun will be up for 10 hours and 39 minutes, setting at 6:16, and it will rise tomorrow at 7:35. The Moon, at full today, will rise at 6:28 this evening.

Tonight we will have a super full Moon. It will be the closest full moon of the year, not that you could really tell. The full moon, or waning moon looks large near the horizon when it’s rising. The same is true of waxing moons setting. The same is true of sunrises and sunsets. However if you look closely at the rising or setting Moon or Sun right at the horizon you will notice that it appears a bit squashed. This is due to atmospheric refraction or bending of the light which makes the them appear higher in the sky than they actually are. It is most pronounced near the horizon. In fact by the time the Sun appears to touch the horizon, it is already completely below the horizon, and would appear be if we didn’t have an atmosphere.

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

Addendum

Suashed Moon at moonrise

The Moon just after moonrise 1 day past full. The Moon appears squashed vertically by about 10% compared to circumscribed circle. Credit Eileen Carlisle.

Atmospheric Refraction

How the atmosphere bends the light of the Sun or Moon rising or setting to appear higher than it actually is. Credit Francisco Javier Blanco González, 2017

 

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02/18/2019 – Ephemeris – Super Moon, super math

February 18, 2019 Leave a comment

Ephemeris for President’s Day, Monday, February 18th. Today the Sun will be up for 10 hours and 36 minutes, setting at 6:15, and it will rise tomorrow at 7:37. The Moon, 1 day before full, will set at 7:52 tomorrow morning.

Ready for some math this morning? This will be easy, because you will only have to think about it. Let’s say the Earth’s radius is 4,000 miles.  That is pretty close to its actual value. OK, it is 3961 miles (6,378 km) at the equator. The Earth is nearly spherical. At 4 this morning the Moon passed perigee, its closest point to the Earth, making tomorrow’s full moon a super-moon. Let’s say it will be at today’s distance of 221,600 miles (356,800 km). That’s center to center. At moon rise or moon set the Moon is near that center to center distance, but if it moves overhead it’s 4,000 miles closer because we are on the Earth facing the Moon. Even though the Moon looks smaller than when it appears on the horizon. It’s an optical illusion that the Moon appears larger when it is rising. Super moon or not.

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

Addendum

The difference in the Moon's distance at rising (or setting) versus when it is overhead

This illustrates the difference in the Moon’s distance at rising (or setting) versus when it is overhead. BTW today’s perigee puts the Moon at only 56 Earth radii from the Earth. The illustration is mine.

01/15/2019 – Ephemeris – Welcome 8:19 a.m. listeners

January 15, 2019 Comments off

Ephemeris for Tuesday, January 15th. Today the Sun will be up for 9 hours and 11 minutes, setting at 5:28, and it will rise tomorrow at 8:16. The Moon, 1 day past first quarter, will set at 3:11 tomorrow morning.

Welcome to the 8:19 a.m. listeners to this program. Due to the two-hour span from the 6:19 and 8:19 airings it was thought to always give you event times in advance, which is why I’m giving tomorrow’s sunrise times. Don’t worry tomorrow’s sunrise time will never be more than 2 minutes before or after today’s. Right now, sunrise times are retreating by a half-minute a day. It’s faster in spring and fall. For more information see my blog: bobmoler.wordpress.com. Transcripts of the program are there with illustrations and additional information. And today a way to create your own sunrise and sunset calendar.

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

Addendum

The times of rising and setting of celestial objects is accurate for only one spot on the Earth.  In the case of the times I give, it’s for my house.  There’s a good reason for it.  I live approximately half way between Interlochen and Traverse City.  In the early days I interpolated from astronomical tables in the Royal Astronomical Society of Canada’s Observers Handbook.  I preferred it to the Naval Observatory’s Astronomical Almanac, which was more expensive.  Anyway I had a relatively flat horizon everywhere but north, so if I climbed on the roof I could check out and verify the rising and setting times.   Note that the times assume a flat sea horizon.

About accurate times:  At my latitude celestial objects rise and set one minute later for each 12 1/3 miles (19.85 km) you are west of me, or a good landmark would be Traverse City West Senior High School.  For every 12 1/3 miles east of there rising and setting events would be earlier by a minute.  The correction for latitude or north and south isn’t that simple. See the illustration below:

Calendar excerpts

These are snippets of calendars for three locations that are in a straight line from south-southwest to north-northeast in the IPR listening area. A line drawn perpendicular to it to the west-northwest is to the Sun’s setting point. Thus the setting times for all three locations are the same. However their rising times are the most divergent, as are the daylight hours.

On my Ephemeris website, not to be confused with the blog that you are now reading, I have rise and set calendars for:  Cadillac, Interlochen/Traverse City (Source for times on the Ephemeris program), Ludington, Mackinaw City, Petoskey, Eagle Harbor – Keweenaw Peninsula, Houghton Lake, and Earth’s Equator at the Prime Meridian.  Go Here:  http://ephemeris.bjmoler.org/calendar.htm.

If you’d like these times for a different location go to the Complete Sun and Moon Data for One Day, or Sun or Moon Rise/Set Table for One Year from the United States Naval Observatory (USNO). It calculates sunrise, sunset, moonrise, moonset, and twilight  for locations in the US and other locations world-wide.  Note that these do not follow the changes to and from Daylight Saving Time.

 

12/17/2017 – Ephemeris – What is a Lagrange Point?

December 17, 2018 Comments off

Ephemeris for Monday, December 17th. The Sun will rise at 8:14. It’ll be up for 8 hours and 48 minutes, setting at 5:03. The Moon, 2 days past first quarter, will set at 3:15 tomorrow morning. |

Newton’s law of gravitation allows for some gravitational equilibrium points around two bodies that orbit each other. Discovered in th 18th century by Leonhard Euler and Joseph-Louis Lagrange these are known as Lagrange or L points. There are five. L1 is between the two bodies. The L1 point between the Earth and Sun is a million miles sun-ward of the Earth, where we station solar observation satellites. L2 is a million miles in the other direction, where there are astronomy satellites looking anywhere but the Sun. The James Webb telescope will join them there. L3 is point on the other side of the Sun, for which no use has yet been found. L4 and L5 are 60 degrees ahead of and behind the Earth’s position in its orbit. These are quite stable. Jupiter has thousands of asteroids in its L4 and L5 locations called Trojan asteroids.

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

Addendum

 

Lagrange points

The 5 Lagrange points about two bodies M1 and M2 orbiting each other. Credit Georgia State University.

10/12/2018 – Ephemeris – The Moon’s phases

October 12, 2018 Comments off

Ephemeris for Friday, October 12th. The Sun will rise at 7:54. It’ll be up for 11 hours and 8 minutes, setting at 7:03. The Moon, halfway from new to first quarter, will set at 9:31 this evening.

The Moon’s changing appearance over the month may seem to be mysterious at first glance. Maybe because one may think that the objects in the sky are somehow different from the familiar objects we see around us on the Earth. In ancient times, especially the Greeks thought that everything in the heavens halfway perfect and spotless. They explained the definite markings we see as the man-in-the-moon as a reflection of the Earth by a spotless Moon. The Moon’s phases are simply light and shadow on a ball in the sunlight. Sometimes, when the Moon appears in the daytime, take a small ball, like a golf ball and hold it up to the Moon, while the ball is also in sunlight, and the small ball will exhibit the same phase as the Moon.

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

Addendum

Moon phases
One of the best explanation diagrams of the Moon’s phases as it relates to the Earth and Sun. Click on the image to enlarge. Credit Wikimedia user Orion 8.
Moon ball
Demonstration of the Moon’s crescent phase with the Styrofoam moon ball we use for Project Astro held up to a light off of the frame to the right. The night side of the ball is illuminated a bit by the translucency of the ball, and the reflection off of my hand. Note the roughness of the ball is visible only at the terminator.
Moonball
Demonstration of the Moon’s gibbous phase with the Styrofoam moon ball we use for Project Astro held up to a light off of the frame to the right. The night side of the ball is illuminated a bit by the translucency of the ball, and the reflection off of my hand. Note the roughness of the ball is visible only at the terminator.

09/27/2018 – Ephemeris – Twilight zone

September 27, 2018 Comments off

Ephemeris for Thursday, September 27th. The Sun will rise at 7:35. It’ll be up for 11 hours and 54 minutes, setting at 7:30. The Moon, 3 days past full, will rise at 9:12 this evening.

It will get dark tonight with the end of astronomical twilight at 9:11 p.m., and a minute later the bright Moon will rise spoiling the dark sky. Speaking of astronomical twilight there are three twilight periods: Civil, Nautical and Astronomical. In the evening civil twilight lasts from sunset to when the Sun drops to 6 degrees below the horizon. The scene around is still quite bright, but car headlights still need to be on. Nautical twilight lasts until the Sun is 12 degrees below the horizon. Bright stars and the horizon are visible for sextant use. After that is astronomical twilight until the Sun is 18 degrees below the horizon, when the stars become more and more numerous. After that it’s officially dark, Moon willing.

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

Addendum

Twilight phases by timeanddate.com.
Twilight phases

More information about twilight, dusk and dawn can be found here:  https://www.timeanddate.com/astronomy/different-types-twilight.html.

08/16/2018 -Ephemeris – The Moon’s phase, a closer look

August 16, 2018 Comments off

Ephemeris for Thursday, August 16th. The Sun rises at 6:46. It’ll be up for 14 hours exactly, setting at 8:46. The Moon, 2 days before first quarter, will set at 11:59 this evening.

With the Moon at a fat crescent tonight, it’s a good time to turn binoculars or a small telescope toward it. The demarcation between the bright part and the dark part is called the terminator. In the case before full moon, it is the sunrise line. After that the sunset line. The Moon’s entire day lasts about 29 ½ earthly days. I am sometimes asked “What’s blocking the light from the unlit side of the Moon?” It’s the Moon itself. It’s the night side of the Moon, just as when we are in night. The Earth itself is blocking the Sun’s light from us. The Moon, like the Earth and all the other planets are spheres lit on one side by the Sun. It’s near the terminator of the Moon where the most detail is revealed by the long shadows cast by the Moon’s features.

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

Addendum

Crescent Moon tonight

The crescent moon as it should appear tonight. Created using Stellarium.  Stellarium always shows details on the night side of the Moon.  The crescent phase of the Moon is now too fat to really see earthshine on it’s night side.

Moon ball

Demonstration of the Moon’s crescent phase with the Styrofoam moon ball we use for Project Astro held up to a light off frame to the right.  The night side of the ball is illuminated a bit by the translucency of the ball, and the reflection off my hand.  Note the roughness of the ball is visible only at the terminator.