Archive

Archive for the ‘Astronomical History’ Category

09/13/2021 – Ephemeris – The Greeks knew the size and shape of the Earth and estimated the distance to the Moon a long time ago

September 13, 2021 Comments off

This is Bob Moler with Ephemeris for Monday, September 13th. Today the Sun will be up for 12 hours and 37 minutes, setting at 7:56, and it will rise tomorrow at 7:20. The Moon, at first quarter today, will set at 11:57 this evening.

The Ancient Greeks used lunar eclipses to determine that Earth is a sphere, and worked on determining the distance to the Moon. From ancient times, the Greeks knew that an eclipse of the Moon was caused by the Earth’s shadow falling on the Moon. Since the Earth’s shadow was always circular, no matter where the Moon was in the sky during an eclipse, the Earth must be a sphere since that’s the only three-dimensional body that always casts a circular shadow. They also used the size of the Earth’s shadow to estimate the distance to the Moon. The lunar distance, on average, is 60.8 times the Earth’s radius away. The first estimates were about one third of that. Hipparchus in the 2nd century BC got much closer. It got even better from there.

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

Partial Lunar Eclipse showing arc of the Earth's shadow

Partial Lunar Eclipse showing circular arc of the Earth’s shadow. Taken 04:15 UT August 17, 1970. Credit: the author.

The size of the Earth was unknown until Eratosthenes did in 240 BC. He came up with the circumference of the Earth to a fairly high degree. The Circumference is equal to the radius of a sphere or circle by 2πr.

09/07/2021 – Ephemeris – The constellation of Cepheus the king

September 7, 2021 Comments off

This is Bob Moler with Ephemeris for Tuesday, September 7th. Today the Sun will be up for 12 hours and 55 minutes, setting at 8:07, and it will rise tomorrow at 7:13. The Moon, 1 day past new, will set at 8:53 this evening.

There’s a faint constellation in the northeast above the W shaped constellation of Cassiopeia. It’s a nearly upside down church steeple of a constellation called Cepheus the king, and husband of queen Cassiopeia. Cepheus’ claim to modern astronomical fame is that one of its stars, Delta (δ) Cephei, is the archetype for the important Cepheid variable stars. Delta is the bottom most of a trio of stars at the right corner of the constellation. In the early 20th century, Henrietta Leavitt discovered that Cepheids in the nearby galaxy the Large Magellanic Cloud varied in brightness with a period that was related to their average brightness. This meant that Cepheids could be used as standard candles to measure the great distances to other galaxies.

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

Cassiopeia and Cepheus finder animation

Cassiopeia and Cepheus finder animation looking in the northeast at 9-10 pm or about an hour after sunset. Created using Stellarium and GIMP.

Delta Cephei finder for September at 9-10 pm, looking northeast. Created using Cartes du Ciel (Sky Chart).

Delta_Cephei_lightcurve

Light Curve of Delta Cephei. The pulsation period is 5.367 days. Note the Magnitude vertical axis, the lower the magnitude the brighter the star is. Blame that on the Greek astronomer Hipparchus, 2nd century BC. It’s like golf scores, the lower the score, the better the golfer. Credit: Thomas K Vbg – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=13887639.

07/23/2021 – Ephemeris – The first exoplanet* found

July 23, 2021 Comments off

This is Bob Moler with Ephemeris for Friday, July 23rd. Today the Sun will be up for 14 hours and 58 minutes, setting at 9:18, and it will rise tomorrow at 6:20. The Moon, at full today, will rise at 9:35 this evening.

In 1995 the first planet was found that orbits another star. It was 51 Pegasi b. That’s the star labeled number 51 in the constellation Pegasus, the flying horse. It was found because it tugged on its star as it orbited it. The planet was detected by the Doppler method, the same method that the police can tell if you’re speeding. A planet doesn’t orbit the center of the star, but the center of their combined mass. It turned out That 51 Pegasi b is a very large planet, half the mass of Jupiter, orbiting its star every 4 ½ days. Its discovery threw everything we thought we knew about planetary system evolution into a cocked hat. Planets just don’t stay nicely in their orbits like we thought. They move in and out! As this planet moved in toward its star, it would have ejected any of the inner planets out of the system.

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.

* A planet was found several years before, orbiting a pulsar, which is a neutron star. Apparently, planets orbiting dead stars don’t count.

Addendum

Pegasi 51b artist's visualization

An artist’s depiction of what exoplanet Pegasus 51b and its star might look like. Credit: ESO (European Southern Observatory) / M. Kornmesser.

06/14/2021 – Ephemeris – Images of the Moon: Then and now

June 14, 2021 Comments off

This is Bob Moler with Ephemeris for Flag Day, Monday, June 14th. Today the Sun will be up for 15 hours and 33 minutes, setting at 9:29, and it will rise tomorrow at 5:56. The Moon, 3 days before first quarter, will set at 1 am.

The waxing crescent Moon shows its cratered highlands and flat lava plains that early telescopic astronomers fancied as water filled and called them seas, so the nomenclature stuck, and we call them seas to this day. When I grew up in the 1950s I was captivated by the moonscapes painted by Chesley Bonestell with their sharp rugged mountain peaks. The actual lunar landscape turned out to be softer, more rounded. The Earth’s surface features are younger than the Moon’s due to plate tectonics, something few geologists in the 1950s believed in. The Moon’s features are generally billions of years old and erosion by meteoroid impacts and ejecta have covered the landscape with a fine dust, over the eons, that smooths out its features.

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

Addendum

Chesley Bonestell moonscape

A Chesley Bonestell moonscape. Note the sharp detail including an arch at center right and an overhang at right. Such was the state of our ignorance before spacecraft like Ranger, Surveyor, Lunar Orbiter and Apollo reached the Moon. Click on the image to enlarge. Credit Chesley Bonestell.

Moonscape photographed by JAXA (Japan) spacecraft Kaguya

Moonscape photographed by JAXA (Japan) spacecraft Kaguya with about the same orientation as the Bonestell painting, except from orbit. Click on the image to enlarge. Credit JAXA/NHK.

Image from Apollo 17 showing lunar erosion

Image from Apollo 17 showing lunar erosion. Even the rocks in the foreground show that they were eroded. The image also shows astronaut Dr. Harrison “Jack” Schmidt. Click on the image to enlarge. Credit NASA.

04/26/2021 – Ephemeris – There’s a full supermoon tonight

April 26, 2021 Comments off

This is Ephemeris for Monday, April 26th. Today the Sun will be up for 14 hours and 2 minutes, setting at 8:41, and it will rise tomorrow at 6:38. The Moon, at full today, will rise at 8:19 this evening.

The full moon tonight is the full Pink Moon, and a supermoon. As down as I am about full moons due to the fact that they light up the sky and flood out the dimmer objects in the sky, I once in a while stop and view it. The time of the full moon is 11:31 tonight, so when it rises tonight we will be looking at the moon from very nearly the direction of the Sun, so there will be few shadows to be had. The crater Tycho is near the bottom or south end of the moon and has long rays of tiny ejecta craters. The full moon is the best time to see these rays, which are easily visible in binoculars, through which Tycho itself looks like a bright dot. In telescopes Tycho looks like a small bright crater with a dark ring around it. The full moon is super bright. It’s daytime over there.

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

Addendum

High contrast full Moow
The full Moon 7 hours before it was officially full. The contrast was greatly enhanced to bring out Tycho’s ray system. The crater Tycho is at the south part of the Moon and appears bright with a dark ring around it. Credit Bob Moler.
Tycho and Kepler
Tycho and Kepler. Artist for Tycho: Eduard Ender (1822-1883). Artist for Kepler, unknown. Source: Wikipedia

Tycho Brahe and Johannes Kepler are inexorably linked in astronomical history. Tycho was famously stingy with the results of his observations. It was only after his death that Kepler was able to have access to them. Mars was the planet that was hardest to model in both the Ptolemaic geocentric and Copernican heliocentric universes, since both assumed the planetary orbits were circular. So both resorted to epicycles in an attempt to tweak their models in an attempt to fit with observational reality.

Both Tycho and Kepler have craters named for them on the Moon. Tycho gets a splashy crater on the southern part of the Moon. Kepler, however, gets a small crater on the plains of Oceanus Procellarum west of the crater Copernicus on the left side of the Moon, as we see it

03/08/2021 – Ephemeris – 45 years ago today I saw and photographed Comet West!

March 8, 2021 Comments off

This is Bob Moler with Ephemeris for International Women’s Day, Monday, March 8th. Today the Sun will be up for 11 hours and 32 minutes, setting at 6:40, and it will rise tomorrow at 7:05. The Moon, 3 days past last quarter, will rise at 5:34 tomorrow morning.

On this day 45 years ago, in 1976, during the first year of these Ephemeris programs I was able to report on, observe and photograph the brightest comet I had seen up till that time: Comet West. It was not supposed to be a bright comet, but as it rounded the Sun, it began to brighten spectacularly. Later I found out that it’s nucleus broke into several fragments, liberating a great quantity of gas and dust. It turned out to be a very dusty comet which ended up in a broad and bright tail. It was going to be visible before sunrise, and this was the first morning in a while it was clear. Even before the head of the comet rose, the tail could be seen rising in the east. I was able to get several photographs of this wonderful comet!

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

Addendum

Comet West at 6 am, March 8, 1976

Comet West, C/1975 V1, as photographed by me at about 6 am, March 8, 1976. The wide, curved dust tail is most prominent with the narrow blue ion tail pointed more directly at the rising Sun. The small summer constellation of Delphinus the dolphin is to the upper right. The diamond shape of stars at the front of the dolphin’s body is an asterism called Job’s Coffin.

In the image above is tilted about 45 degrees to the horizon in the lower left due to the fact that it was on an equatorial mount, where up and down is north and south in the sky, horizontally is east and west. It’s cocked 45 degrees to the horizon because we are at 45 degrees latitude. Actually the angle is 90 – your latitude which around here is 90 – 45 = 45.

I got up early in the morning of March 8th 1976. I had my telescope mount outside because it takes awhile to set it up to true north and everything. The telescope and camera that mounts on it were taken inside. I just left it there covered with a tarp and wasn’t observing too much that winter. When I got up in wee hours of the morning of the eighth I found out that my telescope mount was buried in the middle of a snowdrift, so I had to dig it out. As I was digging it out I looked to the east and saw the tail of the comet rising before the head did. I then redoubled my efforts and got everything set up so I could take photographs of the comet.

I had built a small telescope a few years before for a solar eclipse as a kind of contingency camera in case my automatic cameras I had built didn’t work. It was a 108 mm f/6 reflecting telescope that I attached a camera back to and took some minute or two long exposures that way. I then realized that the sky was getting brighter, so I quickly switched, and took a couple of wide angle pictures with the 50 mm lens with tracking. That’s one of them above that shows the lovely comet with the long tail.

Comet West 108mm f/6

Comet West taken through the 108 mm f/6 telescope around 5:30 am, March 8, 1976 by a much younger me.

12/24/2020 – Ephemeris – Was the Star of Bethlehem a triple conjunction of Jupiter and Saturn in 7 BC?

December 24, 2020 Comments off

This is Bob Moler with Ephemeris for Christmas Eve, Thursday, December 24th. Today the Sun will be up for 8 hours and 48 minutes, setting at 5:07, and it will rise tomorrow at 8:18. The Moon, 3 days past first quarter, will set at 3:50 tomorrow morning.

For many years the most popular theory for the origin of the Star of Bethlehem was a triple conjunction of Jupiter and Saturn in 7 BC. This is because, due to Earth’s motion, other planets from our view point seem to reverse course when we pass them or are being passed in the circular racetrack of the solar system. When Jupiter and Saturn approach each other just before they go retrograde or reverse course they have a chance to pass each other, backup and pass again, then going forward to pass a third time. Jupiter and Saturn did that last in 1981, so it’s a reasonably rare occurrence, especially when it happens in front of the constellation Pisces which was supposedly related to the Jews.

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

Addendum

Jupiter-Saturn Triple Conjunction

Jupiter and Saturn pass each other three times from May to December in 7 BC against the constellation of Pisces. Reload the page to replay the animation. Created using Cartes du Ciel (Sky Charts) and GIMP.

Retrograde motion explained

Retrograde motion illustrated using Mars in 2018. Created using my LookingUp program.

 

 

08/21/2020 – Ephemeris – Great moments in astronomy: The Great Debate in 1920

August 21, 2020 Comments off

This is Bob Moler with Ephemeris for Friday, August 21st. Today the Sun will be up for 13 hours and 44 minutes, setting at 8:37, and it will rise tomorrow at 6:54. The Moon, 3 days past new, will set at 10:26 this evening.

One hundred years ago there were two lectures given to the National Academy of Science by Drs. Harlow Shapley and Heber Curtis. This became know as the Great Debate. Shapley believed that the Milky Way was the entire universe, and evidenced by the distribution of globular star clusters in the sky that the Sun was near the periphery of it, and that spiral nebulae were part of the Milky Way. Curtis on the other hand thought that the Sun was near the center of the Milky Way, however that the spiral nebulae were other island universes, or milky ways of their own. Over the next decade each was proved right in part and wrong in part. We are not near the center of the Milky Way, but those spiral nebulae were indeed other milky ways or galaxies.

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

Addendum

M51 drawing

A drawing of the Whirlpool Galaxy, M51 (NGC 5194 & 5195) by Lord Rosse with his 72 inch telescope in the mid 19th century. This is the only “spiral nebula” I have actually seen as a spiral visually in a telescope, though not as well as he saw it. Public Domain.

M51 photo

With the advent of photography many spiral nebulae were discovered. The Whirlpool Galaxy, M51. Credit Scott Anttila.

Press Release for the Great Debate

This is a copy of the Press release issued for the two presentations of Harlow Shapley and Heber Curtis at the annual meeting of the National Academy of Sciences April 26, 1920 that have come to be known as the “Great Debate”. Credit NAS.

For more on the Great Debate follow this link.

Astronomy has advanced a long way in the last 100 years.  And what’s crazy is that I actually met Dr. Harlow Shapley at the opening of the Planetarium of the Grand Rapids Public Museum around 1960. I was in my first year at Grand Rapids Junior College at the time. I had been a member of the of the local astronomy club for several years by then. Two friends and I became planetarium rats and have wormed our way into volunteering to working with it before a formal structure was set up to operate it.

 

03/02/2020 – Ephemeris – Greek use of the first quarter Moon

March 2, 2020 Comments off

Ephemeris for Monday, March 2nd. Today the Sun will be up for 11 hours and 14 minutes, setting at 6:32, and it will rise tomorrow at 7:15. The Moon, at first quarter today, will set at 2:39 tomorrow morning.

The Moon is at first quarter at 2:57 this afternoon. The ancient Greek philosopher/astronomer Aristarchus* tried to determine the distance to the Sun by observing the Moon at exactly first quarter and measuring the angle between it and the Sun. If we see the Moon at exactly first quarter when the sunrise line called the terminator cuts the Moon exactly in half then the angle at the Moon between the Sun and the Earth is a right or 90 degree angle. If we, on the Earth at that same instant were able to measure the angular distance between the Moon and the Sun. we could theoretically calculate the distance to the Sun. He was correct about the Moon’s distance, but calculated the Sun was at only about 10% of its actual distance.

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

* In the actual broadcast program I erroneously credited the later Greek astronomer Hipparchus.

Addendum

Quarter Mon method of determining the Sun's distance

Quarter Moon method of determining the Sun’s distance by Aristarchus. Credit: andonee

12/27/2019 – Ephemeris – A Decade of astronomical and space firsts

December 27, 2019 Comments off

Ephemeris for Friday, December 27th. Today the Sun will be up for 8 hours and 49 minutes, setting at 5:08, and it will rise tomorrow at 8:19. The Moon, 1 day past new, will set at 6:38 this evening.

The 2010s were quite a decade in astronomy and space. 24 years ago the first exoplanet, that is planet orbiting another star, was discovered: 51 Pegasi b. As of December 8th the number of confirmed exoplanets stands at 4,104. At mid decade we got a close look at the dwarf planet Pluto and its moons, and early this year at the distant object temporarily called Ultima Thule. Early this year the Event Horizon Telescope consortium released the image of a black hole over 50 million light years away. Also the LIGO and Virgo gravitational wave observatories detected two neutron stars colliding which set off a frenzy of activity by astronomers who viewed the aftermath from gamma rays to microwaves.

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

Addendum

Kepler Spacecraft. Credit NASA.

Kepler Spacecraft studied a single patch of sky for several years and has discovered the bulk of the exoplanets. Credit NASA.

Pluto

Enhanced color portrait of Pluto by the New Horizons spacecraft. Credit: NASA/JHUAPL/SwRI

First closeup of Ultima Thule

486958 Arrokoth original dubbed Ultima Thule by the New Horizons team on approach combining low resolution image with the high resolution monochromatic image shows the body in almost true color. Credit NASA/JHAPL/SWRi

Black hole in M87

The first image of the black hole in M87. Credit Event Horizon Telescope.

Neutron Star Collision GW 170817 timeline

Neutron Star Collision GW 170817 timeline. Horizontal axis in seconds (exponential). Click on chart to enlarge. From the High Energy Stereoscopic System website.