Category Archives: Astronomy History

John Glenn, 1921-2016


John Glenn. Wikipedia photo.

Mercury Astronaut John Glenn died on December 8, 2016, at the age of 95.  He was the first American astronaut to orbit the Earth aboard the Mercury 6 spacecraft, Friendship 7, on February 20, 1962.

The American orbital mission proved an opportunity for shortwave listeners to eavesdrop of the communications with the space mission.  This news flash from the May, 1962, issue of Popular Electronics confirms that many American SWL’s were able to tune into the communications to the space capsule, although at press time, it did not appear that there were any confirmed reception reports of the space-to-Earth downlink.


Voice communication from Earth was sent on HF frequencies, with 15.016 MHz being the most important in the Western Hemisphere. On that frequency, SWL’s were able to hear ground stations in Guaymas, Mexico, Corpus Christi, Texas, and others. It was believed that Glenn was transmitting on or near that frequency, although this had not been confirmed at press time. In the Eastern Hemisphere, ground network stations were heard on 7.575 and 10.61 MHz, with ships in the recovery operation above the 15.016 frequency.

The magazine noted that SWL’s probably enjoyed the mission more than TV viewers.

Godspeed, John Glenn.

Lunar Eclipse of July 15, 1916

A partial lunar eclipse took place on this date one hundred years ago, f July 15 1916.  The eclipse was notable for the effect it had on Sir Ernest Shackleton’s Imperial Trans-Antarctic Expedition, an attempted crossing of the Antarctic continent.  The expedition consisted of two parties.  One party, led by Shackleton aboard the Endurance, was to make the crossing from the Weddell Sea.  This party was the most famous, since after the loss of the ship, the party had to travel to Elephant Island, then to South Georgia island, and finally make a dangerous land crossing to a whaling station on the other side of that island.

 A man, fresh-faced with dark, brushed-back hair, seated among a group. He is wearing a naval officer's uniform with a high, stiff collar

Aeneas Mackintosh, Ross Sea party commander. Wikipedia image.

The other party was to enter the continent from the Ross Sea, and was led by Aeneas Mackintosh.  This party would head inland and establish depots for the party making the crossing.  In 1916, five of this party were stranded, and needed to reach the relatively safety of a hut at Cape Evans.  An attempt was made in May, but the ice was too thin.  They had to wait for colder weather, which also meant darkness.  The weather was bad during the full moon of June, but on July 15, conditions seemed good.  But when the moon rose, the men were surprised to find that it was about to be eclipsed.  Fortunately, even though the eclipse continued for two hours, it was only partial, and enough light remained to make the journey.

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Happy Leap Day!

1908 Leap Year postcard. Wikipedia image.

Today is leap day. In order to accomodate the U.S. presidential election and the Summer Olympics, the years in which those events take place require an extra day, which is added on February 29. These events take place in years evenly divisible by four (2016/4 = 504), and for this reason, Pope Gregory decreed in 1582 that such years would contain 366 days, rather than the typical 365. The first leap year took place in 1584. Even though there was no presidential election or Summer Olympics that year, the new system showed incredible foresight.

The addition of a leap year also keeps the calendar in sync with the Earth’s orbit around the sun, which takes approximately 365-1/4 days. Without the modification to the calendar, the seasons would shift by about one day every four years.

However, the Earth’s period of orbit around the sun is not exactly 365-1/4 days. It is actually slightly more, but because of the effect of the Earth’s precession, it appears from the point of view of an observer on Earth to be slightly less, namely 365.24219879 days.

To get things properly in sync, a few more tweaks had to be made. Therefore, years divisible by 100 (which are divisible by 4, and would normally be leap years) are not leap years. Therefore, 1900 consisted of 365 days, and there was no February 29, 1900.

This correction by itself would make the average year measure 365 + 1/4 – 1/100 = 365.24 days. However, to refine the formula even more, another exception is made. Years divisible by 400 are leap years, even though they are divisible by 100. Therefore, 2000 was a leap year, and there was a February 29, 2000.

With this added factor, the average year length is now 365 + 1/4 – 1/100 + 1/400 = 365.2425 days, which is only 0.0003013 days more than the actual length of the year. This means that it will take 3319 years for the calendar to be off by only a single day. But that seems to be an adequate distance to kick the can, and our descendants can deal with the problem then.

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Victory Eclipse of 1945

1945EclipseSeventy years ago today, July 9, 1945, a narrow strip of Idaho and Montana experienced a total eclipse of the sun.  From its sunrise beginning in the northwestern United States, the path of totality passed through Canada, Greenland, Scandinavia, and the Soviet Union. The photo here was taken near Butte, Montana, were the sun rose almost fully eclipsed, with totality a few minutes later. The photo was taken by Peter A. Leavens, and appeared in Life Magazine on July 23, 1945.

Critical frequency during eclipse.

Critical frequency during eclipse.

Ionospheric scientists at Tromsø, Norway, only two moths after liberation, took the opportunity to measure the effects of the eclipse on the ionosphere. Their results show a pronounced dip in the critical frequency during the eclipse.

Interestingly, their report also notes that the Germans had an ionospheric station at Kjeller, used to determine radio communication frequencies after the war. When the station was taken over by Allied forces, the German peronnel were ordered to continue their work, and observations were made at that station as well.

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DX’ing From Outer Space


For about the past century, the planet Earth has been sending out into the cosmos radio signals, and it’s not uncommon to wonder whether anyone has heard them. The subject sometimes comes up in science fiction. For example, in the 1997 movie Contact, the first message received from an extraterrestrial source was, of all things, a speech by Hitler (conveniently complete with both audio and video). It was reasoned in the movie that this was one of the first television broadcasts from Earth, and as soon as the TV DX’ers in some other part of the galaxy received it, they sent it back. Presumably, I Love Lucy and other programs would follow within a couple of decades.

For the reasons explained below, this is relatively implausible. While it would be a relatively easy matter for another civilization to detect the presence of our signals, actually demodulating them (not to mention sending them back) would be considerably trickier. But it’s not totally impossible.

DX’ing From The Moon

But there’s another related question lurking here, and that is how difficult it would be for me to receive radio signals from Earth if I decided to visit the moon or some other place in space. Obviously, radio communications is possible at very great distances, since NASA does this on a daily basis. The question is what those of us with more modest equipment would be able to do.

The question is answered by an April 1977 Popular Electronics article written by Glenn Hauser.

Hauser’s focus in this article is primarily on the moon, and he convincingly shows that reception of FM and TV signals would be relatively easy to accomplish with reasonably good receivers and antennas. When the subject comes up, naysayers frequently point out that very few terrestrial stations use antennas that radiate very much energy “straight up.” It turns out, though, that this is actually the reason why many signals could be heard on the moon. After all, the moon is rarely “straight up.” It can be at many points in the sky, and at some of these points, it’s within the main lobe of broadcast stations on Earth.

Most FM and TV stations use what we think of as “omnidirectional” antennas: In other words, antennas that radiate equally strong signals in a full 360 degrees. But most of these antennas have a certain amount of gain: The effective radiated power of the signal is greater than the transmitter’s output power. This is because the “omnidirectional” pattern of the antenna is not omnidirectional at all. Instead, most of the power is concentrated into a single plane. It’s “omnidirectional” in the sense that it’s headed off toward the horizon in all directions. But it’s directional when you think of it in three dimensions. All of the energy is concentrated toward the horizon. This makes sense for the broadcaster, since all of their listeners are located on an (approximate) plane, bounded by the horizon.

This means that a station’s signal is being beamed toward the moon at two times per day: At local moonrise and local moonset. From the point of view of the listener on the moon, this means all of the stations along the Earth’s approaching and receding limbs, a narrow band circling the Earth. A station located at the North or South Pole would have its antenna pointing at the moon on a constant basis. Every other station on Earth would have its antenna pointed at the moon approximately every twelve hours.

There would still be a slight problem, however, since even on this narrow band, there would be multiple stations on any given frequency. I suspect that on some popular frequencies, this problem would be insurmountable, since the QRM would be just too great.

But there would be some signals that would be quite easy to copy, since they have the frequency to themselves, or share it only with much lower powered stations. Two examples given in the 1977 article is no longer relevant, but they’re good illustrations. Prior to the switch to digital television in the United States, TV channel 68 was occupied by only one station, KVST-TV in Los Angeles, with an ERP of a million watts. And on channel 67, WMPB, the Baltimore PBS channel, was in a similar position. These channels would be relatively easy to monitor from the moon whenever it was moonrise or moonset in Los Angeles or Baltimore. Hauser notes other such examples in Europe and Brazil.

Most of the FM band would be more cacophonous, but there would be some stations operating on relatively clear channels. Due to the FM capture effect, some of these would be relatively easy to hear, even if there was a bit of other activity on the same channel. For example, he cites a number of cases in the educational portion of the FM band (88-92 MHz), where there’s a single high-power station in the United States, with other stations on that channel having much lower power. In those cases, the dominant signal would be easily heard. He also cites a number of high powered Canadian stations operating on channels where only low powered stations existed in the United States. Since the FM situation has been relatively static since 1977, most of these stations would remain fairly easy catches from the moon.

Hauser does point out that longwave and mediumwave (standard AM broadcasts) would be unlikely to penetrate the ionosphere.  Only signals above the maximum usable frequency (MUF) could be heard outside the confines of the Earth.  Therefore, he notes that it’s unlikely that we had much radio leakage to speak of prior to about the 1930’s, when relatively strong shortwave stations started coming on the air.  Since most of these stations operated on regular schedules, it’s likely that they were still radiating, even when the MUF dipped below their transmitter frequency.  Those signals would radiate into space.  Hauser cites one example of a BBC transmission from the VOA station in Delano, California, being copied by a satellite.

DX’ing by Extraterrestrial Civilizations

The issue raised by the movie Contact is touched on by Hauser, but it’s studied in scholarly detail by a NASA report entitled Eavesdropping Mode and Radio Leakage from Earth by Woodrull T. Sullivan III.  While this report doesn’t show a date, it appears to be written post-1978.  It answers the question of what extraterrestrial listeners, with equipment comparable to that available on Earth, would be able to hear.  It turns out that those extraterrestrial viewers would be able to determine quite a bit, although it’s unlikely that they would be able to demodulate the video of speeches by Hitler.

Even though they might not be able to watch our shows, extraterrestrial monitors within several light years of the Earth would be able to make quite a few reasonable deductions about the Earth, even if they were equipped with only Earth-level receivers and antennas.  At least they would have been able to.  It turns out that the best source of information would be the video carriers of UHF television stations.  With the switch to digital television, some of those extraterrestrials might have concluded that the Earth has gone dark.

But those UHF carriers from a few years ago are still working their way through space, and it’s possible that someone is analyzing them.  The article makes clear that the modulation of those signals (the actual audio or video) would be too weak to decode with Earth-level technology.  But the presence of the carriers would be apparent.  And even with this information, extraterrestrials would be able to come to some intelligent conclusions.  They would be able to figure out which star the signals were coming from.  And by keeping close track, they would be able to figure out the diameter of the Earth’s orbit around the sun.

They would even be able to figure out the approximate latitudes and longitudes of individual stations.  This is because the signals would come and go on a regular schedule as the Earth made its 24-hour rotation.  As noted above, stations near the poles would be audible most of the time.  As stations got closer and closer to the equator, they would be audible for shorter periods each twelve hours.  The Doppler shift of received signals would give further clues as to the latitude of the signals being heard.  Eventually, the extraterrestrials would be able to crunch the numbers and figure out the approximate terrestrial locations of the stations.  If the correctly assumed that the locations of these signals were close to the locations of greatest human population, they would even be able to roughly map out the population distribution of the Earth.

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Eclipse of April 7, 1940

1940EclipseSeventy-five years ago today, April 7,  1940, an annular eclipse occurred, the center line of which passed through Texas and the southeastern United States.  Professor N. Wyman Storer of the University of Kansas took the opportunity to travel to Conroe, Texas, the closest point on the center line. There, he and assistants set up the University’s 6-inch refractor, shown here, on the tennis court of the Conroe High School, where he captured a number of good photographs of the eclipse.  The telescope was acquired by the University for $1000 in 1885, and was still in use as late as 1968.  The mount shown here was made of lumber, and cost $3.  The photos taken during this expedition can be found in the August 1940 issue of Popular Astronomy.

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OSCAR III: 50th Anniversary


Fifty years ago, from March 9-27, 1965, the first two-way amateur satellite, OSCAR III, was in operation. The 16.3 kg spacecraft was launched on March 9 from Vandenberg Air Force Base, piggybacking with seven Air Force satellites. Over 1000 amateurs in 22 countries made contact through the satellite’s linear transponder, with both the uplink and downlink taking place on the 2 meter amateur band. Signals were received by the satellite on 144.1 MHz, and were retransmitted on 145.9 MHz. The downlink had a power of one watt, which was divided over the whatever stations were in the passband of the uplink frequency.

A beacon transmitter sending voltage and temperature readings was audible for several months. The orbit was nearly circular, with an altitude of 570 statute miles and an orbital period of 103.5 minutes.

OSCAR3The photo here shows Ed Hilton, W6VKP, and Don Norgaard, W6VMH, working on the satellite’s electronic package in Hilton’s garage. This photo is taken from the March, 1965, issue of Popular Electronics.  A summary of the mission and complete list of contacts made and calls heard during the spacecraft’s 250 orbits is also available online.

Vegetation on Neptune

Vegetation on Neptune (artist's conception).

Vegetation on Neptune (artist’s conception).

This 1914 drawing (an artist’s conception) depicts the vegetation supposed to exist on the planet Neptune. The latest spectrographic evidence suggested the presence of chlorophyll on all of the planets. Surprisingly, “the farther the planet from the sun, the more luxuriant the vegetation.” Accordingly, Neptune contains the lush growth shown here.

The illustration and accompanying text can be found in the April 11, 1914, issue of The Illustrated London News.  The article cites the work of Professor Percival Lowell.

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