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Here are 10 of Arecibo’s coolest achievements

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Old December 7th 20, 06:36 PM posted to alt.astronomy
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Default Here are 10 of Arecibo’s coolest achievements


(At the citation are pictures and graphics.)

Here are 10 of Arecibo’s coolest achievements
Ice on Mercury, pulsar planets and a greeting to aliens are just some of
the radio telescope’s hits
Arecibo telescope
The world-famous Arecibo telescope observed planets around our sun and
other stars, and uncovered sources of mysterious flashes of light, such
as pulsars and fast radio bursts.

By Maria Temming

The sun has set on the iconic Arecibo telescope.

Since 1963, this behemoth radio telescope in Puerto Rico has observed
everything from space rocks whizzing past Earth to mysterious blasts of
radio waves from distant galaxies. But on December 1, the 900-metric-ton
platform of scientific instruments above the dish came crashing down,
demolishing the telescope and spelling the end of Arecibo’s observing days.

Arecibo has made too many discoveries to include in a Top 10 list, so
some of its greatest hits didn’t make the cut — like a strange class of
stars that appear to turn on and off (SN: 1/6/17), and ingredients for
life in a distant galaxy. But in honor of Arecibo’s 57-year tenure as
one of the world’s premier observatories, here are 10 of the telescope’s
coolest accomplishments, presented in roughly reverse order of coolness.

10. Clocking the Crab Nebula pulsar
Astronomers originally thought that apparently blinking stars called
pulsars, discovered in 1967, might be pulsating white dwarf stars (SN:
4/27/68). But in 1968, Arecibo saw the pulsar at the center of the Crab
Nebula flashing every 33 milliseconds — faster than white dwarfs can
pulsate. (SN: 12/7/68). That discovery strengthened the idea that
pulsars are actually rapidly spinning neutron stars, stellar corpses
that sweep beams of radio waves around in space like celestial
lighthouses (SN: 1/3/20).

Crab Nebula
Arecibo observations of the frequency of radio flashes from the pulsar
at the center of the Crab Nebula (red star in the middle) gave support
to the idea that pulsars are rapidly spinning neutron stars.
9. Reborn pulsars
In 1982, Arecibo clocked a pulsar, dubbed PSR 1937+21, flashing every
1.6 milliseconds, unseating the Crab Nebula neutron star as the fastest
known pulsar (SN: 12/4/82). That find was puzzling at first because PSR
1937+21 is older than the Crab Nebula pulsar, and pulsars were thought
to rotate more slowly with age.

Then, astronomers realized that old pulsars can “spin-up” by siphoning
mass from a companion star, and flash every one to 10 milliseconds. The
NANOGrav project now uses such rapid-fire radio beacons as extremely
precise cosmic clocks to search for the ripples in spacetime known as
gravitational waves (SN: 2/11/16).

Pulsar illustration
Pulsars typically rotate more slowly as they age. But data from Arecibo
showed that pulsars can ‘spin-up’ to rotate hundreds of times per second
by siphoning material off a neighboring star (as seen in this artist’s
impression; pulsar in blue).
8. Ice on Mercury
Mercury seems like it would be an unlikely place to find water ice
because the planet is so close to the sun. But Arecibo observations in
the early 1990s hinted that ice lurked in permanently shadowed craters
at Mercury’s poles (SN: 11/9/91). NASA’s MESSENGER spacecraft later
confirmed those observations (SN: 11/30/12). Finding ice on Mercury
raised the question of whether ice might exist in shadowed craters on
the moon, too — and recent spacecraft observations indicate that it does
(SN: 5/9/16).

Mercury's North Pole
Images of Mercury taken by NASA’s MESSENGER spacecraft in 2011 and 2012
confirmed that hints of water ice (yellow) seen on the planet by Arecibo
reside in shadowy regions at Mercury’s poles (north pole, shown; two
craters labeled).
7. Unveiling Venus
Venus is shrouded in a thick layer of clouds, but Arecibo’s radar beams
could cut through that haze and bounce off of the rocky planet’s
surface, allowing researchers to map the terrain. In the 1970s,
Arecibo’s radar vision got the first large-scale views of Venus’ surface
(SN: 11/3/79). Its radar images revealed evidence of past tectonic and
volcanic activity on the planet, such as ridges and valleys (SN:
4/22/89) and ancient lava flows (SN: 9/18/76).

radar image of Venus' surface
Arecibo provided this early view of Venus’ surface using radar in 1971.
2015 image of Venus
Technological advances have allowed Arecibo to get crisper views of
Venus. This 2015 image showcases the planet’s northern hemisphere.
6. Mercury’s revolution
In 1965, Arecibo radar measurements revealed that Mercury spins on its
axis once every 59 days, rather than every 88 days (SN: 5/1/65). That
observation cleared up a long-standing mystery about the planet’s
temperature. If Mercury had turned on its axis once every 88 days, as
previously thought, then the same side of the planet would always face
the sun. That’s because it also takes 88 days for the planet to complete
one orbit around the sun.

As a result, that side would be much hotter than the planet’s dark side.
The 59-day rotation better matched the observation that Mercury’s
temperature is fairly even across its surface.

Arecibo’s early radar observations measured the 59-day rotation rate of
Mercury (shown in this false-color image of MESSENGER spacecraft data,
which highlights chemical and mineralogical features on the planet’s
5. Mapping asteroids
Arecibo has cataloged the features of many near-Earth asteroids (SN:
5/7/10). In 1989, the observatory created a radar image of the asteroid
4769 Castalia, revealing the first double-lobed rock known in the solar
system (SN: 11/25/89). Arecibo has since found space rocks orbiting each
other in pairs (SN: 10/29/03) and trios (SN: 7/17/08).

Other odd finds have included a space rock whose shadows made it look to
Arecibo like a skull, and an asteroid with the improbable shape of a dog
bone (SN: 7/24/01). Understanding the characteristics and motion of
near-Earth asteroids helps determine which ones might pose a danger to
Earth — and how they could be safely deflected.

216 Kleopatra asteroid images
Arecibo radar images in 2000 revealed the strange dog bone shape of an
asteroid named 216 Kleopatra (shown from multiple angles).
4. Phoning E.T.
The Arecibo Observatory broadcast the first radio message intended for
an alien audience in November 1974 (SN: 11/23/74). That famous message
was the most powerful signal ever sent from Earth, meant in part to
demonstrate the capabilities of the observatory’s new high-power radio

The message, beamed toward a cluster of about 300,000 stars roughly
25,000 light-years away, consisted of 1,679 bits of information. That
string of binary code detailed the chemical formulas for components of
DNA, a stick figure sketch of a human, a schematic of the solar system
and other scientific data.

first radio message for aliens
Anyone there?
The first radio message meant for an alien audience (illustrated at
left) was beamed into space in binary code by Arecibo in 1974. The
message encoded information about DNA’s ingredients (green) and its
double-helix shape (blue), a schematic of the solar system (yellow) and
other data about life on Earth.

3. Repeating radio blasts
Fast radio bursts, or FRBs, are brief, brilliant blasts of radio waves
with unknown origins. The first FRB known to give off multiple bursts
was FRB 121102, which Arecibo first spotted in 2012 and again in 2015
(SN: 3/2/16). Finding a repeating FRB ruled out the possibility that
these bursts were generated by one-off cataclysmic events, such as
stellar collisions. And because FRB 121102 kept recurring, astronomers
were able to trace it back to its home: a dwarf galaxy about 2.5 billion
light-years away (SN: 1/4/17). This confirmed the decade-long suspicion
that FRBs come from beyond the Milky Way.

source of fast radio burst
A repeating source of radio waves discovered by Arecibo (radio image,
left) was the first fast radio burst traced back to its home galaxy. The
burst originated in a dwarf galaxy about 2.5 billion light-years away
(visible light image, right).
2. Making waves
Gravitational waves were first directly detected in 2015 (SN: 2/11/16),
but astronomers saw the first indirect evidence of ripples in spacetime
decades ago. That evidence came from the first pulsar found orbiting
another star, PSR 1913+16, first sighted by Arecibo in 1974 (SN: 10/19/74).

By tracking the arrival time of radio bursts from that pulsar over
several years, astronomers were able to map its orbit, and found that
PSR 1913+16 was spiraling toward its companion. As the orbits of the two
stars contract, the binary system loses energy at the rate that would be
expected if they were whipping up gravitational waves (SN: 2/24/79).
This indirect observation of gravitational waves won the 1993 Nobel
Prize in physics (SN: 10/23/93).

illustration of pulsar orbiting star
The first pulsar found orbiting another star, sighted by Arecibo in
1974, provided indirect evidence for the existence of ripples in
spacetime called gravitational waves (illustrated).
1. Pulsar planets
The first planets discovered around another star were three small, rocky
worlds orbiting the pulsar PSR B1257+12 (SN: 1/11/92). The find was
somewhat serendipitous. In 1990, Arecibo was being repaired, and so it
was stuck staring at one spot on the sky. During its observations,
Earth’s rotation swept PSR B1257+12 across the telescope’s field of
view. Small fluctuations in the arrival time of radio bursts from the
pulsar indicated that the star was wobbling as a result of the
gravitational tug of unseen planets (SN: 3/5/94).

Thousands of exoplanets have since been discovered orbiting other stars,
including sunlike stars (SN: 10/8/19). Recent exoplanet surveys,
however, suggest that pulsar-orbiting planets are rare (SN: 9/3/15).

rocky planets orbiting pulsar PSR B1257+12
The first worlds ever spotted beyond the solar system were three rocky
planets (seen in this artist’s illustration) orbiting the pulsar PSR
Questions or comments on this article? E-mail us at

Maria Temming
About Maria Temming
Maria Temming is the staff reporter for physical sciences, covering
everything from chemistry to computer science and cosmology. She has
bachelor's degrees in physics and English, and a master's in science

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By Maria TemmingDecember 4, 2020
Old December 15th 20, 02:36 AM posted to alt.astronomy
Steve Silverwood [KB6OJS]
external usenet poster
Posts: 8
Default Here are 10 of Arecibos coolest achievements

On Mon, 7 Dec 2020 09:36:54 -0800, a425couple


(At the citation are pictures and graphics.)

How did a radio telescope detect ice on Mercury?

Oh, sorry. In reading further, under the part about mapping the
Venusian surface, it says that Arecibo used radar. I was totally
unaware that Arecibo was a transmitter facility as well as a receiver.
I had no idea.


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