Astronomy

What of the following moon-situations would be better?

What of the following moon-situations would be better?


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Okay, so imagine that there is an Earth-like planet, with the following conditions:

  1. It's further from it's sun than the Earth is from the Sun (not much, but enough for weather to be a little colder than the Earth).
  2. It's more or less the same size as the Earth (same proportion of land and water, too).
  3. Since it's further from it's sun, it takes more time to complete an orbit that the Earth (for instance, 400 Earth-days, instead of 365).

Given those conditions, I would like to know which of the following would be more stable for this Earth-like planet to have a similar day/night and moon cycle to the Earth:

  • A moon that's the same size as the Earth's moon, only closer.

OR

  • A moon that's as far away as the Moon is to Earth, only that the moon of this planet is bigger (let's say, twice as big as our moon).

Sorry if it's kind of complicated. Please tell me if it's not understandable and I'll try to edit it so it's as clearly as possible! Thanks in advance :)


Both would be stable. A single moon orbiting a planet is generally stable provided it's comfortably inside the true region of stability, in the Hill Sphere and provided that it's not so large that tidal forces become a stability issue or not so close that it dips inside the roche limit and might break apart.

The only way you might run into instability in your scenarios, is if you have the smaller moon very close, inside the Geosynchronous orbital distance, where the Moon would move ahead of the tidal bulge it creates and that would cause the Moon to be drawn towards the planet and in time, crash into it, similar to how Phobos is expected to crash into/break into a ring system around Mars.

As the planet moves away from the sun it's stable region expands. The geosynchronous orbit is unrelated to the sun, that's between the masses of the planet and moon only, but as long as your moon is orbiting between geosynchronous orbit and inside the stable region of the hill sphere, it should be fine. (unless you give the planet or moons a retrograde rotation, then you need to re-examine the long term tidal effects). For most orbits, the planet rotates ahead of the Moon so the tidal bulge pushes the Moon slowly outwards, but this effect gets weaker as the Moon gets further, so it's generally long term stable over billions of years, unless the planet is very close to the sun and it has a tiny hill-sphere.

Only two well known moons in our solar-system orbit ahead of their tidal bulges that leads to orbital decay (a handful of tiny captured moons do too, but those are so small and their tidal forces are largely irrelevant). Only Phobos and Neptune's wrong way moon Triton orbit ahead of their tidal bulges, resulting in them being pulled towards their planets, not pushed away. Triton is sufficiently distant that it's timing to crash into/break into a ring system around Neptune is billions of years off. All the other moons, for tidal reasons, should be moving away from their planets, mostly very very gradually.

The 4 Jovian moons, however, are more complicated as Jupiter has a gonzo magnetic field, a magnetosphere that's almost wind like and it's moons are tidally locked to each other and it's innermost moon is losing mass to Jupiter's magnetosphere - so… all bets are off when it comes to Jupiter's 4 inner moons.

2 or more large moons can sometimes interact with each other, creating some instability. One moon systems are, more often than not, long term stable.

(too long?)


A closer moon would bring higher gravitational pull and it orbits faster than our moon.

"A moon that's as far away as the Moon is to Earth, only that the moon of this planet is bigger (let's say, twice as big as our moon)."

In this case too the moon cycle won't be similar to ours, since again the size of object matters in gravitation.

but the rotation of That Earth like planet gives day/night cycles which you haven't touched of.


It looks like you are mixing things a little: If earth was farther away from the sun, it will mean nothing to the day/night cycle.

Day/night cycle only depends on the way the earth rotates on itself, not around the sun. So your question is the same for an planet with same orbit as ours as it is for a planet with an orbit a little larger.

To answer your question,

[for it] to have a similar day/night and moon cycle to the Earth:

Both are possible. Day/night cycle greatly depends on initial planet's spin. What changes here is the mass of the earth-like planet we are talking about, and this changes the speed at which the moon rotates around. the gravity of the moon will affect the planets rotation speed over very long time range.

  • first case, planet is heavier to have a moon the size our moon (I assume same mass as ours) rotating faster around - moon cycle is different, but you can have same day/night cycles as ours

  • second case, planet is lighter, the big moon rotates slower, but you can also have same day/night cycles


Where the Grass is Greener, Except When It’s ‘Nonfunctional Turf’

Plus, mammoths in Vegas, watermelon snow, Miami’s looming sea wall and more in the Friday edition of the Science Times newsletter.

If you’re looking for a sign of the End Times, here’s one: Las Vegas, the city where seemingly anything and everything is condoned, has made grass — the ornamental kind — illegal.

Much of the West is experiencing the worst drought in decades, a “megadrought” that has kindled early wildfires and severe water shortages — and the seasonal heat has hardly begun. “There’s a 100 percent chance that it gets worse before it gets better,” Daniel Swain, a climate scientist at the University of California, Los Angeles, tells the graphics editor Nadja Popovich in The Times today. “We have the whole long, dry summer to get through.”

Lake Mead, which sits on the Colorado River (behind the Hoover Dam) and provides 90 percent of the water supply for Las Vegas and southern Nevada, this week reached its lowest capacity since its creation in the 1930s. And several states that draw their water, in strict allotments, from the Colorado River must absorb stark restrictions on its use in cities and for farming.

“We’re kind of at an existential point right now in the West,” said Kyle Roerink, executive director of the nonprofit Great Basin Water Network, in a phone conversation. “Even basic terminology that once was a given — now we’re seeing a shift in the nomenclature toward saying, well, we’re not in a period of drought, we’re in a period of aridification.”

Enter aridification, exit grass. Gov. Steve Sisolak of Nevada just signed into law bill AB356, which requires the removal of all “nonfunctional turf” from the Las Vegas Valley by the year 2027. The effort will conserve about 10 percent of the region’s annual allotment of water from the Colorado River. “It’s a really good time to have put forth something like this,” said Mr. Roerink, whose organization was part of a bipartisan coalition, including the Southern Nevada Home Builders Association, that supported the bill.

The Southern Nevada Water Authority has not yet formed the committee that will actually define “nonfunctional turf.” For now, the category loosely describes the few thousand acres of grass carpeting the region’s street meridians, office parks and housing developments, and amounts to roughly one-third of all the grass in the region.

“The best way to describe it is, it’s the type of grass that’s only used when someone is pushing a lawn mower over it,” Mr. Roerink said. “Other shorthand that became commonspeak during this legislative session was ‘useless grass.’” (That other ostensibly useful grass — at parks, schools, golf courses and single-family lawns — is still allowed, at least for now.)

“Nonfunctional turf” — the very phrase is an existential knot. Is it redundant, or an oxymoron? Either way, it perfectly encapsulates our contorted relationship to nature: Some grass is good, some grass is bad, and all of it (except the kind that grows wild in meadows) is engineered and curated by us.

The challenge isn’t excess grass so much as excess people. Southern Nevada has had explosive growth in recent years, and water usage has increased by more than 9 percent since 2018. Eliminating “useless” grass was a good first step, Mr. Roerink said, but he worried that the water savings would simply be translated into an argument for new development (doubtless with more useful grass).

“What are the Mojave Desert’s limits?” he said. “You know, in some of the areas where Vegas wants to develop is desert tortoise habitat, and there’s not a lot of good desert tortoise habitat left. What’s the future of that going to be?”

The fundamental question is: What counts as a “functional” or non-useless species? Humanity seems dead-set on finding out. We have a knack for seeking out the harshest environments and trying to plant ourselves there, from the Amazon to Antarctica. Lately it’s outer space, with Mars as the ultimate destination. On Monday the billionaire entrepreneur Jeff Bezos announced that he would soon be venturing into space, beating the billionaire entrepreneur Elon Musk to the punch (unless the billionaire entrepreneur Richard Branson gets there even sooner).

It bears noting that Mars has no grass, functional or otherwise, nor discernible life of any kind. (Earth’s deserts, including the Mojave, are where Mars rovers go for practice.) If Martian colonists are fortunate, they might dig up something akin to the microscopic, multicellular rotifers that scientists recently retrieved from Siberian permafrost. The tiny animals — resistant to radiation, extreme acidity, starvation, low oxygen and dehydration — had been effectively frozen for 24,000 years, yet they bounced right back to life and began to multiply.

“They’re the world’s most resistant animal to just about any form of torture,” Matthew Meselson, a molecular biologist at Harvard, told The Times. “They’re probably the only animals we know that could do pretty well in outer space.”

The last time the rotifers were up and about, woolly mammoths roamed the planet, including in what is now the Las Vegas Valley. To the extent that mammoths thought anything, they probably held very strong opinions about who was and was not a “functional” species. Alas, we’ll never know.


1.6 A Tour of the Universe

We can now take a brief introductory tour of the universe as astronomers understand it today to get acquainted with the types of objects and distances you will encounter throughout the text. We begin at home with Earth, a nearly spherical planet about 13,000 kilometers in diameter (Figure 1.6). A space traveler entering our planetary system would easily distinguish Earth from the other planets in our solar system by the large amount of liquid water that covers some two thirds of its crust. If the traveler had equipment to receive radio or television signals, or came close enough to see the lights of our cities at night, she would soon find signs that this watery planet has sentient life.

Our nearest astronomical neighbor is Earth’s satellite, commonly called the Moon. Figure 1.7 shows Earth and the Moon drawn to scale on the same diagram. Notice how small we have to make these bodies to fit them on the page with the right scale. The Moon’s distance from Earth is about 30 times Earth’s diameter, or approximately 384,000 kilometers, and it takes about a month for the Moon to revolve around Earth. The Moon’s diameter is 3476 kilometers, about one fourth the size of Earth.

Light (or radio waves) takes 1.3 seconds to travel between Earth and the Moon. If you’ve seen videos of the Apollo flights to the Moon, you may recall that there was a delay of about 3 seconds between the time Mission Control asked a question and the time the astronauts responded. This was not because the astronauts were thinking slowly, but rather because it took the radio waves almost 3 seconds to make the round trip.

Earth revolves around our star, the Sun, which is about 150 million kilometers away—approximately 400 times as far away from us as the Moon. We call the average Earth–Sun distance an astronomical unit (AU) because, in the early days of astronomy, it was the most important measuring standard. Light takes slightly more than 8 minutes to travel 1 astronomical unit, which means the latest news we receive from the Sun is always 8 minutes old. The diameter of the Sun is about 1.5 million kilometers Earth could fit comfortably inside one of the minor eruptions that occurs on the surface of our star. If the Sun were reduced to the size of a basketball, Earth would be a small apple seed about 30 meters from the ball.

It takes Earth 1 year (3 × 10 7 seconds) to go around the Sun at our distance to make it around, we must travel at approximately 110,000 kilometers per hour. (If you, like many students, still prefer miles to kilometers, you might find the following trick helpful. To convert kilometers to miles, just multiply kilometers by 0.6. Thus, 110,000 kilometers per hour becomes 66,000 miles per hour.) Because gravity holds us firmly to Earth and there is no resistance to Earth’s motion in the vacuum of space, we participate in this extremely fast-moving trip without being aware of it day to day.

Earth is only one of eight planets that revolve around the Sun. These planets, along with their moons and swarms of smaller bodies such as dwarf planets, make up the solar system (Figure 1.8). A planet is defined as a body of significant size that orbits a star and does not produce its own light. (If a large body consistently produces its own light, it is then called a star.) Later in the book this definition will be modified a bit, but it is perfectly fine for now as you begin your voyage.

We are able to see the nearby planets in our skies only because they reflect the light of our local star, the Sun. If the planets were much farther away, the tiny amount of light they reflect would usually not be visible to us. The planets we have so far discovered orbiting other stars were found from the pull their gravity exerts on their parent stars, or from the light they block from their stars when they pass in front of them. We can’t see most of these planets directly, although a few are now being imaged directly.

The Sun is our local star, and all the other stars are also enormous balls of glowing gas that generate vast amounts of energy by nuclear reactions deep within. We will discuss the processes that cause stars to shine in more detail later in the book. The other stars look faint only because they are so very far away. If we continue our basketball analogy, Proxima Centauri , the nearest star beyond the Sun, which is 4.3 light-years away, would be almost 7000 kilometers from the basketball.

When you look up at a star-filled sky on a clear night, all the stars visible to the unaided eye are part of a single collection of stars we call the Milky Way Galaxy, or simply the Galaxy. (When referring to the Milky Way, we capitalize Galaxy when talking about other galaxies of stars, we use lowercase galaxy.) The Sun is one of hundreds of billions of stars that make up the Galaxy its extent, as we will see, staggers the human imagination. Within a sphere 10 light-years in radius centered on the Sun, we find roughly ten stars. Within a sphere 100 light-years in radius, there are roughly 10,000 (10 4 ) stars—far too many to count or name—but we have still traversed only a tiny part of the Milky Way Galaxy . Within a 1000-light-year sphere, we find some ten million (10 7 ) stars within a sphere of 100,000 light-years, we finally encompass the entire Milky Way Galaxy.

Our Galaxy looks like a giant disk with a small ball in the middle. If we could move outside our Galaxy and look down on the disk of the Milky Way from above, it would probably resemble the galaxy in Figure 1.9, with its spiral structure outlined by the blue light of hot adolescent stars.

The Sun is somewhat less than 30,000 light-years from the center of the Galaxy, in a location with nothing much to distinguish it. From our position inside the Milky Way Galaxy, we cannot see through to its far rim (at least not with ordinary light) because the space between the stars is not completely empty. It contains a sparse distribution of gas (mostly the simplest element, hydrogen) intermixed with tiny solid particles that we call interstellar dust. This gas and dust collect into enormous clouds in many places in the Galaxy, becoming the raw material for future generations of stars. Figure 1.10 shows an image of the disk of the Galaxy as seen from our vantage point.

Typically, the interstellar material is so extremely sparse that the space between stars is a much better vacuum than anything we can produce in terrestrial laboratories. Yet, the dust in space, building up over thousands of light-years, can block the light of more distant stars. Like the distant buildings that disappear from our view on a smoggy day in Los Angeles, the more distant regions of the Milky Way cannot be seen behind the layers of interstellar smog. Luckily, astronomers have found that stars and raw material shine with various forms of light, some of which do penetrate the smog, and so we have been able to develop a pretty good map of the Galaxy.

Recent observations, however, have also revealed a rather surprising and disturbing fact. There appears to be more—much more—to the Galaxy than meets the eye (or the telescope). From various investigations, we have evidence that much of our Galaxy is made of material we cannot currently observe directly with our instruments. We therefore call this component of the Galaxy dark matter. We know the dark matter is there by the pull its gravity exerts on the stars and raw material we can observe, but what this dark matter is made of and how much of it exists remain a mystery. Furthermore, this dark matter is not confined to our Galaxy it appears to be an important part of other star groupings as well.

By the way, not all stars live by themselves, as the Sun does. Many are born in double or triple systems with two, three, or more stars revolving about each other. Because the stars influence each other in such close systems, multiple stars allow us to measure characteristics that we cannot discern from observing single stars. In a number of places, enough stars have formed together that we recognized them as star clusters (Figure 1.11). Some of the largest of the star clusters that astronomers have cataloged contain hundreds of thousands of stars and take up volumes of space hundreds of light-years across.

You may hear stars referred to as “eternal,” but in fact no star can last forever. Since the “business” of stars is making energy, and energy production requires some sort of fuel to be used up, eventually all stars run out of fuel. This news should not cause you to panic, though, because our Sun still has at least 5 or 6 billion years to go. Ultimately, the Sun and all stars will die, and it is in their death throes that some of the most intriguing and important processes of the universe are revealed. For example, we now know that many of the atoms in our bodies were once inside stars. These stars exploded at the ends of their lives, recycling their material back into the reservoir of the Galaxy. In this sense, all of us are literally made of recycled “star dust.”


What is a supermoon?

The moon is not a static distance away from Earth — its orbit is elliptical, meaning sometimes it&aposs closer to us, and other times, it&aposs farther away. A supermoon happens when the full moon occurs at a point in the orbit that is close to Earth (specifically, within 90% of its closest distance, or perigee). May&aposs supermoon, which is the third of four in 2021, will be the year&aposs largest, as it&aposs the closest full moon to Earth. It&aposll appear about 7% larger and 15% brighter than standard full moons.


Logistics

The Sub-Saharan Africa Advanced Summer School (SSAASS) will be hosted at Imperial Botanical Beach Hotel. Imperial Botanical Beach hotel is located on the shores of lake Victoria in Entebbe - Uganda,

5 km from Entebbe International Airport. The hotel is within 1 km of the Entebbe Golf Club and the Uganda Wildlife Education Centre is within a 15-minute walk.

All participants will be accomodated at Imperial Botanical Beach Hotel for the duration of the summer school, i.e., from September 6th - 17th, 2021. Accomodation and flight ticket costs will be covered by SSAASS. Rooms will be provided randomly and some of the rooms will be shared. Transport to and from the Entebbe International Airport will be provided.

In order to apply for a Visa to Uganda, one is required to hold a valid passport with sufficiently many empty pages. For our successful applicants, we will request for a copy of your passport so that we can provide you with all neccessary documentation needed for your visa application (i.e., flight ticket, invitation letter, proof of accomodation and travel insurance). We also advise you to please acquire additional information from your travel agent.

All travellers to and from Uganda are required to hold a yellow fever vaccination certificate. Please note that without PRIOR yellow fever vaccination, you will not be allowed to enter Uganda.

We are currently closely monitoring the covid-19 situation and the different travel restrictions set by the Ugandan government. For now, everyone with a negative PCR covid test result certificate issued within 72 hours is allowed to enter Uganda in addition to meeting other entry requirements. We will only cover the covid-test expenses required by participants to return to their respective countries.


Telescope review: Unistellar’s eVscope, the next generation of telescope

At first glance the eVscope looks rather like a conventional reflector, but unlike a traditional optical telescope it uses an extremely sensitive electronic sensor at the focus of its 110mm, f/4 mirror. Image: Ade Ashford.

Sometimes, a great idea comes along at just the right time, when a confluence of technologies makes it possible. Conceived in January 2015 and first exhibited at the Consumer Electronics Show in Las Vegas exactly two years later, the eVscope is one such example, the brainchild of three scientists and one industrial engineer. Together, they founded Unistellar in Marseille, France, to realise their dream of a portable, self-contained and easy-to-use instrument for astronomers that they say is “100 times more powerful than a classical telescope.”

Unistellar entered into partnership with the SETI Institute in July 2017 and later that same year started a successful Kickstarter crowdfunding campaign. Evidently a lot of people are looking for a product like this, because 2,144 backers pledged $2,209,270 to turn the eVscope into reality. To date, Unistellar has delivered over 1,000 eVscopes in Europe, North America, Australia, Japan and elsewhere worldwide, with pre-orders for a further 2,000 units.

The eVscope optical tube and computerised mount. It slides into the head of the supplied tripod and is locked in position by the two rubberised thumbwheels at the top of the tripod. Image: Ade Ashford.

What is an eVscope?

Unistellar’s debut product is very different to a traditional optical telescope. The instrument uses an extremely sensitive electronic sensor at the focus of a 450mm focal length f/4 mirror on a self-aligning computerised alt-az mount. As it tracks its target, an onboard computer automatically applies intelligent image processing, delivering a near-real-time, full-colour image displayed on a miniature, extremely high contrast colour OLED (organic LED) screen that you view through an eyepiece on the side of the instrument, or on a separate smart device connected via Wi-Fi.

An eVscope delivers richly detailed images of nebulae and galaxies that you wouldn’t be able to see in any other way, except photographically and with far greater effort. Unistellar’s triumph lies in managing to distill a telescope on a self-aligning, computerised mount with an in-built camera and sophisticated image processing, into a portable, cable-free and easy-to-use product that runs off an internal battery for an entire night.

Since the eVscope is a wirelessly connected instrument, the Unistellar App running on your smartphone or tablet enables you to automatically locate and track any one of 5,200-plus objects (at the time of writing) in its database, or direct it towards specific coordinates in right ascension/declination, or altitude/azimuth. Thereafter, you can save and share so-called Enhanced Vision images.

Furthermore, the connected nature of the eVscope allows you to participate in ‘Citizen Science’ activities. By activating their device’s Observation Campaign Mode, users can obtain coordinates of newly discovered objects, gather data for researchers, and upload this information to Unistellar’s servers. Thus you can make a real contribution to science by observing comets, supernovae, near-Earth asteroids or occultations of stars by asteroids, which is a unique and rather exciting feature of the instrument.

First impressions

The eVscope arrives in a box whose inner lid confidently tells you to ‘Prepare To Be Amazed’. Assembly is extremely straightforward, as you merely need to open and extend the tripod legs to the required height, ensuring that its head is level according to the built-in spirit level. The integrated tube assembly and mount then slides into position and is secured by two thumbwheels.

At first glance, the eVscope looks rather like a conventional reflecting telescope with a two-tone matte silver and black tube, 55 centimetres long and 14.5 centimetres in diameter, attached to an L-shaped alt-azimuth mount. The instrument’s three-section aluminium tripod has photographic-style locking levers for easy adjustment, even with gloved hands. The eyepiece port lies on the side of the tube close to the intersection of the altitude and azimuth axes – a particularly ergonomic viewing configuration since its position remains largely constant wherever the telescope is pointed in the sky. At the tripod’s lowest, midway and fully extended positions, the average eyepiece heights are 84, 117 and 153 centimetres, respectively.

Contemplating the assembled eVscope for the first time, I was immediately struck by how ‘Apple-like’ it feels. If the tech giant ever made a telescope, an iScope if you will, this is exactly how I imagine it would look. The overall impression is minimalist – there’s no computerised hand controller or keypad, just a single illuminated power button in the fork arm – yet stylishly eye-catching.

The eVscope automatically tracks and applies intelligent image-processing to whatever you’re observing, producing a near-real-time, full-colour picture on a miniature, extremely high-contrast colour OLED screen that you view through an eyepiece on the side of the instrument. There is comfortable eye relief for spectacle wearers with a large range of dioptre adjustment. Image: Ade Ashford.

First-light tests

The eVscope’s start-up position is on the levelled tripod with the tube pointing straight up and the instrument is initialised by pressing and holding the lozenge-shaped power button for about two seconds. The button momentarily glows with a purple border that turns red after the system completes its boot sequence, which takes about seven seconds. You can download iOS 11+ and Android 5+ versions of the Unistellar App, which at the time of writing were v1.0.6 and v1.0.7, respectively. The eVscope generates its own password-free Wi-Fi hotspot that you connect your smartphone or tablet to. Currently, the device supports only direct Access Point Wi-Fi connection. In time, I hope to see an option for Station Mode connections to one’s home network for extended connectivity and remote Internet control.

The first person to connect wirelessly to the eVscope via the app is deemed the ‘Operator’, but up to nine other Unistellar App users can connect to the instrument as ‘Watchers’. If an Operator relinquishes control of the instrument by pressing the ‘release’ button, any connected watcher can then ‘request’ to be an Operator. What’s particularly neat is that while someone is looking through the eyepiece, all ten connected devices can also see the eVscope’s output on their screens. The system’s potential for outreach work, teaching and public demonstrations is obvious. The Wi-Fi range is good enough to operate an eVscope in the garden from indoors, which is good news for those who don’t like the cold!

Autonomous Field Detection

The eVscope has a built-in compass and a three-axis accelerometer, which combined with the GPS data from your phone enables the instrument to initially align itself, but not to the level of precision required for operation. For that, the eVscope uses a patent-pending system that Unistellar calls Autonomous Field Detection (AFD), better known to you and I as plate-solving. Basically, the eVscope’s onboard computer pattern-matches the stars visible in the field of view of its imaging sensor against an internal database of 20 million stellar objects, enabling the instrument to always know precisely where it’s pointed.

AFD is fast and fully automated, so you can go from powering up your eVscope to aligning it in about a minute. Unistellar’s system is a vast improvement on the alignment procedures of conventional GoTo mounts, which usually require you to obtain at least two ‘fixes’ on widely separated named stars or plate-solved positions. The eVscope is therefore ideal for quick observing sessions when you might take advantage of gaps between clouds, or maybe if you have a heavily obscured sky thanks to trees or houses.

By using a virtual on-screen joystick, you can slew the mount to a direction of interest at variable speeds up to about four degrees per second (incidentally, the internal spur gears driven by DC motors are quiet enough not to disturb the neighbours at night). Once you can see some stars on the app’s screen, press the Autonomous Field Detection icon. Within a few seconds a ‘Star Tracking: On’ message appears, and you’re done. At the end of a viewing session, you command the eVscope to ‘Park’ and it automatically powers off.

With the eVscope aligned, you can select the app’s ‘Explore’ tab and search for a target by name, consult a recommended or full list of objects, see what’s in the constellation you’re currently pointing to, search by category, or GoTo manually entered coordinates. Since it’s a connected system and the Unistellar App is under rapid development, the eVscope’s capabilities are continually growing. Unistellar is receptive to feature requests in their online Help Centre (help.unistellar.com), so by all means offer suggestions.

The cross-shaped mount for the Sony IMX224 imaging sensor at the middle of the mouth of the tube might seem excessively wide (the vanes are 7.5mm thick), but it doesn’t generate excessive diffraction or noticeable light loss. There are also gains from not having a secondary mirror. Image: Ade Ashford.

Focusing and collimating the eVscope

Rather cleverly, the eVscope’s dust cap incorporates a removable Bahtinov mask, which any astrophotographer knows is an indispensable aid to precise focus. With it installed over the mouth of the tube, select and GoTo any bright star in the app’s Explore tab. The mask modifies the star’s diffraction pattern into a cross shape with a central spike, so one merely turns the focusing wheel on the base of the eVscope until the spike meets the intersection of the cross and you’re done. I found that the instrument held focus very well between sessions, even when regularly transported. Collimation is also adjusted from the rear of the eVscope, if necessary. The review instrument never needed such alignment, which should allay potential purchasers’ fears that the eVscope might be somewhat ‘delicate’.

Live-Viewing the Moon and planets

As soon as your smartphone or tablet is connected to the eVscope and you launch the Unistellar App, you are in Live View mode by default. The app can automatically take control of the gain (think ISO setting on a camera) and exposure time (up to four seconds), or you can manually adjust the two sliders on screen. Observing the Moon or a bright planet like Jupiter requires deft manual adjustment of gain and exposure. You can use two-finger pinch and spread gestures on your phone to digitally zoom into the image by up to 8× and the same factor is applied to the eyepiece. However, the image zooms from the centre only – you can’t currently pan around a zoomed-in image. [October 2020 update: v1.1.1 of the iOS/Android app now permits you to pan around a zoomed-in image.]

Once you have set optimal gain and exposure set for the Moon and planets, the views will undoubtedly impress novice stargazers, but the eVscope’s resolution of 1.7 arcseconds corresponds to the visual impression of a 70mm aperture conventional telescope.

Observing Jupiter and Saturn in the small hours of late June 2020, I was able to view the two main Jovian equatorial cloud belts and its four Galilean moons, plus Saturn’s ring system, but the detail was no better than one could see in a small, quality refractor at 100×. Furthermore, since the only means of currently aligning the eVscope is on the stars, viewing the crescent Moon or a planet in twilight entails sighting along the tube and manually tracking it with the in-app joystick. Unistellar should implement a Solar System alignment option to address this, but lunar and planetary observing isn’t the eVscope’s strong suit.

The Sony IMX224 colour CMOS sensor at the top of the tube provides the eVscope with a maximum field of 0.6 × 0.45 degrees at 1.7-arcsecond per pixel resolution. Image: Ade Ashford.

Enhanced Vision

At the time of the review, the summer solstice was fast approaching when astronomical twilight lasts all night at my latitude. As a real-world test, I chose to observe from an extensive nearby park in the suburbs of a mid-sized market town that was locally dark, but heavily polluted by LED street lighting just two kilometres away to the east. One of my annual deep-sky challenges is to observe the Lagoon Nebula (Messier 8) at opposition close to 1am BST on or around 21 June when the Sun is just 14 degrees below my northern horizon.

I was keen to see just how well the eVscope performed on the showcase deep-sky objects of summer in astronomical twilight. Given that Messier 8 transits just 13 degrees high in the south at my latitude, I estimated about 1.5 magnitudes of dimming as a result of the dustier, denser atmosphere nearer the horizon, making it quite a harsh test. Having commanded the eVscope to locate and track M8, Live-View easily revealed the open cluster NGC 6530 on the eastern edge of the Lagoon, but no nebulosity.

A touch of the appropriate button engages Enhanced Vision, which is where the eVscope really shows its potential I challenge both novice and experienced observers alike not to be impressed by the results after a few tens of seconds. In Enhanced Vision mode, the output of the instrument’s sensor is continually superimposed (or stacked, in astro-imaging parlance) so that the detail, colour and clarity of the digital image grows as you watch. Given that the eVscope has an alt-azimuth mount, its onboard computer not only has to align and stack each successive image, but it flawlessly removes the effects of image rotation too – unless one chooses a field too close to the zenith, in which case you receive a warning.
The Lagoon Nebula (Messier 8) as imaged in just two minutes of Enhanced Vision with the eVscope at 12:08am BST on 19 June 2020 in nautical twilight from a suburban park. Note that M8 was just 12 degrees above the horizon at the time. Unlike the Dumbbell Nebula image below, this is saved at the full sensor resolution without an information overlay. Image credit: Ade Ashford.
Bright nebulae require just a minute’s Enhanced Vision, but the longer you leave it, the better the results will generally be. My view of the Lagoon Nebula in Sagittarius was transformed in just 30 seconds, and by two to three minutes there were wonders to behold. The gently curved dark lane of dust clearly separated the two brighter lobes of emission nebulae, all exhibiting a great deal of colour, structure and texture. Even the tiny 30-arcsecond-wide Hourglass Nebula was evident, next to the supergiant star Herschel 36. The nearby Trifid Nebula (M20) was not quite so spectacular (I reasoned that the attenuation of shorter wavelengths at such a low altitude faded the blue reflection nebula component), but both the Omega (M17) and Eagle (M16) nebulae yielded surprising levels of fine detail, the latter clearly displaying the famed ‘Pillars of Creation’.

To install the focusing Bahtinov mask, just line up the four notches on its periphery with the four cross-shaped vanes supporting the eVscope’s imaging sensor. Image: Ade Ashford.

Getting technical

The eVscope’s imaging prowess partly stems from the 1.27-megapixel colour Sony IMX224LQR CMOS sensor that lies at the focus of its 450mm focal length, f/4 primary mirror. The IMX224 is renowned for its high sensitivity and low levels of electronic noise, possessing a matrix of 1304 × 976 pixels, each 3.75 microns (0.00375mm) in size. In tests conducted with saved images, the eVscope uses a slightly masked region of the sensor matrix, 1280 × 960 pixels or 4.8 × 3.6mm in size. Plate-solving images revealed a true field of 0.6 × 0.45 degrees, and a resolution of 1.7 arcseconds per pixel. Hence the actual focal length of the review instrument was 453mm and the measured true aperture was 110.5mm.

This eVscope Enhanced Vision capture shows the rich Milky Way backdrop to the Dumbbell Nebula (Messier 27). Note the planetary nebula’s central star and faithfully reproduced colours. An optional information overlay has been added to the picture. Image: Ade Ashford.

Concluding thoughts

So, is the eVscope ‘100 times more powerful than a classical telescope’? During my suburban tests I could routinely detect magnitude +16.5 stars on moonless nights using the eVscope’s Enhanced Vision feature. With a conventional 110mm aperture reflecting telescope I might expect to glimpse magnitude +11.5 stars, so a performance difference of five magnitudes does indeed correspond to a 100-fold difference in brightness.

It’s evident from online chatter in the telescope and imaging forums that the eVscope has polarised opinion. Its detractors sneer that it’s possible to obtain the functionality of the instrument at a fraction of the cost using off-the-shelf components (if you are very proficient with computers and don’t mind a rat’s nest of wires), while its defenders sing the praises of its compact, cable-free, easy to use and powerful on-the-fly imaging capabilities.

While there’s no denying that for the £2,599 asking price of an eVscope one can buy a large and capable conventional optical telescope, I doubt that the latter would be used half as much or would provide a fraction of the pleasure of an eVscope in the hands of a typical keen stargazer – unless they were exclusively interested in the Moon and planets, in which case they should look for another solution. The old adage that the best telescope is the one that you use most often is true, irrespective of price: I suspect that for thousands of observers worldwide the super-portable and ever-ready eVscope easily meets that criterion.

Ade Ashford has travelled the globe writing about astronomy and telescopes, serving on the staff of astronomy magazines on both sides of the Atlantic. His first Astronomy Now review appeared a quarter of a century ago.


Did another advanced species exist on Earth before humans?

Our Milky Way galaxy contains tens of billions of potentially habitable planets, but we have no idea whether we’re alone. For now Earth is the only world known to harbor life, and among all the living things on our planet we assume Homo sapiens is the only species ever to have developed advanced technology.

But maybe that’s assuming too much.

In a mind-bending new paper entitled “The Silurian Hypothesis” — a reference to an ancient race of brainy reptiles featured in the British science fiction show "Doctor Who" — scientists at NASA’s Goddard Institute for Space Studies and the University of Rochester take a critical look at the scientific evidence that ours is the only advanced civilization ever to have existed on our planet.

“Do we really know we were the first technological species on Earth?” asks Adam Frank, a professor of physics and astronomy at Rochester and a co-author of the paper. “We’ve had an industrial society for only about 300 years, but there’s been complex life on land for nearly 400 million years.”

If humans went extinct today, Frank says, any future civilization that might arise on Earth millions of years hence might find it hard to recognize traces of human civilization. By the same token, if some earlier civilization existed on Earth millions of years ago, we might have trouble finding evidence of it.

In search of lizard people

The discovery of physical artifacts would certainly be the most dramatic evidence of a Silurian-style civilization on Earth, but Frank doubts we’ll ever find anything of the sort.

“Our cities cover less than one percent of the surface,” he says. Any comparable cities from an earlier civilization would be easy for modern-day paleontologists to miss. And no one should count on finding a Jurassic iPhone it wouldn't last millions of years, Gorilla Glass or no.

Finding fossilized bones is a slightly better bet, but if another advanced species walked the Earth millions of years ago — if they walked — it would be easy to overlook their fossilized skeletons — if they had skeletons. Modern humans have been around for just 100,000 years, a thin sliver of time within the vast and spotty fossil record.

For these reasons, Frank and Gavin Schmidt, a climatologist at Goddard and the paper's co-author, focus on the possibility of finding chemical relics of an ancient terrestrial civilization.

Using human technology as their guide, Schmidt and Frank suggest zeroing in on plastics and other long-lived synthetic molecules as well as radioactive fallout (in case factions of ancient lizard people waged atomic warfare). In our case, technological development has been accompanied by widespread extinctions and rapid environmental changes, so those are red flags as well.

After reviewing several suspiciously abrupt geologic events of the past 380 million years, the researchers conclude that none of them clearly fit a technological profile. Frank calls for more research, such as studying how modern industrial chemicals persist in ocean sediments and then seeing if we can find traces of similar chemicals in the geologic record.

He argues that a deeper understanding of the human environmental footprint will also have practical consequences, helping us recognize better ways to achieve a long-term balance with the planet so we don't end up as tomorrow's forgotten species.

Then again, he’s also a curious guy who's interested in exploring more far-out ideas for finding Silurian-style signatures: “You could try looking on the moon,” he says.

Lunar archaeology

The moon is a favored target of Penn State University astronomer Jason Wright, one of a handful of other researchers now applying serious scientific thinking to the possibility of pre-human technological civilizations.

“Habitable planets like Earth are pretty good at destroying unmaintained things on their surfaces,” Wright says. So he’s been looking at the exotic possibility that such a civilization might have been a spacefaring one. If so, artifacts of their technology, or technosignatures, might be found elsewhere in the solar system.

Related

Mach Space aliens could have died out long ago, scientist says

Wright suggests looking for such artifacts not just on the lunar surface, but also on asteroids or buried on Mars — places where such objects could theoretically survive for hundreds of millions or even billions of years.

SpaceX’s recent launch of a Tesla Roadster into space offers an insight into how such a search might go. Several astronomers pointed their telescopes at the car and showed that, even if you had no idea what you were looking at, you’d still quickly pick it out as one weird-looking asteroid.

Finding technosignatures in space is an extreme long shot, but Wright argues that the effort is worthwhile. “There are lots of other reasons to find peculiar structures on Mars and the moon, and to look for weird asteroids,” he says. Such studies might reveal new details about the history and evolution of the solar system, for instance, or about resources that might be useful to future spacefarers.

If the efforts turn up a big black obelisk somewhere, so much the better.


UPDATE FOR SUMMER 2021: Due to the COVID-19 pandemic, we postponed the UT Austin Summer 2020 REU-ASSURE program to Summer 2021 and we offered the Summer 2020 cohort the option to participate in Summer 2021. Therefore, we are unfortunately not taking any new applications for Summer 2021. We invite all eligible students who have expressed interest in our program to apply next year for Summer 2022.

The Astronomy Department of The University of Texas (UT) at Austin will host a Summer Research Experiences for Undergraduates (REU) program entitled "Frontier Research and Training in Astronomy for the 21st Century" for eight students for ten weeks from June to August 2021 (exact dates are to be determined). The program (Principal Investigator and Director: Dr. Shardha Jogee) is funded by the National Science Foundation (NSF) REU program and the Department of Defense (Dod) ASSURE program, and involves a synergistic collaboration between the UT Austin Astronomy Department, McDonald Observatory, the Texas Advanced Computing Center, and the Texas Institute for Discovery Education in Science.

PROGRAM DETAILS: The UT Austin Astronomy Department is one of the top-ranked departments in the nation and we are committed to fostering a diverse and inclusive environment in the astronomy community at large. Our REU program aims to engage the full pool of excellence in our diverse nation and to equip students with modern skills needed to succeed in the STEM landscape of the 21 st century. Students in our REU program will enjoy the following:


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Astronomy software relies on accurate data. Version 8 has the latest and best deep-sky and stellar data available. Data is taken from the latest professional, peer-reviewed catalogs and now contains 1.6 million objects. Version 8 includes the latest (2021) Revised NGC/IC catalog by Dr. Wolfgang Steinicke. Other catalogs have been added or updated and many corrections and cross references have been made to the database. Stellar data have been updated to permit high accuracy binary star ephemerides for well-studied visual systems, and predictions of variable star light extrema. Catalog data is treated differently than any other software in the industry. See why.

Accurate ephemerides may be calculated for Sun, moon, planets, comets and asteroids. You can do filtered and sorted searches for asteroids and comets.

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Populations I and II

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Populations I and II, in astronomy, two broad classes of stars and stellar assemblages defined in the early 1950s by the German-born astronomer Walter Baade. The members of these stellar populations differ from each other in various ways, most notably in age, chemical composition, and location within galactic systems.

Since the 1970s, astronomers have recognized that some stars do not fall easily into either category these stars have been subclassified as “extreme” Population I or II objects.

Population I consists of younger stars, clusters, and associations—i.e., those that formed about 1,000,000 to 100,000,000 years ago. Certain stars, such as the very hot, blue-white O and B types (some of which are less than 1,000,000 years old), are designated as extreme Population I objects. All known Population I members occur near and in the arms of the Milky Way system and other spiral galaxies. They also have been detected in some young irregular galaxies (e.g., the Magellanic Clouds). Population I objects are thought to have originated from interstellar gas that has undergone various kinds of processes, including supernova explosions, which enriched the constituent matter. As a result, such objects contain iron, nickel, carbon, and certain other heavier elements in levels that approximate their abundance in the Sun like the Sun, however, they consist mostly of hydrogen (about 90 percent) and helium (up to 9 percent).

Population II consists of the oldest stars and clusters, which formed about 1,000,000,000 to 15,000,000,000 years ago. Members of this class presumably were created from interstellar gas clouds that emerged shortly after the big bang, a state of extremely high temperature and density from which the universe is believed to have originated. These stellar objects are relatively rich in hydrogen and helium but are poor in elements heavier than helium, containing 10 to 100 times less of these elements than Population I stars, because such heavier elements had not yet been created at the time of their formation. RR Lyrae variable stars and other Population II stars are found in the halos of spiral galaxies and in the globular clusters of the Milky Way system. Large numbers of these objects also occur in elliptical galaxies.