Renowned British astronomer Guy Ottewell originally published this piece about Comet C/2021 T4 Lemmon on May 25, 2023. Reprinted with permission. Edits by EarthSky.

Comet C/2021 T4 Lemmon

Comet C/2021 T4 Lemmon was discovered on October 7, 2021, on images taken at the Mount Lemmon Observatory, northeast of Tucson in Arizona. T4 means the 4th discovery or recovery in the first half of October.

Mount Lemmon is the highest point of the Santa Catalina Mountains, one of four mountain ranges around Tucson. It’s not to be confused with Catilina, the conspirator who tried to seize power over the Roman republic in 63 BCE. I’m reminded of my speculation that the Navajos may have seen Canopus, the great star of the south, from one of the four sacred peaks surrounding their land. In fact, it’s shown as the cover picture for the Astronomical Calendar 2023.

When discovered, comet C/2021 T4, because of the geometry of its orbit, appeared quite northerly, at declination +12°.

Comet C/2021 T4 Lemmon is a long period comet

In fact, it’s a long-period comet; if it ever previously dropped from its remote home – at 44,000 AU out – to the inner solar system, it would have been millions of years ago. So during its present passage, it’ll feel gravitational perturbations from the planets that will shorten its period to merely thousands of years.

Its orbit is inclined about 20° to the ecliptic plane. However, it’s going in a retrograde direction, or opposite to the direction in which the planets revolve. The result is that it’ll make a very long rapid sweep across our southern sky.

Finder chart

At present the comet is 60° out in the morning sky, southerly (at declination -13°), 1.75 AU from the sun and 2 AU from Earth. However, it’s still at a dim magnitude of about 11. Then, on June 27, 2023, its distance from us will shrink to 1 AU.

On July 18, 2023, we will pass it at opposition. And around this time, it’ll be nearest to us, 0.54 AU, and brightest, perhaps about magnitude 8 or 7 but still below the unaided-eye limit. Its nearness will make it appear even farther south, at declination -56° on July 20.

Then in the following months it will climb north, becoming lower in the evening sky and more distant. At the same time it’ll be dimming by perhaps 2 or 3 magnitudes. It will reach perihelion, 1.48 AU from the sun, on July 31, 2023. Finally, it’ll ascend across the ecliptic on September 10, 2023, and be at conjunction behind and north of the sun on November 9, 2023.

Of course, we must remember that predictions of a comet’s brightness, and the size of their tails, can be unreliable. That’s because they depend on the melting of ice and release of dust in these lumpy spinning objects.

Comet-Hale Bopp still observable? Wow!

By the way, Alan Hale alerted us (Guy Ottewell) to this comet with a Facebook post on May 22. Alan was discoverer of the great comet Hale-Bopp (C/1995 O1). And, despite now being more than 47 AU away, it’s the first on the Minor Planet Center’s list of currently observable comets, not because of its present magnitude (about 20) but because it is the earliest-numbered non-periodic comet still considered observable at all.

Bottom line: Comet C/2021 T4 Lemmon was discovered from Mount Lemmon Observatory in 2021. It’s currently sweeping through the southern skies.

When to watch: Venus came into view after sunset in December 2022 and has been visible in the evening sky throughout the first half of 2023. Greatest elongation – when Venus will be farthest from the sunset – happens on June 4, 2023. Afterwards, Venus will quickly sink toward the sunset as it races toward its sweep between the Earth and sun around mid-August 2023.
Where to look: Look in the sunset direction while the sky is darkening. You can’t miss Venus as the dazzling evening “star.”
Greatest elongation is at 11 UTC on June 4. That’s a whole-Earth time … for all of us, Venus will still appear in our evening sky, in the west after sunset. At this elongation, the distance of Venus from the sun on the sky’s dome is 46 degrees.
Magnitude at greatest elongation: Venus shines at magnitude -4.4.
Through a telescope: Venus appears 49% illuminated, in a first quarter phase, 23.56 arcseconds across.
Note: As the sun’s 2nd planet, Venus is bound by an invisible tether to the sun in our sky. It’s always east before sunrise, or west after sunset (never overhead at midnight). Venus is the brightest planet visible from Earth and shines brilliantly throughout every morning or evening apparition. Greatest elongation happens when Venus is farthest from the sun on the sky’s dome.

For precise sun and Venus rising times at your location:

Old Farmer’s Almanac (U.S. and Canada)

timeanddate.com (worldwide)

Stellarium (free online planetarium program)

Venus after sunset in 2023 Northern Hemisphere

Venus after sunset in 2023 Southern Hemisphere

A comparison of elongations

Not all of Venus’s greatest elongations are created equal. That’s because the farthest from the sun that Venus can ever appear on the sky’s dome is about 47.3 degrees. On the other hand, the least distance is around 45.4 degrees.

Elongations are also higher or lower depending on the time of year they occur and your location on Earth.

Venus events from late 2022 into 2024

October 22, 2022: Superior conjunction (passes behind sun from Earth)
June 4, 2023: Greatest elongation (evening)
August 13, 2023: Inferior conjunction (races between Earth and sun)
October 23, 2023: Greatest elongation (morning)
June 4, 2024: Superior conjunction (passes behind sun from Earth)

Bottom line: At greatest eastern elongation on June 4, 2023, Venus is as far from the sunset as it will be for this evening apparition.

British astronomer and EarthSky friend Guy Ottewell originally published this piece about star density on his website on May 20, 2023. Reprinted here with permission. Edits by EarthSky.

How many red dwarfs?

Huge stars are rare. And tiny stars (mostly red dwarfs) are numerous in our Milky Way galaxy. Astronomers believe this is true. But it’s based on an assumption … that what we see in nearby space holds true in larger volumes of space, and perhaps throughout the galaxy. We don’t know for sure because we can’t see tiny stars at great distances from our sun. Far from our sun, only the luminous giant stars are noticeable.

Meanwhile, most of the unaided-eye stars we see in our sky – most of the familiar stars for which we have names – are relatively large in contrast to red dwarfs. They are distant and not typical of the total range of star masses and sizes, thought to exist in our Milky Way. A section on the Nearest Stars in my book Astronomical Companion labors this point. So … how many red dwarf stars are there? And is the neighborhood around our sun typical?

It occurred to me that I could illustrate star masses by showing the Astronomical Companion‘s nearest-stars picture. You will see that picture above. It shows a sphere of space with radius 16 light-years. Now compare the image above with the illustration below. The second illustration shows a somewhat more-distant shell of space, 90 light-years in radius.

So … above we have an illustration showing a sphere of space 16 light-years in radius. And below we have a disk-shaped block of space 90 light-years in radius and 10 light-years thick.

Does the density of small red dwarf stars hold true for both?

Plotting the data: How we know

The European Space Agency’s Hipparcos satellite – which flew from 1989 to 1993 (I had to buy it on disks from the Netherlands) – must come close to containing all the stars that inhabit the 90-light-year volume of space, illustrated above.

So by plotting all of the stars measured by Hipparcos, not just those above a certain visibility, we would show the density of stars in our nearby space. And we’d see if the ratio of rare giants to teeming midgets holds as true for a region with a 90-light-year radius, as for a region with a 16-light-year radius.

The difficulty in plotting this was that a picture of the same kind, with stalks connecting each star to a plane so that we can see how they are arranged in space, would be an unintelligible forest of stalks. So – instead of making the same sort of illustration for both 16 and 90 light-years – I tried a view from galactic north, with stars limited to a wedge in declination – included only if within 10° of the celestial equator.

Eventually, the picture evolved to the chart you see above.

It’s a view from galactic north: looking down on the plane of our Milky Way galaxy. Not actually the mid-plane, but the plane in which the sun lies (which is an uncertain distance, maybe 30 light-years, north of the galaxy’s real median plane). We see stars out to 90 light-years from us, but only those that are within 5 light-years north or south of this sun’s plane.

So we are looking at a disk-shaped block of space 90 light-years in radius and 10 light-years thick.

Comparing the 2 charts: What we see

The density of stars does look consistent between the two charts on this page: similar in our closer neighborhood and in the more distant parts. But there are differences.

Consider that – in the 90-light-year-radius chart – the dots for the stars are sized for their absolute magnitudes – their true brightnesses – not their apparent magnitudes as seen from Earth. Colored pink are those that actually look fainter to us: those of apparent magnitude 6 or dimmer. Most of the stars in the outer rings are too dim for the unaided eye. But, in the inner region, we do see the few stars that are among the brightest in our sky because they are nearby and are of about the sun’s size or larger: Sirius, Procyon, Alpha Centauri, Altair.

In the outer regions of the 90-light-year-radius chart, it’s hard to find any named stars; I had to lower the magnitude threshold for them to 5 before finding any even with names of the unfamiliar kind that aren’t really used – Kaffaljidhm is a star in Cetus, Keid is in Eridanus, Alshain is in Aquila.

Do the charts reflect the reality?

So does the 90-light-year illustration really show the density of stars in our part of the galaxy? It’s an approach, but probably an understatement.

My program told me it had plotted 187 stars. The Hipparcos satellite produced two sets of data, called Hipparcos and Tycho. Tycho goes down to about three magnitudes dimmer, and has entries for nearly 9 times as many stars, though with shorter lines of information about each. If I make my program read the Tycho set instead, it takes minutes longer, and packs the picture with 19,164 stars!

Are there really so many more faint stars relatively close around us? I’ll probably be returning to this.

Bottom line: Astronomer Guy Ottewell uses 2 charts – showing 2 different volumes of space – to contemplate and question the density of red dwarf stars in our Milky Way.

Via Guy Ottewell

How do you describe how far apart something is in the sky? The fact is, the handiest measuring stick for the sky’s dome is the one on the end of your arm. You can use the width of your pinky, fist and more to gauge the distance between sky objects. That comes in handy when you’re observing conjunctions between planets, or close planets and stars, or planets and stars and the moon, plus many other space objects. You’ll often find these objects described as being a certain number of degrees, arcminutes or arcseconds apart.

Use this “handy” tool for sky measurements

To begin with, from one side of the sky – or the horizon – all the way across to the other horizon measures 180 degrees, or half a circle. Therefore, from horizon to zenith, the point straight above your head, should be 90 degrees (this is assuming a flat horizon, not a hilly or mountainous region).

The general rule amateur astronomers use is that the width of your fist held at arm’s length equals about 10 degrees. You may look at your fist and the fist of a small child and wonder how both can measure 10 degrees, but the size of peoples’ fists is generally proportional to the length of their arms. Thus, a child with a small fist and small arm will measure approximately 10 degrees from their perspective, just as an adult with a larger fist and longer arm measures 10 degrees from their point of view.

If you want to do a rough check, extend your arm and fist out toward a flat horizon. Then place your other arm and fist on top of the first, and alternate, trying not to wobble, until you have counted nine fists. Your ninth fist should be pointing straight up, over your head, because the zenith is at 90 degrees.

For degrees smaller than 10, focus on just your fingers. At arm’s length, a pinky measure about 1 to 1.5 degrees, and your three middle fingers measure about 5 degrees. For larger degrees, you’ll need to stretch those fingers out. To find 15 degrees, use your index finger and pinky spread apart, and to find 25 degrees, look at the span between your pinky and thumb spread apart.

The Big Dipper works for sky measurements

The Big Dipper is a good target to use in checking your hand measurements. The end two stars in the bowl, the ones that are used to find Polaris, are about five degrees apart. The top two stars in the bowl of the Big Dipper are 10 degrees apart. And finally, using the same far star in the bowl of the Big Dipper that you used for the first two tests (Dubhe, the spot at which water would pour out if it were a real dipper) plus the end star in the handle will measure 25 degrees.

What about the sun and the moon?

How wide do you think the full moon looks? How many degrees would you expect it to measure? Five degrees? Two? One? Most people overestimate its size, but the full moon is a mere half degree across. How about the sun? While instinctually you might want to say the sun is larger, because its actual size is huge if put side-by-side with the moon, we know that the amount of sky the sun and moon take up is equal, a half degree.

We know this without even having to check out the sun with our half-pinky measurement, because we know that during total solar eclipses the moon temporarily slips just in front of the sun, blocking all of its light for a fleeting few minutes.

Now about arcminutes and arcseconds

Once you have a good grasp of degrees, if you want to estimate smaller measurements, you need to know that degrees are further divided by arcminutes. There are 60 arcminutes in one degree, therefore the moon and sun are each 30 arcminutes across. Then, arcminutes can also be divided. So, 60 arcseconds make up one arcminute.

Going back to the Big Dipper, the stars at the bend of the handle are a double star system named Mizar and Alcor and are separated by just 12 arcminutes. People with good eyesight can see the two separate stars without optical aid. Stars closer than this usually require binoculars or a telescope to split. Mizar has another companion that is even closer than Alcor. Mizar’s double star is a mere 14.4 arcseconds away. Arcminutes are written with the same symbol as feet (‘) and arcseconds are written with the inch notation (“).

The sun moves about 15 degrees an hour

Also, you can tell how long until the sun will set by measuring its distance from the horizon. The sun moves about 15 degrees across the sky in an hour. Moving 15 degrees an hour for 24 hours would equal 360 degrees, or a full day from sunset to sunset. (Of course, the sun is not really moving, it’s only appearing to move in the sky as Earth turns.) Remember that unless you are at the equator, the sun is not moving in a beeline toward the horizon. The sun sinks downward at an angle that gets steeper the closer you’re located to the poles .

Bottom line: Degrees, arcminutes and arcseconds are all useful units of measurement in astronomy. Sometimes your own hand – held at arm’s length – can help. For example, your fist held at arm’s length measures 10 degrees on the sky’s dome. Your pinky at arm’s length measures one degree.

On May 1, 2023, Mercury passed very close to the sun. In fact, if its inferior conjunction was about a week later, it would transit the sun. Even though a transit doesn’t happen, Mercury is heading for its greatest morning elongation on May 29, 2023. This elongation is best viewed from the Southern Hemisphere where it rises about two hours before sunrise and will be visible until around mid-June.

At greatest elongation in May 2023

When to watch: Around mid-May 2023 start looking for Mercury! That is, especially if you’re in the Southern Hemisphere, where the ecliptic (the green line on our charts) makes a steep angle with the eastern predawn horizon. Greatest elongation – when Mercury will be farthest from the sunrise on our sky’s dome – will be May 29. But the planet will continue getting brighter after that. So, in early June, although it’ll be edging back toward the sunrise, Mercury will be easier to spot in the morning twilight.
Where to look: Look in the sunrise direction, as the sky is getting lighter.
Greatest elongation is on May 29 at 6 UTC (1 a.m. CDT). Mercury will be shining at +0.6 magnitude that morning. And it’ll be 24.9 degrees from the sun.
Through a telescope on and around May 29, Mercury will appear 38% illuminated, in a crescent phase, and 8.2 arcseconds across. By the way, in mid-June it’ll be almost 75% illuminated by the time it slips out of view for Southern Hemisphere observers.
Note: Once you spot it, notice that Mercury brightens quickly in June, reaching around -1.0 magnitude before slipping away in the morning glare in mid-June.

Mercury in Southern Hemisphere in May 2023

For precise sun and Mercury rising times at your location:

Old Farmer’s Almanac (U.S. and Canada)
timeanddate.com (worldwide)
Stellarium (online planetarium program)

Mercury events in 2023

January 7, 2023: Inferior conjunction (races between Earth and sun)
January 30, 2023: Greatest elongation (morning)
March 17, 2023: Superior conjunction (passes behind sun from Earth)
April 11, 2023: Greatest elongation (evening)
May 1, 2023: Inferior conjunction (races between Earth and sun)
May 29, 2023: Greatest elongation (morning)
July 1, 2023: Superior conjunction (passes behind sun from Earth)
August 10, 2023: Greatest elongation (evening)
September 6, 2023: Inferior conjunction (races between Earth and sun)
September 22, 2023: Greatest elongation (morning)
October 20, 2023: Superior conjunction (passes behind sun from Earth)
December 4, 2023: Greatest elongation (evening)
December 22, 2023: Inferior conjunction (races between Earth and sun)

Heliocentric view of Mercury May 2023

A comparison of elongations

Not all of Mercury’s greatest elongations, however, are created equal. In fact, some are greater than others. That’s because the farthest from the sun that Mercury can ever appear on the sky’s dome is about 28 degrees. On the other hand, the least distance is around 18 degrees.

Also, elongations are better or worse depending on the time of year they occur and your location on Earth.

Seasons make a difference

So, in the autumn for either hemisphere, the ecliptic – or path of the sun, moon and planets – makes a narrow angle to the horizon in the evening. Conversely, it makes a steep slant, nearly perpendicular, in the morning. So – in autumn from either hemisphere – morning elongations of Mercury are best. Then, Mercury appears higher above the horizon and farther from the glow of the sun. On the other hand, however, evening elongations in autumn are harder to see.

On the other hand, in the spring for either hemisphere, the situation reverses. The ecliptic and horizon meet at a sharper angle on spring evenings and a narrower angle on spring mornings. So, in springtime for either hemisphere, evening elongations of Mercury are best. Meanwhile, morning elongations in springtime are harder to see.

Bottom line: Watch for Mercury in the east before sunup around mid-May 2023. Mercury reaches greatest elongation – its greatest distance from the sunrise – on May 29 and then brightens through mid-June. It’s best viewed from the Southern Hemisphere.

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May 2023 meteors … the Eta Aquariids

Moonlight will obscure the 2023 Eta Aquariids.

When to watch: Full moon falls near the peak of the 2023 Eta Aquariid shower. If you want to try watching in moonlight, try the mornings of May 5, 6 and 7, 2023, in the hours before dawn. Why before dawn? See Radiant chart above. The American Meteor Society is listing 15 UTC on May 6 as the shower’s predicted** peak time. But times vary between different experts. And the peak of this shower stretches out over several days. So you can expected elevated numbers of meteors a few days before and after the peak time … albeit in moonlight.
Nearest moon phase: In 2023, full moon will fall at 17:34 UTC on May 5. Moonlight will obscure the 2023 Eta Aquariids.
Radiant: Rises in the wee hours, climbing toward its highest point at dawn. That’s why before dawn is the best time to watch this shower.
Duration of shower: April 15 to May 27.
Expected meteors at peak, under ideal conditions: In the southern half of the U.S., you might see 10 to 20 meteors per hour under a dark sky, with no moon, when the radiant is high in the sky. Farther south – at latitudes in the Southern Hemisphere – you might see two to three times that number.
Note: The Eta Aquariids’ radiant is on the ecliptic, which rides low in the sky on spring mornings as seen from the Northern Hemisphere. That’s why this shower favors the Southern Hemisphere. It’s often that hemisphere’s best meteor shower of the year … but not in 2023, when moonlight will drown out most meteors.

Visit EarthSky’s meteor shower guide for 2023

Report a fireball (very bright meteor) to the American Meteor Society: it’s fun and easy!

The Eta Aquariids’ parent comet

This section is by the late, great Don Machholz (1952-2022), who discovered 12 comets …

The object responsible for the Eta Aquariid meteor shower – that is, its parent comet – is the famous Halley’s Comet. This comet is in a retrograde orbit around the sun. That means it runs around the sun in the opposite direction from Earth and all the other planets. As a result, we pass near its path twice, one time along the outbound portion of the comet’s orbit. That happens every early May, causing the Eta Aquariid meteor shower. The other time is along the inbound portion of the comet’s orbit, and that passage causes the Orionid meteor shower in late October of each year.

Halley’s Comet orbits the sun on an average of every 76 years (the range is from 74 through 79 years due to perturbations of the planets). So, in most years, the comet is nowhere near when we sweep through its orbit, and when debris left behind by the comet enters our atmosphere to create Halley’s two meteor showers.

Perhaps you saw Halley’s Comet when it returned last, in 1985/86. It has been observed since the year 240 BCE. Halley’s Comet will be back in 2061. Presently the comet is traveling away from the sun at about 0.6 miles a second (0.9 km/sec). In the year 2023, Halley’s Comet is beyond the orbit of Pluto.

In November or December of 2023, the comet will reach its farthest point from the sun that binds it in orbit. Then – pulled inexorably by the sun’s gravity – it will curve around and head back toward the inner solar system again.

While waiting for Halley’s Comet to return, watch for the next best thing: the Eta Aquariid meteor shower in early May.

More about this shower’s radiant

If you trace the paths of the Eta Aquariid meteors backward, they all seem to radiate from a certain point in front of the constellation Aquarius the Water Bearer. This point on the sky’s dome is called the radiant of the meteor shower, which nearly aligns with the faint star Eta Aquarii. Hence, this meteor shower gets its name from this star.

Eta Aquarii is one of the four stars making up the Y-shaped Water Jar asterism in the northern part of Aquarius. If you can find the Water Jar in the constellation Aquarius, you’ve as good as located the radiant point for the Eta Aquariid meteors. The alignment of the radiant and the star is, of course, coincidental. Eta Aquarii is some 170 light-years away – trillions upon trillions of miles away – while the Eta Aquariid meteors burn up nearby – only 60 miles (100 km) above Earth’s surface.

Meteor shower radiants are sometimes misunderstood by casual meteor-watchers. You don’t need to know where they are to watch a meteor shower. That’s because the meteors fly every which way across the sky, in front of numerous constellations. However, the higher a shower’s radiant appears in your sky, the more meteors you’re likely to see. For the Eta Aquariids, the radiant soars highest in the nighttime sky just before dawn. That’s one of the reasons why you can expect to see the most meteors in the wee morning hours.

How to view a meteor shower

As with all meteors in annual showers, no special equipment to watch the Eta Aquariids. But a little luck always helps.

Find a dark, open sky away from artificial lights, and sprawl out on a reclining lawn chair.

Make yourself comfortable with a hot flask of you favorite beverage. Keep warm but not so snug that you fall asleep!

Meteor watching is a lot like fishing. Sometimes you catch a good number of them, and sometimes you don’t.

Eta Aquariid meteor shower photos from EarthSky’s community

Bottom line: May’s Eta Aquariid meteor shower has a broad peak and often can be watched over several mornings. But, in 2023, moonlight interferes.

**Predicted peak times and dates for meteor showers are from the American Meteor Society. Note that meteor shower peak times can vary. Back to top.

Read more: Why the Eta Aquariids are best from the Southern Hemisphere.

Meteor showers: Tips for watching the show

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Penumbral lunar eclipse

People in eastern Europe, the Middle East, Africa, Asia, Australia, New Zealand, Antarctica, the South Atlantic Ocean, the Indian Ocean and the Pacific Ocean will see a deep penumbral lunar eclipse during the night of May 5-6, 2023.

Penumbral eclipse begins at 15:13 UTC on May 5, 2023. That is 11:13 a.m. EDT in North America, and the moon isn’t up for the Americas at that time. That’s why this eclipse is not visible from the Americas.
Greatest eclipse is at 17:22 UTC on May 5 with a penumbral magnitude of 0.9655. In other words, at greatest eclipse, nearly all of the moon will be inside the Earth’s outer penumbral shadow. The moon will never go into Earth’s darker umbral shadow. So it will never seem as if a dark bite has been taken out of the moon. Instead, it’ll be a subtle darkened shading on the moon, and, at mid-eclipse, only a small sliver of the moon will fall outside this dark shading.
Penumbral eclipse ends at 19:31 UTC on May 5 (3:31 p.m. EDT).
Duration of eclipse: This is a deep penumbral lunar eclipse with a duration of 258 minutes.
Note: A penumbral lunar eclipse is the most subtle kind of lunar eclipse, one that most people won’t even notice. The moon’s shadow won’t be detected until the disk of the moon is immersed in about 2/3 of the penumbral shadow. Of course, this depends on the atmospheric conditions and a person’s visual acuity.

The full moon and eclipses

If this full moon were truly opposite the sun, there’d be a total umbral eclipse of the moon. That is, the darkest part of Earth’s shadow – the umbra – would cover the moon at mid-eclipse. But this full moon in May sweeps to the south of the Earth’s umbra. So no total or partial lunar eclipse in the Earth’s dark shadow can take place.

Instead, the full moon almost fully passes through the Earth’s penumbral shadow. So it’s a very deep penumbral eclipse. At no time will Earth’s dark shadow take a “bite” out of the moon. Instead, penumbral eclipses are all about subtle shadings.

The May 5-6 penumbral lunar eclipse occurs when the moon is in the constellation of Libra the Scales.

Find the moon’s path with respect to Earth’s umbral and penumbral shadows below.

Visit Timeanddate.com to get an exact timing of the eclipse from your location.

Eclipses in 2023

The May 5, penumbral lunar eclipse is preceded two weeks earlier by a hybrid solar eclipse on April 20, 2023. The fact is, these two eclipses take place within a single eclipse season.

An eclipse season is an approximate 35-day period during which it’s inevitable for at least two (and possibly three) eclipses to take place.

Then later this year, the October 2023 eclipse season will feature a annular solar eclipse on October 14, 2023, and a very shallow partial lunar eclipse on October 28, 2023.

Maps and data for the total lunar eclipse

Visit Timeanddate.com to get an exact timing of the eclipse from your location.

Penumbral lunar eclipse photos from our EarthSky community

Submit your photo to EarthSky here.

More resources

Bottom line: A penumbral lunar eclipse – lasting over four hours – happens overnight on May 5-6, 2023. It’s visible from eastern Europe, Africa, Asia, Australia, New Zealand, Antarctica and Indonesia.

Visit Timeanddate.com to get an exact timing of the eclipse from your location.

EarthSky’s monthly night sky guide: Visible planets and more

The next penumbral lunar eclipse: May 5-6, 2023

An eclipse of the moon can only happen at full moon, when the sun, Earth and moon line up in space, with Earth in the middle. So at such times, Earth’s shadow falls on the moon, creating a lunar eclipse. Lunar eclipses happen a minimum of two times to a maximum of five times a year. As a matter of fact, there are three kinds of lunar eclipses: total, partial and penumbral.

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The three types of lunar eclipses

In a total eclipse of the moon, the inner part of Earth’s shadow, called the umbra, falls on the moon’s face. Then at mid-eclipse, the entire moon is in shadow, which may appear blood red.

Next, there is a partial lunar eclipse, where the umbra takes a bite out of only a fraction of the moon. The dark bite grows larger, and then recedes, never reaching the total phase.

Finally, there’s a penumbral lunar eclipse, when only the more diffuse outer shadow of Earth – the penumbra – falls on the moon’s face. In fact, this third kind of lunar eclipse is much more subtle, and much more difficult to observe, than either a total or partial eclipse of the moon. That’s because there is never a dark bite taken out of the moon, as in a partial eclipse. So the eclipse never progresses to reach the dramatic minutes of totality. And at best, at mid-eclipse, very observant people will notice a dark shading on the moon’s face. Others will look and notice nothing at all.

According to eclipse expert Fred Espenak, about 35% of all eclipses are penumbral. Another 30% are partial eclipses, where it appears as if a dark bite has been taken out of the moon. And the final 35% go all the way to becoming total eclipses of the moon, a beautiful natural event.

What to expect from a penumbral eclipse

Some eclipse photos

Bottom line: There are three kinds of lunar eclipses: total, partial and penumbral. A penumbral eclipse is very subtle. At no time does a dark bite appear to be taken out of the moon. Instead, at mid-eclipse, observant people will notice a shading on the moon’s face.

Next penumbral lunar eclipse: May 5-6, 2023

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May Day is May 1

You might not realize it, but May Day – an ancient spring festival in the Northern Hemisphere – is an astronomy holiday. It’s one of the year’s four cross-quarter days. That is, it’s a day that falls more or less midway between an equinox and solstice. In this case, it’s between the March equinox and June solstice.

The other cross-quarter days are Groundhog Day on February 2, Lammas on August 1, and Halloween on October 31.

May Day also stems from the Celtic festival of Beltane. It was related to the waxing power of the sun as we in the Northern Hemisphere move closer to summer. At Beltane, people drove livestock through lit fires and people danced around them. They were all moving in the same direction that the sun crosses the sky.

In Hawaii, May Day is Lei Day, a statewide celebration of the aloha spirit and the giving of the flower lei.

May Day and maypoles

Of course, wrapping a maypole with colorful ribbons is perhaps the best known of all May Day traditions. In the Middle Ages, English villages all had maypoles. They were part of the rejoicing and raucous merrymaking of May Day.

Maypoles came in many sizes. And there was competition among the villages to show whose maypole was tallest. In small towns, maypoles were usually set up for the day. But they were erected permanently in London and the larger towns.

Here’s a WikiHow on how to do a maypole dance

May baskets can brighten someone’s day

We’re not too far away from a time in the late 20th century when people left homemade May baskets filled with spring flowers and sweets on others’ doorsteps, usually anonymously. I can remember doing this as a child. Maybe it’s a tradition that can be revived.

I love this for a May craft for kids! #maydayhttps://t.co/00NGF4L1I8

— HomeschoolSuperFreak (@HSSuperFreak) April 18, 2023

Bottom line: May 1 is one of four cross-quarter days, midway between an equinox and a solstice. So happy May Day 2023!

Read more: Halloween is a cross-quarter day

Read more: Groundhog Day is an astronomy holiday

First quarter moon falls at 21:20 UTC on April 27, 2023

Lunar X and Lunar V

Have you heard of Lunar X and Lunar V? They are famous optical features on the moon, visible through telescopes. So when the moon’s terminator – or line between light and dark on the moon – is located in just the right place, you can see a letter X and a letter V on the moon’s surface. A sign of an alien visitation? No. Lunar X is a great example of how lighting and topography can combine on a planet or moon to produce a pattern that seems familiar to the human eye.

In reality, the illusion of Lunar X is created by sunlight falling on the rims/ridges between the craters La Caille, Blanchini, and Purbach. The V is caused by light illuminating crater Ukert, along with several smaller craters.

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When are they visible?

Basically, people see Lunar X and Lunar V at each cycle of the moon, but only for a short time. In fact, they’re observable for about four hours around the 1st quarter moon phase.

Bottom line: Lunar X and Lunar V are optical features on the moon, visible through a telescope for several hours around the time of the 1st quarter moon.