Betelgeuse has dipped nearly half a magnitude since late January. Could it be headed for another Great Dimming Event? We also take a look at this spring’s “other” eclipse.

Betelgeuse close-up
The Atacama Large Millimeter/submillimeter Array (ALMA) captured this image of the red supergiant Betelgeuse. One of the largest stars known, it's about 800 times larger than the Sun. Placed at the center of the solar system all the planets out to Jupiter would orbit inside it.
ALMA (ESO / NAOJ / NRAO) / E. O’Gorman / P. Kervella

Indeed it is. But unlike the Great Dimming of 2019–20 its waning so far has been modest. Betelgeuse, located in Orion's right shoulder, ordinarily shines at magnitude +0.4, a close match to neighboring Procyon in Canis Minor. But since late January it's lost some of its luster — at least a third of a magnitude's worth. That may not sound like much especially given the star's variable nature, but the red supergiant star is currently the faintest it's been in the past two years. Could it be at the threshold of another major dimming?

Betelgeuse and vicinity
Betelgeuse and Orion tip westward in this photo taken on March 9, 2024. Procyon and Aldebaran make good comparison stars for tracking the supergiant's changing brightness. It helps that all three stars lie in a nearly straight line at a similar altitude, making comparison straightforward. Betelgeuse faded about 1.2 magnitudes (60 percent) in 2019–20 before recovering in late February 2020.
Bob King

Lest you think you can't detect the fading with your eyes, go out the next clear night and compare Betelgeuse to Aldebaran (magnitude +0.9) and Procyon (+0.4). During the first 10 days of March, I estimated Betelgeuse's magnitude on several occasions at either +0.8 or +0.7 — very similar to Aldebaran and clearly dimmer than Procyon. Other observers have made comparable estimates, while V magnitudes obtained instrumentally with a filter that approximates the human-eye response concur with the visual estimates.

AAVSO Betelgeuse comparison chart
This wide-field map shows Betelgeuse and a number of helpful comparison stars you can use to estimate its changing brightness. Decimals are omitted — 09 represents magnitude +0.9.
Courtesy of the AAVSO

Use the supplied chart (above), courtesy of the American Association of Variable Star Observers (AAVSO), to gauge its brightness yourself. When making an estimate take quick looks. Shift back and forth between Aldebaran and Betelgeuse several times and then do the same with Procyon to settle on a final magnitude. If Betelgeuse's brightness appears halfway between the two then its magnitude is about +0.6. If closer to Aldebaran it might be +0.8, and so on. To compare your results with others or simply to monitor Betelgeuse's changes, go to the AAVSO site, scroll up and enter Betelgeuse in the Pick a Star box, then click Check recent observations.

Betelgeuse's boiling, convective surface — seen in this 3D simulation — may be mimicking its unusually high rotation rate of 5 kilometers per second. More details here.
Jing-Ze Ma

Astronomers and variable star observers have long known that Betelgeuse's light varies with a primary period of 400 days. But since the tumult of 2019–2020 even that pattern seems to have disappeared. To our best knowledge, based on observations using the Hubble Space Telescope and others, Betelgeuse burped up a huge gas bubble that blasted more than 400 billion tons of material into space. The debris later condensed as dust that shrouded part of the star before dissipating. Astronomers detected silicon monoxide in the expanding cloud, a compound commonly found in large stars that can act as a seed to form dust grains. For comparison, the Sun loses only around a billion tons of mass during a coronal mass ejection or CME.

Betelgeuse light curve
This light curve — from March 2019 to March 2023 — reveals Betelgeuse's erratic light variations including the recent dip. Magnitude lies along the vertical axis with UT dates along the horizontal.
Courtesy of the AAVSO

Witnessing stellar evolution from your backyard is a thrill, so I hope you'll cast a glance at Betelgeuse every clear night you can. It remains accessible for Northern Hemisphere skywatchers through mid-April and for Southern Hemisphere viewers through mid-May. What does this pivotal star have up its sleeve, I wonder?

Eclipse for insomniacs

Penumbral eclipse
Earth's penumbra darkens the western half of the full Moon during the penumbral phase of the November 19, 2021, total lunar eclipse.
Bob King

Eclipses come in pairs two weeks apart — one at new Moon and the other at full. April's total solar eclipse has received much deserved press but let's take a quick look at the less publicized penumbral lunar eclipse that will precede it. On the night of March 24–25 the full Moon will cross through Earth's outer shadow, the penumbra. This might be worth ignoring if it weren't for the fact that the Moon moves so deeply into the penumbra it should be baldly obvious to the naked eye.

Penumbral lunar ecilpse on March 25, 2024
Near the midpoint of the penumbral lunar eclipse on March 24–25, even casual skywatchers will notice a smudgy darkness across the lower half of the Moon's disk. Subtract 4 hours to convert times to EDT; 5 hours for CDT; 6 for MDT; and 7 for PDT.
Sky & Telescope / Leah Tiscione

Greatest eclipse occurs at 3:13 a.m. Eastern Daylight Time on March 25th when only a sliver of the Moon's north polar region will poke beyond the shadow's edge. Shading should be obvious across the southern half of the lunar disk. This is a late-night/early-morning event for most of North America and much of South America. Set the alarm for mid-eclipse when the shadow will be unmistakable. I eagerly look forward to this visual appetizer that will presage April's sure-to-be-sensational syzygy.

Others willing to invest more time will catch the first whiff of shading starting about 40 minutes after the Moon first enters the penumbra and up to 40 minutes after maximum eclipse. Here are the best times to watch — centered on mid-eclipse — for a selection of time zones:

  • 3:30 a.m. – 5 a.m. ADT
  • 2:30 a.m. – 4 a.m. EDT
  • 1:30 a.m. – 3 a.m. CDT
  • 12:30 a.m. – 2 a.m. MDT
  • 11:30 p.m. – 1 a.m. PDT
  • 10:30 p.m. – midnight AKDT
  • 9:30 p.m. – 11 p.m. HST

May your nights be stellar!


Image of misha17


March 15, 2024 at 1:59 pm

1. The previous lunar eclipse in the same 18 year Saros cycle was a rare total penumbral lunar eclipse. At mid eclipse the moon was entirely within the Earth's penumbra with the Moon's southern edge just outside, but never reaching, the northern edge of the Earth's umbra. With subsequent penumbral eclipses of this cycle the Moon will pass further and further from the umbra.

2. ... And a half-Saros cycle ago was the lunar eclipse of April 2015, when the Moon's upper limb passed so closely to the umbra's upper edge, there was uncertainty if the eclipse was barely total, or if it was just a ~very~ deep parial eclipse.

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Andrew James

March 17, 2024 at 5:08 pm


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Bob King

March 18, 2024 at 11:01 am

Good info, Misha!

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Will Wilkin

March 17, 2024 at 12:20 am

I just hope Betelgeuse doesn't blow up. I've been starting to really care about this star!

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Bob King

March 18, 2024 at 11:02 am

Babysitting Betelgeuse will guarantee it won't blow up 🙂

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March 22, 2024 at 11:38 pm

It might already have blown up, Will..... sometime in the last 650 years ... we just haven't seen it yet 😉

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March 18, 2024 at 3:15 pm

"Astronomers detected silicon monoxide in the expanding cloud"

When there is enough silicon present in a supergiant's core, the star begins to fuse it into iron, which is the "end game" in stellar evolution since that consumes more energy that it produces.

Hopefully Betelguese's violent convection will keep the silicon from settling near its core, preventing its fusion into iron, but the fact that there is enough silicon inside for the conection to "belch" into space, is not a good sign.

Of course, we are still (probably?) talking about a timeline on the scale of a few cenuries, so we will be able to enjoy seeing Orion in its familiar pattern for a while.

*fingers crossed*

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March 18, 2024 at 3:35 pm

... and I know that the common narrative is that core collapse happens very shortly after iron fusion begins, but could iron fusion occur in "pockets" near the silicon core before the entire core is involved?

If so, it would only would slightly diminish the overall energy output averting core collapse, but the localized energy drop around the "pockets" could distort the convection patterns and "focus" them around the "cooler" areas around the pockets, dragging the silicon near the pockets to the star's surface (and then into space), preventing the pockets from coalescing towards the core.

The last part is wishful thinking and not based on accepted stellar evolution, but if traces of iron or iron oxide can be detected in the dust I'll get ~very~ worried.

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Walter Clayton

March 21, 2024 at 10:20 pm

I've been watching Betelgeuse as much as I could since it brightened last Summer. It's been consistently dimmer than Rigel for most of that time. The weather has NOT been conducive to Astronomy down here in the Treasure Coast of Florida for a LOT of that time, but, I look when I can. Not in a very dark place currently, so, only naked-eye visual observations.

I'll have to find me a new star to compare it to now.

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