How can astronomers know exactly how hot stars are? You can guess from their colors, but to get a precise measurement, you have to look at their spectra.
We spread out the light from the stars into a rainbow-like spectrum and look for patterns of lines, made by different elements and molecules in the star's outer layers. The presence or absence of lines tells you the precise temperature.
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Download video: webbtelescope.org/contents/medā¦
#astronomy #Astro101 #stars
The corporatization of health care has changed the practice of medicine, causing many physicians to feel alienated from their work.Eyal Press (The New York Times)
All latitude bands observed anomalous warmth in June 2023. The largest positive departure were near the Antarctic Peninsula.
Plot shows zonal-mean surface air temperature anomalies (1951-1980 baseline), where latitude = x-axis (not scaled by distance). Data from GISTEMPv4 at data.giss.nasa.gov/gistemp/.
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šØ To no surprise, last month was the hottest June on record for our planet (in this dataset)...
(Preliminary) GISTEMPv4 data/info: data.giss.nasa.gov/gistemp/faqā¦
July in the #Arctic now is a very different place than it was only a few decades ago - just check out the changes in the average sea ice thickness....
Data from psc.apl.uw.edu/research/projecā¦
I will see an ice-free Arctic in my life.
The only question I have left is when precisely that will be.
#Antarctic sea ice remains on its own this year compared to any other July in our satellite record. Keep in mind when looking at this graph that the y-axis interval is 1,000,000 kmĀ². This is a massive deviation from the previous record for the date.
+ More: zacklabe.com/antarctic-sea-iceā¦
+ Data: nsidc.org/data/seaice_index
My visualizations: Arctic Climate Seasonality and Variability Arctic Sea Ice Extent and Concentration Arctic Sea Ice Volume and Thickness Arctic Temperatures Antarctic Sea Ice Extent and Concentratā¦Zachary Labe
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This is another deeply concerning story of an outlier track, that is only surpassed in its shock value by the silences & misleading stories of the outlairs who shape opinion from right wing mainstream medias worldwide.
I am closely watching our planet's temperature lurch upward again (12-month running mean; updated through June 2023)... #HumanCausedClimateChange
+ More climate indicator visualizations: zacklabe.com/climate-change-inā¦
+ Data from: cds.climate.copernicus.eu/cdsaā¦
All data are referenced at My visualizations: Arctic Climate Seasonality and Variability Arctic Sea Ice Extent and Concentration Arctic Sea Ice Volume and Thickness Arctic Temperatures Antarctic Seā¦Zachary Labe
Okay...
For more info: nsidc.org/arcticseaicenews/202ā¦. For more graphs: zacklabe.com/antarctic-sea-iceā¦.
My visualizations: Arctic Climate Seasonality and Variability Arctic Sea Ice Extent and Concentration Arctic Sea Ice Volume and Thickness Arctic Temperatures Antarctic Sea Ice Extent and Concentratā¦Zachary Labe
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The extent of global sea ice is more than 1 million square kilometers below the previous record for the current date. This year is particularly a result of the anomalous Antarctic.
Larger seasonal cycle graphics updated at zacklabe.com/global-sea-ice-exā¦ (satellite era from 1979-2023). Data from nsidc.org/data/seaice_index.
NOTE: Trends and variability in Arctic and Antarctic sea ice are affected by very different atmospheric/oceanic/ice processes and are in opposite seasons! Caution is advised for assessing any statiā¦Zachary Labe
Last month observed below average air temperatures near the South Pole. Elsewhere, the largest warm anomalies were found in the Northern Hemisphere.
Plot shows zonal-mean surface air temperature anomalies, where latitude = x-axis (not scaled by distance). Data from GISTEMPv4 at data.giss.nasa.gov/gistemp/.
Kelly Lepo
in reply to Kelly Lepo • • •Here are some actual stellar spectra, arranged by temperature. The hottest stars are at the top, coolest stars are at the bottom. The letters on the left are āspectral types,ā a classification of stars based on their spectra.
Note how certain lines appear and then fade out as we go down in temperature. Most of the lines are caused by single elements. At the very bottom, we start to see bands of lines. Those are from molecules in the outer layers of stars.
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Image from: noirlab.edu/public/images/noaoā¦
OBAFGKM
www.noirlab.eduKelly Lepo
in reply to Kelly Lepo • • •Why do we see lines? We will have to get into a little atomic physics.
As starlight shines through the outer layers of the star, the gas there will absorb photons that have exactly enough energy to bump their atomsā electrons up to higher energy levels. The energy levels are different for each type of atom.
Since there are fewer photons at certain wavelengths that leave the star, we see narrow, dark lines.
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Learn more: webbtelescope.org/contents/artā¦
Julien š
in reply to Kelly Lepo • • •Very interesting and well explained!
This is also interesting in the context of #astrophotography where we are capturing the light emitted by the inverse phenomena in emission nebulae (explained in the linked article).
Is there a standard nomenclature for these absorption/emission lines, e.g. alpha & beta for hydrogen vs iii in Oiii for Oxygen emissions? Does it correspond to the number of energy level changes the electrons undergo?
Kelly Lepo
in reply to Julien š • • •There is a system, it is confusing.
Hydrogen lines get their own names.
At visible wavelengths, the Balmer series is the most important (HĪ±, HĪ², HĪ“, etc.)
At UV wavelengths, the Lyman series is important (LyĪ±, LyĪ², LyĪ“, etc.)
And at IR wavelength the Paschen series is important (PaĪ±, PaĪ², PaĪ“, etc.)
en.wikipedia.org/wiki/Hydrogenā¦
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important atomic emission spectra
Contributors to Wikimedia projects (Wikimedia Foundation, Inc.)Kelly Lepo
in reply to Kelly Lepo • • •Most other elements are designated by their ionization state and wavelength in angstroms. For example: HeII 4686
He I = neutral helium
He II = singly-ionized helium
He III = doubly-ionized helium
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Kelly Lepo
in reply to Kelly Lepo • • •Some lines are known as forbidden lines. These are normally disallowed, by the rules of quantum mechanics, but can be quite common in the very sparse gas found in astronomical objects, like nebulas. en.wikipedia.org/wiki/Forbiddeā¦
These are designated by brackets. One common forbidden line is the oxygen doublet [OIII] 4959 and [OIII] 5007
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spectral line associated with absorption or emission of light by atomic nuclei, atoms, or molecules
Contributors to Wikimedia projects (Wikimedia Foundation, Inc.)Kelly Lepo
in reply to Kelly Lepo • • •Except for the forbidden lines (which are only emission lines), these names are used for both absorption and emission lines.
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Julien š
in reply to Kelly Lepo • • •Julien š
in reply to Julien š • • •Follow-up question:
In the different emission nebulae images taken with the NIRCam instrument (like webbtelescope.org/contents/medā¦), what emission lines are captured?
Do the hydrogen an other atoms also emit in infrared?
Looking up the Balmer series on Wikipedia, the hydrogen emission lines start in the visible (red) and extend into UV but not in IR.