Explaining the Sodium tail of Mercury 16 days before or after perihelion.

The phenomenon behind the visibility of Mercury's sodium tail is a fascinating interplay of orbital mechanics and light. While Mercury reaches its maximum orbital velocity of about 59 km/s at perihelion, its radial velocity—the speed at which it moves directly away from the Sun—is nearly 0 km/s at that exact moment. However, due to its highly eccentric orbit, the planet begins to recede rapidly after passing this point. Approximately sixteen days post-perihelion, this radial velocity reaches an optimal peak of over 10 km/s.

This radial motion is critical because of the "Sodium Trap." The Sun's atmosphere contains sodium that absorbs light at specific wavelengths, particularly the D-lines (around 589 nm), creating a deep "dark gap" or absorption line in the solar spectrum. At perihelion, the sodium in Mercury's exosphere is aligned with this dark gap. Without sufficient photon flux, the atoms lack the radiation pressure needed to be pushed into a visible tail.

The sodium atoms are supplied to the exosphere by several distinct processes:

Thermal Desorption: Extreme daytime temperatures of 430 °C cause sodium to evaporate from the surface.

Solar Wind Sputtering: High-energy particles from the sun strike the surface at an atomic level, knocking individual sodium atoms loose.

Micrometeorite Impacts: Tiny dust particles strike the surface, causing mini-explosions that throw material into space.

Think of a surfer paddling away from a wave. If the surfer stays still relative to the wave's source, the frequency remains the same. But by paddling away at high radial speed, the frequency of the incoming waves of light shifts. This Doppler effect causes a redshift in the solar light reaching Mercury. Sixteen days after perihelion, the shift is large enough (about 0.02 nm) that the sodium atoms move out of the solar absorption shadow and receive approximately 40% more light.

This increased photon flux provides the physical momentum "kick" needed to accelerate the atoms away from the planet, while simultaneously causing them to glow through fluorescence. This specific timing is why observers look for windows sixteen days after perihelion—such as June 3, 2026 or November 26, 2026—to capture the tail at its most brilliant.

Het fenomeen achter de zichtbaarheid van de natriumstaart van Mercurius is een fascinerend samenspel tussen baanmechanica en licht. Hoewel Mercurius zijn maximale baansnelheid van ongeveer 59 km/s bereikt tijdens het perihelium, is de radiale snelheid—de snelheid waarmee hij direct van de zon af beweegt—op dat exacte moment nagenoeg 0 km/s. Vanwege zijn zeer excentrische baan begint de planeet echter snel afstand te nemen zodra hij dit punt passeert. Ongeveer zestien dagen na het perihelium bereikt deze radiale snelheid een optimaal hoogtepunt van meer dan 10 km/s.

Deze radiale beweging is cruciaal vanwege de zogenaamde "natrium-val". De atmosfeer van de zon bevat natrium dat licht absorbeert op specifieke golflengten, met name de D-lijnen (rond 589 nm), wat een diep "donker gat" of een absorptielijn in het zonnespectrum veroorzaakt. Tijdens het perihelium bevindt het natrium in de exosfeer van Mercurius zich precies in dit donkere gat. Zonder voldoende toevoer van fotonen ontbreekt het de atomen aan de stralingsdruk die nodig is om ze weg te duwen en een zichtbare staart te vormen.

De natriumatomen worden aan de exosfeer geleverd door verschillende processen:

Thermische desorptie: Extreme dagtemperaturen van 430 °C zorgen ervoor dat natrium uit het oppervlak verdampt.

Sputtering door zonnewind: Energierijke deeltjes van de zon raken het oppervlak op atomair niveau en slaan individuele natriumatomen los.

Inslagen van micrometeorieten: Minuscule stofdeeltjes raken het oppervlak en veroorzaken mini-explosies die materie de ruimte in slingeren.

Stel je een surfer voor die wegpeddelt van een golf. Als de surfer stil blijft liggen ten opzichte van de bron van de golf, blijft de frequentie hetzelfde. Maar door met een hoge radiale snelheid weg te paddelen, verschuift de frequentie van de inkomende "lichtgolven". Dit Doppler-effect veroorzaakt een roodverschuiving in het zonlicht dat Mercurius bereikt. Zestien dagen na het perihelium is deze verschuiving groot genoeg (ongeveer 0,02 nm) zodat de natriumatomen uit de "schaduw" van de zonne-absorptie stappen en ongeveer 40% meer licht ontvangen.

Deze verhoogde fotonenstroom geeft de fysieke "kick" die nodig is om de atomen van de planeet weg te versnellen, terwijl ze tegelijkertijd gaan gloeien door fluorescentie. Deze specifieke timing is de reden waarom waarnemers zoeken naar momenten zestien dagen na het perihelium—zoals op 3 juni of 26 november 2026 —om de staart op zijn helderst vast te leggen.

My first Meteorite Sikhote-Alin USSR 1947

The Sikhote-Alin meteorite fall remains one of the most spectacular events in modern astronomical history, occurring on the morning of February 12, 1947, in the Primorye region of Russia (USSR). Unlike many meteorite falls that occur over uninhabited oceans or deserts, this event was witnessed by numerous people who saw a fireball brighter than the sun descending over the Sikhote-Alin Mountains. The bolide entered the atmosphere at a high velocity and began to break apart under the immense pressure of the descent. The final explosion was so powerful that it was heard hundreds of kilometers away, leaving a thick smoke trail in the sky that persisted for several hours.

When the meteorite disintegrated, it created a massive debris field known as a strewn field, covering a significant area of the dense forest. The impact was violent enough to produce over a hundred craters, the largest of which measured twenty-six meters in diameter. Because the parent body was a massive iron meteorite, it did not simply burn up; instead, it showered the taiga with tons of iron fragments. Explorers and scientists who reached the site discovered a scene of total devastation, with shattered trees and jagged metal shards embedded in the ground.

Collectors generally distinguish between two types of specimens from this fall. The first type is the individual meteorite, which traveled through the atmosphere long enough to develop a smooth surface known as a fusion crust, often covered in thumbprint-like indentations called regmaglypts. These are prized for their aerodynamic appearance. The second type, which is frequently found at major events like the ATT fair in Essen, consists of shrapnel fragments. These are jagged, twisted pieces of iron that were torn apart by the force of the main explosion or upon impact with the frozen ground.

Owning a piece of Sikhote-Alin is special. The Sikhote-Alin meteorite is classified as an iron meteorite belonging to the meteorite group IIAB and with a coarse octahedrite structure. It is composed of approximately 93% iron, 5.9% nickel, 0.42% cobalt, 0.46% phosphorus and 0.28% sulfur, with trace amounts of germanium and iridium. Minerals present include taenite, plessite, troilite, chromite, kamacite and schreibersite 

When you hold a piece purchased at a specialized fair like the ATT in Essen, you are holding a fragment of a planetary core that formed billions of years ago, only to be violently delivered to Earth in a remote Russian forest less than a century ago. It serves as a tactile connection to the raw power of our solar system and a permanent reminder of the day the sky literally fell in eastern Siberia.

44 Nysa in M44

This weekend, asteroid 44 Nysa could be observed when crossing M44. M44 or Beehevi Cluster, is a bright open star cluster.

Setting:

TLAPO80/480 with ASI2600MC.

Filter Optolong L-Pro

Exposure : 37x60s (FITS)

Software: SharpCap, ASTAP, CS4

The best fits files were stacked using ASTAP. Stacking was done both on stars as on 44 Nysa. 

Venus, Uranus & Pleiades

Venus, Uranus with Pleiades.

Venus, Moon and Pleiades

During my vacation in Nieuwpoort I could capture Venus, the Moon with Pleiades. I used my Nikon D7500 with Sigma 18-35mm f/1.8 lens.

Venus - Moon

Venus and Moon at Nieuwpoort (B) with Nikon D7500 and 18-35mm Sigma f/1.8 lens.

Venus during blue hour

Image of Venus above the North sea @ Nieuwpoort at the end of the Blue hour. When editing my picture I found a couple of issues. First, the aperture was still set on the Sun (f/29) and my lens is really dirty.

Belgium's Lost Solar System: a tour around Belgoum and now completed with Neptune

See my previous blogpost back in January 4th 2019.
In this blogpost I gave an overview of the sun and planets located in Belgium at a scale of  1 to 40 million.

I found the entire solarsystem around Belgium: 

- Sun in Oudergem

- Mercury in Oudergem

- Venus in Watermaal Bosvoorde

- Earth and Moon in Uccle

- Mars in Hoeiilaart

- Jupiter in Kempenhout

- Saturn in Gembloux

- Uranus in Tongeren

- Neptune was missing in Oostende

- Pluto in Florenville

Finally this year, the statue of Neptune showed up again. Before it was installad at the seashore of Oosternde, now it is installed at Astropolis, Space Science Center of Oostende.

This morning I was in Oostende and made a detour to visit the statue. And finally, yes, I could finish my Belgium tour around the sun and planets.

Near occultation of SAO77121 by the Moon on March 24, 2026

Last Monday (March 24), I was located just north of the graze line for the lunar occultation of star SAO77121. My colleague Bart from Helios had alerted us, allowing me to track the event. As Bart predicted, I was in the area where the star was not occulted. My colleague Lieven also observed the event; he was positioned just south of the graze line and saw the star narrowly escape occultation as well.

Timing UT21h34

Setting: Star Adventurer GTI with Nikon D7500 and 200mm lens

Conditions: Transparency good and Seeing moderate. 

MoonSwatch - Omega Speedmaster Mission to Earthphase Moonshine Gold

Not only I was interesested in the Speedmaster as a Moonwactch but also the fact the MoonSwatch shows the phases of the Moon. And in the case of the MoonSwatch Mission to Earthphase, the watch shows aswell the phase ot the Earth from the Moon. At the 10 o’clock position, the earth phase indicator shows the Earth with oceans that glow blue under UV light. Beneath the earth phase indicator is an illustration of Snoopy and Woodstock on the Moon, marveling at the enchanting spectacle of Earth. The illustration showcases a phrase that appears only under UV light. At the 2 o’clock subdial, is a moon phase indicator with two radiant full moons, both coated with OMEGA’s Moonshine™ Gold. One of the moons is designed in the distinctive style of the world of Snoopy, while the other features a unique snowflake design. The design is unique for every model, ensuring that, just like snowflakes in nature, no two timepieces are ever the same.

I bought the watch last week in Brussels, together with my daughter.

MoonSwatch - Omega Speedmaster Mission to the Sun

Since a couple of years I want to buy the Speedmaster of Omega. The Speedmaster is the only watch qualified by NASA. Just three weeks after receiving NASA’s official qualification, the Speedmaster ST 105.003 made its space debut on March 23, 1965. It was worn by astronauts Virgil “Gus” Grissom and John Young during the Gemini 3 mission. 

Following Gemini 3, the Speedmaster— and its subsequent evolutions— became an essential piece of equipment for every crewed NASA mission. It gained legendary status when astronaut Ed White wore it during the first American spacewalk later that same year, and again during Apollo 8 in 1968, when its crew became the first humans to witness "the far side of the Moon."As the missions advanced, so did the importance of the Speedmaster. On July 20, 1969, NASA achieved its ultimate goal: Apollo 11 successfully landed on the Moon. As Neil Armstrong and Buzz Aldrin descended to the lunar surface, the Speedmaster became the first watch worn on the Moon— a milestone in both space exploration and horological history.

From that moment forward, the Speedmaster continued to accompany astronauts on every Moon landing and remained a trusted tool throughout the Apollo program and beyond.

When a couple of year ago the MoonSwatch was launched, it was my chance to buy this historical watch. But it was only recently when I bought one. I choose the MoonSwatch, a Sun Yellow dial "Mission to the Sun" Speedmaster with Dot over 90!

Saturn November 17

Imaging Saturn on November 17, 2025 with ring tilt of 0,38°.

Editing was done using the newest version of AstroSurface W3.

Setting: TAL200K, ADC, Barlowx2, ASI715MC

Filter: IR/UV Cut

Software: SharpCap, AstroSurface, CS4, DeNoise AI, WinJupos.

Saturn with new ASI715MC Camera

First time this year capturing Saturn. The tilt of the rings are almost zero with 0,45°, a Saturn with edge on rings is not the Saturn we typically know from the books. But still interesting view.

I used my new camera ASI715MC with small pixels. I forget to keep an eye on the whitebalance on sharpcap. I made image both with and without IR/UC cut filter.

Compared with my ASI224MC

Setting is same as previous year; it was difficult to get blue/red out even when using my ADC.

Mercury, Venus, Jupiter and Moon at sunrise

 At UT3h21 this morning I was able to capture Mercury which was only 3° above the horizon. The sky was special with Mercury, Jupiter, Venus and the Moon and a golden hour background.

Venus-Jupiter Conjuction

Venus passes south of planet Jupiter this morning. I got up very early and went to Schaffen to get a free eastern horizon. Images mad with my Nikon D7500.

Moon and Pleiades

 

Moon and Pleiades.
Set up: TLAPO80/489 f/6 on EQ8 and Nikon D7500

Bracketing and HDR using CS4

Moon Venus Mercury

Nightscape of Venus, Moon and Mercury.

Mars Profiler - Mars Map - Mars Mapper

When observing Mars, this website can be used which structures you imaged or drawed. 

Mars Profiler 

Mars Feb 3, 2025

 

Image of Mars on Feb 3, 2025. The polar cap is clearly visible aswell other structures on the disk.

Setting

TAL 200K @f/26 using Barlow X3

ASI224MC camera and IR/UV blocking filter

Sofware: SharpCap 4, AstroSurface and CS4

Jupiter and Transit of Io with Shadow and outbreak in NTrZ

 

Transit of Io on Jupiter with shadow. Moon Ganymede can be seen left on above picture. Also visibel is the "outbreak" in the Northern Tropical Zone (NTrZ).

The ADC with my Barlow x2 was replace with a Celestron Barlow X3 (on loan from Helios colleague).