r/askastronomy

If say, a curious teenager that has no knowledge of astrophysics wants to learn more about it and maybe pick it up as a hobby, where do you start? This field is so complex that it can get overwhelming for people that are absolute beginners. Any friendly advice?

Why is it the same hohmann transfer orbit period from mars to Earth?

I would believe Mars has a faster window to return to earth.

The earth goes around the sun in 365 days.

Mars goes around the sun in 687 days.

The mars to earth hohman transfer is when Earth is around 75-80 degrees behind Mars in orbit

That leads me to believe the mars to earth window times isnt 26 months but closer to every year since eventually the earth will always be behind Mars.

About 35 years ago (1990), I wrote a science popularization article about the Tunguska event (1908), one of the largest explosions caused by a cosmic body in recent history.

In that article, I explored a speculative idea: the possibility that a comet with an unusually high deuterium content could, under extreme conditions, be associated with energetic processes beyond a standard kinetic explosion.

To be clear, even back then, in the article itself, I considered both the existence of such "deuterium-rich comets" and the possibility of any kind of thermonuclear reaction to be extremely unlikely. I explicitly rejected both as realistic explanations, presenting it only as a conceptual idea.

However, recent observations of the interstellar object 3I/ATLAS report unusually high D/H ratios. In particular, measurements in water (H₂O) indicate a value of about D/H ≈ 0.95% (± 0.06%), which is orders of magnitude higher than typical values in the Solar System.

This does not validate any kind of nuclear fusion-based mechanism, of course. But it does raise an interesting question:

Could objects with significantly enhanced deuterium content be more common (or at least possible) than previously assumed?

Back in 1990, I concluded that such objects likely did not exist. Today, I'm not so sure anymore.

For reference, the original article was published in Karma 7, February 1990, titled “El misterio de Tunguska”.

I’m curious to hear how current models of interstellar chemistry explain such high D/H ratios, and whether this kind of enrichment has clear formation pathways in cold environments.

Recent discovery preprint:

https://arxiv.org/abs/2603.06911

This Artemis II mission has gotten me very curious about the relative positions of the earth, moon, and sun during the drive-by. I’ve been scouring the internet for animations or images, but ones that include where the spacecraft, earth, and moon are relative to the sun at the exact moments of observation are so few and far between. I couldn’t find any for Apollo 13’s mission either! Why is that?

noob question: what, if any, are the lower/upper time limits of a earth-like planetoid - by which I mean any relatively round non-gas-giant object in stable orbit around a host star - to complete one full orbit around the star?

I imagine it is restricted downwards by the habitable zone or stable orbit restriction, and upwards only by the habitable zone outer limit, but I lack the expertise to make any guess on these

Questa notte sono in campagna e guardando il cielo stellato mi sono soffermata sue tre “stelle” equidistanti e che si muovevano in linea retta. La prima arrivata a una certa “altezza” si affievoliva fino a scomparire, dopo 10 secondi esatti ricompariva dall’orizzonte una nuova stella mantenendo così la fila composta da tre corpi luminosi. Questo processo è andato avanti per 10 minuti, poi me ne sono andata perché non capendo e avendo freddo ho deciso di rimanere con questo dubbio… non ho fatto video perché non ho un telefono così “potente” da poter riprendere questo fenomeno, se qualcuno mi sapesse dare delucidazioni o avesse visto qualcosa di simile sarei felice di avere una risposta. Grazie!

I understand time dilation due to relativity stipulating light speed being the same for all observers everywhere in the universe. Relativity explains that very well and I understand it.

But gravitational time dilation, I do not understand, nor do I know how to calculate. How and why does it occur? What is the formula for it?

All I understand is that objects with enormous masses age slower than smaller ones. But why and how? I never got a clear answer.

i think the closest we ever gotten to these ships were the space shuttles, but those were really bad i reckon