天文学是研究宇宙中从电磁波谱中辐射（或反射）能量的物体。如果你是天文学家，很有可能你会以某种形式研究辐射。让我们深入了解那里的辐射形式。为了完全理解我们周围的宇宙，我们必须审视整个电磁波谱，甚至是高能粒子所产生的高能粒子。某些物体和过程实际上在某些波长（甚至光学）中是完全不可见的，因此有必要在许多波长中观察它们。通常情况下，直到我们看到许多不同波长的物体，我们甚至可以识别它是什么或正在做什么。辐射描述了基本粒子，原子核和电磁波在空间中传播。科学家通常以两种方式参考辐射：电离和非电离。电离是从原子中除去电子的过程。这种情况在自然界中一直发生，它只需要原子与光子或具有足够能量的粒子碰撞来激发选举。当发生这种情况时，原子不再能够保持与粒子的结合。某些形式的辐射携带足够的能量来电离各种原子或分子。它们可能通过引起癌症或其他重大健康问题对生物实体造成重大伤害。辐射损伤的程度取决于有机体吸收了多少辐射。辐射被认为是电离所需的最小阈值能量约为10电子伏特（10eV）。有辐射的几种形式，上面这个阈天然存在：伽玛射线：γ射线（通常用希腊字母γ指定）的电磁辐射的一种形式，并表示在宇宙的光的最高能量形式。伽玛射线是通过各种过程产生的，从核反应堆内的活动到称为超新星的恒星爆炸。由于伽马射线是电磁辐射，除非发生正面碰撞，否则它们不容易与原子相互作用。在这种情况下，伽马射线将“衰变”成电子 – 正电子对。然而，如果伽马射线被生物实体（例如人）吸收，那么可以进行显着的伤害，因为它需要相当大量的能量来停止伽马射线。从这个意义上讲，伽马射线可能是对人类最危险的辐射形式。幸运的是，虽然它们在与原子相互作用之前可以穿透几英里进入我们的大气层，但我们的大气层足够厚，以至于大多数伽马射线在到达地面之前就会被吸收。然而，太空中的宇航员缺乏对它们的保护，并且仅限于他们可以在航天器或空间站“外”花费的时间。虽然非常高剂量的伽马辐射可能是致命的，但重复暴露于高于平均剂量的伽马射线的最可能结果（例如宇航员所经历的）是增加患癌症的风险，但仍然只有不确定的数据就此而言。 X射线：X射线与伽马射线一样，是电磁波（光）。它们通常分为两类：软X射线（具有较长波长的X射线）和硬X射线（具有较短波长的X射线）。波长越短（即X射线越硬），它就越危险。这就是为什么在医学成像中使用低能量X射线的原因。 X射线通常会使较小的原子电离，而较大的原子可以吸收辐射，因为它们的电离能量间隙较大。这就是为什么X射线机能很好地对像骨骼这样的东西进行成像（它们由较重的元素组成），而它们是较差的软组织成像器（较轻的元素）。据估计，X射线机和其他衍生设备占美国人们所经历的电离辐射的35-50％。 Alpha粒子：α粒子（由希腊字母α表示）由两个质子和两个中子组成;与氦核完全相同的成分。专注于产生它们的α衰变过程，α粒子以非常高的速度（因此高能量）从母核中射出，通常超过光速的5％。一些阿尔法粒子以宇宙射线的形式到达地球，可能达到超过光速10％的速度。然而，一般来说，α粒子在非常短的距离内相互作用，因此在地球上，α粒子辐射不是对生命的直接威胁。它被我们的外部氛围吸收。但是，这对宇航员来说是一种危险。
Astronomy is the study of objects in the universe that radiate (or reflect) energy from across the electromagnetic spectrum. If you are an astronomer, chances are good you will be studying radiation in some form. Let’s take an in-depth look at the forms of radiation out there. In order to completely understand the universe around us, we must look across the entire electromagnetic spectrum, and even at the high-energy particles that are being created by energetic objects. Some objects and processes are actually completely invisible in certain wavelengths (even optical), so it becomes necessary to observe them in many wavelengths. Often, it’s not until we look at an object at many different wavelengths that we can even identify what it is or is doing. Radiation describes elementary particles, nuclei and electromagnetic waves as they propagate through space. Scientists typically reference radiation in two ways: ionizing and non-ionizing. Ionization is the process by which electrons are removed from an atom. This happens all the time in nature, and it merely requires the atom to collide with a photon or a particle with enough energy to excite the election(s). When this happens, the atom can no longer maintain its bond to the particle. Certain forms of radiation carry enough energy to ionize various atoms or molecules. They can cause significant harm to biological entities by causing cancer or other significant health problems. The extent of the radiation damage is a matter of how much radiation was absorbed by the organism. The minimum threshold energy needed for radiation to be considered ionizing is about 10 electron volts (10 eV). There are several forms of radiation that naturally exist above this threshold: Gamma-rays: Gamma rays (usually designated by the Greek letter γ) are a form of electromagnetic radiation, and represent the highest energy forms of light in the universe. Gamma rays are created through a variety of processes ranging from activity inside nuclear reactors to stellar explosions called supernovae. Since gamma rays are electromagnetic radiation, they do not readily interact with atoms unless a head-on collision occurs. In this case the gamma ray will “decay” into an electron-positron pair. However, should a gamma ray be absorbed by a biological entity (e.g. a person) then significant harm can be done as it takes a considerable amount of energy to stop a gamma-ray. In this sense, gamma rays are perhaps the most dangerous form of radiation to humans. Luckily, while they can penetrate several miles into our atmosphere before they interact with an atom, our atmosphere is thick enough that most gamma rays are absorbed before they reach the ground. However, astronauts in space lack protection from them, and are limited to the amount of time that they can spend “outside” a spacecraft or space station. While very high doses of gamma radiation can be fatal, the most likely outcome to repeated expose to above-average doses of gamma-rays (like experienced by astronauts, for instance) is an increased risk of cancer, but there is still only inconclusive data on this. X-rays: X-rays are, like gamma rays, electromagnetic waves (light). They are usually broken up into two classes: soft x-rays (those with the longer wavelengths) and hard x-rays (those with the shorter wavelengths). The shorter the wavelength (i.e. the harder the x-ray) the more dangerous it is. This is why lower energy x-rays are used in medical imaging. The x-rays will typically ionize smaller atoms, while larger atoms can absorb the radiation as they have larger gaps in their ionization energies. This is why x-ray machines will image things like bones very well (they are composed of heavier elements) while they are poor imagers of soft tissue (lighter elements). It is estimated that x-ray machines, and other derivative devices, account for between 35-50% of the ionizing radiation experienced by people in the United States. Alpha Particles: An alpha particle (designated by the greek letter α) consists of two protons and two neutrons; exactly the same composition as a helium nucleus. Focusing on the alpha decay process that creates them, the alpha particle is ejected from the parent nucleus with very high speed (therefore high energy), usually in excess of 5% of the speed of light. Some alpha particles come to Earth in the form of cosmic rays and may achieve speeds in excess of 10% of the speed of light. Generally, however, alpha particles interact over very short distances, so here on Earth, alpha particle radiation is not a direct threat to life. It is simply absorbed by our outer atmosphere. However, it is a danger for astronauts.